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T2 vs T2R vs TrueTrac vs Wavetrac vs My Sanity

Hi folks. As you may have noticed from the title, I'm looking at differentials. I currently have an Auburn unit back there. Has to be 20 years old or so. I had one event last year where it looked like it was spinning only one wheel (I've kept an eye on it since then and never seen it again). I had previously purchased a 28 spline TrueTrac for a pretty good deal from a fellow autocrosser. He was breaking axles and needing to go to 31 spline. I went to install it and found I already had 31 spline axles. Since I'm going to need to buy a new one no matter what, I want to get the best and not have doubts about my decision (yeah, sure, Chris, that'll happen).

My car is a full-weight 1995 Mustang GT. I have always guessed it at around 3200 without the (fat) driver in it. Has a 427w that made 625hp in the in-car configuration on the engine dyno (so let's say 530rwhp). TR-3550, 3.73s, and (currently) 315 Falken RT615k+ square. But will be trying out some take-off 305 slicks next year.

Car does standing starts at autocross on grippy concrete (where I'll be going to 315 Yokohama A052 or Nankang CR-S). I do street drive VERY occasionally with some Dunlop all-seasons. Has about 600 miles since I put the engine in in May 2021 including a season full of autocross and 4 track days if that tells you anything about how often I street drive it. Mainly looking for best performer at the road course and autocross. I don't drag race the car, though I wouldn't mind giving it a try sometime (wouldn't want it to grenade if I did, but not concerned about being overly fast there).

I know there's some highly subjective opinions on the different diffs I mentioned above. Usually from folks that have used an open/TrakLok diff then went straight to one of these, liked it, and have stuck with it. I certainly understand that view. Not trying to discount good experiences with a particular one or anything, but I've basically been told to use all of them at some point and there's a ton of people with good and bad experiences with them all. Thus the sanity issue. Everyone I know has given me one of the above as their suggestion, but never any info on what the difference feels like or how it affects the car, et. Looking for a boil-down of sorts with maybe some objective facts about which one may work better. Maybe there's certain conditions where one of them shines more. Maybe there's certain diffs that won't survive under X conditions. What sort of handling changes should I expect to see if the car is handling fairly well now? Any thoughts for me here based on the car and use?

(I know that I should also have a specific idea of what I want to fix when making changes. I usually try to. In this case, I really don't, because I don't have any reference point of other cars with one of these type diffs. My experience has been limited to stock TrakLok and now this Auburn that seems to be more drag race-oriented. I do know I would like to be able to use more power on corner exit, mainly at AutoCross, but I'm not 100% sure this will make any difference there.)
 
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for an explanation of units let's look at this article..

With that, the current GT4 uses a "ramp" style diff, we used something similar in kart racing for our axle clutches, depending on the "ramp" angle the lockup could occur at different levels such as, it could come in sooner or more harshly depending on the ramp, you also had a way of determining when it was "all in" in the kart example. In a car, not so much, but it seems by doing some experimenting with different ramps you could fine tune the degree of lockup within the units operating range.. great concept, great possibilities if you are a race team, if you are a guy working out of a 2 car garage, sounds more like an expensive rabbit hole if you are not careful.
The stock type limited slip works extremely well, low maintenance, dependable as an anvil and by using different types of clutch material and shims, you can vary the lockup on these as well.
The True Trac hit the market around the early 2000s and made a big splash, but there were issues with dependability, although most people I know liked them and thought they were superior to the Torsen, they seem to be abuse adverse in the long run, maybe great for a street car.
The Torsen has been the standard for years, it was what was used by almost every competitor in PWC and Grand Am, they are solid dependable units and pretty much a fire and forget, their strength over most other units seems to be in corner exit, I don't think you could ever go wrong using a Torsen.
There is another, somewhat oddball unit out there called the "Phantom Grip" it is brain dead simple and basically preloads the spider gears against the case, the internal springs are adjustable so the slip can be changed, they are designed for smaller cars and I actually ran one in my SCCA MG Midget with great results. I wish they made these for larger cars, maybe they do now, it might be worth a look.
1660829877462.png
 

racer47

Still winning after 30+ years
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W2W Racing
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20+ Years
SE WI
I've had a couple Eaton TrueTracs. I think they are the best diff for the money available. My current s197 is 600 whp, never spins one tire even in the rain and has no bad manners. Plus it can take drag race launches. I run high speed autox with A7s from a standstill without issue. The torsens are supposed to have more bias, which is good, but if I'm not spinning one tire than I have plenty of bias.
 
I ran a TruTrac for years in my CP and EM cars, but that was the 9" version which has 90lbs of friction preload built into it.

I put one in my S197 a few years back when I prepped it for CAMC. I fought inside wheel spin issues the entire time I had it in the car that were corrected when I put a T2R in this winter. I also changed some other stuff so it may not be a 100% true comparison, but I was speaking with one of my other S197 CAM competitors this past weekend and he asked about what diff I had. he had the exact same issue with his TruTrac that went away when he went back to the T2R. HIs rear suspension setup was consistent across that timeframe.

DaveW
 
I started with the stock Boss Torsen and replaced it with an Eaton TruTrac. Had traction issues with the stock Torsen. Now I have to get real sloppy to break the back end loose. I love the TruTrac. Never tried a T2R and I'm sure it's great but when Billy Johnson said he used nothing but TruTracs in his cars I decided to go with it. It's held up about 5 years so far.
 
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Take this with a grain of salt, please;
I put my cambered rear end in and purposely made no other changes so I could see what affects it had before considering any other upgrades. While my diff was apart we saw the tru track had some wear so all that was available at the moment was a T2r so we went with that. The car hooks up great, but there is a mid corner push that I can't seem to get rid of. I have done everything to cure it, heavier rear springs, higher roll center, added a rear sway bar, softened the front sway bar.....all these things will make it looser, but the push never goes away. I am trying 150# softer front springs this weekend and if that doesn't work I'm going back to a tru track, which is what I have suspected all along....stay tuned.
 
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CT
Just put an Eaton trutrac in my car and only have one weekend on it but I am very happy with it so far. I had a stock clutch type limited slip in it before and there is no comparison. I’m able to rotate the car now and it feels so much more predictable. I can’t comment on the other diffs.
 
With that, the current GT4 uses a "ramp" style diff, we used something similar in kart racing for our axle clutches, depending on the "ramp" angle the lockup could occur at different levels such as, it could come in sooner or more harshly depending on the ramp, you also had a way of determining when it was "all in" in the kart example. In a car, not so much, but it seems by doing some experimenting with different ramps you could fine tune the degree of lockup within the units operating range.. great concept, great possibilities if you are a race team, if you are a guy working out of a 2 car garage, sounds more like an expensive rabbit hole if you are not careful.

I am indeed a guy working out of a 2 car garage! I'm trying to run with smarter guys with better skills, better cars, and more money, So while I want something good, I have to balance it with my capabilities and budget. I've done it in all areas...I use the Maximum Motorsports struts, for example, that are non-adjustable. I don't know that I am "tuned in" enough to adjust them properly, along with the thousand other adjustable things on the typical road course car. I may go to adjustable eventually, but for my level, right now, I figured they would just get in the way of working on driving. I kind of feel the same way about the adjustable rears.

I started with the stock Boss Torsen and replaced it with an Eaton TruTrac. Had traction issues with the stock Torsen. Now I have to get real sloppy to break the back end loose. I love the TruTrac. Never tried a T2R and I'm sure it's great but when Billy Johnson said he used nothing but TruTracs in his cars I decided to go with it. It's held up about 5 years so far.

That was one thread (and the associated article) I found after posting this. I wish I had found it before. That does hold some sway (not so much because of who's saying it, but the information posted in that debate). Along with the T2R not being a good fit for hard launching...probably won't be an issue, but I don't want to have to wonder or worry.

Take this with a grain of salt, please;
I put my cambered rear end in and purposely made no other changes so I could see what affects it had before considering any other upgrades. While my diff was apart we saw the tru track had some wear so all that was available at the moment was a T2r so we went with that. The car hooks up great, but there is a mid corner push that I can't seem to get rid of. I have done everything to cure it, heavier rear springs, higher roll center, added a rear sway bar, softened the from sway bar.....all these things will make it looser, but the push never goes away. I am trying 150# softer front springs this weekend and if that doesn't work I'm going back to the tru track, which is what I have suspected all along....stay tuned.

Please let me know how it goes! This will be a winter project most likely. Although I'm actively trying to resist the urge to order another part that will just sit in the garage for a while lol.
 
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I recently installed the Eaton on my 2011 GT and have done a couple track days and an autocross with it. Biggest handling differences I have noticed are that I can put more power down sooner, the car rotates and turns in better under power, and when the back does let go it is smoother and more progressive, easier to catch.
 

Dave_W

Cones - not just for ice cream
588
687
Exp. Type
Autocross
Exp. Level
20+ Years
Connecticut
I think the biggest difference between the clutch-style and helical gear style diffs is maintenance. The clutch packs will wear and slip and need to be replaced on a somewhat regular basis.

The second big difference is what happens if one wheel has no traction - it's in the air. A clutch diff will typically still send power to the wheel on the ground, while most "torque-sensing" diffs won't.
 
Can't say if any of my experience will correlate to yours given my car makes less than half of your hp (maybe 275whp and even less tq), but I'll throw my Trutrac experience in on an autocross S197.

Previously ran a rebuilt TracLok with SVT carbon/kevlar plates. Car was very pushy on turn in but would rotate extremely well on corner exit, face the car a very "loose" feel.

This season I've switch to the Trutrac and have mixed feelings so far (same gear ratio, same power, same tire/size, with the only real additions being new upper control arm/diff bushing). The highlight of the Trutrac for me is the turn-in, its phenomenal. The car is also much more predictable on throttle and gives the car a "tight" feel. On the other hand the car has a mid/corner exit push, it doesn't rotate the same as it used to on throttle. I prefer a looser setup, so I've been experimenting with shock rebound and tire pressures to get the car behave to my liking.

I'd imagine a car with more power/tq should have no problem with on throttle rotation with a Trutrac, but others will have to chime in on that

Looking forward to seeing how your build pans out,
-J
 
I think the biggest difference between the clutch-style and helical gear style diffs is maintenance. The clutch packs will wear and slip and need to be replaced on a somewhat regular basis.

The second big difference is what happens if one wheel has no traction - it's in the air. A clutch diff will typically still send power to the wheel on the ground, while most "torque-sensing" diffs won't.

That is one of my issues...I'm not coming from a stock unit where I'm having to maintain it. I have an Auburn cone type that's currently working. I had one event last year on this new engine that I was spinning one tire only. Prior to that, I had a year of autocross and a handful of track days (all done with a second person driving the car with me). No issues during any of that. It was 1 event where I struggled with traction, then I started watching for it and it never happened again to my knowledge.

On the traction with 1 wheel in the air, I don't think I'm ever having that happen. I'm usually not hitting curbing hard enough to do it. It never happens in autocross.

Can't say if any of my experience will correlate to yours given my car makes less than half of your hp (maybe 275whp and even less tq), but I'll throw my Trutrac experience in on an autocross S197.

Previously ran a rebuilt TracLok with SVT carbon/kevlar plates. Car was very pushy on turn in but would rotate extremely well on corner exit, face the car a very "loose" feel.

This season I've switch to the Trutrac and have mixed feelings so far (same gear ratio, same power, same tire/size, with the only real additions being new upper control arm/diff bushing). The highlight of the Trutrac for me is the turn-in, its phenomenal. The car is also much more predictable on throttle and gives the car a "tight" feel. On the other hand the car has a mid/corner exit push, it doesn't rotate the same as it used to on throttle. I prefer a looser setup, so I've been experimenting with shock rebound and tire pressures to get the car behave to my liking.

I'd imagine a car with more power/tq should have no problem with on throttle rotation with a Trutrac, but others will have to chime in on that

Looking forward to seeing how your build pans out,
-J

Interesting perspective. I wouldn't say I like my car loose at autocross...but it does go faster when I drive it that way. I had to work on getting the back end out there my first two years. My cousin drove a 99 Trans Am with LS3 and a very good AutoX setup...he was also a former dirt track driver. So once my car got to a similar point, I started copying what he was doing. But I always felt like it was a compromise, to drive it with the throttle because it was struggling with something else. It was faster, but maybe not as fast as it could be if the problems were fixed, if that makes sense. I could be entirely wrong on that, though.
 
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That is one of my issues...I'm not coming from a stock unit where I'm having to maintain it. I have an Auburn cone type that's currently working. I had one event last year on this new engine that I was spinning one tire only. Prior to that, I had a year of autocross and a handful of track days (all done with a second person driving the car with me). No issues during any of that. It was 1 event where I struggled with traction, then I started watching for it and it never happened again to my knowledge.

On the traction with 1 wheel in the air, I don't think I'm ever having that happen. I'm usually not hitting curbing hard enough to do it. It never happens in autocross.



Interesting perspective. I wouldn't say I like my car loose at autocross...but it does go faster when I drive it that way. I had to work on getting the back end out there my first two years. My cousin drove a 99 Trans Am with LS3 and a very good AutoX setup...he was also a former dirt track driver. So once my car got to a similar point, I started copying what he was doing. But I always felt like it was a compromise, to drive it with the throttle because it was struggling with something else. It was faster, but maybe not as fast as it could be if the problems were fixed, if that makes sense. I could be entirely wrong on that, though.
When I ran my SN95 in NASA autocrosses, I never actually lifted the rear tire, but it was so unloaded that it might have well been, you can do that without hitting curbs with a good handling car and trick rubber.
In the end it seems you still have 3 choices, the stock type clutch pack unit, strong, reliable, maybe not the best performer
the TR2, pretty much the industry standard that is rugged and performs well
The Truetrac style that seems to perform best but may not be quite as consistent
You have horsepower out of the wazzoo, so it really comes down to how short the courses are, In Florida, our parking lot courses are a maximum of 70mph for insurance reasons, so it would seem the TrueTrac (#1) or the TR2 (#2)would be the best choice, if you have long sweeping corners then the pendulum swings more to the TR2 (#1) or the clutch pack units (#2) would be a better choice. I really don't think you can make a decision without considering the type of tracks you run. It's like anything else, the TR2 is the standard, but on any given day, depending on the course layout, it will get beat by something else.
Welcome to your nightmare.. lol
 
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I went from a stock tractionLOK to a truetrac and here are my thoughts:

One thing that hasn't been mentioned here is bias ratio. You can have a tracktionLok be in perfect condition with freshly rebuilt carbon rings, pack them in a way to make them lock up tighter, etc, yet your BIAS RATIO will still be inadequate depending on your application.

The "depending on your application" part is key here.

In my experience, a freshly rebuilt traction-LOK with the carbon fiber discs packed extra tight was adequate bias ratio for my car when I was on 255 width, 300tw tires. The car would lock up both rear wheels great. 255 width tires (unless they are a crazy sticky compound) will struggle to make enough grip to overcome the bias ratio of a fresh traction-lok diff. This was my experience.

With that being said, as soon as I went to 315 width tires (and a grippier compound nonetheless), the same traction-lok diff which did fine on 255's was utterly useless, and would one wheel peel even in higher speed, 3rd gear corners.

The way selecting a diff should go should flow like this IMO:

1.) How built up is the suspension on my car?
2.) How sticky of a compound will I be running, and how wide?
3.) What environment do I drive the car in? Do I currently have one wheel peel?

Based on the above, you would come to the conclusion of T2 3:1 bias ratio being enough (I think the truetrac is also 3:1?), or concluding that you need the big dog T2R w/a bias ratio of 4:1. Or, you answer the above questions, and realize that you don't even need an aftermarket diff.

IE, hoosier slicks, stupid grippy suspension and well prepped track surface is a perfect use case for the 4:1 bias ratio of the T2R because a car with that setup will be creating SO MUCH grip, and therefore need so much bias ratio. But autocrossing on mediocre pavement on 300tw tires? T2R is completely overkill.

FWIW I like my truetrac, but didn't notice any difference in corner entry. The oversteer is also a bit snappy at times, which required tuning out in the rest of the suspension to help counter. But for me an aftermarket diff was an absolute necessity given the one wheel peel I was getting.
 
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Here are my subjective impressions about the difference in throttle rotation off the apex. For context I have an '11 GT with stock power, good suspension, and 200tw tires, I usually run in advanced HPDE run groups and the car is very much a dual duty street/track setup:

In my experience, the stock Traction Lok in my '11 GT didn't really rotate much at all on throttle unless and until the rear tires had lost grip and were sliding. Coming off the apex, the feeling was one of measuring in as much power as you could without the back end stepping out too much. This was fun at times and nerve wracking at others depending on the corner and the runoff, but it never felt totally easy or predictable to find the line. By comparison, with the TruTrac in this situation as you roll on the power coming off the apex it feels like the rear is pushing or "rotating" the car towards the inside of the corner but, and this is the key part, without the back end actually sliding out. If you over-cook it, the back end will still slide out and then you have throttle rotation for sure, just like with the stock TracLok, but when this happens, the breakaway feels more progressive and easier to catch than it did with the TracLok.

When the stock Traction Lok is fully engaged, both rear wheels are fully locked and turning the same speed. That never happens with a Torsen or Truetrac. This mechanical difference is noticeable in terms of how the car feels putting power down off a corner. To me the stock Traction Lok felt like a balance between understeer as the front would get light and oversteer as the back would eventually slide out. The Truetrac feels more like the front is getting pushed into the corner and rear is following. OP, you asked about subjective feel so I'm trying to fill that in a bit. Good luck!
 
I went from a stock tractionLOK to a truetrac and here are my thoughts:

One thing that hasn't been mentioned here is bias ratio. You can have a tracktionLok be in perfect condition with freshly rebuilt carbon rings, pack them in a way to make them lock up tighter, etc, yet your BIAS RATIO will still be inadequate depending on your application.

The "depending on your application" part is key here.

In my experience, a freshly rebuilt traction-LOK with the carbon fiber discs packed extra tight was adequate bias ratio for my car when I was on 255 width, 300tw tires. The car would lock up both rear wheels great. 255 width tires (unless they are a crazy sticky compound) will struggle to make enough grip to overcome the bias ratio of a fresh traction-lok diff. This was my experience.

With that being said, as soon as I went to 315 width tires (and a grippier compound nonetheless), the same traction-lok diff which did fine on 255's was utterly useless, and would one wheel peel even in higher speed, 3rd gear corners.

The way selecting a diff should go should flow like this IMO:

1.) How built up is the suspension on my car?
2.) How sticky of a compound will I be running, and how wide?
3.) What environment do I drive the car in? Do I currently have one wheel peel?

Based on the above, you would come to the conclusion of T2 3:1 bias ratio being enough (I think the truetrac is also 3:1?), or concluding that you need the big dog T2R w/a bias ratio of 4:1. Or, you answer the above questions, and realize that you don't even need an aftermarket diff.

IE, hoosier slicks, stupid grippy suspension and well prepped track surface is a perfect use case for the 4:1 bias ratio of the T2R because a car with that setup will be creating SO MUCH grip, and therefore need so much bias ratio. But autocrossing on mediocre pavement on 300tw tires? T2R is completely overkill.

FWIW I like my truetrac, but didn't notice any difference in corner entry. The oversteer is also a bit snappy at times, which required tuning out in the rest of the suspension to help counter. But for me an aftermarket diff was an absolute necessity given the one wheel peel I was getting.

The Torsen T2 is 2:1 TBR. The T2R is 4:1. (I *think* the factory Boss unit is between those, 2.7:1).
The TruTrac is also in the middle 3:1.

This is the kind of thing I was looking for, but I can't make it make sense to me.

I guess the answer to the questions above is that the suspension is fairly well done, the car has fairly good grip on sticky tires (and will have even stickier tires next year, 315 Yokohama A052 square, the bees knees for AutoX especially on our grippy concrete surface, and used slicks for the track).

Here are my subjective impressions about the difference in throttle rotation off the apex. For context I have an '11 GT with stock power, good suspension, and 200tw tires, I usually run in advanced HPDE run groups and the car is very much a dual duty street/track setup:

In my experience, the stock Traction Lok in my '11 GT didn't really rotate much at all on throttle unless and until the rear tires had lost grip and were sliding. Coming off the apex, the feeling was one of measuring in as much power as you could without the back end stepping out too much. This was fun at times and nerve wracking at others depending on the corner and the runoff, but it never felt totally easy or predictable to find the line. By comparison, with the TruTrac in this situation as you roll on the power coming off the apex it feels like the rear is pushing or "rotating" the car towards the inside of the corner but, and this is the key part, without the back end actually sliding out. If you over-cook it, the back end will still slide out and then you have throttle rotation for sure, just like with the stock TracLok, but when this happens, the breakaway feels more progressive and easier to catch than it did with the TracLok.

When the stock Traction Lok is fully engaged, both rear wheels are fully locked and turning the same speed. That never happens with a Torsen or Truetrac. This mechanical difference is noticeable in terms of how the car feels putting power down off a corner. To me the stock Traction Lok felt like a balance between understeer as the front would get light and oversteer as the back would eventually slide out. The Truetrac feels more like the front is getting pushed into the corner and rear is following. OP, you asked about subjective feel so I'm trying to fill that in a bit. Good luck!

Everything you said here about how the TracLok feels is how I feel about the Auburn diff right now, but explained 10x better than I could've.

Thanks for sharing!
 

Frank.JD.Perez

FJD Performance
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