Detroit Truetrac

Diablo2doorram · Feb 3, 2022

I have been hoping Eaton would come out with a true positraction. My understanding the TrueTrac is still an open diff and does not spin both wheels in the same direction until it slips. Hope they make an E-locker soon but would settle for a "true posi"

Govtman · Feb 3, 2022

Jwithing said:
So, in budgeting for a 6.4 swap, I've learned that a Detroit trutrac will be immediately necessary as the extra power will eat up the stock LSD pretty quick.

I've never messed with gears or diffs before and I couldn't find any good walk throughs on this forum or YouTube videos. Based on that, I figured $500 in labor based on other comments, so I figured I'd reach out to some shops... a little shocked at the quote below. At that price, I'll just have to suck it up and figure it out myself. Anybody have any good walkthrough directions, maybe a good shop manual that covers this? Any specialty tools needed other than for setting backlash?

View attachment 484071

Local all terrain/rock crawling shop here is charging me $1100 to put a Detroit TT in my '19 Classic and replace all bearings/seals/gear oil in rear end.

Looks like they double charge you for the gear oil?

Jwithing · Feb 3, 2022

Govtman said:
Local all terrain/rock crawling shop here is charging me $1100 to put a Detroit TT in my '19 Classic and replace all bearings/seals/gear oil in rear end.

Looks like they double charge you for the gear oil?

Yes, looks like double charged for oil to do a 500 mile flush.

kurek · Feb 3, 2022

Diablo2doorram said:
I have been hoping Eaton would come out with a true positraction. My understanding the TrueTrac is still an open diff and does not spin both wheels in the same direction until it slips. Hope they make an E-locker soon but would settle for a "true posi"

In terms of rough terrain performance the distinction is effectively moot on 2013+ trucks.

The clutch-based anti-spin diff is wide open until acted upon by enough resistance to load up the clutches. On older vehicles that load was initially provided by the preload springs but starting in 2013 Rams were equipped with a traction control enhancement that loads up the differential using the service brakes which produces a much more positive clutch engagement than preload alone could do and basically eliminates wear on the clutches from regular driving.

A torsen or truetrac diff has a torque ratio that is basically fixed, for example 3:1 or 6:1 so when the difference in effective torque (at the wheels) is less than that ratio it behaves as a full locker and when the difference in effective torque is greater than that ratio it behaves as an open differential. Historically this would mean that if you had one wheel off the ground (zero torque) the other wheel would not be compelled to move and the diff would act as if it's open, but if you had one tire on gravel and the other on asphalt there would usually be enough resistance on the gravel side to make it act as a spool. Again the BLD traction control steps in and supplies load to the free side of the diff and causes it to lock up but that part is reactive and requires wheel spin to happen first.

Aside from the obvious advantage of nothing to wear out a truetrac diff is also immediate (not reactive) and its operation is linear. There's not some specific tipping point or delayed reaction. This is what makes them so good on loose surfaces where both wheels are almost always in contact with the ground and have some traction - behavior is immediate and predictable before traction control even knows there's a problem. If you're on extremely loose surfaces and can take driveline load off the axle it will behave like an open diff and allow cornering without skidding. If you apply power or engine braking while cornering then skids or hops are likely.

No such thing as a perfect diff for all occasions but I've never once felt the need for a full locker in my Ram, BLD does a great job in concert with the anti-spin diff. But if cost wasn't a factor I would rather have a truetrac for dirt roads and light snow.

62Blazer · Feb 4, 2022

Diablo2doorram said:
I have been hoping Eaton would come out with a true positraction. My understanding the TrueTrac is still an open diff and does not spin both wheels in the same direction until it slips. Hope they make an E-locker soon but would settle for a "true posi"

That is not a very good description of the operation. While the TrueTrac and more traditional clutch based "posi" use different methods, the end result is basically the same. Honestly the comment about "does not spin both wheels in the same direction until it slips" simply does not make any sense. If you are driving down the road on the pavement how can both wheels not be going in the same direction? I ran a TrueTrac in the back of a K5 Blazer for years, including doing a lot of off-road, and it was always smooth in the power transfer meaning both tires would always spin. Not like one tire would sit there and spin and suddenly it would lock up. Eaton does make a differential called the Gov-lock which has been a factory option in Chevy trucks for a long time that will do that, but it's a completely different setup.

HEMIMANN · Feb 4, 2022

kurek said:
In terms of rough terrain performance the distinction is effectively moot on 2013+ trucks.

The clutch-based anti-spin diff is wide open until acted upon by enough resistance to load up the clutches. On older vehicles that load was initially provided by the preload springs but starting in 2013 Rams were equipped with a traction control enhancement that loads up the differential using the service brakes which produces a much more positive clutch engagement than preload alone could do and basically eliminates wear on the clutches from regular driving.

A torsen or truetrac diff has a torque ratio that is basically fixed, for example 3:1 or 6:1 so when the difference in effective torque (at the wheels) is less than that ratio it behaves as a full locker and when the difference in effective torque is greater than that ratio it behaves as an open differential. Historically this would mean that if you had one wheel off the ground (zero torque) the other wheel would not be compelled to move and the diff would act as if it's open, but if you had one tire on gravel and the other on asphalt there would usually be enough resistance on the gravel side to make it act as a spool. Again the BLD traction control steps in and supplies load to the free side of the diff and causes it to lock up but that part is reactive and requires wheel spin to happen first.

Aside from the obvious advantage of nothing to wear out a truetrac diff is also immediate (not reactive) and its operation is linear. There's not some specific tipping point or delayed reaction. This is what makes them so good on loose surfaces where both wheels are almost always in contact with the ground and have some traction - behavior is immediate and predictable before traction control even knows there's a problem. If you're on extremely loose surfaces and can take driveline load off the axle it will behave like an open diff and allow cornering without skidding. If you apply power or engine braking while cornering then skids or hops are likely.

No such thing as a perfect diff for all occasions but I've never once felt the need for a full locker in my Ram, BLD does a great job in concert with the anti-spin diff. But if cost wasn't a factor I would rather have a truetrac for dirt roads and light snow.

I'd read latest Gen heavy duty dumped AAM Trac-Rite (torsen) axle. Do you know if this is the case?

Dusty · Feb 4, 2022

Diablo2doorram said:
I have been hoping Eaton would come out with a true positraction. My understanding the TrueTrac is still an open diff and does not spin both wheels in the same direction until it slips. Hope they make an E-locker soon but would settle for a "true posi"

Not familiar with Torsen or True Trac differential systems, but your understanding seems to more closely match how traction control works.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Build date: 03 June 2018. Now at: 064366 miles

Sking80 · Feb 12, 2022

JB Weld said:
I agree with the comment to get the converter you want and wait to afford the diff swap if needed.

I just installed a Trutrac in my '19 Classic and it was easy. If coarse with 33,000 miles all my seals and bearings are in great shape.

No need to change extra seals, bearings, etc. I purchased the Trutrac from Jegs @$525, ring gear bolts for $40 ( make sure they're for ZF, not earlier) and Timken bearings and races @$65 off Amazon. I also (finally) bought a magnetic base dial indicator for $45 and borrowed a torque wrench to torque ring gear bolts to 166 ft/lbs. I also made a tool to torque the side adjusters, about $15 in materials.

I noted backlash @ .006" before. I didn't worry about how the gear pattern was because I set the backlash back to .006" and never pulled the pinion, so that depth didn't change. The 9.25 ZF has side adjusters instead of shims. I adjusted backlash and torqued adjusters to 75 ft/lbs to eliminate gear deflection.

How long did it take to do it

JB Weld · Feb 20, 2022

I would say 4-5 hours?? That's probably on the high side. No hoist, no impacts and some time wasted trying to beat the break rotors with a dead blow. (Ended up removing rotors from the axle shafts after they were out of the housing) Also had to make the tool to torque the side adjusters.

knightjp · Mar 20, 2022

If you have a 3.92 gear ratio and you swap it for a Detroit TrueTrac, what does that do for your gear ratio? Do you still have a 3.92?

Just a question for my info.

NOV87 · Mar 20, 2022

No effect to the gear ratio. You can replace the existing gear with a different one at the time of TrueTruc install.

knightjp · Mar 21, 2022

NOV87 said:
No effect to the gear ratio. You can replace the existing gear with a different one at the time of TrueTruc install.

So when ordering the Truetrac, do I have to tell them what gear ratio I've got?

Wild one · Mar 21, 2022

knightjp said:
So when ordering the Truetrac, do I have to tell them what gear ratio I've got?

They might ask,so it wouldn't hurt to tell them,but odds are they won't ask your gear ratio.I'm guessing you don't know what gears you have if you're worried about telling them. Your build sheet will tell you what gears you have,or you might get lucky and still find it on your diff. It'll be a little sticker on the drivers side axle tube ,it'll have your gear ratio printed in tiny numbers on it,if it's still readable.If your truck is a 4X4 it'll also have the gear ratio printed on the front diffs sticker.If you have a dealer handy,they can also tell you what gears you have by using your VIN number.

JPT · Mar 21, 2022

I don't know our axles, I know gears/lockers from my jeep days (Ive done a few ARB Locker Installs, lunchbox lockers, and Detroit Locker installs). Gear ratio only matters to a carrier swap if there is a carrier break. That means that when you change gears in that axle, gears below a certain ratio uses 1 design carrier, and gears above use a 2nd design carrier. Basically it is how close the ring gear mounting surface (on the carrier) is to the pinion gear (left and right on the carrier). To make up for carrier breaks, some ring and pinion manufactures developed "Thick cut" gears, which make up for the additional spacing allowing you to keep your current carrier across the axle ratio break.

If an axle doesn't have a carrier break, there is only one carrier design (Open/Limited Slip/Locker/Spool), so just order the carrier for the correct axle. From what I can find (with no gear/carrier install knowledge on my truck), I only see one carrier for our rams. This would mean, even if they ask, it wouldn't matter what ratio you tell them.

knightjp · Mar 22, 2022

Wild one said:
They might ask,so it wouldn't hurt to tell them,but odds are they won't ask your gear ratio.I'm guessing you don't know what gears you have if you're worried about telling them. Your build sheet will tell you what gears you have,or you might get lucky and still find it on your diff. It'll be a little sticker on the drivers side axle tube ,it'll have your gear ratio printed in tiny numbers on it,if it's still readable.If your truck is a 4X4 it'll also have the gear ratio printed on the front diffs sticker.If you have a dealer handy,they can also tell you what gears you have by using your VIN number.

You are not wrong in your assessment. I don't know the ratio. Hoping it is a 3.92. To be honest, my current one is new to me, bought used with not much info. My previous one had a 3.21 ratio. I bought that new.
Thanks for the info on finding out. I will certainly look into it.

All this is new to me, so my assumption about replacing entire diffs were that there would be some kind of change to the ratio that you already have.
I like the idea of having a truetrac in both the front and back like a Humvee. Not sure if that is possible. I know that Ford Raptors have a torsen (same as a truetrac) in the front.

kurek · Mar 22, 2022

knightjp said:
I like the idea of having a truetrac in both the front and back like a Humvee. Not sure if that is possible. I know that Ford Raptors have a torsen (same as a truetrac) in the front.

Our front axles use a center disconnect for 2wd which takes the place of manual hubs that would have been used in antique trucks. This center disconnect means that one of the front tires is always directly connected to the differential and since our front differentials are open it just spins the stub shaft backward while we drive, this eliminates the rotation of the ring and pinion, front driveshaft and bottom half of the transfer case while in 2wd which saves fuel, improves throttle response and braking, and reduces noise+vibration.

It should also be noted that hypoid gears are made to interface on one side, in other words the ring and pinion gears in our axles are quietest, strongest and most efficient when torque is delivered to them from the engine while traveling forward. If you would install a Torsen or other LSD in the front axle, or if you disable the CAD in your existing front axle and then go for a long drive in 2wd on the highway you'd discover that it makes a bit louder gear whine and it also gets a lot hotter because the gears are being loaded from the opposite side than they're designed to run on. You're pushing on the "back" of the teeth. This heat build up can be significant and it can degrade the oil and rubber seals. On 4wd vehicles with plastic vent assemblies on their front diff it can be enough to melt the vent.

Raptors have a torsen front diff but they also use disconnecting wheel hubs instead of a center disconnect. These things are related and necessary for any 4wd truck that has a non-selectable front traction aid.

knightjp · Mar 22, 2022

@kurek Thanks for that explanation. Now it makes sense why the TRX doesn't have such a diff in the front. Ram does it differently.
Also, I now get why there are so many threads on the F150 forums about failed hubs when engaging 4WD.

Diablo2doorram · Sep 13, 2022

62Blazer said:
That is not a very good description of the operation. While the TrueTrac and more traditional clutch based "posi" use different methods, the end result is basically the same. Honestly the comment about "does not spin both wheels in the same direction until it slips" simply does not make any sense. If you are driving down the road on the pavement how can both wheels not be going in the same direction? I ran a TrueTrac in the back of a K5 Blazer for years, including doing a lot of off-road, and it was always smooth in the power transfer meaning both tires would always spin. Not like one tire would sit there and spin and suddenly it would lock up. Eaton does make a differential called the Gov-lock which has been a factory option in Chevy trucks for a long time that will do that, but it's a completely different setup.

Obviously you have never jacked your rear up to see what happens. The wheels spin in opposite direction if you don't have positraction. Good news for all of us that what a true positraction "Locker" ARB now has one available. RD259 is the part number. Good for all 4th gens! Great drivability, is an open diff when not Locked.

knightjp · Sep 13, 2022

Diablo2doorram said:
Obviously you have never jacked your rear up to see what happens. The wheels spin in opposite direction if you don't have positraction. Good news for all of us that what a true positraction "Locker" ARB now has one available. RD259 is the part number. Good for all 4th gens! Great drivability, is an open diff when not Locked.

This is an Air Locker? Is it for the front or the rear diff?

bm02tj · Sep 13, 2022

The LSD in 2011 and newer has no preload so wheels will turn opposite when jacked up same as open diff

Detroit Truetrac

Junior Member

Member

Senior Member

Senior Member

Senior Member

Senior Member

Senior Member

Senior Member

Junior Member

Senior Member

Senior Member

Senior Member

Senior Member

Senior Member

Senior Member

Senior Member

Senior Member

Junior Member

Senior Member

Senior Member

Similar threads

Forum statistics

Share this page