Is there a way to know if a used front differential is good?

[neoplanet]

Hi.  The title is probably self explanatory.  If I get a used diff, is it just plain risky, or can it be understood whether the thing is one of the good ones or not before I replace my noisy one with it?

 

Much thanks for any insight.

Edited November 21, 2017 by neoplanet

[lewisweller]

6 hours ago, neoplanet said:

Hi.  The title is probably self explanatory.  If I get a used diff, is it just plain risky, or can it be understood whether the thing is one of the good ones or not before I replace my noisy one with it?

 

Much thanks for any insight.

My front differential made a quiet but noticeable whine noise. I changed the fluid twice in a year and didn't find anything metallic or abnormal, I bet its still is fine now for the new owner and he can't even hear it, must be deaf! So if yours is not totally buggered why not just change the fluid for Redline heavy duty shock resistant 75w90 diff oil and run it until something happens.

 

For the second hand option :

Well if you could hear it in operation in the donor car before removing that's ideal but unlikely. 

You could try a bench test, rig up something to drive it. 

Or strip it down and check it before you go to the hassle of removing your old one. 

From my understanding the diff usually becomes noisy from the bearing(s). Chipped tooth also possible visual inspection will identify that. 

Erm you could get the Used one and just buy the new bearings etc and refurb it so you know it's gonna be perfect when you install it. Bearings aren't expensive and ive seen somewhere a how to for the rebuild. 

 

Good luck. 

[neoplanet]

Thanks.  I think I did see some DIY on youtube about rebuilding this exact diff.  I did try the fluid change and no diff!  Still had the noise.  There were actually beautiful swirls of brass colored fine grains in the old oil.  So THAT can't be good.  I do wonder where exactly that metal is coming from.  Maybe the bearing is shot and the gears are misaligned & wearing?  Cuz I don't think bearings are made of that color/alloy.  I put in the redline oil.  Still making the same sound.  Sightly worse a couple thousand miles later.  Any idea what exactly would produce that color metal shavings?  I'll ask my local guys that are probably the ones to install it whether they think the health of the replacement can be determined.  I'll report back.

 

Thanks again.

[rik881]

Take some pics while you are at it. I changed a rear diff last week which had a horrible knock but everything seemed to work exactly the same as the replacement.

[dpatel710]

I added Lucas oil heavy duty oil stabilizer to my front diff and it really quieted down the whining it was making - not really applicable though since you have metal in the oil.