Sahara Lee

I will be re-gearing in the next month or so. While I have the diffs cracked open changing gears, bearings and seals, I would like to replace my open carriers with Detroit Eaton TrueTracs. I have read that Eaton won't warranty TrueTracs with tires over 33". Maybe that is old info, maybe not.

My 2010 Unlimited Sahara has D30 front and D44 rear with stock 3.73 gears, 315/70R17 Duratracs on 17x9 M/T Classic IIIs, 4" Rancho Sport Lift. I will be going to 4.88 gears.

Could anyone with knowledge/experience with TrueTracs tell me what part number lockers (if any) are recommended for my rig?

Thanks!

river2c

The 33" tire limitation is very old information. The Truetrac has been upgraded substantially in the last decade and it's as strong as any locker/lsd on the market. You can run any size tires you want with them. I think Eaton will warranty up to 38" tires if I'm not mistaken.

Dana 30 - 912A585
Dana 44 - 913A589

planman

Gears and overhaul kits:

JK Non Rubicon 30/44 Gear Package and Master Overhaul Kits

Truetracs:

Eaton Detroit Truetrac (DETROIT_TRUETRAC)


Call when you order. You'll get a package deal and be able to verify you got the right parts.



And...of course you already know that with an 07-11 automatic and 35s:

Going with 4.88s will run only about 120-130 engine rpm lower than 5.13s at 70 mph.

There are no reliable reports in the last 7 years of 5.13s breaking in a Dana 30 while running 35" tires that wouldn't have broke 4.88s.

Unless you were going to run full lockers and offroad with a significant amount of wheel spin, with sudden traction, there is no reasonable concern about strength for you to do 4.88s instead of 5.13s.



Here is the torque and horspower information for the 3.8L engine with stock and Hypertech tunes:





Notice that the stock torque curve increases fairly significantly between 2000 and 2500 rpm before it starts to level out.

Also, notice that the rear wheel horsepower increases significantly between 2000 and 2500 rpm.

The extra rpm from running 5.13s over 4.88s would increase your rear wheel horsepower from about 80 to 90--more than a 10% improvement.

The extra rpm from running 5.13s over 4.88s would increase your rear wheel torque from about 180 to about 185. With the extra rpm and a good tuner, it would increase to over 200.

The extra rpm by itself would increase your performance more than an aftermarket, cat back exhaust and a cold air intake.

The extra rpm will not reduce your engine life.

The extra rpm will not reduce your fuel economy.


In fact, your fuel economy would be higher with 5.13s over 4.88s. Here is why:

With an automatic, when the transmission downshifts on the highway, the converter is flashed and the transmission downshifts with an extra level of slippage to allow the engine to produce higher rpms. You can see for yourself if you drive down the highway at 70 mph and then push the overdrive button to turn off the overdrive. Notice the rpm level of the engine at that 70 mph speed. Now, put the transmission back in overdrive. Then, depress the accelerator hard so that the transmission downshifts from overdrive to 3rd gear. Notice that the rpm levels in 3rd gear with the downshift are much higher than the rpm levels when the transmission is just in 3rd gear with the converter locked instead of flashed.

What kills fuel economy in an 07-11 automatic is frequent downshifting due to the engine not producing enough torque and horsepower to hold a highway speed because the engine rpm levels are not high enough.

This is why--all other things being equal--an 07-11 automatic that gets driven in windy or hilly terrain at 70-80 mph will get worse mpg with 4.88s than with 5.13s or 5.38s.


Finally, know that for an 07-11 automatic on 35s to run about the same engine rpm as a stock 07-11 6 speed Rubicon on stock Rubicon tires/wheels, the 07-11 automatic would need 5.38 gears.

The 07-11s have histories of transmissions overheating due to insufficient gearing causing frequent transmission downshifting. This would not have occurred if 07-11 automatics came with 4.88s and 32" tires from the factory.

nthinuf

Yep, up to 38's.

FAQ

Ran one in the front of my full size Ram on 37's for 10 years. (back when the warranty was up to 33's). When the rear detroit locker decided to explode, it was replaced with a second truetrac. Great traction device.

MTR

Let's us know how the truetracs work out for you once you get them installed.

planman

I've ran TrueTracs in our 04 TJ. They worked flawlessly in every terrain or road condition, except for when a tire lifted off the ground--ie, rock crawling.

Sahara Lee

Funny, TrueTrac must have some resistance on spinning tire to engage. This is exactly what BDL provides on a JK when a tire lifts.

planman

The trick with the TrueTracs is to tap the brakes to provide resistance when a tire is hanging in the air. It does need some resistance to engage.

I'll probably install a TrueTrac in the front and a Detroit Locker (or Yukon equivalent) in the rear in my Ram 3500 truck when I regear it.

Sahara Lee

Thanks river2c and all others. I verified those part numbers with Eaton tech support then placed an order through Summit Racing who beat the pants (price wise) off everyone else.

GunDude

I went to Gulches off rd. Park Sunday. I did all the red and blue trail(easy/mod.) With just the rear TruTrac and it worked great. Even on a small rock step.
I have the abs/bds kill switch and wanted to see how good just the trutrac worked. Now, to save for regear and front trutrac.
Also need to back and do one or two of the easy black trails lol.