Limited Slip Recommendations

[Greg_FW]

For the second time in fewer years I am spinning my inside wheel on corner exit. More on left-handers than rights, but that must be me.

So I am again in the market for a new Ltd Slip Diff. Otherwise I'm going to go with a Detroit Locker like what was on the car when I bought it.

Any advice/thoughts on an LSD for my 3rd Gen?

[jeffburch]

Torsen T2R

Kinda like a HANS and a helmet. Must haves.

jb

[chicane23]

I would second the Torsen T2R

[Wirtz]

Same here. Been working very well for me.

[AI#97]

If you like driving a loose car and want it predictible in both directions and instant feel....do NOT use a torsen. I'd recommend an eaton std or HD. I have had a standard in my car since 2001...pulled it apart this offseason and it's perfect. It's also cheaper than a T2R and can be found on ebay in the sub 350 range.

[Boudy]

Torsen T2R

Matt: Interesting, got "tech"?

Boudy

[mitchntx]

Several threads on various F-Car forums about recently purchased T2Rs cracking cases.

I have one.

[ShadowBolt]

Several threads on various F-Car forums about recently purchased T2Rs cracking cases.

I have one.


I put a new T2R in the 17 a few months before selling it. They are pricey but mine worked great. I read that problems had just started a few months prior to my purchase.

The 55 has "FMS rear locker diff" (whatever that is, it's what Tony called it in the sales add) and at ECR in the rain I thought it was gone but in the dry it feels like it's working okay.
JJ

[mitchntx]

I'm wondering if it's HP related.

The cracked one I have has about 5K miles on it and came out of a 400HP open road race car.

I picked up an old T2R that was worn out. I'm hoping to get the case from the old and insert the guts from the newer one.

[Boudy]

I haven't heard anything about them cracking. Mines only got 6 or 8 events on it but it's fine so far. I first had an Auburn which started inside wheel spinning at about it's 3rd or 4th event before the T2R.

Matt's issue seems to be performance related. Any info on that?

Boudy

[marshall_mosty]

Basics:
Torsen
Gear type diff that has a preset non-adjustable preload. Typically the T-2R works best for R/R applications. No parts to wear out. Should last "forever". If the preload doesn't work for you... you are SOL as the preload can't be adjusted.

http://www.torsen.com/files/Torsen%20T-2%20Technical%20Sheet.pdf



Eaton
Clutch style limited slip that is MUCH stronger than the OEM units. Bias ratio (preload) is adjustable by installing different springs.

Is the Eaton Posi Rebuildable?
Yes. There are three main types of service kits available - internal spider and axle gear kits, clutch kits, and preload spring & plate kits.

Can I upgrade my Eaton Posi?
Yes. Both the clutch disks and the preload springs can be upgraded. Posi units come equipped with 400lb of preload. They can be upgraded to 800lb, or even downgraded to 300 or 200lbs options.
Clutches - There are several types of clutch service kits. They range from the OE, 18 disc (standard), the 24 disc (high performance), and the modern day, high tech 14 disc carbon fiber design.


http://www.eaton.com/EatonCom/ProductsServices/PerformanceProducts/Products/Differentials/PosiLSD/index.htm




Just my .02, but if I ever get tired of rebuilding my stock Trac-Lok, I'm going with an Eaton based solely on the adjustability.

Another "expert" opinion.


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DIFF DIFFERENCES
Which differential would be best for road racing, in my 300hp Porsche? The question arises because a supplier suggests that a plate-type limited-slip is better suited to road racing than a worm gear style torque bias diff. I have used both and found Iliked the torque bias diff. I thought it was a better design, from what I read. The supplier states that the lsd will be better in corner entry and exit. What is your opinion?

Clearly, both worm gear and clutch pack differentials have their adherents, and both are used successfully in racing. You say you have experience with both types, and have already formed a preference. The most obvious answer would be that you’ve already answered your own question, and don’t need advice.

However, the situation is actually a bit murkier, because the behavior of both types of differential can vary according to design and tuning details. Both types are similar in that they generate a locking torque in response to the total torque being transmitted. In both types, the locking torque depends on pressure angles. In a ZF-style clutch pack design, the angles are those of the ramps on the spider shaft and the housing halves. In a worm gear design, it’s primarily the helix angle on the gear teeth, and secondarily the pressure angle of the tooth profile. Lubricant choice also influences behavior.

Consequently, all clutch pack diffs don’t act alike and neither do all worm gear diffs. A lot depends on how a specific example is tuned.

That said, the clutch pack design probably offers a greater range of tuning options, and probably greater wear resistance. With the worm gear designs, we are trying to make gear teeth act as a friction device. Clutch discs are designed to be a friction device; gear teeth can be made to act as a friction device, but they are less comfortable in that role.

This affects the ability of the differential to maintain consistent properties over time, and its longevity.

The pressure angles determine how rapidly locking torque builds as transmitted torque increases. The preload in the diff determines how much locking torque there is when no torque is being transmitted. A clutch pack is easily preloaded, and it maintains its preload relatively well, especially if the preload is applied by springs or some other compliant system such as dished clutch plates. Worm gears can also be preloaded, but because they are not very compliant, the preload rapidly goes away as the teeth wear.

One limitation in worm gears is that the pressure angle is generally the same for forward torque and rearward torque (as when engine braking, or when transmitting brake torque from a single rear brake, as seen in FSAE cars). In a clutch pack diff, we can use different ramp angles for power and decel.

Another peculiarity of worm gear designs is that because power and decel apply force to opposite sides of the gear teeth, preload doesn’t have identical effects in both directions. If we preload the gears in the direction they’re loaded under power, what happens under decel is that we have diminishing friction with increasing reverse torque, until the preload is overcome, at which point locking torque is zero. As reverse torque increases beyond that point, locking torque builds again. With a clutch pack, preload has similar effect in both drive and decel modes.

This does mean that we can make a worm gear diff act different in drive and decel, but not in a manner that’s independent of preload.

One interesting, though uncommon, trick we can use in a worm gear diff is to use plain thrust washers to absorb the thrust of the worm gears in one direction, and needle thrust bearings to absorb the forces in the other direction. This can afford us some limited measure of difference in friction depending on torque direction. Last year’s North Carolina State University FSAE car had a diff like this.

It will be clear, however, that using these tricks is not nearly as straightforward as varying the ramp angles in a clutch pack diff.

Finally, neither option is ideal, because neither is speed-sensitive. Both clutch pack and worm gear diffs rely on Coulomb friction, which is largely dependent on normal force and not speed. We would rather have the locking torque vary with the speed difference between the wheels, either entirely or at least in part. This argues for either a pure viscous limited-slip, or a design that uses a pump, driven by relative ouput shaft rotation, to load a clutch pack, or a design that combines viscous effects with a clutch pack.

[GlennCMC70]

MM is right. I avioded clutch types due to me being only exposed to Aburns. Those are not rebuildable.
I already had a T2R in my street car, so I moved it to my CMC car. Eaton is my top pick right now in either a clutch type (rebuildable and adjustable) or the True Track which is a Torsen copy w/ less pre-load. I would like to play around w/ a spool for a few events.

[donovan]

I use a Torsen T2.

Years ago (2003) when I was building my car I talked to a Tech at Torsen about the difference between the T2 and the T2R. He explained that the T2 is a lifetime part aside from a catastrophic failure or case wear. The T2R does have a wear item with added Spring for the extra bias and some sort of friction washer or friction shim (don't remember what he called it).

He also explained that the extra bias in the T2R would only be noticeable in tight corners like an AutoX, and for RR/Open-Track the T2 would be better.

I have not priced them, but back then the T2 was $400 and the T2R was $600.

I have heard that Torsen is now telling people to use the T2R for RR/Open-Track...

I saved $200 and have not had second thoughts about it. I would but a T2 again and save the money if I was in the market.

David D.

[RichardP]

The T2R does have a wear item with added Spring for the extra bias and some sort of friction washer or friction shim

The general story I've heard is that some time after that, Torsen deleted the preload from the 8.8 application. It's only difference now is just a higher bias ratio. The True Track is similar and has a bias ratio between the T2 and the T2R.


Richard P.

[michaelmosty]

I originally bought a T2 and ran it in my car for about 3 events. IMO it was a piece of crap. I bought a T2R and have used it for the last 3 years and love it.
I don't know if the T2 I got is just bad or what. It is sitting in a box in my garage if anyone want to buy it. :(

[AllZWay]

I just run a stock T2 and so far it has been perfect for 4 years of racing.

[donovan]

I originally bought a T2 and ran it in my car for about 3 events. IMO it was a piece of crap. I bought a T2R and have used it for the last 3 years and love it.
I don't know if the T2 I got is just bad or what. It is sitting in a box in my garage if anyone want to buy it. :(

28 spline?

$50

[michaelmosty]

I originally bought a T2 and ran it in my car for about 3 events. IMO it was a piece of crap. I bought a T2R and have used it for the last 3 years and love it.
I don't know if the T2 I got is just bad or what. It is sitting in a box in my garage if anyone want to buy it. :(

28 spline?

$50
28 spline, yes
$50? :shock:
I need to put it on ebay and see what I get.

[David Love AI27]

I need to put it on ebay and see what I get.

Let me know when you do!!

[donovan]

I originally bought a T2 and ran it in my car for about 3 events. IMO it was a piece of crap. I bought a T2R and have used it for the last 3 years and love it.
I don't know if the T2 I got is just bad or what. It is sitting in a box in my garage if anyone want to buy it. :(

28 spline?

$50
28 spline, yes
$50? :shock:
I need to put it on ebay and see what I get.

be sure to explain in that eBay ad how much you disliked it.

$75! :-)

[cjlmlml]

$76

[AI#97]

Torsen T2R

Matt: Interesting, got "tech"?

Boudy

My experience in having driven them all including the auburn I just put in my truck is that the torsen can and will light a single rear tire and can either be overpowered and not work, or takes that miniscule fraction of a second and allows some slip of one tire, then bites and causes a very slight "chirp". this has all been in cars of 300+ rwhp. CMC cars might not have the power to do it, but you guys are generating nearly the same torque as my AI car. However, the lack of torque could compound the problem in the T2/R as it takes power to generate the pressure bias...?

The clutch type diffs are all as good as you set them up. Ford Trac Locs are all rebuilt with additional clutches to make them last....or make them work nearly as tight as a spool. Eatons use a kevlar clutch pack that can take a TON of abuse and the gears are of much higher grade steel...billet I believe as opposed to the cast crap in a ford unit. My Eaton had the 400# preload springs in it and I just upgraded to the 800 lb springs and LOVE it!!! If you want to put your foot in the gas and rotate the car, it does it instantly and very predictably and equally...especially in transistions like 13, 14 and 15 at TWS. The car did start to push a little and was fixed with a rear bar adjustment.

I have seen people for years look for ways to eliminate bias and "induce" spool like behavior with springs and thicker clutch packs. Personally, I could care less if the inside tire "scrubs" in the parking lot...I don't race there. also, consider standing starts...don't want ANY bias there especially if different grip levels from left to right.

I too would like to try a spool but just don't need to at this time. Maybe if I go to a monster motor I might just for strength.

YMMV but that is my "expert" impression of having driven them all except a spool.

BTW, Auburns are rebuildable. If they put it together, it can be disassembled and rebuilt. The story of not being rebuildable was because Auburn wouldn't sell the parts. Yukon gear used to sell kits to do so but I have not personally done it. After looking at the one I just put in my dodge, it would be easier than rebuilding my eaton.

[AI#97]

Oh, and if you are looking to eliminate rotating mass....a spool usually weighs 5 to 10 lbs less than a clutch type diff..... ;)

[Boudy]

Thank you sir.

Boudy

[Greg_FW]

Lots of great information from the best source: experience. Thanks for all the feedback!

[Hood]

I like Marshall's post in that it tells you the mechanics involved with both types of diffs. However, the feel of each diff can be, at times, drastically different. Having driven my CMC car with a 'spool' I can tell you that the car feels way different than with a clutch-type or gear-type posi. First the spool...The car has an unstable feel under braking, especially if there is any transitional elements in that particular part of the course. Turn-in suffers as you transition off the brakes and will tend to understeer more as you add throttle (unless you are in a high horsepower car and can just hang the tail out Trans-Am style). I had to alter the shock settings in order to drive the car comfortably at the limit. Otherwise, massive trailbraking was required to get the car pointed in the right direction. This shock alteration further enhanced the bad stability problem under braking and I quickly realized that something needed to change. I put a clutch posi in and immediately the car was eager to turn in but would allow some inside wheel spin (not enough clutch preload) resulting in a slower exit speed. I was a die hard clutch posi advocate until I recently tried a Detroit TrueTrac. Wow! is all I can say. The car was instantly more stable under braking, had better mid corner behavior and I could apply throttle sooner without making it push OR oversteer. With the clutch-type posi, when throttle is applied, it wants to become very close to a locked diff. It allows some differential wheel speed at higher loads but acts more like a locked diff than not. This can also cause a push. With the gear-type posi, it always allows wheel speed differential while both wheels are being powered. This causes less of a push. Again, as Matt was saying, these are my observations based on using all of these in different environments (autocross, drag racing, road racing, etc) Yeah, I know, drag racing may not be relevant in this case but you get your experience where you get it.

[HoustonNW]

I had a lot of one wheel spin at Cresson. I can probably drive around it at TWS but may as well not show up to Hallett with a bad rear diff.

Is the Detroit TrueTrac still a good choice? Do I have to remove the ring and pinion to install it? If yes then I'll have to find a shop in Houston, any suggestions?

Paul Costas with Witchdoctor Motorsports (do you know him Gary?) makes an argument on frrax.com for a Powertrax No-Slip for a driver at my level. I like the idea of installing it without disturbing the ring and pinion but I cannot figure out if they offer one for the 1998 Camaros:

http://www.richmondgear.com/powertrax/chevycarns.pdf

Can anyone read that application chart and confirm yes or no?

Thanks.

[Casey_SS]

I had a lot of one wheel spin at Cresson. I can probably drive around it at TWS but may as well not show up to Hallett with a bad rear diff.

Is the Detroit TrueTrac still a good choice? Do I have to remove the ring and pinion to install it? If yes then I'll have to find a shop in Houston, any suggestions?

Paul Costas with Witchdoctor Motorsports (do you know him Gary?) makes an argument on frrax.com for a Powertrax No-Slip for a driver at my level. I like the idea of installing it without disturbing the ring and pinion but I cannot figure out if they offer one for the 1998 Camaros:

http://www.richmondgear.com/powertrax/chevycarns.pdf

Can anyone read that application chart and confirm yes or no?

Thanks.

Me too...but only in Little Bend and Buzzard's Neck. Where was your wheel spin happening? Did you make suspension changes for Cresson? I went up ~25% in spring rates and think that was more of a factor than the diff "going bad". I went with the Auburn Racer's diff (clutch style diff w/ 800lb preload springs) before Hallett last year and it's been flawless up to now. I still can't say anything bad about it. The slippage I got at Cresson was pretty easy to drive around with just a line change - braking later w/ more trail-braking to slide the rear, turning in 1/2 car length earlier, then hard on the gas to stop the slide and straighten the car completely fixed it. No 1 wheel peel at all. Dunno if it was any faster but it sure was fun :) With a smoother radius sort of line, it would spin the inside tire from apex to track out. Just a data point for you to play with...may or may not help.

What diff is in your car now and how old is it? Was last weekend the first time you noticed the problem?

[rpoz27]

Matt Bought me an eaton and gears for the GN off ebay for $630 for Xmas. get the eaton and be done with it.

[Alien]

I think the powertrax can be installed without removing the ring gear since you are reusing the carrier. Tho I *think* it MUST use an open diff carrier. If you have the T2 that was stock in the LS1 cars, I believe you'll have to replace the carrier (from a V6?) and that may be why it's not listed in that link. Pretty sure you'd use the 10-bolt 7.625" 28 spline one, 92-0776-2805 or 92-0776-2885

With any diff swap, I don't see why you'd have to remove the pinion gear. I've done it by just swapping over the ring gear to the new carrier (LEFT HAND THREADS!) and checking the backlash/pattern. Have never needed to shim anything so far since I've always reused the gears in the rearend, YMMV. If you're installing new gears, it's a whole 'nuther story.

[Sidney]

For Sale:

Eaton/Detroit Locker Truetrac posi.

Part Number 911A319.

For GM 7 1/2 rear diff.

Brand new in box.

Sold car before getting it installed.

Summit price is $409.95.

Make offer.

Sidney Franklin
Bloomington, IL

SFrank944@aol.com

http://i1224.photobucket.com/albums/ee377/Sidneyfranklin/Detroitposi2.jpg
http://i1224.photobucket.com/albums/ee377/Sidneyfranklin/Detroitposi1.jpg

[HoustonNW]

Me too...but only in Little Bend and Buzzard's Neck. Where was your wheel spin happening?

I noticed it in the uphill Wagon Wheel and Horseshoe corners, which seemed to overheat the rear tires more than usual and the car got very loose everywhere. However, now that I think about it, it was spinning at the uphill #5 at ECR and in the slow corners at MSRH along with the standing starts.

Did you make suspension changes for Cresson? I went up ~25% in spring rates and think that was more of a factor than the diff "going bad".

No changes other than going to poly bushings in the rear sway bar.

I went with the Auburn Racer's diff (clutch style diff w/ 800lb preload springs) before Hallett last year and it's been flawless up to now. I still can't say anything bad about it. The slippage I got at Cresson was pretty easy to drive around with just a line change - braking later w/ more trail-braking to slide the rear, turning in 1/2 car length earlier, then hard on the gas to stop the slide and straighten the car completely fixed it. No 1 wheel peel at all. Dunno if it was any faster but it sure was fun :) With a smoother radius sort of line, it would spin the inside tire from apex to track out. Just a data point for you to play with...may or may not help.

What diff is in your car now and how old is it? Was last weekend the first time you noticed the problem?

I don't know the history on the diff in the car now but I do think that a lot of my wheelspin in the last three races have been from one wheel so it definitely seems to be getting worse.


I think the powertrax can be installed without removing the ring gear since you are reusing the carrier. Tho I *think* it MUST use an open diff carrier. If you have the T2 that was stock in the LS1 cars, I believe you'll have to replace the carrier (from a V6?) and that may be why it's not listed in that link. Pretty sure you'd use the 10-bolt 7.625" 28 spline one, 92-0776-2805 or 92-0776-2885

Not sure I can figure out what is needed to use the Powertrax, I've never even opened up a diff before. However I just got a $625 labor quote from Late Model Racecraft (where we had the dyno day) and so I think I will learn!

With any diff swap, I don't see why you'd have to remove the pinion gear. I've done it by just swapping over the ring gear to the new carrier (LEFT HAND THREADS!) and checking the backlash/pattern. Have never needed to shim anything so far since I've always reused the gears in the rearend, YMMV. If you're installing new gears, it's a whole 'nuther story.

No new gears, I guess I'll buy a magnetic base dial indicator to make sure that I don't need to re-shim. New tools are always good.

Trutrac, Eaton, Auburn - maybe I'll just flip a coin.

[HoustonNW]

OK, I've decided on the Trutrac. It seems that the torque-distributing diffs (Torsen) have the best performance under braking and that is where I need the most improvement.

Eaton recommends dino oil only, no synthetic. The factory weight is 75W-90. Any recommendations on brands? Is the weight OK for race use?

I am planning on replacing the ring gear bolts and probably the diff carrier bearings. Can I get the bearings off the old diff carrier and reuse them? Any tricks to getting the bearing races out of the housing?

[Alien]

If it's a new carrier without bearings already on it, buy new bearings and get those pressed on. I wouldn't try to remove the ones on your current carrier to try reuse them, not worth it. The races fall out when you remove the diff bearing caps off the housing.

[mitchntx]

OK, I've decided on the Trutrac.

Now is not the time to skimp. Do it once and forgetaboutit ...

It's easy to take $1000 worth of nice parts and turn them into metal dust in very short order.

Also make sure you order model specific. Not all 10 bolts are the same.

Redline diff fluid. I use 80W120 because the 75W90 was puking out the vent, especially in August.