differential chatter

[slepys14]

I got a helical diff off ebay from an s15. it makes a very noticeable chatter at low rpm 2-3.5, when I am in third and forth. I am hopeing that it is just a carrier bearing! any ideas? "I know watch out for the deals on ebay"!

[Hijacker]

You didn't shim it up right, and the ring and pinion are rattling against each other now.

[ashoe]

That is what I am thinking. 2 shims 1 thick and 1 thin go on the side facing away from the ring gear. 1 thin shim goes on the other side. Good luck. I've got one of these and it is awesome.

[Hijacker]

It's a bit more complicated than that, Ashoe. The 'thin' shims are different thicknesses, and you really need to shim the diff up using the proper thickness shims, which is different for every diff. Cramming the old shims in is a gamble as to whether it works properly or not. Most times you end up with an improperly set backlash and end up with what's happening to the OP. You really need to have an assortment of shim thicknesses and test fit them to properly shim the unit.

[slepys14]

where can I get an assortment of shims? also do I just shim up each side so it is tight? I really do not know anything about this! thanks.

[Hijacker]

Nissan has the shims. They're not cheap either. You want them tight, but not too tight. With the ring gear uninstalled, it should give adequate resistance to being pulled on. Like if you try to spin it, with a tug, it should make about 1/2-3/4 rotation.

Then you have to run prussian blue on the ring gear's teeth to make sure the backlash is adjusted properly. Backlash is how the teeth of the ring gear is meshed with teeth of the pinion gear. You want to see clean spots the shape of a comet (big end facing the diff unit) near the center of each tooth.

Backlash is adjusted by moving the differential around by altering the thicknesses of the shims around. Say you have .10" on one side and .12" on the other side for shims for a total of .22" of shimming. You find that you need to move the differential to one side by a few 100ths of an inch, so you need to use .08" for one side and .24" for the other side.

To be honest, differential shimming is something that you need to be taught in person. It's very hard to convey the steps over the internet.

[slepys14]

thanks for the great input HiJacker! If I took it to a nissan dealership would they know exactly what to do?

[ashoe]

Nissan has the shims. They're not cheap either. You want them tight, but not too tight. With the ring gear uninstalled, it should give adequate resistance to being pulled on. Like if you try to spin it, with a tug, it should make about 1/2-3/4 rotation.

Then you have to run prussian blue on the ring gear's teeth to make sure the backlash is adjusted properly. Backlash is how the teeth of the ring gear is meshed with teeth of the pinion gear. You want to see clean spots the shape of a comet (big end facing the diff unit) near the center of each tooth.

Backlash is adjusted by moving the differential around by altering the thicknesses of the shims around. Say you have .10" on one side and .12" on the other side for shims for a total of .22" of shimming. You find that you need to move the differential to one side by a few 100ths of an inch, so you need to use .08" for one side and .24" for the other side.

To be honest, differential shimming is something that you need to be taught in person. It's very hard to convey the steps over the internet.

I wish i had known this when I did mine... Well I was planning on painting my diff and putting aluminum bushings on it soon anyway. I guess i'll rebuild it too.

[slepys14]

I used the stock ring-gear, does that still mean that it needs shims?

[2projects2many]

I used the stock ring-gear, does that still mean that it needs shims?

Yes, because the original carrier, & the LSD are most definitely not exact to each other- one is probably wider than the other. Even if you take a carrier from 1 '91 and place it into another '91 case- the shimming will be different due to castings, maching, etc; EVERY one you ever do needs to have the backlash adjusted to that case & carrier (or LSD).

[slepys14]

thanks, that is the clearest response that I have gotten! that is exactly what I needed to know.

[carkook]

ya i would re adjust the preload check backlash pinion resistance and put marking grease on ring gear and see where the pinion is coming in contact with it at.

[slepys14]

I installed a s15 helical diff into my s14. there is a lot of play and it needs shims badly. unfortunately it did not come with any and the stock diff did not have any. I looks like I am going to have to guess what size I need? I checked courtesy parts, and each shim is $16.50. OUCH!!! can anyone tell me exactly which ones I need? or where I should start? And are they any cheaper anywhere else? thanks!

[johnnyballs180]

what would happen if they were shimmed wrong? i mean, what would it feel like, sitting in the driver's seat?