Differential lash question.
 

So I pulled my rear pumpkin out, swapped in a quaife LSD, dropped the pumpkin at my local shop to set lash and mesh. Picked it up today and they told me that the tightest he could get it was .009 without messing up the gear mesh. Should I be concerned, is it going to make noise being out of spec. Dont have time to install it until the end of the week.


Thanks :)

Well I set mine at .006” with used 3.69 gears. Thats max for the factory spec.

I thought that might be possibly a little loose and be noisey. I called my buddy at the race shop and he said the pinion depth is more of a contributer to noise than backlash is.

He said to set it up with the best contact pattern, and dont sweat the backlash number, which is what I did.

I havent installed it yet, so we will see..

I'm going to be pulling my out soon for the OS Giken. So I'm interested in this.

Put some of that marking grease on it and look at the pattern. It will tell you if you need to mess with it. Study up... I don't think it's an easy task to get it right. That's why most shops won't mess with it.

My OS Giken went in perfect without needing to mess with the shims. I don't recall anyone needing to mess with the shims as long as they didn't change the gears.

Mine is quiet as a mouse after 10 dragstrip runs and 1000 miles of street cruising.

So nothing wrong with .006" backlash.

Before installing the OS Giken. .0025" backlash.
After installing the OS Giken. '0025" backlash.

eastwest's was .0035" when I did his Z1 diff cover and SPL diff bushings.

Both ours patterns for drive and coast was good. Right in the middle. Mine doesn't make any noises that I can hear.

Whats interesting is my original diff was a little noisy on coast when I pulled it out with only 32K original miles on it.

The spare one I built and just swaped in with used gears, is super quiet. Gear mileage unknown...

I hope it's not a problem to raise this topic. I have finally gotten delivery of my OS Giken LSD which I'm planning to install this weekend. When I spoke to the sales rep, he assured me that the LSD is manufactured with such precision that he thinks it's not necessary to go and buy different shims for additional adjustment.
From what I understand, if I just pull out the visco LSD, replace the flange and add the OS Giken LSD - there is still a fair chance that the backlash will not be the same as factory, regardless of how well I install it. So my concerns boil down to the following:
-contact between the teeth is critical, and this I understand is the main point to adhere to.
-backlash may differ and it will not necessarily ruin the diff if it's off by a few 1 thousands...Or will it?
-should I postpone LSD installation until I get a load of shims - just in case?

I also thought to measure backlash on stock visco LSD, before I remove it - just to check what is the factory setting, and maybe aim for that. Thank you for any opinions and advice.

<bump> would appreciate any help with this, if anyone could chime in. Thanks!

I also installed my osgiken diff without any added shims. As long the gear mesh looks good you should be fine. I would think you’d run into problems if you would be swapping out the final drive gear ratio. Just make sure you have new seals and new side bearings

That's exactly the answer I was hoping for. Did you measure backlash or did you just YOLO it?
I'm not changing the final drive as I like the current setup. New seals are in the whole package.

Also - I got 3 liters of oil in the package, I'm guessing it's enough for 2 tanks? I.e. one for the break in for the first 300 miles or so, and then I swap the oil? Or is it not needed to break it in?

Yes I did measure the backlash just to make sure its not crazy out of spec. It has been years ago but I'm positive it was somewhat close to spec. Make sure you get ring gear marking paint as well to check the mesh. 3 liters for 2 fill ups might be slightly short but I also have higher capacity cover. You will know after first fill up whether will need more or not. I assume you got the osgiken diff fluid?

Yes, I got the OS Giken stuff. I'll do like you suggested, thanks a lot for your inputs!