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Old 12-31-2007, 12:18 PM   #1
BonzoHansen
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Join Date: Aug 2005
Location: Hamilton, NJ
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2nd Gen Subframe Repair

Ok, Scooter is working on a 70 or 71 Camaro for someone and asked me about rotted frame mounts.

First, here are the frame measurements for a 70-73 subframe (IIRC 70-73 are all the same; 74-81 frames would different – they were changed to accommodate cats). Courtesy of http://www.pozziracing.com/

Here is how WildBillyT and I replaced one of the mounts on the frame for my 1977 Z28

First I made a cardboard template of the pad. Then Bill cut the bushing area out with a plasma cutter – a cutoff wheel would work too. We purposely left the alignment hole alone.

That small hole is used to align the frame to the body. There is one on each side. You use dowels through the frame into the body. On my 77 Z28 the LH side has a matching hole and the RH side has a small slot, allowing for frame variance. You hang the frame loosely, then align the LH side with a dowel, then bring the RH side into spec. Older models may vary, but I don’t think so.

Front (cowl area) body mounts – note alignment holes. Yes, all of that rust was removed & the areas were painted.
RH, LH as viewed from under car.
(tunnel)

Rotted mount pad. They get worse then this, but the metal here was quite thin. Note small alignment hole.


Bill then welded in a piece of 1/8” steel. Using the template, I used a hole saw to cut the basic bushing hole. After which I had to slightly enlarge and then smooth the bushing hole using a roloc disc on my 90* die grinder. The hole is larger then the bushing itself, allowing for minor frame alignment.


Afterwards, I smoothed the welds out on the top part and painted the frame. It looks as good as new. The alignment hole was rounded out for the dowel as well.


Here is the bottom of the same mount area. I did not grind the welds out of there. I’m sure a numbers matching restore guy would have. I made sure the welds did not interfere with the bushing.


I used Global West solid interlocking subframe mounts. I experienced no NVH issues using these types of mounts, but guys who also used poly motor mounts do (just like in a 3rd or 4th gen where the stub is part of the body). I used new rubber motor & trans mounts, so I had no issues.


There are other brand mounts out there that basically do the same thing. Some will allow you to lower the body ½” or even ‘wedge’ the body by using full height in the back, ½ height in the middle, and no bushings in the front (at the rad support). But I have heard of guys having issues with panel alignment, clutch linkage problems, and exhaust clearance issues when doing that, so I used stock height bushings.

A shot of a rear frame mount.

A shot of a cowl (middle) frame mount.
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