Rear Trailing Arm Bushing Thru-bolt

[Thomas S.]

67 big-block - I noticed 2 shims on outboard side of the left rear trailing arm moving freely. On further investigation it appeared that a shim was missing. The shims on the car are the correct type (not slotted) so the only possibility I can see is that if one fell out, it must have be a slotted type.

the castle nut also appeared to over tightened since its slots were well below were a cotter-pin would have worked properly.

can the through-bolt be removed and replaced with the arm in position? I realize I could use a slotted shim for that gap, but would prefer to keep it correct.


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[Gary B.]

https://www.forums.ncrs.org/showthre...263#post804263

Gary

[Gary B.]

[Thomas S.]

Re: Rear Trailing Arm Bushing Thru-bolt

Mine actually looked like that as well until I tightened a bit. Even the photo you shared has the cotter pin just barely in the slot. Any thought on removing the bolt with the trailing arm in place, or is that likely to lead to unintended consequences?

[Gary B.]

[Thomas S.]

Re: Rear Trailing Arm Bushing Thru-bolt

Good catch on the extra lock washer. That would definitely get a proper config. There a lot of comment on slotted vrs no slotted shims. The simplest thing would be to use a slotted shim to make up the difference, and bit the bullet at some future point when the trailing arms are removed. The car is handling fine and no unusual wear on the tires.

I'm chasing some suspension noise and went through the entire under carriage verifying torques. Lots of tightening to specs. Still got rattle so this is one more thing to eliminate. The actual noise I'm getting is coming from the front wheel area when on a rough surface. I have a Mohawk lift that allows me to raise the car using wheel adapters. Banging of the front tire with a rubber mallet will cause the noise which seems to be coming from the spring. Off topic so I'll stop. Thanks for replying.

[Leif A.]

Re: Rear Trailing Arm Bushing Thru-bolt

Tom,
Check the interior side of the trailing arm and be sure there is a similar washer under the bolt head. That, along with the lock washer would make up the difference allowing a cotter pin to fit into the castle nut correctly.

[Thomas S.]

Re: Rear Trailing Arm Bushing Thru-bolt

Interior side has the flat washer, I believe the lock-washer on the outboard side will do the trick. Thanks for the input.

[Timothy B.]

Re: Rear Trailing Arm Bushing Thru-bolt

Thomas,

When you install the outboard lock washer and loosen the bolt push the trailing arm in tight so the bushing is against the inboard shims then get some slotted shims and fill the outboard gap snug then tighten the bolt and install the cotter pin. Don't try to remove the bolt from the frame because you will fight the spring.

To the best of my knowledge that bolt is used for the rear front differential mount so that may explain why it's just a bit longer when in the trailing arm.

[Thomas S.]

Re: Rear Trailing Arm Bushing Thru-bolt

That is my exact plan and thanks for confirming the approach. Gary had pointed out the missing lock washer which I will install - I was also missing on left trailing arm as well.

[Duke W.]

Re: Rear Trailing Arm Bushing Thru-bolt

This needs to be done on a modern alignment rack in order to get the proper amount of rear toe, which is absolutely critical to handling stability on these three-link IRS Corvettes. Get a selection of OE type "captured" shims. Then educate an alignment shop on how to do this job per this thread.

https://www.corvetteforum.com/forums...-distance.html

Once set up on the rack use a pole jack to jack up the rear spring about one half inch so the link bolt is loose. This removes the load from the trailing arm and tire. In addition to having the car in first or reverse and the parking brake firmly set I also recommend double chocking the opposite front wheel.

Once the spring load is removed from the trailing arm, remove the through bolt, set the trailing arm to achieve as close to 1/32" as possible with radial tires and up to 1/16" inch with bias ply tires, then measure and trial fit shim stacks to both inner and outer positions. Once the best trial fit is achieved, remove the shims and install the packs with and extra 1/32" worth of shims on each side.

IMPORTANT: The last installed shim (a thick one) should be a slight interference fit requiring light tapping with a small hammer to seat.

This is the reason the extra 1/32" worth of shims is added prior to final installation once the gap is fully filled.Once the bolt is installed and the nut just barely snug, remove the jack from the spring, bounce the car up and down a couple of times to ensure that it's a proper ride height, then torque the nut and check that toe is in the correct range.

While you're at it you might as well check both sides and correct both to the above per wheel toe-in spec. With the captured shims you will never loose one, and the reason most slotted shims are lost is due to importer installation... not having that slight interference fit on the last shim and then properly torqueing the nut to spec with the suspension at normal ride height.

Duke

[Thomas S.]

Re: Rear Trailing Arm Bushing Thru-bolt

Thanks for this detailed procedure. You also answered a question about how the final oem shim stack combination is determined. i had assume there was a preliminary stack (trial fit) which was subsequently remove and replaced with the correct type. The comment about release the spring pressure with a pole jack was also a question I had and you confirmed it. Now to find a shop that is willing to follow these instructions.

This all started because of some rattling one the driver side. The rubber mallet method was used and there were loose fender fasteners, and many bolts that need to be torqued to spec. The inside baffle of the passenger side pipe was shot and it was definitely rattling so I replaced it along with new support bushings. the heat riser was also rattling away and that is now wired opened.

I also noticed a loose rivet on the upper A-arm that is making noise as well. Hopefully, I will eventually find the problem, or at least rule out most of the possibilities.

Thanks for the valuable info.

[James W.]

Re: Rear Trailing Arm Bushing Thru-bolt

I used some of these slotted shims I had machined along with the non-slotted shims to get the correct toe. I also used the flat washer, lock washer and castle nut on the outer end. I've also included a drawing of a trailing arm shim fabrication drawing. This slotted shim will sit inside the frame pocket and not fall out.