[Brock1030]

Have a new bushing set for a 1979 Trans Am and had seen a citation that the correct bolt size for positions 2 and 3 on the subframe for a late November 1978 W72 car is 9/16, so purchased grade 8 but when tightening, it popped as if the cage nut is broken, but it is not - no rust on the car and all in great shape.

Possible explanation is that I have the wrong size/thread. Could it be metric? Any direction? Thanks so much.

[Don 79 TA]

i'd have to search on what bolts i used, but i know it was not metric on my TA
surpringly i had your typical surface rust/age to deal with, but all went in rather well
i know i bought them from Bolt Depot
if needed i can search
but, if you have the old bolt, can you run it through and does it do the same thing?

[Brock1030]

Thanks so much for your reply, Don and good news on the metric sizing. Do not recall if I have the originals, as this was part of a frame off resto with tear down about a year and a half ago. Good thought though, so will look and report back.

Nonetheless, this bolt size and thread should be part of the info archive for our cars for others as they do resto work in the future.

[78w72]

almost positive the bolts arent metric for all 78 cars. if the originals are in good shape & not heavily rusted, can they be reused? good point above to try the originals to see if they do the same thing.

the cage nuts can & do break even on lower rust cars, its just a poor design with only some small spot welds holding the cage in place. sounds to me like the cage broke & the nut is spinning. should be easy to confirm that, it will feel tight then "pop" as the nut turns in the cage, it will do that every quarter turn or so. metric threads wouldnt pop, they would feel cross threaded & harder to turn from the first turn or 2.

if these are original type rubber bushings, the original bolts can be reused if in good shape. if they are polyurethane, most companies include new gold cadnium plated bolts or will sell them.

the cage nuts can be rewelded by cutting an access hole in the floor, or you might get lucky on the 2 front ones by placing a big screwdriver or crow bar in there to apply pressure to hold the nut, ive done that before on rusty parts cars to get the subframe out.

good luck!

[Trevor78]

As mentioned in other post, they are 5/8" under the body, and 1/2" at radiator support.

[Skip Fix]

My 81 had standard bolts also in those locations.

[Brock1030]

Thanks so much for the responses. If they are 5/8, that would explain why the 9/16 that I tried is not tightening. Will get out there this afternoon and check further, so we can confirm. Will report back.
Thanks so much!

[Brock1030]

Update: the subframe bolts that go into the body are indeed 5/8 x 4 and not 9/16 x 4, as I had seen on several sites. I did save the old ones, but did not check them, as they could easily have been mistaken in appearance for 9/16.

So, when tightening, the 9/16 went in, but popped, as they are not quite big enough to torque down. Thus, the pop was that and not the cage nut breaking loose - thanks be to God!

Went to the hardware store this afternoon and bought 4 grade 8, 5/8 x 4, and with a good bit of PB blaster for ease of tightening on the cage nut, all 4 bolts went in just fine and were each torqued down to 85 ft. pds., as per spec.

Interesting in checking some of the available kits for the 1979 Trans Am, with the rubber bushings and bolts, the bolts are 5/8, but they are only 5/8 x 3 - an inch short! Also, note that the two core support bushing bolts are not the same 5/8 x 4, but rather 1/2 inch for some reason.

Lesson learned to pay closer attention!