When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
After a 45 minute drive in summer traffic, my T56 Magnum suddenly developed a massive oil leak. Once I got the car up in the air and cleaned off, it appears that there is a crack in the main case at the bottom where the tail housing bolts up. The trans is 4 years old and has maybe a couple thousand miles on it.
I had dynod the car the day before the leak started and it made 715whp/662wtq. The car is an ’88 RX-7 with an 8.8” IRS, Detroit TrueTrac and street tires. I never launched the car and it never wheelhopped or did anything I’d consider abrupt. There’s not much traction in 1st-3rd either. The car didn’t leak a drop on the dyno and made it an hour home from the dyno in hot traffic without issues or leaks as well.
Has anyone seen a failure like this before? Any suggestions on a fix? I can’t seem to find a new Magnum main case anywhere online. Are they interchangeable with base T56 cases? Thoughts on welding or using sealants?
I just had 4l80e case welded up, If you find the right shop it can fixed to be as good if not better than it was before. The guy who welded mine does aluminum block repair quite often on big inch drag and tractor pull engines.
The transmission is as-delivered from Tremec. I honestly have no idea how it happened. Did some street driving and noticed a trail of fluid when I pulled back in my driveway. The car is on rubberband 18" street tires and really doesn't hook up well below 70mph.
I'm about 3/4 done getting the trans out of the car, so hopefully I'll have it fixed soon. I'm going to see if whoever will be welding it is comfortable doing so with the gears left inside the case. I really don't wanna have to pull the reverse and 5/6 gear stuff to empty the case just so it can be welded back up, but if it has to happen, oh well.
Given that's a flange area and pretty thick....bound to require a fair amount of welding to fully restore it ?
Strange issue for sure though. Would be nice to see it with that end case off. You'd think it is related to that bolt...maybe too long, or hydraulic locked with sealant or something causing it to crack ?
So, bad news turned worse after I got the tail housing off the trans. It looks like a steel piece inside the trans broke off and worked its way back to the magnets in the bottom of the case. It then looks like the reverse gear jammed the steel piece into the case, causing the crack. I need some more tools to pull the reverse/5th/6th stack out in order to pull the case, but best I can tell, the part is the shift interlock plate (#156 in the diagram).
Thinking back, the day the trans started leaking, the car stalled backing out of the garage. I think that was the chunk getting grabbed by the reverse gear.
Anyways, Reverse, 5th, &6th all look fine. There is zero metal in the bottom of the trans (other than the chunk) and almost nothing on the magnet.
A new interlock is $30 and the case can either be repaired (more damage than expected), or cough up $400 and buy a new case. Welding everything up, having it leak, and having to redo it would be worth way more than $400 of headache imo.
If you (or someone) weld it, just make sure you drill a hole both ends of the crack before welding it. Its pretty good material to weld with tig, i dont see a problem with that. And clean it well and make sure it has no oil on the otherside, so it wont lift that oil through the crack when it heats. Blocks, transmissions, anything can be weld, ask me how i know..
Edit. Dmn, maybe i was little late with this post..
Thanks,
I'm more worried that the crack is bigger than what's visible. You can see in the first photo how it actually pushed the flange out where the crack is. I'll know more after I get the case off and remove the magnet.
That's a pretty important pice. Surely there were some symptoms of shifting problems with that breakage, before it got to the stage of causing the case damage ?
Honestly, there were no symptoms. I traced the trail of oil several miles, so who knows how long it was actually cracked. I did drain a few quarts of ATF off out after and there was no metal in the fluid or on the magnet (minus the chunk!).
All 6 forward gears and reverse worked fine!
If it were mine, I’d buy a case. I know that it can be repaired, but after paying the welder, your only a few hundred away from a new un-repaired case. Just my opinion, which is worthless.
If it were mine, I’d buy a case. I know that it can be repaired, but after paying the welder, your only a few hundred away from a new un-repaired case. Just my opinion, which is worthless.
I got the case off the trans and everything looks great. As far as I can see, the only thing damaged is the interlock. Gears look fine, no metal anywhere to be found. Also, the interlock was still on the shift rod and still operated fine. I'm kind of curious when it actually broke, could have even happened before I bought the trans since I got it second hand.
Going to call D&D tomorrow and price out parts. One annoying thing, I think the new Magnum cases come bare with no bearing races or small parts. All of those bits and pieces will definitely add up if I can't salvage them from the old case.
I spoke with 3 different large trans builders/distributors and no one had a Magnum case at all. Hanlon Motorsports were nice enough to ask Tremec USA about availability. Tremec was unable to give them a delivery date, but did say only 2 cases had ever been purchased from them and none of their vendors currently had them in inventory.
Sooo, looks like I'm going to have it welded up.
Wanted to update this if anyone is interested. I ended up replacing the interlock and having a friend weld up the case. I put everything back together and no more leaks and the trans shifts great.
07-29-2019, 07:30 AM
Cracked T56 Magnum Main Case 
