Hi all,

I just picked up a 2004 Evo from a good friend. He's owned it for the last 130,000 miles (230k total on the never opened motor) and she's been in service as both a daily driver, NJ-VA roadtripper and wicked AutoX'r in that time. She's just about ready to become an Enduro racer. I will be tuning her on HDPE and AutoX next spring with plans to make her a full racecar for the likes of WRL, AER, LeMons, etc.

Situation Summary - at about 225k (Aprill 2019) while on the highway from NJ to VA doing around 65 for 5+ hours, the rear diff (we think) partially locks up and drags. As my friend wrote to me "he'd have full tread at the start of the drive and at the end, the rear tires worn to near slicks and the pumpkin was extremely HOT. temp gun showed no high temps anywhere else at the time. This is what we assume to be the original stock diff. He proceed to purchase a used unit with approx. 80k on it. He stacked it to JDM spec (because AutoX) and installed. at just less than 5k of use, it did the same thing as pumpkin #1 on a drive between NJ and VA again. Tires in both cases were RE-71Rs

In both cases, if you let it cool, it works fine. Around town and even AutoX, no issues. but run over 2/3 hours on the highway and it happens. It's barely noticeable to start he explained, car just started to feel loose. The drag is even on the tires. both RL and RR are worn down the same and no flat spots.

I have spoken with Jon at TRE and he will be rebuilding the diff to race spec for me, but we both believe there may be something external to the rear diff and it's just a victim and not the culprit.

Purpose of this thread - I am looking for input as to possible external reasons two diffs have failed in the same way. I'd hate to put a new TRE diff in and have the issue happen to that.

Please feel free to ask any questions and I'll do my best to answer (or ask him).

What we know (or think we know)
Pumpkin #1 was original and stock. It did the NJ-VA run 2X a week for 3 years with never an issue before April 2019. When pulled from the car, it was opened for visual inspection and nothing looked damaged.
-This diff did get so bad when it happened that the engine had trouble moving the car forward. Also, he could feel the rear tires skipping over expansion joints in the road. Let it cool down and it operated normally again.
-Jack the rear up and the whole diff was tight, neither wheel would spin freely.

Pumpkin #2 was used and claimed to be an 80K unit. JDM spec was done before install. less than 5k on it in the car before exhibiting the same issues. Did not run it to the point the motor strained though as he knew the symptoms this time.


Thanks in advance for your help
Ray

 

Just shots of the tires to show the carnage

RR

LR

 

Hows the alignment?

 

It's it's set for 0 toe in the rear with -1 degree of camber.
I have not confirmed myself yet.
The records I have show the car has been set that way for years.
The car tracks straight when driving.

What are you thinking?

 

I'd suspect a lot of tow in or tow out.

 

Years ago I owned a rear drive Ford. I bought this car new and found that after I drove at highway speed for about 30 minutes I'd get this noise from the differential. I took it to the dealer after I had driven all the way to California and back. Out around Las Vegas on the hot desert the rear tried to bind but I kept going. Anyway, the dealer reveled that Ford had built some rear differentials with the pinion set too deep in the ring gear and with heat the teeth would bottom out.

Edit: Now that I think about it, it was more of a vibration rather than a noise after driving 30 minutes at speed.

 

We had thought of that too, but two Diffs in a row? I know my life options are bad luck or no luck, and in this case I'd love for it to be that. Then a TRE rebuild would solve everything.
I just want to make sure there's nothing external and I don't ruin a 3rd diff/pumpkin. Not to mention a pair of rear rubber each time too.

When it's not 19 degrees outside, I'll rotate the tires and see if I can recreate the situation by doing some laps on the local highway. Maybe I can find some more details for this puzzle.

 

Any chance it can be something with the transfer case. You said 04 so I don’t think you have acd

 

Right, no ACD.
We thought about it but don't think so as
1. No issues with the front diff
2. Normal temps of the T-case when the rear pumpkin was at it's hottest and locked up
3. When on jack stands the diff itself is "tight" meaning You cant turn either wheel.

But if the T-case WAS somehow turning the rear driveshaft slower, that would put added pressure on the ring and pinion fighting against the tires that would want to spin at a higher speed. I could see a possibility of how this could generate heat which eventually would make the entire pumpkin hot enough and tighten up the diff as the heat potentially breaks down the fluid.
I would expect the transfer case to be hot as there should be an equal and opposite situation happening at the front diff.

Admittedly, I am new to all wheel drive so feel free to tell me where I'm wrong.
I know that we are trying to diagnose in a theoretical situation here. I'm really just hoping to find ideas of what to look at and test at this point.

Thanks for responding

 

I am trying to figure out what could cause this issue.

If possible could you put the Evo in the air and put it in first gear, accelerate, and let the wheels spin. Then it could be easy to diagnose with someone on the bottom of the Evo what is happening in the drivetrain to cause this failure.

Another thing that could be happening is a worn out bushing or bearing in the driveshaft. It could be at the lower connection and this is possible since the driveshaft is three pieces connected together.

 

Silly question but your rear tires are the same size, right? The first thing I think of with those symptoms is having different tire circumferences side to side.

 

They started as four matched sizes! I will take A measurement though to see you if they are different now. Maybe one side has a bad bearing which causes slower rotation and as it drags the size changed and then it just continues to get worse. Except when I let go of the wheel at speed she continues to track straight. In this scenario I would kind of expect a pull to one side or the other.
Thanks for the info I will certainly check this out.

 

My initial thoughts were something like this. Some sort of pressure against the input shaft, the causes a little bit of binding on the pinion and ring, which causes a pumpkin and fluid to heat, etc... Something something something and then the diff gets super tight and the whole unit starts to drag.

I will have these checked out too
Thank you for the reply