99 Lumina LTZ subframe into a 90 TGP

[Dark Ride]

I'm trying to put the Lumina subframe into the TGP because the lumina's subframe is totally clean and rust free, and the TGP's is bent and rusty beyond all belief. The problem I'm running into is the bolts. The lumina has 18mm and the TGP has 15mm and they are smaller and have different threads. I'm considering just drilling out the subframe mounts in the body and tapping them to the new bolts. I've looked at the backside of the bolt mounts and it seems there should be enough material there to still support everything as it should, since I would be shaving about 1/16th of an inch. What do you guys think, will I be safe?

[Crazy K]

WHY?????????????????

 

You can just use the 15mm lower retainers with 15m bolts. I can see the 18mm being stronger, but not worth the effort unless you are gonna go to the Baja 500.... and everything else is virtually the same.

 

One other difference is the cradle is slightly different in that it has the added passenger side mounts for the LQ1... but they will not affect anything...

[GnatGoSplat]

I can't say for sure that's safe, but wouldn't it be easier to use 15mm bolts and just change the insulators to the ones designed for 15mm bolts?

[Dark Ride]

You can just use the 15mm lower retainers with 15m bolts. I can see the 18mm being stronger, but not worth the effort unless you are gonna go to the Baja 500.... and everything else is virtually the same.

 

One other difference is the cradle is slightly different in that it has the added passenger side mounts for the LQ1... but they will not affect anything...

 

Thank you! I didn't realize the old bolts and retainers would work with the new. Are you talking about using the old lower retainer cup, with the new bushings, or will I have to put in new lower subframe bushings (The TGP ones are shot.) When I looked in the center of the new cradle mounts (in the center of the bushings themselves) it looked like the bolt fit snug, and of course it wouldn't with the smaller bolt, or does that not matter since the retainer will center the bolt properly and I'll torque it tight.

 

Thanks,

Mitch

Edited September 1, 2010 by Dark Ride

[Crazy K]

Bushings should be the same, or at least close enough. there are actually fe1 and fe3 bushings in later years.... so the difference is most likely stiffness, and probably not shape.

 

So yes, just use your 15mm lower cup if still good. if you need good ones, find any 93- W-body car in the j/y and take some cleaner ones off... noting that a later year car may be a better donor.

 

BUT... I think you need to verify if the 15mm and 18mm upper metal retainer has the same hole size too... lemme find some parts and answer that later....

 

 

 

 

Pro-Tip: coat the bushings and the frame surface as well as the metal inner parts of the bushing with silicone dielectric grease to fend off dry rot and rust. don't forget to properly torque the bolts in place.

[Dark Ride]

Awesome, Thanks! The lower cups off the TGP are usable but very rusty, and I won't be reusing the bolts since they started to round off when I was breaking them loose. So maybe I'll visit my junkyard again. Unless of course you have some clean ones you'd like to get rid of.

[GnatGoSplat]

Bushings are the same, the upper piece that GM calls a spacer and the retainer also differ.

[Crazy K]

I actually have those parts... PM me...

[Dark Ride]

One other difference is the cradle is slightly different in that it has the added passenger side mounts for the LQ1... but they will not affect anything...

 

I just noticed this, is that what the square piece of steel welded to the passenger rear corner of the subframe, and if so can I cut it off?

 

EDIT: I Pm'ed you

[Crazy K]

pmed.

 

Yes that brace is for 91+. There is also a minor change on the front right of the frame which results in the addition of the bolt holes for the front 3.4 mount. They affect nothing so i would let em be and not alter the frame.

[Dark Ride]

Just curious if you ever got a chance to get those parts for me, I can get the bolts from GM if necessary, but the spacers and retainers are really expensive from them.

 

Thanks,

Mitch