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Old 04-22-2007, 01:17 PM
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How to adjust caster on older cars???

I would like to rebuild the stock suspension on my 41 Pontiac. Upgrading to better brakes, power steering, etc. is not difficult, but I don't know how to change the basic geometry.
This car, and many through the 50's, came with a zero, or negative caster. I would like 3 - 3 1/2* positive caster as this works well on later coil spring/A frame suspensions.
Bending spindles is scary.
Relocating the upper A frame mounts would work technically, but will it put too much bind on the steering knuckle mounts?
Has anyone shimmed the upper and lower mounts to create caster?
Would heating and twisting the upper and lower A's work?

IMO. the later GM subframes everyone uses are the same basic layout as the 40's - 50's gm suspension. (i'm not talking about the disc brakes/power steering portion, just the the suspension). A relatively easy, inexpensive, way of adding caster would be great for those of us who want to keep the stock frame/suspension components. Has anyone solved this, or has the real technical knowledge to help solve it?

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Old 04-22-2007, 01:43 PM
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First I would send you down to the local pick-a-part or wrecking yard so you can see where we place the shims on the later GM. Take your toolbox and you can come home with a can full of those things for reasonable..

Then go to stock car products or Speedway and order some alignment tools..Lot less frustrating to just DIY this than trying to explain what you want to some newbie alignment guy..at least for me..

to adjust camber one adds or removes shims from both mounting bolts of the upper a-arm..to adjust caster one adds or removes shims from either the front or rear mounting bolt..like say if you need more you shim the front mounting bolt more and the rear bolt less..The objective is to get the alignment correct with the minimum number of shims..

Takes a bit of trial and error if you have not done this before..Make sure you have the mounting bolts properly torqued before you go driving..

This is about all I know about it..

Sam
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Old 04-22-2007, 02:32 PM
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yea, you can use shims and eccentics for camber adjustment, just have to figure out where they go, but just looking at it, you will be able to figure that out
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Old 04-22-2007, 09:26 PM
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how to adjust caster on older cars

Was that a misprint guys? Or are we talking about 2 different things. My camber is fine. I need more caster. Upper and lower inner A frame mounts are basically parallel to each other. Uppers mounted "down" to the top of the frame, lowers mount "up" to the cross member. I'm not a mechanic, but I think the mounts you are describing mount to the side, and shims will effect camber, mine is done with a concentric pin on the knuckle. I don't know how caster is adjusted on those front ends. My caster is set with a threaded bolt for the upper knuckle mount that only provides -1/2* to +1/2 *of adjustment.
I may try to post some pics or diagrams.
Pontiac 38 to 54 is basically the same. Also Olds from about the same time. I suspect Buick, but haven't seen one.
Chevy with the Top Hat frame has some similarities, but the chevy is lighter and the frame is pretty much straight making sub frames and mustang IIs much easier to do.
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Old 04-23-2007, 06:19 AM
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You could tig weld the mount holes in the top a arm pivot shaft, then re drill them 1/8 rearward. This won't give much improvement, but every little bit helps. I swapped the top wishbones left to right on my HQ Holden ute and picked up 4 deg pos caster. You may not have the same offset..... but then again it's something else to measure.
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Old 04-23-2007, 08:29 AM
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Quote:
Originally Posted by IanRiordan
You could tig weld the mount holes in the top a arm pivot shaft, then re drill them 1/8 rearward. This won't give much improvement, but every little bit helps. I swapped the top wishbones left to right on my HQ Holden ute and picked up 4 deg pos caster. You may not have the same offset..... but then again it's something else to measure.

After some sleep I was thinking the same thing..Any way welcome to the world of Hot Rodding where we figure out how to do this..Sounds like the factory did not provide a lot of adjustment in those.

Some pictures would help so we might be able to come up with a fix.

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Old 04-23-2007, 10:25 AM
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I believe the adjustment is inside the upper control arm. Remove the grease plug on upper shaft and rotate with an allen wrench i believe. I'll double my shop manual later.

It's really unnessessary to have that much caster. Not really needed for non power steering cars. I would rather have it at 0 or whatever the spec is. If you want 3 degrees I would get a suspension thats designed for it IMO.

Disc brake kits are available for that car. No modifications to spindle required.

Last edited by chieftain; 04-23-2007 at 11:34 AM.
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Old 04-23-2007, 03:03 PM
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re: How to adjust caster on older cars???

First off, thanks for responding. It helps just to have someone to kick around ideas.
Ianriordan = I'm having similar thoughts, but i'm afraid the offset would put the upper and lower knuckle mounts in a bind. Guess I need to take it apart and see how much leeway is there. Never even thought about swapping sides. Worth a look.
Onemoretime = Had an ancient mechanic tell me the zero (or negative) caster was to deal with the old rutted dirt roads, especially without power steering. Also speed limit back then was 45, max. Positive caster (like on a bike front end) makes them kind of self centering and works much better at freeway speeds. Apparently the concept of 3 or 4 degrees of caster wasn't a consideration. I've tried pictures, but they don't help. I'll take some more when I tear it down and separate the pieces.
Chieftan = 100% correct on the caster adjustment. It drives OK with the 1/2 * I've cranked into it, but I did a brief stint with an alignment shop back in the early 70's and learned a few basics : When they "wandered" like mine is doing we increased the caster. If we went too far, we would get "rough road shimmy". Between these 2 (3 to 4 * usually) was the best setup. Trouble was, I didn't learn enough to modify a front end. Hear the dirt track guys have played with every concievable modification. Maybe one of them will jump in.
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Old 04-23-2007, 04:49 PM
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My 55 suspension is still very similar to your 41. Luckily for me 58 (the last year before the "widetrack") arms were for ball joints and the lowers are a bolt on and made a mount for the upper. I havn't got it up on the alignment rack to double check everything, but should get some decent caster out of it.
Without some special arms made or modified to make the change i'm not real sure how else it would be done on your 41.
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Old 04-23-2007, 09:18 PM
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re: How to adjust caster on older cars???

I've got a manual for the 49 - 54 coming. Hope it has the same details, specs pictures and layouts my 41 manual has. I should be able to tell conclusively what will work (yea, right).
Do you have a manual on yours? Would be real curious to see just how new I could go on front end/brake parts without clipping the frame.
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Old 04-23-2007, 10:19 PM
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re: How to adjust caster on older cars???

BTW. Just checked the Fatman site. He doesn't have a MII for these cars.
He has a subframe he sells that you can stub in, and then do a MII on that.
Might as well stub in the GM
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Old 04-24-2007, 01:12 AM
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I think at this point I would measure the existing face of drum to face of drum and get a track width and then measure up the frame rails and then it is off to the pick-a-part and find myself something that would work under there..Might get lucky and even find something with power steering and everything we need..

I like the idea of finding a later model frame clip and putting that in on account of if I need some ball joints. or rotors and pads I can then go to the parts store and just get the ones that fit that clip..Much nicer than going aftermarket..

Any way take a deep breath and think this through until a workable solution is found..

Sam
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Old 04-24-2007, 03:13 AM
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On a previous post I mentioned how some 20 odd years ago we made a friends 39 Pontiac handle just bt modifiying the stock ifs and adding a rear sway bar.
If your scared of knuckle bind, just weld and redrill the wishbone mount holes to rotate the whole assy through an arc. This will give you some anti dive as well as caster.
This zero caster thing is bull. Early (buggy sprung) Fords ran 3 deg in the front crossmember alone. The larger wheel/tyre combo you run, the more caster needed to centre it. M/Benzs since 1972 have run upwards of 8 deg and are easy to steer with your knee over 120 mph, I drove semis for a couple of years and if it went hard we just put more wedges under the spring.
Watch a Benz on full lock in a parking lot and check the camber change on lock - this spells GRIP. With my Holden mocked up at ride height with -30 min camber & 9 deg caster it goes to -3 deg 40 min camber at full lock on the outside and the inside tyre is just under +3,30 ........are we gunna turn in or what?
Many people bag king pin front ends, but those old GM ifs's were strong and lasted well if you could use a grease gun. Is the m2 front that good? It looks kinda flimsy to me, I know they're in common use but so is mcdonalds - popular but still not food.
Ian.
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Old 04-24-2007, 01:38 PM
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re: How to adjust caster on older cars???

I'm not a fan of the MII.
I want to discuss your last post in depth, I am not rushing into this.
But I have to leave town for a week, so I'd like to pick this up when I return. don
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Old 04-24-2007, 03:59 PM
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Quote:
Originally Posted by chieftain
I believe the adjustment is inside the upper control arm. Remove the grease plug on upper shaft and rotate with an allen wrench i believe. I'll double my shop manual later.
IF that Pontiac is similar to a '49 Olds, as oldguy829 mentioned in the 2nd post, then the following page from the Olds service manual matches (and backs up) your memory:

http://edge-op.org/1949_Oldsmobile/index.php?page=73
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