Decel noise

[TerryLiv]

This is a 91 DSM AWD with Clutch pack Rear LSD, sprung 6 puck South Bend Clutch, Fidenza AL flywheel.

I get a coast down/decelleration noise that sounds something like a loose pinion bearing in the rear differential. Mostly happens between 4,000-2,000 RPM's when coasting with the clutch engaged.

The noise reverberates up the drive shaft with the typical wa-wa-wa sound.

The rear differential has recently been overhauled by TRE, so I trust that the pinion bearing is not loose.

Driveshaft U joints are all good.

Any thoughts.

Thanks,

Terry

[TerryLiv]

Does anyone have any thoughts on this for me?

Please,

Thanks,

Terry

[thiazole]

Lose flywheel bolts?

[Overkill]

Transfercase might be getting worn out if its never been rebuilt allowing play. Decel noise in general is always quite common Terry so unless this is progressively getting worse it way be normal.

Maybe when you broke you half shaft something else got hurt as well.

[yokotabrat]

Have you tried shimming the driveshaft carrier bearings? I recall something on NABR about setting the angle of the driveshaft by using the factory shims/washers where the carrier bearing bolts to the body to alleviate coast down noise.

[Cloud]

You are running a very light flywheel and that amplifies drivetrain backlash as the engine inertia is no longer 'steadying' the drivetrain. I got the 'wah wah wah wah' noise on decel after my fidanza, this isn't to say that something isn't wrong, but that even the in-spec amounts of backlash in the drivetrain gave me a similar noise as well.

[TerryLiv]

Have you tried shimming the driveshaft carrier bearings? I recall something on NABR about setting the angle of the driveshaft by using the factory shims/washers where the carrier bearing bolts to the body to alleviate coast down noise.

Bert,

That post was primarily trying to get the angles all as equal as possible to avoid power loss. Yes, I have done that.

Thanks,

Terry

[TerryLiv]

You are running a very light flywheel and that amplifies drivetrain backlash as the engine inertia is no longer 'steadying' the drivetrain. I got the 'wah wah wah wah' noise on decel after my fidanza, this isn't to say that something isn't wrong, but that even the in-spec amounts of backlash in the drivetrain gave me a similar noise as well.


Brian,

Thanks. Answers like this give me more encouragement to live with it, rather than spending countless hours trying things that don't work.

Terry

[TerryLiv]

Transfercase might be getting worn out if its never been rebuilt allowing play. Decel noise in general is always quite common Terry so unless this is progressively getting worse it way be normal.

Maybe when you broke you half shaft something else got hurt as well.

Transfer case has never been rebuilt other than when I replaced the 22 spline parts with 23. It doesn't have any significant slop though. I checked that recently.

I may have to put it back on 4 jack stands where it belongs and see if I can find any other problems that are new ones.

Thanks,

Terry

[mitsunut]

Terry,
What oil are you using in the rear diff and t case? I am using red line hd shockproof and it did quiet down the back lash noise. No rebuild on the rear diff or t case. Original rear end , 145k miles, and t case unknown. I know the sound, had it bad before the last tranny rebuild . I did quiet down the exhaust some more and haven't noticed any louder noise . I do have the d shaft carrier bearings filled with windshield urethane on one and rtv on the other. Hope this helps.
Jim.

[TerryLiv]

Terry,
What oil are you using in the rear diff and t case? I am using red line hd shockproof and it did quiet down the back lash noise. No rebuild on the rear diff or t case. Original rear end , 145k miles, and t case unknown. I know the sound, had it bad before the last tranny rebuild . I did quiet down the exhaust some more and haven't noticed any louder noise . I do have the d shaft carrier bearings filled with windshield urethane on one and rtv on the other. Hope this helps.
Jim.

Jim,

Same oil in both as you. 220,000 miles on my transfer case. Drive line carrier bearings are filled too.

Thanks,

Terry

[Overkill]

Brian is correct about the lightened flywheel and it is something I noticed as well when I installed mine. The only way to combat this is having some sort of rubber touching the driveshaft to absorb and dampen the harmonics.

The best way I know of is to fill the carrier donuts with window well sealer so they are contacting more of the driveshaft around their circumference. I have heard of ghetto methods such as wrapping a bungy cord loosely around the driveshaft, but not something I would suggest doing.

[deShaneO]

3 DSMs, 3 ACT2600 /Fadenza flywheel combos all made noise after that mod. The first car I thought something was wrong. The second car I thought something was wrong but maybe it was normal. Last DSM, I'm going with normal noise. :)

-dang, I've owned 3 dsms, I must hate myself.

[deShaneO]

3 DSMs, 3 ACT2600 /Fadenza flywheel combos all made noise after that mod. The first car I thought something was wrong. The second car I thought something was wrong but maybe it was normal. Last DSM, I'm going with normal noise. :)

-dang, I've owned 3 dsms, I must hate myself.

correction 3rd car has a JUN with ACT2600

[Overkill]

I've had over 20 so consider yourself lucky! :-P

[thiazole]

Now that I think about it, my Spec 2+ did the same thing. It went away when I switched to Jack's clutch.

[thiazole]

Edit: or at least the noise wasn't nearly as noticeable with Jack's clutch.