Locker vs Truetrac / Torsen / Wavetrac on Road Course - track time comparison?

[Ron Sutton]

I bought my center from Roush as well, detroit locker 3.60:1 gear. Sounds like I got lucky. My locker is not nearly as harsh as you describe. Actually, I just went in the garage to 'test' it. Lifting one tire and then the other, my locker will 'ratchet' at about 20 ft-lb.
I'm assuming you're grabbing the tire & turning it. I'm not sure if that is the most accurate way to determine what spring rate is in it.

I also went out to do a little road testing to refresh my memory on how she feels when driving. If I'm completely off the gas pedal, the rear ratchets quite freely. I couldn't hear if it was ratcheting under moderate throttle (sustaining speed), but at some point (as I just tested on a skidpad) the inside rear starts to squeal and kicking the rear out isn't far behind.
Either ...
a. Your car is rolling so much the inside rear tire isn't loaded enough to compress the springs & disengage the locker.
-or-
b. You have too high of a spring rate & the locker is not disengaging.
c. Or the internals are not sliding well & sticking.


That's interesting to hear that a locker is the preferred differential for full size road race applications. I've been reading about how to drive around a locker rear when road racing, but didn't get the impression that many folks preferred them. What's the reasoning on the preference?
The older standard lockers were harsher when unlocking on corner entry, so the driver had to deal with that. This is minor on the newer versions. The most common challenge is the locker failing to unlock when you need it to. This happens when the internals catch on burrs or the spring rate is too stiff. When the locker is working correct, there is nothing to "drive around."

When the locker works correctly, it is the most reliable, durable & consistent differential. Many (not all) differentials that utilize helical gears to distribute the power to the rear wheels actually see the distribution change with wear, which affects the corner exits.



Can you expand on what is the right set-up for a locker rear on a road course?
It is not complex, thank goodness. And when you get it right, it's right forever (almost) unless metallic trash gets in the internals.

The internals need to be "blueprinted" which means they need to be checked for clearances & all the edges deburred ... a lot like a manual transmission. Once deburred & sliding smoothly, getting the correct spring rate is the only other thing.

Eaton's standard spring tests 74# @ .610". This is ok if the car has big slicks, but we have had better success with the 58# springs.

I strongly believe the lubricity of the gear oil plays a role, but I can't quantify this. We run a very slick synthetic gear oil called "ShockProof" from Redline. It comes in different viscosities and we run the version appropriate for the power level we're running.



Additional info on my car that might be useful:
-55% front weight bias, 3620 lb - no driver (bias doesn't change with driver)
-~80% front roll couple, car is a bit on the understeer side on a skidpad with gas just enough to maintain speed (but not sliding rear at all)
-6.9* caster both sides, 2.5* camber both sides, 0" toe. 0* camber on ford 9" floater rear
-Have outer front tire wear. Tire temps on skidpad agree (say, 125 outer, 123 middle, 105 inner after 5 consecutive turns with no heat in the tire before). Rear tire temps on skidpad are good.
-I'm probably losing some camber to body roll

My thought is to add some roll stiffness to the rear to get closer to neutral.

Would really like to know what a locker wants regarding chassis set up and driving style.

Thanks,
Wade

From your tire temps it is clear your car has a push that has nothing to do with the locker. You have too much roll for your caster ... or too little caster for your roll angle. But I don't want to imply that caster alone or roll angle alone will fix it. As you know, everything affects everything else.

[72BBSwinger]

Steve, the challenge with buying a used NASCAR locker is you don't know what springs are in it. We tune the locker with different spring rates from 25# to 125#. The softer the spring the easier it releases when turning. The stiffer the spring, the more it takes to get it to release. On big tracks like Daytona & Talladega the last thing you want is for the locker to release. So they run the 110# to 125# springs.

If you bought a used locker with that much spring rate, it would be a bear to get it to unlock. With street tires, I don't think the tires have enough grip to force those 110# to 125# springs to unlock consistently ... and would on occasion simply slide the tire instead.

For short track ovals, road racing & autoX, the hot ticket is softer springs. I typically like the 58# spring for these applications.



Lockers are the most common & preferred differential in most full size car road racing applications.

They turn left & right equally ... unless ...
a. You have different rate springs on the right & left side.
b. You bought a CTR Detroit Locker, designed for oval track racing that only unlocks turning left. You can tell when you take it apart, because it only has one spring.

This is news to me, also didnt know you could taylor a Detroit like that.

[rustomatic]

Ron, you've added some great clarity here--in a couple posts, I learned more here than in a whole day of scanning other crud online. I'm very much looking forward to seeing your new business come to life. Now if only the autocross scene in the Sacramento area hadn't diminished so much for the coming season...

Steve, the challenge with buying a used NASCAR locker is you don't know what springs are in it. We tune the locker with different spring rates from 25# to 125#. The softer the spring the easier it releases when turning. The stiffer the spring, the more it takes to get it to release. On big tracks like Daytona & Talladega the last thing you want is for the locker to release. So they run the 110# to 125# springs.

If you bought a used locker with that much spring rate, it would be a bear to get it to unlock. With street tires, I don't think the tires have enough grip to force those 110# to 125# springs to unlock consistently ... and would on occasion simply slide the tire instead.

For short track ovals, road racing & autoX, the hot ticket is softer springs. I typically like the 58# spring for these applications.



Lockers are the most common & preferred differential in most full size car road racing applications.

They turn left & right equally ... unless ...
a. You have different rate springs on the right & left side.
b. You bought a CTR Detroit Locker, designed for oval track racing that only unlocks turning left. You can tell when you take it apart, because it only has one spring.

[Uhcoog1]

Thanks for the tips, Ron!

I've got a gameplan laid out to find the oversteer side of neutral, and test tire temps every step of the way there. The thing I am most curious to see is how much the tire temps and wear change due to roll couple changes without any alignment changes.

Guess I'll add pulling and blueprinting the locker to my list, albeit at the very bottom. When I get there, I'll definitely contact you about new springs, etc. Will you be selling small parts like that when you get up and running in a few months?

Wade

[HellPhish89]

huh.. the guys over on tech hate the tru-trac since eaton took over. havent heard about issues with the wave trac

[Ron Sutton]

Thanks for the tips, Ron!

I've got a gameplan laid out to find the oversteer side of neutral, and test tire temps every step of the way there. The thing I am most curious to see is how much the tire temps and wear change due to roll couple changes without any alignment changes.

Guess I'll add pulling and blueprinting the locker to my list, albeit at the very bottom. When I get there, I'll definitely contact you about new springs, etc. Will you be selling small parts like that when you get up and running in a few months?

Wade

Yes, all the regular ProTouring stuff plus the special niche stuff like this. We offer blueprinting & gear set-up services also, for the guy that doesn't want to do it himself. (But it's pretty easy to do.)

[Ron Sutton]

Ron, you've added some great clarity here--in a couple posts, I learned more here than in a whole day of scanning other crud online. I'm very much looking forward to seeing your new business come to life. Now if only the autocross scene in the Sacramento area hadn't diminished so much for the coming season...

What has changed in the Sac AutoX scene?

[parsonsj]

I used a locker in my old 67 Nova, and the only issue I ever had was turning while backing up. Otherwise the locker wasn't that noticeable. Out of boredom and while making other mods to de-tune the car for better street manners, I switched to a TrueTrac. I found the TT made more noise on u-turns than the locker ever did. I didn't have to "drive around" either of them.

Most high end cars that see a lot of track time usually end up with lockers. They are, by far, the most durable and consistent diff to use.

[mmosley]

Thank you Ron. I have a Mopar 8-3/4 with a Detroit Soft Locker and 3.90 gears. I have been agonizing over this issue for a while trying to decide if I should switch to a torsen diff. Sounds like I would be best served staying with what I have. Is there any literature on servicing the locker? I looked on Eaton's site, read their "manual" and saw some listings for springs but did not see the one you listed. Looks like there is not much too it, I have done similar work before but never worked on a locker before. I have never had an issue leading me to believe I need a lighter spring, but I have been running 325 drag radials which are pretty sticky. So a street tire may be an issue, I guess I will find out. I'll keep my money in my pocket until then.

[Ron Sutton]

Thank you Ron. I have a Mopar 8-3/4 with a Detroit Soft Locker and 3.90 gears. I have been agonizing over this issue for a while trying to decide if I should switch to a torsen diff. Sounds like I would be best served staying with what I have. Is there any literature on servicing the locker? I looked on Eaton's site, read their "manual" and saw some listings for springs but did not see the one you listed. Looks like there is not much too it, I have done similar work before but never worked on a locker before. I have never had an issue leading me to believe I need a lighter spring, but I have been running 325 drag radials which are pretty sticky. So a street tire may be an issue, I guess I will find out. I'll keep my money in my pocket until then.

You're welcome.

Just so I don't lead anyone astray. All of my advice is based on track use. Like John said ...

They are, by far, the most durable and consistent diff to use.

But they are too coarse, harsh, noisy for some guys in their daily driven (or often driven) street car. It's a personal choice.

[HellPhish89]

You're welcome.

Just so I don't lead anyone astray. All of my advice is based on track use. Like John said ...



But they are too coarse, harsh, noisy for some guys in their daily driven (or often driven) street car. It's a personal choice.

its all a compromise i suppose.
a couple q's:
who do you think makes the most forgiving locker and
how would you set one up to be more street friendly?

[Ron Sutton]

its all a compromise i suppose.
a couple q's:
who do you think makes the most forgiving locker and
how would you set one up to be more street friendly?

Utilizing the Detroit SL "Soft locker" and softer internal springs is the extent of my knowledge & experience. I'm sure there has to be someone with more experience than me using them on the street, so let's hope they chime in.

[Nothingface5384]

didnt know the wavetrac had any issues...excluding the ford version and the shortening of axle shaft for install
I've always read wavetrac was a stronger version of truetrac and also had built in preload
I wish someone would come out with either a wavetrac S trac or platnium track for an 8.5!
I never cared for how mine trutrac acted like an open on some instances

[chetly]

A locker is not good for left AND right turns.

Tell Mike Maier that... Running a locker will not effect your car if you set the car up for a locker. He runs one in his CP Mustang as well as the Blue 66 that he has run at optima, RTTC, Good-Guys, etc etc etc. with everything from a 300 hp 302 to the fire breathing Roush-Yates motor we just put back in the car.

[Flash68]

I'm pretty anxious to see which springs are in my Roush locker now.....

[Matt@BOS]

I'm pretty anxious to see which springs are in my Roush locker now.....

Me too. I'm thinking I will probably need to have them changed out in the one I bought.

Matt

[riles]

Me too. I'm thinking I will probably need to have them changed out in the one I bought.

Matt

Ditto. I'll give Roush a call and see what they use.

Thanks Ron, for all you do, to help guys like me.

[Ron Sutton]

I'm pretty anxious to see which springs are in my Roush locker now.....

Me too. I'm thinking I will probably need to have them changed out in the one I bought.

Matt

Ditto. I'll give Roush a call and see what they use.

Thanks Ron, for all you do, to help guys like me.

Calling Roush Yates Performance where you bought the lockers won't be of much help, because they just get them from the race teams (theirs & others) and list the info they're given. Roush, and all teams, run a few different rates depending on track size. if you were buying a complete diff with gear ratio, that would be an indicator, but that's all.

The only way to "know" is to take the locker apart at some point & test the two springs in a valve spring tester. Whatever the load is at .610" ... is the spring rate everyone works by. It is not uncommon for the two springs to be different rates. Some builders at the teams make the lockers act like a circle track locker ... to a degree ... by putting a heavier spring in the right side.

Of the currently available springs, I suggest a 58# spring for AutoX. When I get our online store open in April, we'll have the high quality ones.

I'll let the cat out of the bag ... we're bringing a 40# spring to market for Detroit lockers that is optimum for street, AutoX & road course track days. $69.50 a pair.

[shmoov69]

Ron, I bought my locker from Eaton about 8-10 years ago and wondering what it would have in it? Is not quite obnoxious, but certainly very clunky and jerky at low speeds. Makes the car push under acceleration also, but there could be multiple factors there as well. LoL! What would it need for an "all around" car? Drag, auto-x, street and a tiny bit of road course sprinkled in?

[Bonehead]

I'm thinking I'll give the TrueTrac a try. Unless I come across something really gnarly that would cause me to think otherwise.