2nd Gen Subframe Repair

[BonzoHansen]

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.

[johnjzjz]

for many years we used an over sized washer and welded it to the frame end bracket sometimes both sides but what you did - will work and looks very trick --- no rubber mount ---

hope you don't think i am stepping on your fix but i had a different result when we used hockey pucks and made the tab solid ( somewhat ) and it did not have to be perfect we just drilled it out when it was centered ( PUCK )

: all the street cars with solid mounts i have owned had issues with windshields cracking in the corners - when we put the rubber back in it stopped maybe it was just a coinsurance -- i see you said you had no problems doing it but my shop did --- jz

[WildBillyT]

Thanks for the credit, Scott!
I repeated this same process on the subframe of my '69. Came out nice. The only thing that is not mentioned (which may be needed) is some forming of the patch panel with an oxy/ace torch if you need to replace part of the angled section as well as the flat section.

[BonzoHansen]

As always WB!

He's right, I forgot we had to bend that piece a bit. And by we I mean Bill. But in retrospect we probably could had avoided that with a bit more careful cutting of the old one.

And JohnJZ, it''s all good, there is certainly more then 1 way to skin a cat. I have not heard issues with the WS cracking you mentioned. Did those cars get sub frame connectors are well?

[Ian]

I had the frame mounts redone on my old 76. just took the frame to a frame shop and they welded in some really big washer looking things.

[BonzoHansen]

That is common. I think the 1st gen kits include them.

[johnjzjz]

Originally Posted by BonzoHansen

As always WB!

He's right, I forgot we had to bend that piece a bit. And by we I mean Bill. But in retrospect we probably could had avoided that with a bit more careful cutting of the old one.

And JohnJZ, it''s all good, there is certainly more then 1 way to skin a cat. I have not heard issues with the WS cracking you mentioned. Did those cars get sub frame connectors are well?

yes sub frame conectors but they for the most part were NYC street cars with big blocks ( roller coaster roads ) add to the problem --
the big looking washer thing menchioned is what i was talking about - jz

[PolarBear]

Thanks for the info Scott! This is what I need and I should be able to fix the frame next time I go over there.
I guess I was wrong about that slotted hole being askew, I thought it was on the 71.

[PolarBear]

Anyone have a frame laying around without any rust around the mount holes? Eventually I will need to re-drill the holes for the alignment hole. I would like to make a pattern for the alignment hole if possible. I think it needs to be an early frame as opposed to a later one.