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-   -   rear suspension change needed? (http://www.hotrodders.com/forum/rear-suspension-change-needed-98442.html)

grouch 09-18-2006 06:32 PM

rear suspension change needed?
 
3 Attachment(s)
Do I need to mess with the basic original design of the rear suspension on a '49 Olds?

The goal is to have a car that's fun to drive occasionally, not a daily driver nor a dragster. The weight of the car means it will never be a sports car, so I'm not going to try to get it to corner like one. The heavy frame and lots of space up front begs for an engine with lots of torque, so I'll have to beef up that rear end.

Other than the differential and shocks, what's wrong (and what's right) with the original design? The radius arms(?) in the attached image are about 45 inches long.

I intend to make a 5" to 7" drop. The thing had 8-1/2" clearance under the differential, originally! Can this drop be achieved with this design, getting the differential up higher into the step of the frame, so that at normal ride height the frame itself is the lowest part of the car? Will that result in a ride so harsh it won't be a decent cruiser any more?

Thanks!

Deuce 09-20-2006 08:27 AM

The setup you have was used by race cars for years ... and works well. The Oldsmobiles of that era were advanced in design over most of the other vehicles on the road in 1950.

I would upgrade the axle to something a little more user friendly ( a 9 inch Ford ;) ) but retain the basic suspension system ...

Deuce ...

powerrodsmike 09-20-2006 09:34 AM

Deuce is right, I would add that your current setup lends itself to easy spring changes so you can get your ride height and spring rate changed to suit your needs :) Also, a set of air bags will be really easy to install on that setup.
As far as a harsh ride is concerned: Folks will lower a car by using up all of the suspension travel, then try to keep it from bottoming out the frame on the axle by putting stiffer springs. :( Bad idea.

You can C- notch that frame some to get some of your clearance back. A spring relocation would help also.
I would think that the front suspension is going to be more of a challenge. What does it look like?

later, mikey

OneMoreTime 09-20-2006 09:42 AM

Quote:

Originally Posted by powerrodsmike
Deuce is right, I would add that your current setup lends itself to easy spring changes so you can get your ride height and spring rate changed to suit your needs :) Also, a set of air bags will just about install themselves in those mounts.
As far as a harsh ride is concerned: Folks will lower a car by using up all of the suspension travel, then try to keep it from bottoming out the frame on the axle by putting stiffer springs. :( Bad idea.

You can C- notch that frame some to get some of your clearance back.
I would think that the front suspension is going to be more of a challenge. What does it look like?

later, mikey

Only thing I would say is to "Z" the chassis in the rear by adding a piece of box tube to the top of the frame rail to gain back any strength lost by making a "C" cut in a chassis rail..Just my way..

When I set up a chassis to be as low as possible I measure the sidewall of the tires and set the bottom of the chassis at that height..set it on blocks at design ride height and then it gets a lot more clear as to what has to be done to get the chassis to that point..

Refer to my journal to see how I do it..others have other ways that work for them..

Sam

grouch 09-20-2006 02:21 PM

2 Attachment(s)
Deuce: Those long, hefty arms look great for transferring the push but I wasn't sure if the design was completely obsoleted by later ones. For straight-line travel, it looks like the harder it shoves, the more it has to lift the car. If I can find my dream donor car, a '76 Cadillac, I'll probably adapt its rear end to this setup instead of getting a Ford 9". The rear track of that Caddy is just 1.7" wider than the Olds. Or were you talking about somehow putting the Ford 9" into the existing housing?

powerrodsmike: The harsh ride is what I want to avoid. Easy spring changes sounds good, in case I get the itch to find out what it will do in a 1/4. :) When I took the shock links off and the panhard bar loose, the frame jumped up quite a bit, with the right side considerably higher than the left. I was hoping modern springs might have some magic to be shorter without being harsher. If the frame has to be notched to get both lower and retain a good ride, so be it! The front suspension does worry me. Images attached.

OneMoreTime: I will make sure the frame is at least as strong when finished as before. I don't mind intruding on the trunk space. To mock it up and find out how much the frame has to be altered, I need the donor car on hand, at its normal ride height?


I know where I want to end up with this car; it's getting from here to there that I don't know about. There's a huge difference between putting a car back to specs in a service manual and creating a unique mutant. Without you folks being willing to share what you know, I'd have been lost down any of multiple blind alleys by now.

OneMoreTime 09-20-2006 04:48 PM

Grouch,
What I would do is take the springs completely out and then block the chassis at the finished ride height..Then I can see just what I need to do to get there from here..

the minum ride height that I will use is the height of the tire sidewall..If you are planning on using some of those 35 or 40 series tires then the car winds up with about 2-3 inches of ground clearance..Plenty low enough for even the most hard core low rider..with a 70-75 series tire you will have about 7" of ground clearance..

Now if you are using coil overs the distance between mounting points is 12" on the front and 14" on the rears..

You can go to stock car products.com and get the springs that you need for reasonable last time I checked..and check out their tech on chassis setup as it is very educational....

Also if you can find any of the books by Carroll Smith on suspension and chassis they are well worth the money..try Steve Smith autosports.com for those..

Sam

home brew 09-20-2006 05:20 PM

The Knowledge Base has a huge amount of info on suspensions. Here a link to the "Common Suspension Discussions":

http://hotrodders.com/kb/suspension-...uspension.html

grouch 09-20-2006 09:51 PM

Thanks home brew. I had missed that "rear axle to frame clearance" thread and it's just what I need to know. The original has a lot of suspension travel as well as a lot of ground clearance.

It looks like Deuce has about 4" in that C'd frame in his journal and that's also what was mentioned in that thread. Even when the body was on the frame, this Olds had almost double that much clearance to the stop. With the body off, it has 9" from axle to the rubber bumper and 12" from axle to the frame. (The rubber stop is positioned on the forward sloping part of the frame). This is encouraging.

I remember the first time I drove the Olds, it was remarkable how much that suspension absorbed. There is a set of railroad tracks in Leitchfield, KY that used to eat tourists' cars, before they fixed it. You go up a hump of about a car length and it suddenly flattens out to go over the tracks. There was nothing between the tracks but crumbled asphalt. Natives going into town would crawl over the tracks. Tourists heading out toward the lake would launch up that hump and slam down between the tracks. That Olds simply rose up and settled, no matter which way you went. It kind of wallowed side to side in the rear if you hit the tracks at an angle. Highways and travel patterns have changed a lot since its era.

BillyShope 09-21-2006 08:03 AM

Quote:

Originally Posted by grouch
The weight of the car means it will never be a sports car....

As someone has already pointed out, you already have a suspension layout similar to the NASCAR Cup cars. With approximately the same weight and CG height, there's no reason why the car can't be made to handle. Of course, if you want it to handle like a sports car, you have to accept the same level of harshness. Even a stock Miata has a harsher ride than a conventional car.

Frisco 09-21-2006 08:35 AM

Quote:

Originally Posted by grouch
Do I need to mess with the basic original design of the rear suspension on a '49 Olds?

The goal is to have a car that's fun to drive occasionally, not a daily driver nor a dragster. The weight of the car means it will never be a sports car, so I'm not going to try to get it to corner like one. The heavy frame and lots of space up front begs for an engine with lots of torque, so I'll have to beef up that rear end.

Other than the differential and shocks, what's wrong (and what's right) with the original design? The radius arms(?) in the attached image are about 45 inches long.

I intend to make a 5" to 7" drop. The thing had 8-1/2" clearance under the differential, originally! Can this drop be achieved with this design, getting the differential up higher into the step of the frame, so that at normal ride height the frame itself is the lowest part of the car? Will that result in a ride so harsh it won't be a decent cruiser any more?

Thanks!


Here are a few thoughts from me. Back in 1959 I owned a '50 Olds Coupe. It had a '56 Olds engine, '38 Cad/LaSalle trans with Corvette shift linkage. Suspension was basically stock except for cut coils in the front to lower it about 3". I ran the largest rear tires I could get at that time (8.20-15) and the rear wheel wells were radiused (Full radius). You might consider this for ease of rear wheel removal if you do lower the car as much as you mentioned. That car rode great and although I never tried any high speed type road racing, it handled very nicely. I did have new shocks on it.

As to the strength of the rear end; I believe your '49 rear is the same as the '50. If that is the case, third members from both Olds and Pontiac up to 1956 will interchange. That third member/rear end assembly was "the way to go" at the time ('50's thru '60's). It was the "9" Ford" rear of that era and is plenty strong for the application you have described.

ENJOY!!! :thumbup:

grouch 09-21-2006 08:47 PM

Quote:

Originally Posted by BillyShope
As someone has already pointed out, you already have a suspension layout similar to the NASCAR Cup cars. With approximately the same weight and CG height, there's no reason why the car can't be made to handle. Of course, if you want it to handle like a sports car, you have to accept the same level of harshness. Even a stock Miata has a harsher ride than a conventional car.

I'll replace the bushings on those support arms and concentrate my modifications on the springs and shocks layout. I didn't mean it would be doomed to handle like Holstein in a mud wallow. It's just that big, heavy body stuck up in the air and the fact that I don't want a ride so stiff you can count pebbles means that the car will never be king of the curves. As you point out, if I accept a harsher ride, I can improve the handling.

Every design is a collection of compromises. The feedback I've received here has convinced me that this rear suspension design doesn't have any compromises that interfere with my goals. Because of how much I don't know about suspensions, I was afraid I had the automotive equivalent of a conestoga wagon suspension under it. :)

Quote:

Originally Posted by Frisco
Here are a few thoughts from me. Back in 1959 I owned a '50 Olds Coupe. It had a '56 Olds engine, '38 Cad/LaSalle trans with Corvette shift linkage. Suspension was basically stock except for cut coils in the front to lower it about 3". I ran the largest rear tires I could get at that time (8.20-15) and the rear wheel wells were radiused (Full radius). You might consider this for ease of rear wheel removal if you do lower the car as much as you mentioned. That car rode great and although I never tried any high speed type road racing, it handled very nicely. I did have new shocks on it.

As to the strength of the rear end; I believe your '49 rear is the same as the '50. If that is the case, third members from both Olds and Pontiac up to 1956 will interchange. That third member/rear end assembly was "the way to go" at the time ('50's thru '60's). It was the "9" Ford" rear of that era and is plenty strong for the application you have described.

I'm 47 years behind and 2 weeks ahead of you on the radiused rear wheel wells. :D See http://www.hotrodders.com/forum/what...e-96254-2.html the 49-flames-8.jpg attachment.

In the shop manual, it talks about the differences between the internals of the rear end used for the 6 and the 8. You were likely dealing with a rear end from a "Rocket 88" or 98. I'm still a little nervous about hooking a high torque big block to that old differential. I'd prefer to be able to use engine, transmission and rear end from a donor car.

grouch 09-22-2006 04:14 AM

1 Attachment(s)
It's early in the AM, so this might be the result of sleep deprivation instead of clear thinking. What about doing a kind of Z-ing of the frame for the drop? Hope the attached image is readable. Only one side shown cut. Blue lines are where it would appear to need reinforcement.

Is this crazy, or just more trouble than needed?

OneMoreTime 09-22-2006 08:06 AM

Pardon the pun
 
That is ZZZ..actly how we do it..do it at the front as well and you will have a nice low stance and not have to go thru the misery of dropped spindles and all that sort of thing..

Sam

grouch 09-22-2006 02:45 PM

1 Attachment(s)
Thanks OneMoreTime. Attached image shows both ends Z'ed. The rear looks fairly simple: A bit of jigging to hold everything in place, cut, re-weld, remove jig. The front is complicated by the extra frame rails, the coil spring hats incorporated into the crossmember, and the anti-sway bar mounts.

OneMoreTime 09-22-2006 03:23 PM

On the front if you stay just behind the crossmember,,kinda like doing a clip then it can save a bunch of work..

Of course on the front you will lose some height in there so you will need to remodle the radiator support and inner fender wells to accomodate the modification...You may need to do something different on the radiator as well...

Good luck..

Sam


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