Finally fixed my coast-down rumble ( "wub wub" noise )

[Luke]

All it took was rebuilding my driveshaft ( new U-joints crosses, new carrier bearings ), replacing the stock transfer case with a 15K miles replacement, and installing a 60K miles 4-bolt rear diff /ubbthreads/images/graemlins/ooo.gif

The t-case was the source of most of the drivetrain slack.
Rear diff was a distant second, and the driveshaft rebuilt changed nothing.

YMMV.

 

Good job. While you're at it change the exhaust hangers too.

 

i wonder is thats what my noise is. i thought it was my exhaust at first but after looking at it a bit i wasnt able to see where it was touching.

 

[Luke]

Quote:
Good job. While you're at it change the exhaust hangers too.



Haha.. is that a joke ? But yeah, I did check the exhaust clearance when I bought the car 6 years ago.
I had a muffler shop redid the hangers and gave it more clearance all around.

IMO, exhaust hanger is an unlikely culprit of coastdown rumble.
If it were the exhaust, it would make noise at a certain rpm range, and won't matter whether you're decelerating or accelerating.

What surprised me actually was the fact that my worn t-case would make rumbling noise that seemed to be coming from the rear of the car.

 

what was the sound like?

 

[CP]

I still haven't tracked mine down. I've rebuilt the driveshaft (replaced the carrier bearings AGAIN in the last few weeks), just got back a freshly rebuilt 4-bolt rear diff, and installed an AL-case t-case a few months ago. I may try another t-case to see if that's it.

I get noise and vibration at certain throttle positions, and a loud ratt-a-tat-tat sometimes during decel.

 

[Luke]

Hi Cy:

Did you try the procedure described in the service manual, where you set the rear parking brake and see how far you can twist the driveshaft back and forth ? This procedure will tell you if you rear diff is worn.

Additionally, I was able to check for transfer-case wear by jacking up just the rear of the car, disconnecting the driveshaft to rear-diff connection, then twist the driveshaft back and forth and check for play. Also watch the driveshaft and see if it is the driveshaft end-to-end twisting, or if the play is at the transfer case.

Between those two procedures, I was able to figure out whether the transfer case or the rear diff should be replaced first.

 

[CP]

The rear diff was just freshly rebuilt, so it must be the t-case since the new carrier bearings and fresh diff didn't cure my problem /ubbthreads/images/graemlins/dunno.gif

I'll disconnect the DS from the read diff to check the t-case for play this weekend. Thanks.

 

[JNR]

Glad you solved the problem!

What did you have to do with the T/C? A full rebuild?

Mine is *relatively* new, mileage wise, but the jokers who towed it didn't do it on a flatbed (rear raised; front wheels rolling) and have a feeling this caused some issues...They did it for a good 50-60 miles and didn't seem concerned that it was AWD /ubbthreads/images/graemlins/banghead.gif

The joker I bought the car from, who shipped it, was no help in resolving this issue, so I have to take the brunt of whatever this is gonna cost, argh!

 

[Luke]

I bought my replacement transfer-case from a fellow dsm-er. It only has 15K miles.
He got this transfer case new from a dealership as a free recall replacement.

This transfer case looked brand new when I got it..
no grime, no rust, just very new looking.
Definitely got lucky on this purchase.

 

[JNR]

Oh, I see...I was thinking your 15k transfer case was the culprit.

Hmmm, I have a feeling mine got ruined, uggh! However, I'm gonna check the easier things like driveshaft and so on, first and pray it's not the T/C.

 

[Luke]

Hmm.. the center differential in this car is in the transmission.

I hope they didn't fry your center diff.
Theoretically, the center diff is the first thing that would overheat from 2WD towing..

Good luck..

 

[JNR]

Yeah, I certainly hope not! The car runs fine overall (drivetrain), other than the noise on decel; it's more of a 'crahh' noise that is like a loose something or another, then a 'wub wub', so maybe it's something simple.

I have it on video (when they pulled up with the flatbed tow truck - they put a VW on the bed, but towed mine /ubbthreads/images/graemlins/mad.gif ), but it's been 3+ years and like I said, the a-hole owner pretty much ignored me after he got his money...

Definitely something I'm gonna look more into after gettig it back up running.

 

[Cornflake]

Quote:
Hi Cy:

Did you try the procedure described in the service manual, where you set the rear parking brake and see how far you can twist the driveshaft back and forth ? This procedure will tell you if you rear diff is worn.

Additionally, I was able to check for transfer-case wear by jacking up just the rear of the car, disconnecting the driveshaft to rear-diff connection, then twist the driveshaft back and forth and check for play. Also watch the driveshaft and see if it is the driveshaft end-to-end twisting, or if the play is at the transfer case.

Between those two procedures, I was able to figure out whether the transfer case or the rear diff should be replaced first.




great stuff i need to try to figure out which i need first aswell

 

[Luke]

Just an update.. Swapping from 3-bolt LSD to 4-bolt LSD did not reduce the rear end noise as much as I originally thought.
I still have rumbling noise on deceleration.. very faint.. but still there..

I think, next, I am going to double check the driveshaft carrier bearings shims.

On another note, I now have a spare 3-bolt LSD rear diff for sale
It's in pretty decent condition, because as it turns out swapping to 4-bolt rear diff did not make the noise goes away.

Oh well.. more work..

 

[CP]

I put all new carrier bearing shims (bushings) in and it didn't do anything to quell the decel noises.

 

[Luke]

Hi CP:

For some reason, none of my carrier bearings have shims on it.. just bushings..

Do you know the procedure to figure out the proper shims thickness ?
I don't see this mentioned in the manual.

I think either the previous owner lost the shims, or that my car came with zero shims.. The latter is unlikely though.

 

[CP]

I guess I don't have any "shims" either then. All I've got going through the 4 carrier bearing mounting holes is a rubber grommet on each side (new) with a metal dowel thing that goes up through the middle of each one. Maybe that's our issue /ubbthreads/images/graemlins/dunno.gif

I get a rumble depending on what my throttle foot is doing during cruising, and on coastdown, I sometimes get a metal grinding noise that's very pronouced from outside the car. If shims ARE missing, how do I determine what needs to be shimmed and how many/where to place them?

 

[Luke]

When I bought new OEM carrier bearings, the kit came with shims ( washers ) of various thickness. They are supposed to lower the carrier bearings just the correct amount so that the driveshaft sections are straight or at the correct angles.

From what I've read, U-joint is not a constant velocity joint, meaning that as driveshaft sections turns for one revolution, it speeds up and speeds down periodically.

The adjustment is to get the two U-joints to be "in-phase", so that they cancels each other's vibration.

I wish I knew how to make this measurements so I can shim the carrier bearings.

 

[spoulson]

I believe the idea behind the carrier shimming is to set backlash. Set a shim behind the ring-side bearing and then place a dial indicator against a ring tooth. You are required to be within a threshold of backlash. I don't know Mitsu's spec, but 5-7 thousandths seems to be a typical number on American cars. Then load up the other bearing shim to set preload on the carrier.