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Strut rod bushings: Thickness affecting caster?

Kern Dog

Life is full of turns. Build your car to handle.
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Hey guys,
A local friend is in the process of rebuilding the front suspension and steering in his '68 Charger. Today he pulled the strut rods and noticed that the bushings in the rebuild kit (rubber) are thicker than the stock ones by a fair margin. I used urethane in my car and cut the rear one back so they matched the overall thickness of my worn out stock ones.
Tomorrow I'm going to do a side by side mock up with new bushings on one side and the new ones on the other. My guess is that even with both sides cranked down, the new bushings will still be thicker, resulting in a slight loss of caster.
Obviously any loss of caster is bad.
The upper control arms already have new stock type rubber bushings installed so it might be late to use the Moog offset bushings.
I am curious who has dealt with this and if so, did you just cut away part of the bushing to get it to be as thick as stock?
 
Could it be that it's just old rubber and shrunken down with time, or is he sure he got the right parts? Does it look like they'd even fit with a press? I would think that any change in alignment would be moot, how much change would be needed to loose 1* of caster or less? I'm not a wizz about front suspensions but don't see that big of a deal if there's no modifications. I'm sure others will chime in. Good Luck
 
Geez....I'm no suspension expert either, but I agree with 69a100. Unless the thickness is so ridiculous it's not even close, I would "suspect" the thicker ones will just compress more. How that would affect the alignment, I couldn't say for sure.

Just thinking out loud here....IF the new/thicker bushings cannot compress down to "new stock size", then I think that would force the lower control arm back and angled out.....more castor & more toe out. Use your own judgement if they're too thick or not.
 
The problem is that any further rearward movement of the strut rod also pushed the control arm back, with it goes the lower ball joint. This does affect caster and is one of the reasons behind the production of adjustable strut rods.
The new bushings are 1/4" thicker. I worry that by cranking them tight enough to compress to match the originals, they may split.
 
I would install the bushes as they are. The strut rod just holds the lower arm in position.
The caster and camber are adjusted in the top A arm eccentric bolts.
There should be a sleeve so you do not crush the rubber bush when you torque the strut rod nut I think it is 62 foot pounds.
 
I appreciate the responses but I think that you guys are not seeing it as it is.
A thicker bushing will move the inner washer rearward along with the strut rod. This moves everything rearward. Any rearward movement results in a loss of Positive caster. The upper control arm adjustment for camber and caster does not have a huge range. Most cars can get no more than 2 degrees with regular bushings and maybe 4 with the offset Moog K7103 bushings. I was able to get 4 1/2 degrees in my 70 Charger but I chalk that up to a positive tolerance stack.
When viewed from the side, an imaginary line is seen through the top and bottom ball joints. The upper ball joint must always be further to the rear than the lower.
I had a 73 Dart with a bent K member. It wasn't that obvious except for a small dent. The RH LCA sat so far to the rear, I could not get any positive caster from it unless I removed the strut rod and just mocked it up without a bushing in it. The 3/4" of bushing made a huge difference. I had to replace the K member and afterwards, it lined up great.
 
^^^ what he said @steve340

There is a crush sleeve in there. If you run the nut down tight and it's against the sleeve the installed 'hieght' is the same. If the bushing is too big it will squeeze out a little more than the originals.
 
Are the lower arms installed? If yes measure the distance from arm to bracket at normal ride height. Then install bushings and measure again. Lower control arms are not meant to be place in a bind with everything installed. Suspension movement will only esculate the castor problem if not corrected.
 
I had the same problem. From memory I was going to cut down the bushes - I think it's a common issue and there were measurements and drawings from the A bodies forum I think. In the end I was able to leave them alone, as my new mancini racing strut rods were too long themselves and I had to have them turned down. I had a bit more taken off the shoulder to accommodate the thicker bush.
20170807_172503.jpg
It all works well.
20170913_130126.jpg
 
Thank you for that....Steve Wall is pretty sharp regarding suspension stuff.
 
If I remember correctly when you tighten up the strut rod nuts you tighten them till the nut stops (bottoms out) So if the new bushings are thicker they will just compress more and assuming both bushings are the same thickness the rod will be in the same relative position.
 
One way to find out is to put it together and then take it to be checked.....and if you end up with a few degrees of negative caster, then you'll know what you need to do.
 
I appreciate the responses but I think that you guys are not seeing it as it is.
A thicker bushing will move the inner washer rearward along with the strut rod. This moves everything rearward.

You are correct Kern Dog. When I was rebuilding my Abody Barracuda, I had a bent strut rod and wanted to find a replacement. Couldn't find anyone at the time that offered them and I wanted to get it back together so we straightened it on my neighbors press.

But!!.... While looking for replacements, I was talking to Matt @ Firm Feel about the solid strut rods that they offer. I didn't go with theirs because he was telling me that they machine theirs shorter to accommodate the thicker poly bushings. So you are correct that the thicker poly bushings push everything back. He told me that the thicker bushings do not compress much and can cause issues with stock length strut rods, which is why they chose to make theirs shorter to accommodate the poly bushings they sell.

The way I see it is you have a couple options.... Go back to rubber bushings and you will be fine, or if you want poly bushings, you could order their shorter strut rods (or anyone's adjustable strut rods). Might even be able to have a machine shop cut the ledge down on your stock strut rods to accommodate the thicker bushings. If it were me, I wouldn't do that though as the stock length strut rods seem to be getting hard to find.
 
Isn't someone making adjustable strut rods? If you have access to a lathe, looks to be like they wouldn't be all that difficult to make them from stock rods....
 
I had the same problem. From memory I was going to cut down the bushes - I think it's a common issue and there were measurements and drawings from the A bodies forum I think. In the end I was able to leave them alone, as my new mancini racing strut rods were too long themselves and I had to have them turned down. I had a bit more taken off the shoulder to accommodate the thicker bush. View attachment 656194 It all works well.View attachment 656184


I cut my Mancini rods down in a lathe also.
 
You guys are getting me nervous about the solid Mancini rods I just ordered for my Bee. Their description states that they are the exact same length as stock. Not so?
 
I understand a few people have had issues with them. I contacted Mancini and was told they were fine, they sold lots of them and everyone was happy. This was a load of b.s. as they were clearly longer (see pic). Luckily a local guy turned them down for about $20 a side. Other than the length they are good - very solid.
20170706_134825.jpg
 
One way to find out is to put it together and then take it to be checked.....and if you end up with a few degrees of negative caster, then you'll know what you need to do.
What he said in that comment up there (1).jpg

I guess I'd really have to be there to see what's going on KD. But if it's that bad, why can't you grind down the bushing some? I say this cause I used a poly bushing when I replaced the tranny mount in my A100. I stuck out to much to fit in the mount so out came the grinder to fit it. YES, I know this is different then steering but sometimes you gotta do what works. BTW, that really straightened out my driveline and the van drives tons better. Good Luck
 
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