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Sebring GT build

4102 Views 35 Replies 6 Participants Last post by  123pugsy
Thought I would post this up and see if there was any interest in it. This is a project that I have been working on for a long time. I’ve changed it several times during the build and had numerous personal and family health issues along the way. It’s taken way longer than I thought it would, but that’s the way most car projects go.

The car is an old Austin Healey kit car called a Sebring that was built in the 80’s. I really like Cobra’s, but was looking for something with a little more room and practicality than a Cobra. I want to use it for long cruises like the Power Tour and vacation trips. My idea was to build something along the lines of a European GT (Grand Touring) car, but using American power and hot rod tech. The fact that the car had been titled originally in the 80’s meant no emission rules to deal with due to the 25 year old rule in my state (Louisiana) and the fiberglass body meant no rust to deal with. I bought the car in Florida and drove it home, but within a few months I blew the whole thing apart for a total redo. It just wasn't the car I wanted. Loved the basic styling, but the performance sucked. Not only was the car slower than it should have been, but it handled terrible and had a nasty habit of trying to change lanes if you got on it really hard. The MII rear suspension just wasn't up to the job.

A few specs on the car as I bought it:

350 SBC low HP crate motor with Q-jet carb
Very restrictive single exhaust
Camaro T5 trans
Mustang II suspension front and rear
Mustang II brakes front and rear
Folding soft top (sort of)
Removeable hardtop

I threw everything away except the main chassis rails and the body. Even the interior has been changed. The new car will have an LS1/T56 combo and a 3-link rear suspension. The front end is still loosely MII based, but there are few parts from an original MII left. The chassis has just came back from the powder coater and I’ll start this thread with engine and rear end. Here is a pic of the car as it was the day I got it home.

I’m using the Healey factory works rally cars for styling ques. The car won’t look like this when done. I’ve added several trim parts form an original Healey to make it look more like the original car.
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That's cool, I remember seeing the ads for those, always lusted after a Cobra kit myself but also like the A-H/Sebring and the kit Porsche 356 Speedster C (like the 356 flared fender race version in the movie "King of the Mountain" if you've ever seen it...Dennis Hopper, Dan Haggerty, Harry Hamlin road racing on LA's Mulholland Drive)
It ought to ba a rocket with a LS/T56 combo!

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Nice project. I have a friend that has something similar to this - problem is I can't remember any of the details right now but I'll try to get some photos of it the next time I'm up there. I know it has a different engine/trans in it but not sure of what else was done to it.
Yeah, I always liked those California Speedster 356's. I was into VW's many years ago. If I had found one of those, I might have built it instead. They look very aggressive with the flared fenders. The 356 replicas were probably one of the first kit cars to be very close cousins to the originals. After all, they were basically just hot rodded VW's to start with.

Chasracer, I would love to see pics of your friends car. It's always nice to see what someone else has thought of. The Sebrings are not super rare, but you don't see them everyday. I've ran across a bunch of Cobra's at shows, but only 1 or 2 Sebrings.
I think that I should also add that I’m building this car as a long distance cruiser, in the model of a European GT car. I want to use it for things like the Power Tour and vacation road trips.

The engine I had planned for this car was an original aluminum LS1 that was coded for a Corvette. It was never installed, but had been test fired. I’ve had it for several years. It was a first year engine from 1997 and came with really poor heads. GM only used the heads for a few months in early production. If you’re curious the casting number is 339K. I picked up a set of CNC ported heads from a local machine shop with the intention of swapping them out. That plan went bad when I discovered that sometime in it’s past, the engine got some water in 3 cylinders. They had just enough rust in them to ruin the block. The very early LS blocks couldn’t be bored, only honed a few thousandths and there wasn’t enough meat to clean them up. The good news is that the rotating assembly was perfect, as in looking like it just came out of the box, bearing and all! I couldn’t find a good standard bore 5.7 block, so I had a 4.8/5.3 iron block bored out to standard 5.7 bore. Iron 5.7’s were apparently common several years ago. Still hard to believe that GM left enough meat in those blocks to be bored that far. I also had the block decked for squareness and new cam bearings installed. The old style LS rod bolts were also swapped out for later parts.

The cam I picked for the new build was a Trick Flow cam with 216/220 @ .050 with .560 lift on both the intake and exhaust. I also picked up a set of Harland Sharp roller rockers. After I started the pre -build mock up, I discovered that the CNC heads I bought had chambers that were too small. My static compression was going to be over 11.7 to 1 and my dynamic compression was going to be around 8.5 to 1! That wasn’t going to work, so to keep things moving along, I bought a set of Trick Flow Fast as Cast 220 heads with larger chambers that dropped my static compression to 10.7 to 1 (dynamic to around 7.7 to 1). Trick Flow recommended at least 10.5 to 1 for the cam I am using. The cam may not use the latest high intensity lobe design, but Trick Flow said years ago when they started selling it, that it is not prone to valve float and easy on the valve train. To me, that is very important for a long distance cruiser.

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Another thing I added was a better windage tray. I’m already using an LS2/LS3 Corvette oil pan. The Vette pan is pretty close in size to the LS Camaro (F body) pan, but has more baffling.


The windage tray is by Improved Racing. I comes with a very close fitting crank scraper and has extra baffling with trapdoors.


Crank scraper


New windage tray compared to the factory part.

I also intend to install an Accusump oil accumulator. The LS Vette engines with the low profile oil pan like mine were known to have oil starvation issues if cornered really hard. Bob Bondurant’s driving school was losing engines to this issue. The GM engineers recommended adding an extra quart of oil for tracking the car. That sounded like a bandaid solution that would cause a lot windage. The Accusump is like poor man’s dry sump system and should cure the starvation issue without all the windage. Here’s a video if you want to know about it. This is a moroso accumulator, but the principle is the same:

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I will say that building an LS engine is a little different than the old school motors I’m used to. This thing took about 3X longer to build than I’m used to, mostly due to constantly stopping to research things to make sure I was doing it right. Kinda felt like I was building my first engine.

There are several things that I don’t really like about them. All the torque to angle bolts drive me crazy. I like just setting a torque wrench and having at it. I did replace the head bolts with ARP’s just to get away form the torque to yield bolts. The rest of the bolt are reusable, but they are still have to be torqued with an angle gage.

Then there is the oil pump setup. You have to disassemble the pump and scrape up enough feeler gages to shim everything into alignment. Sure seem like they could have came up with a better system. It's pretty obvious that this engine was designed to be assembled by robots that don't need alignment aids.

I also don’t like the fact that the timing cover and rear seal plate have to be aligned manually. Get it wrong and you’ll have leaks. Come on GM, I don’t think it would have bankrupted you any sooner to add a couple of dowel pins. At any rate, I did luck into the GM tools to align the covers at a local pawn shop.

Also, apparently the LS engines are prone to breaking timing chains if you’re making a lot of high RPM pulls. Especially if you don’t have chain damper. My engine block had the boss for a damper, but wasn’t drilled. I made a quick drill jig out of aluminum and drilled and tapped the block. Line up was the tricky part, but it turned out OK.

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The last thing I had to do was get the intake sorted. I’m using a 2x4 Holley EFI setup. I found this for sale on another forum and thought it would look a lot better than the standard LS intake. The squat stock LS front throttle body intakes just don’t look right to me on an older car. I thought this setup looked more like it belonged on a 60’s muscle car.

I couldn’t find much info on using this thing. The throttle bodies flow 1000 cfm each and are progressive like a standard 4 barrel carb. 2000 cfm is a ludicrous amount of air for a 350 CI engine. The linkage that came with it has both TB opening together. At this point I really don’t want to disconnect the secondaries. I may have to eventually, but I consider getting it to work without that as a challenge.

The only complaint that I read from someone that actually used it said that it had touchy throttle response. That stands to reason if they didn’t try to slow down the throttle opening. There’s a 1000 cfm on the primaries alone. That’s a lot of air for a small amount of throttle opening. I’m going to attack that problem 2 ways.

First, I came up with a throttle linkage that slows down the opening on the initial tip in. It uses a cable wheel/cam that has an offset axle. This changes the ratio as it’s opened. I didn’t build that part. It came off a 90mm FAST LS throttle body that I had laying around. You can see the off set compared to a stock GM cable wheel.

I had to mount the throttle cable on the right side of the engine. There wasn’t a lot of room on the left due to the fuel rails being close to the TB’s. The FAST cable cam was designed to work on the right side too. I built this mount that transfers the throttle movement to the left side. It’s cut from 6061 aluminum and has a 3/8” stainless shaft. Another nice thing about the FAST cam was that it had it’s own torsion return spring. I transferred that over to the new mount.

This is the linkage on the left side. The way the pivot is positioned (close to the center of the shaft), it slows the initial opening down even more. It spends much of it’s initial travel moving more vertically than it does moving backwards. After the first 30 or so degrees. It speeds up considerably. I am getting full stroke on the TB’s. So far, the combo seems to be working like I wanted it to. The proof will be in the driving.
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The second part of my strategy is to limit total airflow with a restrictor plates. EFI isn’t as sensitive to big TB’s as having an oversize carb. There is no need to keep air velocity high through the boosters for a good signal (there are no boosters!). A 105 mm TB will flow somewhere around 1100 CFM, as far as I can tell. Those are being installed on 5.3 engines regularly with no issues, but the 2000 CFM that this thing can flow is just crazy. A 5.7 engine can only flow so much air based on volumetric efficiency and RPM. I doubt my engine will need more than 850 CFM (if that much).

This restrictor plate limits air flow to around 1200 CFM for the pair. I know the primary bores will most likely need to enlarged. My “back of the envelope” estimation says a pair of plates will flow 350-400 CFM , wide open, on the primary side, but the progressive linkage stages the secondaries well before half throttle. Since this is port EFI, the restrictor plates only have to flow air, no fuel. This pic is of the unfinished plate. The holes have been radiused on both sides.

This is just an experiment and may be crazy. I can always pull them if they cause issues.

I also had to build a custom throttle cable mount. The car will have cruise control, so had to have 2 cables.
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Next, I needed a nice air filter that looked like it belonged on a 60’s era hot rod. I like the look of the Shelby Cobras and other hot Fords in the sixties that had long oval air cleaners on the 2x4 setups. I wanted something similar, but with a finned top. My plan was to have it wrinkle powder coated and then polish the tops of the fins.

The only air cleaner I could find that had the look I wanted was from Speedway Motors. It was cast aluminum and had the fins, but it was very poorly finished. The filter element supplied with the air cleaner wouldn’t even fit the top or bottom. All surfaces were as cast. Except for a couple of tapped holes, no finish machining had been done at all. It was adjustable for different carb spacing, but I didn’t much like the parts supplied. They were thin aluminum castings and looked pretty fragile. Rather than send it back, I decided to make it work.

The first thing to take care of was making the filter fit. The castings worried me, because I had no idea of their quality. They weren’t flat either which was expected.

Here is the issue. With the filter seated on one end, this is how far it hung over the opposite end.

Step one was machining the lower half flat on the bottom to make setup a little easier. I had to shim the center with cardboard to give it some support. I knew better than to try and clamp it flat. I’m pretty sure it would have snapped as it had a pretty good bow in it.

Then I flipped it over and cut the filter cavity.

After machining, the filter fit as it was supposed to.
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Random side now about the movie King of the Hill. This is triggering some memories from my childhood. I don't know if I read it in a book, or magazine, or saw a movie. But this King of the Hill movie is not it. I did read a lot of Hot Rod Magazine's when I was younger in the early 80s. I did a quick Google search but there are no more movies about this that I know of.
Any ideas?

Then it was time to do the top section. This one was a little more difficult since there were no good surfaces to clamp on. I had to just catch the edge of the lip. This one had to be shimmed in several places with cardboard, too. I used cardboard and paper because it was easy to work out the thickness needed and it wouldn’t scratch up the aluminum. I had to clamp this one very lightly, because it had a good bow in it, also. I added the mag-base dial indicator to keep a close eye on any movement while cutting.

The filter fits both halves now.

Here is the air cleaner mocked up on the intake. Now it’s time to tackle the base plate that adapts it to the throttle bodies.
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I machined the base plate adapter from a piece of 1 ¾ 6061 plate. This is probably overkill, but it is very solid and does a good job of reinforcing the cast filter base.

Not much drama during the mill work, other than a ton of shavings. Getting the internal openings cored out was a little tricky. I cut the first side of the core 1 1/4” deep.

Then I flipped it over and finished the throttle body openings.
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Here is the finished base plate with the adapter in place. The brass component is an air temp sensor for the EFI. I may need to move it to an intake manifold passage. Holley recommends that for a better read on conditions. Of course, there is only one tapped hole in the manifold and it’s not in a good location. I'll have to drill and tap another one, just something else to do!

This is from the top. With the tie down bars in place. I still need to add self-locking nuts. The filter element was damaged in shipping. I have new one, but won't install it until I'm ready to start the engine.

I had to add some supports for the filter. There wasn’t enough thickness in the castings to cut a deep groove and whoever designed it didn’t think to add any supports.

Here is the completed air cleaner on the engine. I know it is too tall and will need to be machined down later when the body and hood is back on. I intend to convert the non-functional air scoop in the Healey hood into a cold air intake, so I need the air cleaner to fit as high as possible. The valve covers are just temporary. I need to check firewall clearance before I get some better looking finned covers.

These are the valve covers I’m considering.

For what it’s worth, I accidently came up separately with almost the exact same combo of parts that Trick Flow offers as a complete top end kit. On their dyno, with a basically stock LS1 short block, the combo made 515 HP! Now I’m not naïve enough to believe that I’m going to make that much with my engine. Published dyno HP numbers are inflated with tricks to sell parts and magazines. I will be running a full exhaust system, full accessories, normal water temps, and have real world intake air temps. Still, I would expect it to make 450 with a decent tune if TF’s numbers are to be remotely believed. Hard to imagine that it could make that much power with such a relatively small cam. Must be some really good heads!

Also, the long tube headers were not my first choice. I actually was going to run some tri-y style LS6 manifolds, but they didn’t match the Trick Flow heads very well. The ports and passages in the manifolds were too small to match the heads. The headers will have to be modified to fit the chassis. They’re close, but not close enough.
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With the engine done as much as possible right now, I turned to the rearend and rear suspension. The rear suspension is a 3 link with an offset upper link and it has a Watts link for lateral location. The upper link is moved to the right of the car’s centerline. When the anti-squat kicks in, in theory, this should load the right tire a little more than the left to help compensate for the right side’s tendency to lose traction due to torque. Factory Five does this on their Cobra replicas, but their offset is a lot more than mine. I was shooting in the dark on the amount of offset and decided that little was better than too much. I didn’t want to create a handling issue that couldn’t be tuned out.

These are pictures are from early in the build and a lot has changed, but the basic layout is the same:

The 9” Ford I’m using now is actually the second rearend that I have had in this car. The first was a shortened 8.8 Explorer axle. The big Explorer axle looked wrong to me every time I was under the car. Even though I narrowed it and centered the pinion, it still just looked wrong. The whole thing just looked too big and heavy. Plus I wasn’t satisfied with the 3rd link bracket. I couldn’t weld on the cast housing (and trust it) so I was forced to bolt the top bracket over the rear cover. I was never really happy the way I attached it and you couldn’t pull the back cover without disconnecting the 3rd link, so the axle could just flop around.

The current Watts link is also the second version and a little different than the one in the early build pictures. The first build had it in the way of pretty much everything, especially the exhaust. Don’t get me wrong, the geometry was correct and the parts fit, but it just wasn’t as good as I felt it could be. I had been kicking around redoing the whole rear suspension, but really hated to take the time. When I discovered that I had made a screw up on the lower links brackets, I decided to ditch the whole mess and start over.

I had picked up a nice older smooth back 9” Ford axle in a trade a few months ago and decided to go back with it. I like working on the drop out gear carriers better than the open backs like the 8.8 and , most important, the 3rd link brackets could be welded to the housing. I was also convinced from eyeballing the two rearends, that the 9” might actually be lighter. With an aluminum chunk, I knew it could be several pounds lighter.

I found a bunch of different weights listed online for both rearends, but none of the info really agreed. Besides, most 8.8 weights you find seem to be for a Mustang type 8.8. The Explorer rearend is a whole different animal. It almost looks like a light duty ¾ ton truck rearend compared to a Mustang type rear. I had another Explorer rearend that I had picked up cheap when a salvage yard closed near me. Just for my own info I stripped both the 9” and the Explorer rear down to the bare essentials, no brakes, to keep things even and weighed them. The box in the picture is a new pinion yoke. I added that because the 8.8 didn’t have a yoke and I wanted to keep things as equal as I could. Turns out, I was right. The 9” was 19 lbs. lighter than the 8.8 Explorer. In the spirit of full disclosure I have to add that the 9” had 28 spline axles and small bearings, while the 8.8 had 31 spline axles. The 8.8 was a few inches wider, too.

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I shortened the 9”, centered the pinion due to tunnel clearance and added a small brace to the back. I was concerned that with the 3rd link, I was adding stresses to the housing that it wasn’t really designed for. The brace also gave me more surface to weld the 3rd link brackets on. The bearing housings were changed to the big bearing Torino style since I had already had a brake setup I built using Mustang Cobra SVT brakes that fit the Explorer axle. The Torino ends are pretty much identical to the Explorer flanges. The SVT brakes use a vented 11.6” rotor and a caliper with a built-in emergency brake. The setup is a lot lighter than the Explorer rear brake setup and should stop better.

These are the tools I made to align the ends. I used 2” shafting based on a conversation with a fellow I know that builds fabricated 9” housings. I originally made these to narrow the 8.8 and had to make some new end tools for the Torino housings. The rectangular end pieces sure make aligning the ends easy. I didn’t get a picture of the bushings that went in the 9” carrier. Turns out they were the same diameter as the 8.8 carrier bearings, so I didn’t have to make them over.

I have to say that the brace on the back of the housing gave me a lot of trouble. Of course, the heat from welding pulled the tubes toward the brace. I expected this, but it moved way more than I thought it would. This is the first housing I’ve straightened with a brace and it was chore to say the least. I gave the only piece of beam I could have used to build a straightening jig with to a friend for something he was doing. That left me with just heat and shrink to move it around. It took a lot of heating and shrinking over several hours. Occasionally, I would have to stop and let the whole thing cool down or it would just quit moving, but eventually I got it straight. The line up tools, and ultimately the axles, just slid in.

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The chunk for the rearend is cast iron at this point. I’m considering swapping to an aluminum carrier later when I decide on the final drive ratio. The gearset is an old 3.25 Ford brand set that I had. They are pretty worn and didn’t have really good pattern (even in the original stock setup from Ford). I set them up as close to the original pattern as I could get and set the backlash to what it was when I took them out. I'm not really happy with them and will definitely change them ASAP, but they will give me a starting point to judge what gears I want to run.

As it stands now, with the transmission ratios and 26” tires I’m running, the gear splits with the 3.25’s are almost exactly the same as the LS6 powered Z06 Corvette though 5th gear. I was originally planning to use an LS6 cam, so this made sense then. My gut tells me that the cam I’m actually using will probably be happier with more gear. I’m thinking that I will wind up with 3.50 – 3.73 gears.

Going by the dyno pulls I’ve seen for both my cam and the LS6 cam I may not be too far off with the 3.25’s, though. The cam I’m using doesn’t appear to give up much, it anything, in low end torque over the LS6 cam. My problem is the 2.97 first gear in my trans. If I go too high numbered on the rear gears, I risk making 1st gear too short to really be of any real use for ordinary driving. Luckily, the gearset in this transmission has a .64 6th instead of the more common .5 ratio, so my cruise RPM’s wont make as much of a drop. Because this is primarily a long distance cruiser, I don’t want to run any more rear gear than I need to keep the cam happy. Time will tell. For now, this gearset will get me by for engine break in.

I also swapped in an Eaton TRU-TRAC Torsen style limited slip differential. I’ve never ran one, but like the idea of how they work. One crazy issue I ran into was finding ring gear bolts that were the correct length. This is a 9” Ford, so that stuff should be easy to find, but not with this diff and ring gear combo. The flange on the Eaton diff was thicker than the Ford diff and I think the ring gear bolt holes were a little on the shallow side of Ford’s tolerance. I tried 4 different sets, from stock Ford large head bolts to ARP bolts. They were either too long and bottomed out or they didn’t have enough thread engagement to be safe (IMO). I wound up making a threaded collet to hold the too-long large head Ford bolts so that I could shorten them in the lathe. Even then, I had 3 holes that required lengths shorter than the rest. Crazy, but true.

I used an aluminum Daytona pinion carrier and solid crush sleeve (actually a solid sleeve and shims), too. The Daytona carrier pushes the yoke about .200 further forward on the pinion splines than the stock carrier. This means that you either have to run a thin pinion nut or machine the nut mating surface in the yoke deeper. I chose to cut the yoke deeper to use the stock pinion nut, so it took a ride in the mill.

I also got ambitious and built the handy, dandy carrier stand. In the past, I just rolled them around on the bench, which pretty much sucked. The stand sure makes things easier.
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I swapped over to 31 spline axles, too since I needed new ones for the shortened housing anyway. The axles I bought were from Quick Performance. Nothing special. They were just regular cut-to-fit axles that they cut for me. I was able to order them with the correct hub diameter for the SVT brake rotors.

The axles came with studs already pressed in, but I had to change them out. I wasn’t comfortable with the amount of lug nut engagement that I had with the aluminum wheels I’m running. The new studs are from Moroso. I was not impressed with the Chinese bearings that the axles came with, either. I’m glad that I ordered them with loose bearings for me to press on. I needed a bearing spacer to get past the thick caliper mount and had to install that before the bearings went on. I went with Federal Mogul bearings from my local parts store.

This is the axle after powder coating and reassembly.

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Here are a few pictures of the Cobra SVT brake conversion I did. I started out with a fabricated two piece steel bracket that was bolted together, but eventually carved one piece brackets out of 6061 aluminum. The new brackets weigh about half of what the steel ones did.

I think I should mention that it probably looks like I have the rotors on the wrong side. All of the slotted rotors I’ve seen have the slots slanting backwards at the top. However, I’m running Baer brakes in the front and they have directional, curved vain rotors with slots. They have the slots slanting forward at the top. Even though the rotors where clearly marked right and left, it looked different enough to make me question whether it was right. I looked at a Baer produced installation video and they make it a point to say that the forward slant is correct for their rotors. Since the rear rotors I’m using have straight non-directional vanes, I decided to swap them around to match the fronts.

I just recently found out that Baer makes a rear disc kit that appears to be basically the same thing I built! I originally got the idea from a Mustang site. They were talking upgrading Mustang brakes and it sounded good, but the SVT caliper brackets wouldn’t fit on the Explorer axle I was using then. So, I came up with my own brackets. Interesting to me that Baer felt it was a good enough upgrade to sell it under their name. That also explains why their tech knew exactly which master cylinder to recommend when I told him I was using SVT brakes.
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While I was redoing the rearend, I also changed the way the Watts link brackets attached to the axle. You can see from the picture I posted above, that they hung way out behind the axle. This put them in the way of pretty much everything.

I pulled them in closer to the axle tubes and raised them. The old system was more adjustable, but that adjustment wasn’t really usable if you ran the exhaust out the back of the car. The new setup had to have link bars with a dogleg in them. The left link was fairly simple, but the right link had to have a hook in it to go over the exhaust pipe. While they look radically different, they both hit the same points in space. I built a temporary jig off of the left link and used that to build the right link. Because of the dogleg, the pivot on one end had to be non-swiveling, otherwise the link would just flop around, but it also needed to be able to move forward and back since the lower links travel in an arc. For that, I used some Energy Suspension universal poly bushings and installed grease fittings. The other end uses heim joints.

The new axle brackets

I have several poly bushings on this car and I’m fitting all of them with grease zerks. I bought a new grease gun that I filled with silicone grease with PTFE (Teflon). This stuff is called Super Grease and looks exactly like the grease that comes with most ploy bushings. Hopefully, by being able to give them a shot of grease occasionally, I can keep them moving free and avoid the poly bushing groan and moan. Here’s a link to the manufacturer’s page:

Silicone Lubricating Grease with Syncolon® (PTFE)

I’m going to use this grease to lube the carb linkage that I built, too. It’s got a broad temp range and is supposed to be virtually impervious to water. It comes in standard 14 oz grease gun tubes.
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