After many phone calls, I finally found an 85 LSD rear in a bone yard not far from me. I'm gonna go take a look at it this weekend. Good or bad, what should I specifically be looking for? How many miles do these rears live? 50k? 100k? 150k? 200k? What's the max miles I should accept or does it really matter? How will I know if it needs to be rebuilt and what's involved in rebuilding one if I need too? I know that's a lot of questions but I don't wanna get hosed on my purchase. TIA

 

Nobody has an opinion? A non-Mazda guy told me I should pass on it if it had more than 100k. I have a feeling they last longer than that.

 

i donot think that rebuilding them is all that involved.
life all depends on how they were taken care of..

other guys can tell you the proper way to test it.. but try spinning one wheel and see what happens to the other.

 

riffraff,
Rebuilding a 3rd member is not a Sunday evening task.

inittab,
Someone told me to check this once, I dont know how good the test is, but my LSD fails it (I think it has to do with the lash): Crawl under the car and try to turn the driveshaft by hand, if there is any free play (where the driveshaft turns but the wheels do not) then you have a problem. There is no good way to test if the LSD is worn out without driving it in a situation where the rear wheels have unequal traction.

 

nimrod../. i realise that is it not a sunday evening task, but i figured that it would be a half day one. no?

 

Well I went ahead and yanked the junkyard axle out today. What a PITA job that was. The doner car had 135k on it and the axle had a lot of surface rust but not much more than my current 82k axle. I couldn't test the play in any of the parts because the brakes were seized tight to the disc's. It's a $150 gamble but I have hopes for this thing. Oh, and BTW, there was a yellow sticker attached to the back that stated that it was a limited slip diff. I suppose my first task will be to get the brakes off and get the thing sandblasted and go from there.

 

wel good luck on the project.. hope it is not a waiste of your time and money

 

My dads 79 has 400k miles on it, the only things that have been replaced are the clutch, one brake light, and the engine.

 

my friend replace his at 193k miles. and he drive it hard.

 

Mine has 150k on it and it is VERY tight. You can't go around tight corners in the wet without the inside tire spinning a little.

 

All sounds of encouragement. That's great!

I didn't grab the master cylinder because, quite frankly, I wouldn't trust it for a mile. My plans include an entire brake system rebuild with the proper master cylinder and braided steel lines too! Can't wait!

 

It all depends on how the car is driven since the LSD is clutch based in these cars... If nobody has done any tire anahilating burnouts, it'll be good... But if that sucker was kickin up the rubber smoke at every green light, you can bet it's hosed.

 

You bring up a good point Pele, but My trans am has 125k on it and I do tire melting burnouts just about everywhere (I mean everywhere ) and the LSD still works great. The clutch is a different story...... Hey innitab: I can't wait to see your car after you do all the brake stuff.

 

hey what do you mean after! aren't ya gonna help me?

 

Clutch pak LSD units wear pretty well. They do start to judder/bounce/vibrate as they get older. Also, you can help this with the proper rear end friction modifier. I don't suggest you rebuild one unless you are a good wrencher with lots of tools and experience. Getting the gear lash set right is not too easy to do. If you get it wrong, you trash the ring and pinion really fast. Have a shop or driveline place do it.

 

Sounds like sage advise.

Can you explain exactly what you mean by "proper rear end friction modifier"? Thanks.

 

I think Mazdatrix sells lsd friction modifier just for these units. They sell these types of additives at the parts houses. Its mentioned in the technical data of the factory service manual. The main thing is that the unit is going to seem rougher, especially while turning a sharp corner and accelerating at the same time. Don't let it bug you if its working ok.

 

I have a lsd for sale on my 84 gsl...take the whole car for 350.00...has engine , interior , lsd...why pay 150 for a lsd when you can have most of the car for 350.00...anyone want it , let me know..cjf

 

you want help? I'll help. you need help

 

Hey cjf; does the car run? What color interior? Let me know.

 

Preventative maintenance?

Okay, I've got the rear stripped of all the brake parts, lines, etc and I've done a wire brushing of it. It's not looking so bad anymore. Now that the rear is in this rather naked state, it seems to be a perfect time to consider maintaining any internal parts, bearings, whatever. My current plan is to sandblast it then do a POR-15 job on it. I purchased POR-15's "Engine Painting Kit". The kit includes everything you need to repaint an engine. My logic being that an axle is more/less like an engine. I'll let you guys know how it comes out. So... should I just paint it, wish for the best, slap it on the car and go? or what? TIA

 

Sandblasting is great. But everything has to be sealed up perfectly, because if it's not, you will NEVER get all the blasting medium out, and it will work to destroy bearings in a hurry.
Your other option is removing residual rust by chemical means.
Search for products engineered for marine application if no one here supplies you with a list.

 

I would do bearings and seals if you have the bucks. Since the third member pops out by itself, you can always replace the lsd alone later. The POR 15 sounds great. I have thought about the Rhino truck bed coatings for under car stuff.

 

I just got the car all put together again and the LSD seems to be fine. It doesn't produce any whining noises and so far appears to work properly. I do notice that when starting out with the front wheels turned I do get a shuttering from the rear. I think this is normal, yes? Right now I'm running 'el cheapo gear oil in it but I have some RedLine MT-90 sitting on the shelf. Below are the before and after pics.