Hi there, I have a 1990 F-250 4X4 with a 4.10 limited slip rearend(10.25). I posted here for a quick response...

I am wondering a couple of things, as to one, if the front is also limited slip, but moreso the following: I got stuck yesterday in snow, and i put it in 4 low and the wheels were spinning in the cavity they had made. the thing is that only the rear right and front left were spinning, i found this out when i got out and tried jumping on the truck to get free. so it was as if the rear axle wasnt working right. but then today i tried my first burn out in it and i left twin black stripes...

a mechanic friend of mine said that the clutches may be worn, if it is the clutch type. so another question is what kind of mechanism is it?

thanx in advance.

 

I don't think there was a front limited slip option in this generation of full size trucks. The factory rear units were just a clutch type trac lock differential.

You may have a weak limited slip. Or if the diff fluid had been changed, the friction additive may have not been put in.

However, the factory limited slips are not as positive acting as some may like.
The reason you may have left twin marks on the pavement is that the weight and traction at each rear wheel is roughly the same.
When you get stuck and one wheel starts digging a hole, you will have less down pressure on that side. Therefore, less traction at that wheel. You may have found the working limit of the LSD and it wouldn't transfer power to the other rear wheel with traction and down pressure.

Jason

 

so now some more questions arise, so i might replace the clutches...now, could i find more agressive ones to put in? also, is there any special LSD fluid i add, as in what is it and who has it? i am looking to change all fluids this spring and put Royal Purple products in the tranny, t-case and both differentials

 

I don't think they make any different kind of clutch material. I have added an extra clutch disc and steel to make it more positive acting. I'm not sure if this is possible with the 10.25, tho.

The friction modifier can be purchased from Ford. If I remember, 2 bottles are recommended. And then fill with new oil to the fill plug.

Another trick I forgot to mention when dealing with a LSD is to try to modulate the brakes a little bit. This will cause some power transfer when the wheel without traction is forced to stop or slow down.

Jason

 

RCrawler is right. Ford Traction Loks are low bias limited slips, so they are easily overcome. Not much you can do about it. People have added a Belleville spring or an extra plate to a Traction Lock to increase their bias ratio, but then they are like a spool and quite miserable on the street.

As RCrawler said, you can help in a low traction situation by applying a little foot brake, or a little parking brake (apply it about halfway). The technique is called "brake pedal modulation." That will help the limited slip transfer a little more torque from the low traction side to the higher traction side. It works well but you have to watch that you don't overheat the brakes. I wowed some friends recently by getting their car out of a snowbank this way.

I put a Detroit Truetrac in my '86... simply wonderful. It's got more bias (3.5:1 vs 1.8:1) than the factory setup but because it a gear type limited slip, it doesn't have many adverse symptoms. Plus it doesn't have clutch plates to wear out.

Actually, a plate type limited slip will hold slightly more tightly with less friction modifier than with more, but it will chatter badly in turns.

Bottom line, if your truck has lots of miles, and you need a good limited slip, I'd invest in a rebuild kit. Fairly easy to do. Not expensive. You'll get about 30K miles at optimal performance levels.

 

so lay out the overall options that would allow me a more agressive grab...i want something that would grab as soon as the other starts to spin...

also, what could i do to the front axle? i would rather not weld the spiders up front

 

another friend is telling me that i prolly have a 8.8...would this be in a 12 bolt though? jeez im confused lol

 

nope...he now figgurs a 10.25 too...hmmm

 

i was looking at a true trac worm gear kinda thing but for 570 bux? DAMN! maybe eBay will have them cheaper

 

ok, so where could i get the clutch packs online, i only see them for the 8.8"

 

You DEFINITELY don't have an 8.8"
I've found that "friends" usually don't know what they are talking about.
You might also use the friction modifier made by the same company as your oil (Royal Purple) but I'm not SURE if it will matter. If you don't use R.P. I'd use the Ford stuff.

By the way Jim Allen KNOWS HIS STUFF about this so do what he recommends. He co-wrote a book on differentials with Randy's ring and Pinion (I have an autogaphed copy, snob,snob) and has written for a lot of the "4 Wheelin'" magazines.
Take his advice!

I'd be inclined to put a Tru-Trac in as well. They work well and there's no clutches to wear out.

 

Ford 10.25 Differential Cases & Spider Gears Auto Parts: YPKF10.25-PC-14, YPKF10.25-PC-E, YPKF10.25-PC-L, YPKF10.25-PC-SH, YPKF10.25-S-35, YPKF10.5-PC, DS 42345, FORF100500, FORF100501,

Jason

 

Didn't read what type of trans. auto or manual? but t.case is usually always the same fluid as trans.( if auto.) so if inner seal leaks there is no contamination to trans.from the fluid in t.case.

 

i as well have this same prob with my 84 f250 4x4 i wish theyd all grab cuz i only got stuck twice once i went off the road with my plow into a ditch and bottomed out the other time i got stuck in a 6 foot drift plowing snow! haha so is there any tricks for me without gettin a posi trac or somethin mine has 237,000 miles on it to.. if i had all 4 spinnin i easily couldve gotten out in the drift situation proly not the field tho

 

the LF axle is the limited slip. i got stuck and couldnt get that locker to work. So i wasnt going any where.