Trailing Arm Shims Original?

[Jack O.]

I removed my trailing arms and was surprised that on both sides my shims still had the GM part number labels (see pictures). The part #'s don't match the assembly manual so are these perhaps GM replacements put in when someone else did the trailing arms? The car is very clean underneath but it would be surprising if these were the originals. Are shim changes ever needing during an alignment?

Jack

[Mike M.]

Re: Trailer Arm Shims Original?

over the counter service replacements . mike

[Joe L.]

Re: Trailer Arm Shims Original?

I removed my trailing arms and was surprised that on both sides my shims still had the GM part number labels (see pictures). The part #'s don't match the assembly manual so are these perhaps GM replacements put in when someone else did the trailing arms? The car is very clean underneath but it would be surprising if these were the originals. Are shim changes ever needing during an alignment?

Jack

Jack-------


You don't mention the year of the car but I presume it's a 1969. While I believe that some late 1969's used some slotted-style shims (mine did for a few shims), slotted shims were generally not originally used for 1969. The part numbers of the shims shown did not even exist in 1969. In addition, original shims would not have had SERVICE parts labels, even if slotted shims were used.

However, original or not, I highly recommend the use of ONLY slotted style shims for any 63-82 Corvette.

[Jack O.]

Re: Trailer Arm Shims Original?

Thanks. So even though they've been replaced before I suppose it still makes sense to replace the shims with the same thickness as a starting point. Does an alignment sometimes require shim changes?

[Steve G.]

Re: Trailer Arm Shims Original?

Thanks. So even though they've been replaced before I suppose it still makes sense to replace the shims with the same thickness as a starting point. Does an alignment sometimes require shim changes?

The alignment doesn't require changing shims, just repositioning them. The total stack thickness is important. That's what ensures that the inner sleeve in the bushing will tighten securely in the frame. To adjust toe shims are moved from one side of the arm to the other so that the total stack remains the same. Re-assemble with the same shim thicknesses on each side of the arm as were there when you took it apart, making sure your pack is made up of a reasonable number of thin shims.

[Larry M.]

[Jack O.]

Re: Trailer Arm Shims Original?

Thanks for the advice. The slotted shims I removed had no cotter pin installed so I guess the last installer simply left it off.

It's amazing what gets left off these cars over the years. I was investigating why my gas tank overflow hose kept hanging out of the bumper, consulted the assembly manner, and found that someone decided the inner bumper brackets were not really needed.

[Terry M.]

Re: Trailer Arm Shims Original?

Thanks for the advice. The slotted shims I removed had no cotter pin installed so I guess the last installer simply left it off.

It's amazing what gets left off these cars over the years. I was investigating why my gas tank overflow hose kept hanging out of the bumper, consulted the assembly manner, and found that someone decided the inner bumper brackets were not really needed.

Sometimes nothing is left off and the only problem is we don't have a good idea of the assembly process. Even thought the hole for the long cotter pin to hold in the slotted shims appeared in later 1969 model year production, the cotter pin was not used until the last week of 1970 model year production (July 1970).

[Larry M.]

Re: Trailer Arm Shims Original?

Sometimes nothing is left off and the only problem is we don't have a good idea of the assembly process. Even thought the hole for the long cotter pin to hold in the slotted shims appeared in later 1969 model year production, the cotter pin was not used until the last week of 1970 model year production (July 1970).

[Joe L.]

Re: Trailer Arm Shims Original?

All------


I've used slotted shims for my 1969 for years and I've never used a cotter pin. I've never lost a shim on the road. The trick is to make sure the shim pack is tight, make sure the nut is tightened to the specified torque, AND make sure the shims are tucked down into the frame pocket.

[David L.]

Re: Trailer Arm Shims Original?

The 1963-1968 Corvettes used 4 3/4" long shims with 2 holes (17/32" dia.) with the following GM part numbers and thicknesses:
GM # 3846595 (1/4"), 3846596 (1/8'), 3846597 (1/32"), and 3846598 (1/64"). These were also sold over the counter (Gr. 5.380).
To change the location of these shims the 3846867 bolt would have to be removed. The later slotted shims made adjustments a lot easier.

As per Chevrolet Parts History (service parts):
3846595 to 3965192 in Feb. 1973 to 3983392 (4 1/2" X 1/4", 17/32" oblong hole) in May 1973
3846596 to 3965193 in Oct. 1969 to 3983393 (4 1/2" X 1/8", 17/32" oblong hole) in Sept. 1972
3846597 to 3983394 (4 1/2" X 1/32", 17/32" oblong hole) in Jan. 1973
3846598 to 3965195 in May 1969 to 3983395 (4 1/2" X 1/64", 17/32" oblong hole) in Feb. 1972

3965194 to 3983394 in Feb. 1972

Dave

[Terry M.]

Re: Trailer Arm Shims Original?

Joe,
The points loss for the cotter pin too early would be minimal, and IMO not worth the time to remove the cotter -- but of course we all make our own decisions.

You, of course, are right that if the slotted shims are properly installed the cotter is not necessary.

[Jack O.]

Re: Trailer Arm Shims Original?

Thanks everyone for all the great information! Do the trailing arm bolts use plain flat washers? The ones I pulled off are about 1/8" thick and are "stepped" on one side.
Jack

[Joe L.]

Re: Trailer Arm Shims Original?

Thanks everyone for all the great information! Do the trailing arm bolts use plain flat washers? The ones I pulled off are about 1/8" thick and are "stepped" on one side.
Jack

Jack------


Trailing arm bolts use BOTH flat washers and split lock washers. The flat washers were 15/32" ID, 15/16" OD, and 3/32" thickness. They were zinc plated. I know of no "step" on these washers. The split lock washers were 7/16" ID, 25/32" OD and 9/64" thickness. They were phosphate finished.