Differential noise

[Jack J.]

[Dan H.]

Re: Differential noise

My 64 with Eaton posi was rebuilt, made noise when turning etc, put GM synthetic rear end oil in with two tubes of additive, quiet at last !!!
Dan

[Gary R.]

Re: Differential noise

Depends on how it was rebuilt- what type of clutches and setup. Also, can it be a tire rubbing? The Eaton posi is much better than the DANA used in 63-4 but work the same when setup in the stock configuration.

[Jack J.]

[Dan H.]

Re: Differential noise

Jack, I had the rear end rebuilt with steel clutch disc, did dozens of figure 8s etc, still popped. The rear end shop removed the rear end twice looking for problems and insisted on using the regular rear end oil. My friend John Marquadt (John's FI) told me to always use synthetic oil and additive in the rear ends, that fixed the noise, 20K miles later, runs quiet. GM 75 90 synthetic.
Dan

[Jack J.]

[Mark E.]

Re: Differential noise

Always use the GM additive; don't substitute for another brand.

[Duke W.]

Re: Differential noise

AFAIK they're all the same for any clutch type LSD - GM, Ford, Mercedes, BMW... The NAPA part number for a 4 oz. bottle is NCB 4285V.

Duke

[Jack J.]

[Patrick H.]

Re: Differential noise

Silly question - why drill and tap? It's not that difficult to suck the fluid out through the fill hole, especially since it's usually not a frequent process.

[Jack J.]

[Patrick H.]

Re: Differential noise

I just see it as one more place to leak if it's not sealed well.

[Duke W.]

Re: Differential noise

GM did not recommend a change interval for the axle or transmission. The problem is that Positraction differentials generate wear particles as the clutches wear. If you've ever disassembled a Positraction axle that has never had an oil change you will likely find the oil pitch black and a sludge at the bottom that result from the wear particles both in suspension and that drop out to the bottom of the axle.

Based on my experience with my SWC and Cosworth Vega I recommend changing Positraction axle oil every 30K miles and 60K miles for non-Postraction axles and manual transmissions. Given that interval and the rate these cars typically accumulate mileage, I don't see any point of attempting to add a drain plug. For one thing there is no boss in the casting for such a plug, so there is minimal thread, and, as previously stated, this can be a leak source. There's also a finite chance that a botched job could damage the carrier beyond repair.

Axle oil container should state "SAE 80W-90 GL-5 within the API "donut" with one to two 4 oz. bottles of limited slip differential friction modifier additive for Positraction axles that you can buy from any parts source. The same oil without the additive should be used in manual transmissions.

SAE 80W-90 GL-5 is the modern incarnation of the Mil-L-2105 oil recommendation for both axles and manual transmissions in owner's manuals, service manuals, and AMA specs from the C-1 to early C-3 era. The SAE spec replaced the mil spec sometime in the mid seventies.

Duke

[Gary R.]

Re: Differential noise

Duke has some good info there.

I would like to add comment on drain plugs though. I have tapped 100's of non NCRS iron diff's for drain plugs. No one ever said they leak. there is enough wall to tap them where I do. It works great. Make changing the gear oil a fast, clean operation. If the diff was rebuilt, then it should be heat cycled with new gears, and the oil changed at 500 miles. That's the procedure I use and have for many years with success. I use Lucas oil but any quality oil can be used and I change it out at 8-10k miles. Needless, maybe - maybe not, but it has worked for me.

With respect to the clutches, if fiber coated clutches are used, they will start to smudge at the first turn. The oil will be black in 100 miles or less and it will continue until the fiber is worn away and chattering starts up. Solid steels however don't wear down like that and show maybe 002-003 wear per clutch over 100k miles based on the many I have taken apart and inspected, literally 100's of them.

[Frank E.]

Re: Differential noise

GM did not recommend a change interval for the axle or transmission. The problem is that Positraction differentials generate wear particles as the clutches wear. If you've ever disassembled a Positraction axle that has never had an oil change you will likely find the oil pitch black and a sludge at the bottom that result from the wear particles both in suspension and that drop out to the bottom of the axle.

Based on my experience with my SWC and Cosworth Vega I recommend changing Positraction axle oil every 30K miles and 60K miles for non-Postraction axles and manual transmissions. Given that interval and the rate these cars typically accumulate mileage, I don't see any point of attempting to add a drain plug. For one thing there is no boss in the casting for such a plug, so there is minimal thread, and, as previously stated, this can be a leak source. There's also a finite chance that a botched job could damage the carrier beyond repair.

Axle oil container should state "SAE 80W-90 GL-5 within the API "donut" with one to two 40 oz. bottles of limited slip differential friction modifier additive for Positraction axles that you can buy from any parts source. The same oil without the additive should be used in manual transmissions.

SAE 80W-90 GL-5 is the modern incarnation of the Mil-L-2105 oil recommendation for both axles and manual transmissions in owner's manuals, service manuals, and AMA specs from the C-1 to early C-3 era. The SAE spec replaced the mil spec sometime in the mid seventies.

Duke

I thought with the brass syncros in the Muncies, GL-4 should be used. Could you comment on that??? Also I think it's one to two 4oz bottle of friction modifier. Please correct me if I'm wrong....