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Discussion Starter #1
I have an Eaton TruTrak installed in my track car. It was new and installed by a pro when I built the car 3 years ago. Drivetrain and Differential ? Racing the Exocet

I used to think this was a suspension problem, and made some changes to try and fix it. But now I'm thinking it's really a differential problem.

I have two corners at High Plains Raceway that are the biggest problem; turn 2 and turn 11. Turn two is a flat single radius somewhat tight right hand corner. Turn 11 is a decreasing radius, slightly banked wider right hander, that is mostly uphill (love this corner). https://highplainsraceway.com/contact-us/track-details-and-location/

In the corners, the inside (right) wheel spins until the car is pointed straight. Then it hooks up and goes. If I feather the throttle, I can keep the tire from spinning, but that costs me time. If I keep my foot in it, I can feel that tire spinning, but the car still accelerates, and I get a quicker lap time. Especially in turn 11, the tire will actually leave a long black mark, about a car length long or so. It's sort of acting like an open differential. But the car does accelerate, so power is getting to the left wheel.

In theory, the Eaton should sense that the right tire is slipping, and transfer power to the left until the right wheel isn't spinning any more. Then when both tires are getting traction, it should work like an open differential. But that doesn't appear to be happening.

Do you think this is a differential problem? Or is it still a chassis problem? Is this a somewhat know failure of the Eaton Gear? I did a google search but couldn't find anything.
 

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Do you know if your Tru Trac has a spring in it like the Torsen 2R?

The gear design of the differential requires that the inside wheel apply at least a reasonable amount of resistance to the differential for it to work. If your inside wheel is close to lifting such that the wheel is not getting much of any grip the differential will not provide the expected limited slip. The T2R has a spring in it for this exact reason. The spring takes care of the required pre load from the unloaded wheel.
 

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I have a Torsen in one of my vehicles. I have been told to NOT run friction modifier in it. The worm drive gears rely upon friction to transfer the load, as I am told. I would try different lubes, non syn, lighter wt, etc, before I pulled it. I am sure your installer is experienced, but I get a lot of good information, whenever I call Randy's Ring and Pinion. They might be able to pin point the problem, if there is one.
 

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I had an Eaton TruTrac in my FFR for 4-5 years. Never had any problem w/ spinning an inside wheel. Per Wade, I ran standard gear oil in it w/o any additives. his understanding was that the gears needed some friction to work. But what did happen to it was the side gears (the ones that the axle splines engage) and/or the main housing wore and those gears had a ton of slop. No parts available so I went back to a standard Ford lim slip unit but w/ CF clutches. I wondered if the idea of running standard oil vs synthetic had increased wear but no way to know.
 

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Discussion Starter #5
I had an Eaton TruTrac in my FFR for 4-5 years. Never had any problem w/ spinning an inside wheel. Per Wade, I ran standard gear oil in it w/o any additives. his understanding was that the gears needed some friction to work. But what did happen to it was the side gears (the ones that the axle splines engage) and/or the main housing wore and those gears had a ton of slop. No parts available so I went back to a standard Ford lim slip unit but w/ CF clutches. I wondered if the idea of running standard oil vs synthetic had increased wear but no way to know.
I'v used a trutrak before, without anything like this. I don't know if there's a spring in there or not. I'll have to look at the diagram and see. If there isn't, maybe swapping to a torsen would be a good idea.

IIRC, about 4-5 years ago there was a real shortage on parts for these units.

I now have royal purple in there, and no friction modifiers. I used the same in 10 years of racing the Cobra. I did not know that synthetics were not recommended. I think I will try a Penzoil gear lube in a higher viscosity and see what happens. If that fixes the problem, we'll call it good. If not, maybe I'll switch to a T2. Add that to the winter upgrades list. :)
 

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I had the same problem as you with my cobra years ago. It was about 3-4 years old and the inside tire would light up. I think it's worn out. It made the car hard to control powering out of any of the turns.
I switched to Auburn autocross road race differential. It's been 5 years and still works great. I run standard gear oil + friction modifier per their instructions.
 

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Discussion Starter #7
I had the same problem as you with my cobra years ago. It was about 3-4 years old and the inside tire would light up. I think it's worn out. It made the car hard to control powering out of any of the turns.
I switched to Auburn autocross road race differential. It's been 5 years and still works great. I run standard gear oil + friction modifier per their instructions.
I'm thinking the same thing. This is only the third season I'v been racing this car, and it doesn't see street time.

I'm going to try a higher viscosity gear oil for the next race, in a couple of weeks. Then over the winter I'll pull it out and replace it.

I was looking at the Auburn Gear web site last night. I didn't see the road racing diff listed for the 8.8. But I didn't really search that hard. I might just give them a call and order what I need.
 

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I think I would contact the manufacturer and see what their rebuild timeline and processes are. Many times differential units will wear and just need to be shimmed or have clutches replaced. To not at least explore this could be like changing an engine because the valves needed adjusting. Not a good use of your racing $$.

If there are any type of clutches in your diff, then fluid choice will definitely have an effect on diff performance.
 

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Discussion Starter #9
I think I would contact the manufacturer and see what their rebuild timeline and processes are. Many times differential units will wear and just need to be shimmed or have clutches replaced. To not at least explore this could be like changing an engine because the valves needed adjusting. Not a good use of your racing $$.

If there are any type of clutches in your diff, then fluid choice will definitely have an effect on diff performance.
The big advantage to a worm gear is that there are no clutches to wear out or slip. And - in theory - fluid type is not nearly as important.

I could pull this one out and have it rebuilt. But the new one only lasted 2 1/2 seasons. I don't really want to put the same thing back in there. I would spend almost the same money as new, but be right back in the same place in 2 1/2 years.

I will consider an Auburn vs. Torsen T2
 

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Discussion Starter #11
That is what I thought to, only gears, no friction plates, or clutches to wear. But, the gears apparently wear too. It must not take very much for it not to function properly.

This is what I have Bob

https://www.summitracing.com/parts/aub-542039/overview/
Apparently, something isn't working right. Surprising, after only 2 1/2 seasons in a light weight low powered car. The last one I used worked well in a slightly heavier car with a lot more power for 10 years of abuse.

I sent a e-mail to Eaton to see what they say.

I'll probably end up with that Auburn diff.
 

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Bob: Sorry to hear about your problem with the Truetrac. I had one in my FF roadster and really like the way it worked, then again I only put 4K miles on the completed car before selling it. I just received a 9" 3rd member from Strange for my Mustang restomod. The Truetrac unit looks way different in the 9" form as compared to the 8.8". So different in fact that I did not immediately recognize it as a Truetrac. The vendor had to have me look up pictures of the 9" version to verify what I had was indeed a Truetrac.

If you get any vendor feedback on the problem, please post so that we can understand the failure mechanism.

Alan
 

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Discussion Starter #13
I sent them an e-mail. They sent me one back that said it was too complicated to discusse via e-mail, and I should call them. I tried calling a number of times. Either I couldn't get through, or they didn't know and asked me to call back.

I switched to a heavier dino gear oil. I raced today, and still have the same problem.

Well, I'll just switch to an Auburn over the winter.
 

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Mr. Cowan,

Your car is spinning the inside tire because the TBR (torque bias ratio) of the differential is too low for the percentage of the rear roll stiffness in the car's suspension. There are two options.

1) Reduce the percentage of rear roll stiffness by installing softer rear springs or swaybar, or installing stiffer front springs or swaybar. Changing springs isn't the best idea as that will change level ride behavior. Changing the front or rear swaybars is the better option. This change will of course make the car have less oversteer/more understeer.

2) Change to a differential which has a higher TBR such as a Torsen T2R.

The amount of friction in the differential does have an effect on the TBR, so using lubricants with less friction (synthetic oils, friction modifiers) will lower the TBR and tend to make your problem worse. This effect will be small.

If you want to understand why as of this is so, see the link below.

https://forums.corral.net/forums/15701281-post21.html
 

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Discussion Starter #15
Through a strange series of events, I ended up putting the same center section back in there. This time, set up by a different guy who really knows what he is doing. That resolved the problem! There was nothing wrong with the parts, it was just set up wrong. I didn't think of that.

Anybody want to buy a new Auburn diff?
 
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