Shimming Shocks

[Brakin80]

In the middle of a suspension rebuild. Discovered a shim under the front mounting bolts of the front right shock. Would this be something that could have been done at the factory to fine-tune the caster? Or is this a previous owners attempt at a tweak?

I preface this by saying that I am assuming that shimming the front or back of the shock would have an impact on caster. If I'm incorrect then I'm sure I'll here so pretty fast. Be gentle.

We were thinking it may be factory. The car went through a mild resto 15 years ago (a 1960 MKI BN7). At that time we know the suspension on that side had been swung out of the way to clean up the frame. Because the caster has always been out by a degree the wrong way on that side, we think that the PO inadvertantly put the shim under the front of the shock, instead of the back, where we think it originally belonged (to get the caster right).

What do you all think?

 

[Keoke]

Well Brakin80, I don't think I ever heard of that. Certainly, it is not a factory attempt at tuning. Further, I doubt that one degree of caster differential would be detectable in driving the car and the design of the top suspension does not offer much hope in changing castor angle with a shim---Keoke-?

 

[Brakin80]

So any idea why someone would stick a shim in there? What in the world would they have been trying to achieve?

Brakin80

 

[Keoke]

So any idea why someone would stick a shim in there? What in the world would they have been trying to achieve?

Brakin80

Don't know unless the tower is bent or the shock arms were bent, possibly the shock plate may have been installed crooked at some time and they were trying to level the shock absorber.---Keoke

 

[Dave Russell]

It would require moving the entire shock about 1/4" to the rear to increase caster by one degree, a change that would be barely noticeable. A shim under one edge would not change the caster enough to notice. Maybe it was an attempt to level something as Keoke says. If the shock mounting surface was not completely flat, a shim "could" prevent breaking the shock body when the mounts are tightened.

Caster, about two degrees, was originally achieved by mounting the rear of the lower control arm lower than the front which tilted the bottom of the kingpin forward about two degrees in relation to it's top. If the caster is off on one side, look at the bottom control arm mounts or maybe a bent control arm.
D

 

[anthony7777]

brakin80, the p.o. may have stripped the threats on the mounting bolt in the area that its usual depth is required, by shimming it he may have raised it enough to be able to use undamaged threads on the lower portion of that bolt. sounds spooky but possible, thats the only thing i could imagine. /bcforum/images/%%GRAEMLIN_URL%%/savewave.gif

 

[Brakin80]

Ooops! When I said the shim was under the front two bolts, I meant the ones closest to the tyre. That would imply a potential change to camber NOT caster. Would the shim be enough to effect the camber? The problem is we have two tyres cambered in the same direction, so they are both leaning right.

Two more things we have come across in this project. The original trunnion bushings had brass sleeves (pretty out of round). The replacement bushings have NO sleeve in them. Do you really require the sleeve, or have they improved the rubber composite so they are not longer needed?

The last thing. In attempting to remove the last two shock bolts on that side, we can't get them freed up. The nut underneath the shock mount plate is spinning with the bolt, and there is not way to get a wrench up inside that box - the nuts are between the bottom of the mount plate and the shock 'cone'. There are four holes in the shock 'cone' but they are not aligned with the nuts. Were the nuts originally spot welded into place? Did we break the weld and that's why they are spinning? Or should the holes in the 'cone' have corresponded with the nuts to give you access?

PO woes or lack of knowledge. Either way, I'm a learnin.

 

[Keoke]

/bcforum/images/%%GRAEMLIN_URL%%/lol.gif OK now we know why the shim was there, the hold down bolt could not be tightened. No the shock mounting plate if it is good can be cut away to give access to the spun nut on the under side. Using vise grips lock the bolt elevated in place and weld the nut back to the plate. Failing to make this type of repair will require that the Shocks mounting plate be cut off and replaced. Alternatively, and more precise a metal plate can be made with threads that match the shock bolt's and their location which is then slid in under the existing plate by cutting one side open and welding it in place. This is a Bugger no mater which way you go!

The Brass offset bushing was I guess a modification that lets you set the Camber on each side of the car. It sounds as if you will be required to replace them rather than use the standard rubber ones.---Fwiw---Keoke

 

[Dave Russell]

Ooops! When I said the shim was under the front two bolts, I meant the ones closest to the tyre. That would imply a potential change to camber NOT caster. Would the shim be enough to effect the camber? The problem is we have two tyres cambered in the same direction, so they are both leaning right.

Two more things we have come across in this project. The original trunnion bushings had brass sleeves (pretty out of round). The replacement bushings have NO sleeve in them. Do you really require the sleeve, or have they improved the rubber composite so they are not longer needed?

The last thing. In attempting to remove the last two shock bolts on that side, we can't get them freed up. The nut underneath the shock mount plate is spinning with the bolt, and there is not way to get a wrench up inside that box - the nuts are between the bottom of the mount plate and the shock 'cone'. There are four holes in the shock 'cone' but they are not aligned with the nuts. Were the nuts originally spot welded into place? Did we break the weld and that's why they are spinning? Or should the holes in the 'cone' have corresponded with the nuts to give you access?

PO woes or lack of knowledge. Either way, I'm a learnin.

It appears that you may have more than one problem. The "shims" would have very little effect on caster or camber.

The original trunion bushings would have had concentric steel bushings of about 1/16" wall thickness in them. The steel tubes are to allow fully tightening the upper trunion to shock arm bolts without excessively crushing the rubber. The inner bushing "could" be offset in an attempt to change camber. There is not physical room to gain enough offset to make much camber change. it takes about .180" of offset to achieve 1 degree of camber change.

There are some other car models that have different length shock upper control arms. Your original upper arms should measure about 8.5" center to center. Other car models had 8.2" & 7.9" upper shock arm lengths. It's possible that someone has installed one or both shocks with the wrong length shock/upper control arms.

The shock tower mounts have nuts that are originally spot welded from the bottom side. If the welds break there are a couple of fixes, but not easy.
1- You can cut access holes in the shock tower sides & attempt to reweld the nuts.

2- You can cut a slot in the shock tower, remove the nuts, & insert a new one piece steel plate that has 4 tapped holes, align the plates & reweld/fill the slots. These plates are commercially available or you can male them from 1/4" steel plate.

3- You can entirely remove the top of the shock tower & weld on a repair top which is also commercially available. Some of these tops have external adjustments for caster & camber.

I'll leave it to others to discuss the merits of each method. They've all been done many times. You haven't really said "how much" the camber is out so it's a bit hard to make suggestions. DO check the shock arm lengths first.
D
PS - Keoke, I doubled with you. Since we generally agree, I'll leave it on.
D

 

[Brakin80]

Thanks for the clarification Keoke and Dave. I now know what needs to be done. Will network with our areas club to find someone to do that work, as I'm not a welder myself. This forum is invaluable, especially with members such as yourselves.