I was just thinking about flushing my Diff fluid with some nice new stuff when it hit me...

My car has 4 disc brakes which implies I have an LSD. Now I don't know if its from locking up or the LSD being toast but my car snaps to the left when you break hella hard; which makes me think that possibly my clutch pack is going...

And then it dawned on me, who said it was a Clutch pack LSD?

I couldn't find any mention of it in my Haynes Book, they were nice to add the 4 disc brakes to the revisions section, but made no mention of the LSD.

So my question after all my blathering is simple:

What kind of LSD do our cars use?
Where is the service Information?

I hope you guys can help, it will make my life so much easier to just refresh the LSD and the Diff fluid in one shot rather than have to take it apart multiple times.

Okay, I'm gonna shut up now and let you guys throw your thoughts in on this.

 

Will you forget the Haynes manual and download a copy of the FSM for your car.
The answers for the LSD can be found in the FAQ section.

As far as the comment about it snaps to the left when you brake hard.
If when stopping quickly your car pulls to one side it is usually the caliper is bad, has nothing to do with the diff.

 

Yeah, the brakes make more sense to me. As for the FAQ, it does nothing to tell me what TYPE of LSD it is...

Cone? Clutch Pack? Other?

I can't seem to find info on the LSD in the service manuals from the FAQ link...

 

Anyone taken apart their LSD? Or have pictures of one thats been taken part?

 

It's a clutch packed.

 

Okay so it's what I thought... Alright thanks man!

 

You didn't look hard enough. Section 9 of the 85 FSM.
.
.
.
.
.
.

 

Its basically a copy of the Spicer Power-Lock clutch LSD,which is known to be one of the most robust factory LSD's made, and is still used quite a bit to this day.

It has the same 4 pin spider,conical preload springs and split case carrier.The spring condition and disc thickness determine the initial LSD grip and how well the tires stay hooked up when under light load.This preload is overcome when turning,to allow differential action which is the primary cause of the wear to the discs.When you romp on it,torque input from the engine compresses the two disc packs together tighter,which increases grip.So,even a worn out unit will hold tight if you apply enough input torque.....such is the case with my car.They will also grip upon decel,when the wheels apply reverse torque into the drivetrain.The spider pins have ramps on both sides,which makes this possible.The angle of the ramps is how racers tune their LSD's to be aggresive or mild when they start to lockup.

You can see one of the spider pins and the ramps in this pic,as well as the two halves of the carrier blocks that compress the disc packs.......

 

...plus they supposedly cost a fortune to rebuild. I'm waiting for mine to go out, trying to baby a 185,000+ diff sucks. The Guru diff or Torsen seem to be the way to go instead of trying to rebuild the stocker.

BTW...if the LSD goes out completely...is the car still driveable...will it basically become a peg-leg car or will it not drive at all???

 

The stock LSD's are very durable. I recently got one for my car and installed it only to find the breakaway torque was very low at well under 30 ft-lbs. So I pulled it apart expecting to find some very worn components. To my suprise every single friction plate and thrust washer was well within the wear limit with most only showing a few thou of wear. In this case, all that will be needed to bring the LSD back to better than new is machining the left case as detailed in the thread below by OLD RX-7. I won't have to replace a thing. One should never assume the LSD can't be repaired until you pull it apart and measure all the components.

https://www.rx7club.com/1st-gen-archive-71/drivetrain-lsd-shot-need-rebuild-kit-581550/

 

Huh, thanks for the help guys... I just had the rex on the lift earlier this weekend and found out my LSD is still functioning great after 233,000+ miles on it... I am going to swap the diff fluid in a week or two depending on when I get some cash.

And to answer your question Jamie, I was under the impression that if you LSD failed your diff would just act like an open ended differential...

Then again I have never looked into or tested this theory out...

 

The next question is: what is the best fluid to use in the Differential. I'm using Redline.

 

I hear Redline or Royal are good fluids to use...

 

Ive been running Redline for a long time with no problems.

Synthetic oil is nothing special these days,almost every PU truck in my fleet comes with it from the factory and we go 50K miles on rearend oil changes with no problems.Many of our Dodge and Chevy trucks run the Dana Spicer LSD and they work pretty well.But these are rental truck,so longevity after 100K miles isnt any concern to us since they get sold promptly afterwards.
The main thing on a performance vehicle is to change the oil regularly.Not because it cant last a long time,but because there is no filter or cooler in a typical rearend.Shearing hypoid gears do use up the high pressure additives over time,but metal and fiber contaminaion from gears,bearings and clutch discs will accelerate wear on everything the instant you pour the oil in.
Regular,hot drain intervals will help to flush out the accumulated particles and keep things tighter,longer....regardless of what type of oil you run.I change my Redline every 20K miles,a few $8 quarts of oil are nothing compared to the cost of gas or tires,in the long run.