Rear end rebuild?

MrAwesome987

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I have noticed recently that my 09 GT's rearend slips a good bit, especially when going up my steepish driveway. I'll pull in, and the right rear wheel will spin a bit before going up the drive way. I have also noticed that when on the lift, while diagnosing an issue with the park brake, I could easily spin one tire free of the other (one side wasn't engaging at all with the park brake).

Anyways, my question is this... Should I replace the clutches, or is it better to just replace the carrier with something better? (I've heard the factory LSD is pretty bad?) Thanks..
 

07 Boss

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I have noticed recently that my 09 GT's rearend slips a good bit, especially when going up my steepish driveway. I'll pull in, and the right rear wheel will spin a bit before going up the drive way. I have also noticed that when on the lift, while diagnosing an issue with the park brake, I could easily spin one tire free of the other (one side wasn't engaging at all with the park brake).

Anyways, my question is this... Should I replace the clutches, or is it better to just replace the carrier with something better? (I've heard the factory LSD is pretty bad?) Thanks..

First off if you tire is spinning with the parking brake on that has nothing to do with the rear end. The brakes are attached to the axles not the transmission. If your brake is not engaging that is probably a cable or caliper issue.

Jack the car up. With the car in neutral the wheels should spin in the same direction. With the car in gear they should spin in opposite directions. This will tell you if the lsd is working at all. If the lsd is determined to be working then you have to find out how well it's working. To do that you have to jack up only one wheel and then apply a torque wrench to see if you can get the clutches to slip. You will have to look up the torque specs from the manufacturer. But with one wheel spinning and the other not while going up your driveway tells me that it's going out. When was the last time you did a burnout?
 

MrAwesome987

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First off if you tire is spinning with the parking brake on that has nothing to do with the rear end. The brakes are attached to the axles not the transmission. If your brake is not engaging that is probably a cable or caliper issue.
I wasn't clear in what I was saying here, but what I meant was... I had an issue where the park brake was only applying to one wheel. During troubleshooting of this issue on the lift, I found that the free wheel was extremely easy to turn, even with the other side stationary (due to the park brake). Since it's an LSD, I assumed it would have been somewhat difficult to spin them in opposite directions.

Last burnout was a few weeks ago I guess, I didn't check for two lines, but the rear end did skate around a bit.
 

Flusher

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With both rear wheels off the ground:

In an open diff or a burned up LSD, one wheel will easily turn the opposite direction of the other, as motion is transmitted through the spider gears. This will happen regardless of the transmission being in park or in gear. If the transmission is in neutral, one wheel and the driveshaft may turn while the other wheel does not turn.

In a functioning LSD, both wheels should turn the same direction while the transmission is in neutral. With the transmission in gear or in park, the wheels should not easily be able to be turned by hand.

Each LSD has a breakaway torque that allows differential action. Once that torque limit is reached, the wheels will rotate in opposite directions, with the transmission in gear or park.

Running different tire air pressure, side-to-side, for extended periods, will cause heat and wear on LSD clutch packs.
 

07 Boss

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First off if you tire is spinning with the parking brake on that has nothing to do with the rear end. The brakes are attached to the axles not the transmission. If your brake is not engaging that is probably a cable or caliper issue.

Jack the car up. With the car in neutral the wheels should spin in the same direction. With the car in gear they should spin in opposite directions. This will tell you if the lsd is working at all. If the lsd is determined to be working then you have to find out how well it's working. To do that you have to jack up only one wheel and then apply a torque wrench to see if you can get the clutches to slip. You will have to look up the torque specs from the manufacturer. But with one wheel spinning and the other not while going up your driveway tells me that it's going out. When was the last time you did a burnout?


Oops, OK. No, if one wheel is locked up it should take some force to move the other. Sounds like you need new clutch packs. Or like you mentioned get a new chunk to put in there. I went with an Auburn Pro LSD over a helical gear set up for my Mustang and have been happy. I did just get a new 9" TrueTrac for my firebird build though. I've always run a clutch type posi or a locker but the guys at Strange talked me into the geared set up this time.

Are you running the car hard, and at what power level? For a street/strip car, up until my last purchase, I've always gone with a clutch posi. AutoX or Road I might lean toward the helical gear. A dedicated drag car would get a locker.
 

Juice

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It is not that difficult to spin one wheel by hand, vehicle in the air, while the other wheel is stationary, There should be some resistance, but to test that, you need to do the above. Measure and compare to manufacturer spec.
That said, many ppl forget that under load, the spider gears are forced against the clutches and that load actually assists in the LSD action. On my 91, with a LOT of miles, I can somewhat easily spin on wheel by hand. On my 2013 8.8, there is definitely more resistance to spinning one wheel by hand. Yet both cars will burn both tires without issues.
Put a Torsen in there, and issue is solved. Or, just drive it as is and save money if there are no issues otherwise.

Ps: my parkbrake was messed up on one side also when I got my 07. The bottom slide for the one caliper was stuck in the bracket. So the dealer simply disconnected the cable on that side. Fucking brilliiant assholes.
 

Pentalab

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For street use, my Eaton Tru-trac works pretty damned good. It has a 3.5:1 bias ratio. Uses dino oil, 75W-140. Zero maintenance. Oem LSD is a dead loss..as is the GT-500 carbon fiber version. When the tru-trac was installed, I had a whiteline watts link installed at the same time. Previous to that, I had the DSS-DS installed. The entire combo is night and day better than oem.

Tru trac is half the price of the torsen.
 

Juice

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Shit, a few years ago, a Torsen was half the price of a Torsen today. Prices for parts on these cars can get rediculous.
 

MrAwesome987

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Are you running the car hard, and at what power level? For a street/strip car, up until my last purchase, I've always gone with a clutch posi. AutoX or Road I might lean toward the helical gear. A dedicated drag car would get a locker.
I do the occasional burnout, but other than that, I don't drive it that hard. Car makes 460ish to the tire, so not an insane amount.

I went ahead and replaced the oil and added the Ford friction modifier. Can't tell a difference (no real surprise).

I am interested in the Torsen/Tru-Trac... Are they pretty bullet proof in these cars?
 

Juice

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Torsen is for road racing, sends power the the wheel that has traction. I hear they do wear. I should have gotten one when they were $550. :( Don't know much about True tracs.
 

Pentalab

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Eaton tru-tracs are pretty much bomb proof. They send TQ to the wheel with the most traction. The absolute max difference in TQ between each wheel is the bias ratio. Say one wheel on dirt, one on asphalt. With the tru-tracs 3.5:1 bias ratio, if one wheel is on dirt, it gets 'X' amount of tq. The wheel on asphalt gets 3.5 'X' tq. The Torsen has a 2.7:1 bias ratio. You can also get bias ratio's as high as 4:1. On the hwy, if only wet on one side, flying around corners, the dry side will get more tq than the wet side. If it's just a drag race at the lights, in the dry, the tq split is 50-50. If one side spins, more tq is transferred to the other wheel.

VMP sells the tru trac in 2 versions. Normal version has 3 x side gears. HD version has 4 x side gears.... BUT requires the use of moser / strange engineering axles..due to higher spline count on the hd version. VMP sez the HD version is typ used for drag racing, once your 60' is down to 1.4 secs. Normal version is ample for street cars..even high rwhp cars.
 

Midlife Crises

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I have the Eaton Tru-Trac in my 2010 GT. It’s the one with 3 Helical gears, works with C clip or eliminater axles with 31 splines. It doesn’t make any noise and launches straight every time. It is not recommended to use synthetic lube with the Tru-Trac.
 

Pentalab

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I have the Eaton Tru-Trac in my 2010 GT. It’s the one with 3 Helical gears, works with C clip or eliminater axles with 31 splines. It doesn’t make any noise and launches straight every time. It is not recommended to use synthetic lube with the Tru-Trac.
I have the same setup as you... in my own 2010 ( mine is an auto). I have just the small Roush M90, LT's, 94 tune, twin 62mm tb. 386 rwhp / 370 rwtq. Low 12's in the 1/4 mile.

I have seen torsens... blown to bits when used for drag racing. The pix are here, on S-197.

The tru trac with 3 helical gears is ample for most folks. The HD version with 4 helical gears and the HD box it's contained in...is even stronger..and I think $150.00 more.
 
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Pentalab

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I have the Eaton Tru-Trac in my 2010 GT. It’s the one with 3 Helical gears, works with C clip or eliminater axles with 31 splines. It doesn’t make any noise and launches straight every time. It is not recommended to use synthetic lube with the Tru-Trac.
yeah, 75W-140 dino oil.
 

07 Boss

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I do the occasional burnout, but other than that, I don't drive it that hard. Car makes 460ish to the tire, so not an insane amount.

I went ahead and replaced the oil and added the Ford friction modifier. Can't tell a difference (no real surprise).

I am interested in the Torsen/Tru-Trac... Are they pretty bullet proof in these cars?


At your power levels I would recommend a regular clutch type posi unit but that's me. Any of the major brands are all good, Yukon duragrip, Eaton posi, or Auburn Pro will all be good enough and perform well. All of these besides the Auburn (because of the cone clutches/case) are rebuildible. I've been running the Auburn for years on the street and at the drag strip with no problems. It is very predictable and has decades of proven reliability/durability.
 

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Can you all confirm that the TruTrac is noise free? I really like it, but its making some litte noise during engagement in corners and a rattle on coast when I press the clutch. But, I was not able to find Dino oil in Germany and used synthetic Castrol 75w140 with no LS modifier.
 

MrAwesome987

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When was the last time you did a burnout?
Did a pretty good burnout last night on the way home from work. It definitely spun both tires, and the marks appeared to look the same. Guess it's still got some life left in it..?
 

Midlife Crises

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Can you all confirm that the TruTrac is noise free?
The Detroit TruTrac buy Eaton does not make any noise on the hi-way or in town. Then again the T56 mag and the ten year old Magnapacs could be fooling me.
 

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