Anyone experienced rearend issues (twisting cradle cracking)

[supraslo]

The first car that I had these issues with, gave a knocking sound like a center support bearing noise. I lifted the car up and the cradle was cracked in about 7 different spots. We replaced the cradle and welded strips of steel over the spots where the cradle had cracked. I run into this issue on 4 other cars, and repeated the first procedure. However, on my car. The cradle did not crack, the differential housing itself twisted inside the cradle. It moved clockwise and opened up the bolt holes to where the diff bolts to the back of the cradle. I have not checked the top bolts to see if they opened the bolt holes, but I do know that every bolt in the entire housing/cradle are tight. Has anyone else had issues like this and how were they corrected???

 

[supraslo]

Am I the only one without traction issues????

 

[shaeff]

Time to fully reinforce it!

Here's mine, welding done by Slow66 here on the forums:

Before: cracked and dirty as hell- click to enlarge






After: reinforced and primered:

 

[gofastgeorge]

Two thirds of all the Mk3s that I have parted out, or stipped parts off from in scrap yards have had cracked rear sub-frames.
If you are building a big HP engine,
some time should be spent addressing this issue.
Big sticky tires, and killer clutches don't help the problem either.

I am thinking about running a piece of .750 x .125 wall Chromoly tube along the bottom edge for the rear cradle.

 

[BorHor]

Now to look at mine.

 

[themadhatter]

holy shit i'm checking mine in the morrning. shaeff how much did it cost you to get your subframe reinforced like that and did it make any differance in the way the car drove?

 

[Poodles]

It seems to be mostly on the pre-89's that I've seen...

I would like to confirm that though.

 

[supraslo]

very interesting how you have reinforced it. I may try something similar. The idea I had in my head was real close to that. I guess I will let you guys know how well it holds up after a few hard launches this season.

 

[shaeff]

holy shit i'm checking mine in the morrning. shaeff how much did it cost you to get your subframe reinforced like that and did it make any differance in the way the car drove?

Bryan didn't really ask me for money, but I paid him. I know he wants to start doing more fabrication for hire, so this was a prime opportunity for both of use. I gave him somewhere around $100 or so, and we worked on it/ planned it all day.

Also, we got food, and whatnot...

It seems to be mostly on the pre-89's that I've seen...

I would like to confirm that though.

It seems to be, but I cannot confirm that either. The '89+ subframes had two extra braces on the bottom, around the differential. I picked up some '89+ braces and will put them on in conjunction with the work Bryan (slow66) did.

 

[IJ.]

I did a heapObracing when I built my IRS 9".

Neither of my subframes (1 x 86.5 and 1 x JZA70) had any signs of cracking but we don't get snow here and I think rust contributes to the cracks along with loose Diff fasteners.

 

[miekedmr]

I just got started on reinforcing mine during my spring break, because it had some cracks. I didn't get much done but at least now I have ~3 months to plan what I'm going to do.
Bryan did a great job on shaeff's... If I didn't enjoy doing the work myself I'd be asking him to do it.

 

[shaeff]

^ I would have done it myself, but I'm not a welder... yet. Besides, Bryan is awesome, and if I had just started welding, I wouldn't trust it on something that needs structural rigidity. I'm buying a welder right before summer.

 

[WhtMa71]

Shaeff do you remember how thick that plate was and what thickness wall tubing Bryan used on your subframe? I might be doing mine in the near future.

 

[suprabad]

You guys are all running 5 speeds right?

Mine is auto and I just started getting a metalic "tink" sound when I put the trans in drive or go from drive to reverse (it's not u-joints as I'd originally thought).

Then I thought it might be coming from inside the pumpkin (and may well be), but now I'm wondering if this "tink" sound might not be the rear-end moving around in the subframe. I'll get it up on a lift and see.

Anybody getting a similar sound due to the housing, or was it inside the pumpkin?

 

[miekedmr]

if I had just started welding, I wouldn't trust it on something that needs structural rigidity. I'm buying a welder right before summer.

I thought about this, but the worst case is that it ends up no stronger than stock and cracks again...

and really, I don't mind having to go back and redo things until I'm satisfied. It'll add up to a lot of grinding and welding, but in the end I think I'll have the part I want and the experience to go with it.
Even the first plate I put on there is a ways from being done. I've got to clean up the welds around the edge, then I'm going to drill holes every so often in it and weld on the inside circumference. (The way it is now, that big area could just flex away from the body of the subframe if it wanted)

 

[shaeff]

Shaeff do you remember how thick that plate was and what thickness wall tubing Bryan used on your subframe? I might be doing mine in the near future.

1/4" maybe? I honestly can't remember. Hopefully Bryan will chime in, and if not, I'll direct him here. The tubing is very thick. It's left over stock from the roll cage in his dragster, which is good to 6 seconds or so.

I thought about this, but the worst case is that it ends up no stronger than stock and cracks again...

and really, I don't mind having to go back and redo things until I'm satisfied. It'll add up to a lot of grinding and welding, but in the end I think I'll have the part I want and the experience to go with it.
Even the first plate I put on there is a ways from being done. I've got to clean up the welds around the edge, then I'm going to drill holes every so often in it and weld on the inside circumference. (The way it is now, that big area could just flex away from the body of the subframe if it wanted)

Yeah, I just wanted this to be the last time I have to drop the subframe. It'll be going together with a heap of new parts, too. I'd like to only be inspecting things, rather than removing/replacing/re-welding them. It's been so long since I've just been able to enjoy the car, that it really just needs to be done.

 

[suprabad]

I can't help but think it might be about the same amount of work to build a new subframe when it's all said and done.

Just off the top of my head...I think I would build a jig using the old subframe (to make sure everything lines up) and then fashion the new one out of square and rectangular steel, cut and weld in steel tube stock to house the bushings. Sort of like the front subframes that are popular for mustangs etc.

This way you're not trying compensate for rusty, distressed metal, not to mention it should be quite a bit stronger than the original "pressed and welded" design.

If you can weld and cut I don't see how it would be all that complicated.

 

[Slow66]

The plate material was 1/8" steel, and the tubing was .120 MS.

 

[adampecush]

I can't help but think it might be about the same amount of work to build a new subframe when it's all said and done.

Just off the top of my head...I think I would build a jig using the old subframe (to make sure everything lines up) and then fashion the new one out of square and rectangular steel, cut and weld in steel tube stock to house the bushings. Sort of like the front subframes that are popular for mustangs etc.

This way you're not trying compensate for rusty, distressed metal, not to mention it should be quite a bit stronger than the original "pressed and welded" design.

If you can weld and cut I don't see how it would be all that complicated.

For a competent welder, this should be easy. For somebody that thinks they are a good welder but does things like cool off freshly welded parts by dunking them in water, this could be a nightmare.

 

[Clueless]

For a competent welder, this should be easy. For somebody that thinks they are a good welder but does things like cool off freshly welded parts by dunking them in water, this could be a nightmare.

welding on it and then dunking the part in water right after will cause it to crack again. I'd need to check mine when I get under it again...