Rumbling diff!!

[stephen low]

Now that I've got my car running in test mode, one of the issues I have is the amount of noise coming from between the seats and presumably from the diff.

Am running a Jag LSD and to my ears it is very noisy but I have very limited exposure to other similar diffs in action. The car has no insulation or upholstry yet but I doubt this would reduce the noise by much. The noise level varys with power on and backing off but disappears completely with clutch depressed.

Firstly does it appear I have an old cluncker of a diff that needs attention or might it be another source? This wouldn't surprise me given the state of some of the front suspension parts I have replaced to date - my kit was a roller from previous hands, so it's all their fault!!

If the diff. can anyone recommend a reputable Melbourne diff specialist, as I understand getting Jag diffs right and to suit our lighter application is a somewhat dying art.

I look forward to any advice anyone can throw my way.

Cheers

[Rebel1]

Stephen, are you running the approved oil for the powr-lok diff?.

It may not help if the diff is stuffed but the PL diff uses either:

Castrol hypoy L.S.
BP limslip 90/1
Shell S8096B.

These are straight out of the Jag manual for PL diffs but they may be superceded by later, newer, and better diff lubes.

Cheers

[NASSTY]

Hi Steve,

Have you tried a friction modifier? This was suggested to me by other Cobra builders who have had similar diff noises. Penzoil make it as do others. When used the noise was greatly reduced. Hope that helps.

[stephen low]

Am running the oil suitable for the application and in fact changed the oil after the first real drive but that didn't correct the noise.

Haven't used any modifiers yet as I see that as a stop gap rather than fix.

reading old posts, Spiteri and Roddy jag mechanics were suggested, are there any diff mechanics/shops any one can suggest as well?

Cheers

[fsstnotch]

If the noise disappears completely with the clutch depressed, I would be looking more toward the transmission than the Diff. Is the noise like.. a howling sound?

This is a good reference for diff noises

Diagnosing Differential and Driveline Noises

We don’t know which sounds worse—us singing show tunes in the shower or a howling differential. While there is no help for our singing, we can help you diagnose the sounds coming from a differential gone bad.

A clunk, whine, or howl can signal a worn-out pinion gear, bad bearings, or a faulty gear installation. Sometimes, the noise is not differential-related, but is caused by other driveline or axle components. The guide below will help you match up the noise you’re hearing with the differential or axle component making it—or at least get you in the ballpark.

Noise: Howl while decelerating (gears previously quiet)
Cause: Loose pinion bearing preload

Noise: Howl with whir or rumble while accelerating at any speed (gears previously quiet)
Cause: Worn rear pinion bearing or worn gear set

Noise: Howl without whir or rumble while accelerating at any speed (gears previously quiet)
Cause: Worn gear set due to lack of lubrication or overloading

Noise: Howling while accelerating over a small speed range (gears previously quiet)
Cause: Worn gear set due to lack of lubrication or overloading


Noise: Howling after gear set installation
Cause: Faulty gears or improper installation

Noise: Low-pitch rumble at all speeds over 20 miles per hour
Cause: Worn carrier bearings

Noise: Whirring during acceleration/deceleration at about 10 miles per hour
Cause: Worn pinion bearings

Noise: Banging or clunking while making a turn, backing up, or rapid deceleration (like on a freeway off-ramp). Noise gets worse in warmer weather
Cause: Posi chatter due to improper lubrication; worn clutches or spider gears; improper assembly


Noise: Banging, crunching, or popping while making a turn. Noise not affected by temperature
Cause: Badly worn or broken spider gears

Noise: Banging or heavy clicking every 2-3 feet during acceleration and deceleration
Cause: Damaged or broken pinion gear tooth or teeth


Noise: Banging or heavy clicking every 2-3 feet during acceleration or deceleration, but not both
Cause: High spot or heavy chip on pinion gear tooth

Noise: Banging or heavy clicking every 8 feet during acceleration and deceleration
Cause: Damaged or broken ring gear tooth or teeth

Noise: Banging or heavy clicking every 8 feet during acceleration or deceleration, but not both
Cause: High spot or heavy chip on ring gear tooth

Noise: Clicking while decelerating from 20 miles per hour to a complete stop
Cause: Worn carrier case-side gear bores

Noise: Rumble or clicking that gets worse during hard turns
Cause: Bad wheel bearings

Noise: Driveline squeaking or grinding at any speed
Cause: Worn or damaged U-joints

Noise: Clunking when depressing the throttle pedal (takeoff)
Cause: Worn U-joints; worn spider gears; worn axle splines; excessive gear backlash; loose yoke splines; worn slip yoke splines

Noise: Clunk immediately after taking off from a stop
Cause: Worn slip yoke splines

Noise: Steady vibration that increases with speed
Cause: Worn U-joint or out-of-balance driveshaft

Noise: Cyclic vibration that varies in intensity. Intensity increases at a specific speed range, worsens during deceleration
Cause: Pinion angle too low (not parallel with front yoke on driveshaft)

[NASSTY]

100ml bottle of modifier was about $12. The guys I know using it haven't looked back. Their diffs quieten'd up a lot as well as the clutch packs in their LSD's worked more progressively. As I understand it, the problem with oils is that they keep on changing composition but we still use diffs that are almost 30 years old. I'd give it a go before taking the diff to a specialist. Mike Roddy rebuild my diff. It's a 3.07 LSD.

[David Hodgson]

Hi Slowy,

The diff being mounted directly to the chassis, ie metal to metal without insulators (rubber bushes) will transfer all mechanical noise. This was amplified when I fitted the hollow roll bar. my plan is to foam fill the bar to reduce the noise.

Mine and others that i have heard that have recond. diffs, emitt a whiring/meshing noise.

I would not worry unless it is accompanied by a grinding noise.

I have seen a couple of U.S kits that use a large bush on the top mount instead of direct plate.

[stephen low]

Fsstnotch

Thanks for the noise reference I'll use this a bit more to diagnose but almost think its like a constant rumble like mentioned for the worn carrier bearings. plus there is the occassional clunk or click so I guess there are a few worn bits beneath too.

But it does sound like its right there between the seats, possibly a function of this direct connection to the chassis issue.

Al

What sort of money was it for Roddy to reco the diff?

David

The noise is too loud for me to live with long term so I want to fix it sooner rather than later.

Thanks for the comments.

Cheer

[David Hodgson]

Originally Posted by stephen low

David

The noise is too loud for me to live with long term so I want to fix it sooner rather than later.

Thanks for the comments.

Cheer

Mine was ok until the roll bar was fitted. It's not unbearable, just damn annoying.

[NASSTY]

Hi Slowy
pm sent

[cameron02]

I have to agree with FSSTNOTCH,

If the noise dissapears when the clutch is depressed then it may be the gearbox that is the problem. Are you sure the noise is comming from the diff and not the gear box?

[JBo]

Try changing the rear dif oil (with the proper straight weight) and adding friction modifier. This solved all my rear differntial noise. I suspect the problem, if it persists may be difficult to diagnose. Pushing in the clutch is the ultimate in deceleration, ie changes the load on all components aft of the clutch. As the trans is still spinning (it is hooked too rear wheels after all), the noise could be in either component. Assume you've done the obvious undercar checks for loose bolts and rubbing marks. The chart above is a good go/no go way to elininate some potentials though.