Trailing Arm Question

[Paul A.]

[Mike T.]

Re: Trailing Arm Question

Paul - When I bought my NOM 65 L78 Roadster nearly 3 years ago, the cosmetics had been done and done fairly well. The mechanicals...not so much. I wound up tearing out the differential and trailing arms. When I put it all back together, the old original shims were pretty crusty (Portland Oregon car from new) so I replaced them with the later slotted shims. That meant to retain them I needed to drill the frame to allow me to use one of those long cotter pins. I put the shims in and had ballparked where the hole needed to be drilled. Marked it with a centerpunch and used some 12-inch long drill bits to make the hole. The frame pocket in that area is made of multi layers of steel so it's a long ordeal to drill through all of it...and of course, both sides of the pocket. I used a small diameter bit to begin with. Greased the tip, drilled for 5-10 seconds, regreased the tip, drilled again, rinse repeat a bunch of times. Took freaking forever but that's the way you have to approach it because if you lean too hard, go too fast and not enough lubricant on the cutting edge, you'll burn out the bit and no more cutting going on.
IMG_4411.jpgIMG_4412.jpg

[Scott P.]

Re: Trailing Arm Question

Paul, Mikes method is good. I have drilled several customers cars for the slotted shims. I just put a shim on each side of the TA and up in the pocket, then drill for the center of the outer one then proceed to the inside shims hole. You will be getting real close to the fender when you drill the inner hole so be careful.
I will go look where I bought the last 1/8 x 4" cotter pins for you or just send me an email with your address & I will send you two N/C.
Fogaley@sbcglobal.net Drills are not two expensive so get the best you can, I bought a cheap one and it unraveled the twist backwards while drilling the hole. Go get good stuff. Scott

[Paul A.]

[Alan D.]

Re: Trailing Arm Question

Here is another little trick a member (Ralph) did,

1. I welded the arm onto the 1/4" shim only. I then drilled and tapped a 10-32 hole in the center of the shim so that I could attached thinner shims to it "as needed" via a drilling a clearance hole in the thinner shims and attaching them with a 10-32 screw. In affect; the shim pack was sandwiched together with a screw which is NOT visible when it's buried inside the frame cavity.
2. Because I had access to a machine shop; I was able to do the "slotting" in Bridgeport milling machine; however, this could be done with a hack saw. All shims in the "shim pack" must be slotted, the thin ones area bit more difficult to do.
3. Sketch attached showing modification.
4. Picture of actual shims attached ------ the one on the left is a 63-67 shim which had been slotted and has the 10-32 hole for the thinner shim containment, the one on the right is a 67 & up shim.
5. Due to variation I highly recommend making a modified shim identical to my sketch out of 1/4" plywood to make sure it works before making it out of steel.

Have a picture of that shim however unable to post, if needed can work on problem later today.

6. Some guys simply do the slotting with OUT the arm ---------- this will work perfectly; however, you are at great RISK because they have been know to loosen and fall out while driving !
7. This worked out perfectly for me because it met the NCRS 1966 requirement PLUS the guy who performed my rear alignment had no problems removing the shim pack without removing the training arm bolts. Note: I slotted and drilled plenty of extra shims for him to get the desired shim pack thickness he needed to align the car.

[Mike T.]

Re: Trailing Arm Question

Paul - As Scott pointed out, you want to spend some time determining where to drill by loading up some shims on the inside and I've found that if I use one as a template on the outboard side of the pocket and try to move the shim up to the bolt/nut, that will also help you figure out where 'X' marks the spot to drill so you're trying to run the cotter pin right through the shim holes. Yes indeed, that long drill bit will get close to the parts you don't want to make contact with but a steady hand and some patience (which I'm typically is short supply of) will help here. Good luck.

[Paul A.]

[Mike T.]

Re: Trailing Arm Question

Paul - the commonly found extended drill bits are a foot long like the top pic I posted earlier and that length helps you keep your distance from the exterior of the body.

[Paul A.]

Re: Trailing Arm Question

Got it. Thanks Mike

[Leif A.]

Re: Trailing Arm Question

Paul,
How many miles per year do you drive your Corvette?

[Paul A.]

Re: Trailing Arm Question

Leif, I use my Corvette as much as the northeast weather allows me to.

[Joe L.]

Re: Trailing Arm Question

My 66 has new, yes slotted trailing arm shims. I would like to install the front Long cotter pin that secures the shims in place. I have the bolts tight but I did noticed one of the thinner 1/8 shims was loose after a few trips. As per the AIM, the front long cotter pin is not present. Due to the fact that the slotted shim was not used in 66 therefore pins unnecessary I assume. So the holes to accept the pins are not there either. Has anyone drilled and installed the pins. Looks really tight to get a drill in there. Maybe a r/angle bit. Thoughts…yay or nay?

Paul-------


If you install the shim packs by driving in thickest shim on one side and tuck the shims down into the "pocket" in the frame, you really do not need the cotter pins. My original owner late 1969 had the frame holes for the cotter pins but never originally had the cotter pins installed. Some of my original shims were "2 hole" and some were slotted. I changed to all slotted fairly early on. Installed as I described, I never lost a shim in 200,000 miles.

[Scott P.]

Re: Trailing Arm Question

Paul, Im going to do this procedure Sunday, so if I may take some more pics for you to look at I will.
This Gentleman bought a 66 BB convertible that had been restored but because of several motor problems had never got to drive it. Two weeks ago he drove it and the Poly Trailing Arm bushings lasted 12 miles before becoming a hand full of pieces. So I pulled the TAs and will drill the frame this Sunday doing it the way I described to you.
Scott

[Con X.]

Re: Trailing Arm Question

Just did this. First 2 photos compliments of another forum member Greg. The last from John.

[Paul A.]

Re: Trailing Arm Question

Scott, Thanks again for the pins, as stated received I them yesterday! Install Procedure to follow.
Con, Thanks for the pics. I like the way one of the shims was used as an exterior template, Great idea.