Rear Subframe Crack Rebuild (finished)

stonecoretx

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Something was wrong with the rear of my ma70. It was making a "click/clunk" noise that was really bothering me. the nosie happened when at a coast (no load on differential) I figured it was a wheel bearing or crush sleeve in differential. It would happen once every full rotation of the wheel, happened the most when coming to a stop. wheel bearings were fine, diff was full of lsd gear oil. I found a missing front differential mounting bolt (2 in front 4 in back) but there was enough play that the diff would slam onto the subframe when accelerating causing a HUGE crack in the rear subframe above the differential. little did I know that this is actually a big problem with our ma70's. especially pre-89. Supras with manual transmissions are more prone to this problem. torquey launches cause stress on subframe where the differential bolts up to it. my subframe was also bent in a certain spot becuase the crack caused it to flex. my stabalizer bars were bent to heck as well from the flexing.
A side note is that many other cars with independent rear suspension are prone to the problem including the BMW 3 and 5 series, Honda S2000, Nissan/dautun S-chassis 240,180, and 300zx, to name a few. I suggest everyone should (if not already done so) CHECK YOUR SUBFRAMES!

To fix or not to fix.....

So I bought a Rear subframe from a Supra that had an engine fire, along with an extra differential.
(the "newer" subframe already had a small crack that had to be cleaned up and welded shut)
I welded 1/4" steel plates and support bars to make sure this would never happen again. the plates are at where the nose of the differential mounts to the subframe, and the bars connect it all together,
with the new support i'm possitive that this will never happen again even at 1000+ torque. the last thing the car needed is 20lbs of steel to the rear but as long as i dont have to worry about it cracking again!













 

stonecoretx

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here is a little motivation. notice it cracke at the front mounting bolt points and afer that climbs up above were the nose of the diff is the "ditch"







this is a pre-89 and a post-89 side by side notice that toyota tried to fix the problem with added "targa support bars"




























someone makes this part that keeps the diff from moving/flexing. pretty sweet, i still want it.


 

Piratetip

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I make front poly subframe bushings.
Superpro makes rear subframe bushings as well as ronniek
 

Leatherhead

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I removed my rear subframe this week and discovered that it is split completely through over the front of the differential. I am still trying to locate a new one (If anyone knows of one near Eastern Washington I would love to know about it!), but I am curious how this bracing has been holding up. I am concerned about thermal damage to the subframe, so if anyone has been running one they have welded extensively on I would like to hear how well it has worked.
IMG_3415.jpg
Not only is it cracked all the way through, but there is a chunk missing.
 

supraguy@aol

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You could find a good welder to fix and reinforce that, since it's not a rusty piece of junk.
 

Piratetip

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Yeah that's what I was thinking.

Looks to be very clean minus the cracking.

Pretty easy fix.
 

Leatherhead

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I got hold of a subframe in better shape, so I'm not bothering with repairing this one (at least for now, who knows what future projects might need). I'd like to get back to my question about the reinforcements. Has anyone else reinforced their subframes like this? How well has it held up and has it been effective? I don't want to take away too much of it natural flex, just keep it from cracking.
 

hvyman

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you dont want it to flex. thats why they crack.