Rear LSD - What does it cost to rebuild? Any other options? - Diesel Forum

cmb1998 · 11-17-2008, 03:14 PM

I have a new to me 1999 SD F350 4x4 with about 90K miles on it. The axle code is D6 (4.30 with LSD). I was launching the boat last week and one tire fell off the ramp into the sand. Couldn't get traction to the other. I have done the same thing with my last truck (Tundra with LSD) and it would have no problem getting traction to the other tire.

I am guessing the LSD needs to be rebuilt? Whats the cost for that generally? Is it cheaper to just drop a locker in there? Any other options?

Thanks,

Chris

lubbockguy1979 · 11-18-2008, 07:11 PM

if you currently have a limited slip you have a few options. i personally would replace the lsd rather than rebuild it. the experience i have had with lsd is they are great when new but when they go they can tear up alot and axle components arn't cheap. i would look into something similar to a detriot true trac because of durability and it is still streetable. a full on locking diff will be hard on tires but offer the most traction. while expensive the arb air locker would offer the best by being a full locker when activated and a open diff when off. before i would go to the point of a rebuild i would check the rear axle and make sure i had the correct limited slip oil and the condition of the lsd.

Lightningfast01 · 11-23-2008, 09:50 PM

I swear by the Eaton/Detroit TruTrac diffs. Smooth, quiet, seamless traction. I have never spun one wheel on any surface. It was $550 bucks on eBay. I run Mobil1 85-140 oil on it and added the neat 08 diesel rear diff cover. The alum rear cover was only $32 bucks from the dealer and has a cool heat sink. My stock posi was pure crap, I got stuck on a flat dirt road once. I have owned Aubruns, Eatons etc, none even come close to the all gear, no gay clutches TruTrac...

Heavy_Metal · 11-24-2008, 09:34 PM

Jesus......you guys are jumping off the deep end here.

Have you ever had the fluid changed in the rear diff?

Did you do it? or did you use a retard employing oil change place such as jiffy lube?

If so, did you add friction modifier? You need this or you have "one-wheel-peel".

4oz is reccommended but the more you add, the more it acts as a spool. You should just stay with the manufacturers spec. of 4oz.

Lightningfast01 · 11-24-2008, 09:40 PM

wrong, HM. The additive increases slippage in the diff. When clutches start gripping and chattering you add that stuff to reduce friction and make it slip more. Regular dino fluid grabs the best but needs the slippery additive to reduce grab and chatter.. Synthetics are slippery enough most don't require the additive. All gear diffs are the best like the Torsen diffs. Ford has reduced their posi performance in favor of saver trucks that don't spin out on soccer moms.

sawtooth · 03-15-2009, 06:41 PM

Quote:

Originally Posted by Lightningfast01

wrong, HM. The additive increases slippage in the diff. When clutches start gripping and chattering you add that stuff to reduce friction and make it slip more. Regular dino fluid grabs the best but needs the slippery additive to reduce grab and chatter.. Synthetics are slippery enough most don't require the additive. All gear diffs are the best like the Torsen diffs. Ford has reduced their posi performance in favor of saver trucks that don't spin out on soccer moms.

You are correct, the additive makes the clutches slip even more. I have a truetrac as well and its way better than the factory with no down sides. Get one and you will love it.

akrewat · 03-16-2009, 01:27 PM

Once upon a time, there was a note in the Owner's Manual on how to get the "limited" Ford limited-slip to actually try to grip when one wheel was in a very low traction situation.

Put on the parking brake, and apply power. This works best if you have an auto. As you apply go-pedal, ease off the parking brake very slowly. You MIGHT get the limited-slip clutches to grab and apply power to the other wheel this way.

Reason being, if you can get any torque applied through the differential, this will force the spider gears outward, applying pressure to the limited-slip clutches.

Also, the standard 8oz of limited-slip additive makes the Ford Traction-Lok very wimpy almost to the point of not working whatsoever. If you change the fluid, add only 2oz, and see how it works. If it chatters too much for you in slow-speed turns like the parking lot, add another 2oz, and try it again. At some point, the chatter should be almost gone, but the limited-slip actually still works.

Of course, the clutches might just be worn out and you need new clutches.

In terms of cost, the clutches are not too expensive, probably somewhere in the $30-100 range, but the labor to do it is going to cost you.

Also, some people have had some luck getting an extra clutch in there, which makes it VERY stiff, and it works great, but then it wears out that much quicker.

If it were me, I'd try the fluid change and a very small amount of friction-modifier (additive) like only 2oz first. Drive it around a few days and see how it works.

Also, try that parking brake trick. I've tried it and it actually helps. Even power-braking (foot on brake while applying engine power) helps quite a bit.