Diff woes (bad clunking on overrun) after being setup by shop...

**Stefan** · 10-12-2008, 11:16 AM

Bought secondhand F-series 4.1 casing that had been rebuilt
Took and my current 3.5 diff with Truetrac centre to diff shop to have truetrac swapped in and diff set up
Diff shop did this, ended up being bigger job as they replaced crush tube and seal too
Installed diff, took for test drive round block. Clunked badly on decelleration, like something was loose (not whine). Got up on stands, checked that all bolts were tight, and had mechanic mate identify source of noise while running. Always on deceleration and at particular revs a lot of clunking/knocking comes from the front part of the diff

Now, I've called shop and they say that a noise that isn't constant has nothing to do with backlash or the work they did, and likely a crownwheel/pinion problem although they didn't notice anything when they had it apart. They know it was a secondhand diff and are blaming this, though they're happy for me to drive it over and have a listen. I bought the diff from a reputable toymodder who had driven on the diff and I believe them that it had no problems.

Any thoughts? Is it safe to drive on a diff that clunks terribly?

**Smokey228** · 10-12-2008, 11:31 AM

If it clunks on decel, check the back lash by hand... Put it in neutral, handbrake down, jack up the diff and see how much 'freeplay' it has back and forth by twisting the tailshaft... Or better still, remove the tailshaft and see from the source... Twist that section, until the rims move, the 'free' section is the back lash and it shoulnt be much at all! A coule mm maybe..??

Cheers,
Jase

**SillyCarS** · 10-12-2008, 11:54 AM

take it to another diff shop, dont mention previous work done and see what they say

backlash only needs to be a couple of tho out for fuck ups to occur, may not be able to sense with rear end up

it could be (now i cant remember the techinical name) at a particualr rpm how the gear is allowed to hover in between teeth

or as the diff shop had said it could be the truetrac centre

**Stefan** · 10-12-2008, 12:09 PM

I'll check the backlash.

Truetrac centre is NOT the problem, it's new and was in my 3.58 diff with no issues whatsoever (diff was perfect other than beign the wrong ratio). What I mean to say is that shop is suggesting problem with the 4.1 diff.

I'd love to go to another shop and just get it sorted but there aren't any other diff places in Hobart to my knowledge. However, just setting the backlash may be within the realm of other mechanics if I provide the shims...

**cambelt** · 10-12-2008, 03:52 PM

The shims are a big issue for smaller diff shops but most that have been in business for a while can improvise and make shims. The main thing that goes wrong with toyota diffs is the pinion comes loose , and if they have done 400000klm the crown and pinion are will be worn and maybe whine.
The backlash between the CW and pinion is really the only cause of clunks , or the pinion flange spline is worn ( thats more of a click tho)Dave

**Stefan** · 15-12-2008, 09:40 PM

Well, I think I've fixed it.

I noticed that the half-shaft flange on one side of the diff had a lot of movement in and out, like the circlip wasn't working. Replaced it tonight with another flange, still a little bit of play on this side (none on the other) but it's a lot better.

It still makes this ratatat ta ta ta ta ta noise as the car comes to a stand still, and I noticed it was whiney at 80, but the bad clunk is gone. I really don't think this shop did a very good job at all - should have just chucked my centre in the diff as it was.