4x4Wire's TrailTalk Forums: More A/T problems... More results are in

Having run standard and synthetic lubes in differentials I have noted the following differences. The Redline was the only lube that prevented my LSD unit from chattering.

On a sports car I used to have after a long highway drive when I got onto surface streets the rear diff was very hot and the clutches grabbed like crazy. Draining the lube showed lots of metal on the magnet presumably from the clutches.

This problem was rcontinued with several different gear lubes and LSD additives including factory Mitsubishi LSD additive. I took the LSD unit apart dressed the clutch plates down and contemplated reducing the factory preload or putting new ones in. At $40 per plate and about eight of them that was not a good option. Cleaned up with fresh Vavoline non synthetic lube the problems continued.

On a whim (out of desperation) I tried Redline gear lube.

Problem gone.. Simple as that. Diff ran much cooler, minimal metal on the magnet after 10,000 miles of use, no noise. Synthetic lube in the gear box yielded good results as well. Finaly it shifted smoothly when cold.

As far as Dougs transmission goes it does seem he has a problem but the question is cause and effect. On a sample of one where there seems to be a correlation of lubricant choice to a possible wear issue and or over heating there is no way to know for sure that the oil is the problem. For all we know better film strength may have prevented an incipient failure from happening sooner.

On the other hand perhaps the lube is not all its supposed to be. If that the case is it fair to say all synthetics are bad? Not in my book. We might be able to say that one did not work.

Another point is the biggest difference in ATF formulations is the friction modifiers. This is what comes into play as the clutches are just starting to engage and the oil film is thinning. Electronic controlled transmissions that use feedback to modify their shifting are sensitive to this. Our older designs typically don’t really care.

That leaves film strength for bushing life. I cant imagine a bedded in set of bushings staring to fail on a lube change.

Overheating says slippage.

IF the slippage is a clutch pack the transmission would have been sintered long ago. They don’t slip for very long.

If it’s the converter there are scenerios I see for running hot on the highway.
Non lockup type unit:

1: the transmissions converter is a non lockup design and the loading of taller tires roof rack has exceeded what the design is capable of. The excess slippage generates more heat than the transmission can handle. This hurts fuel economy and lubricant life. Since the unit is running hard all the time wear rates are increased.

2: The cooling system of the transmission is faulty, perhaps combined with higher than normal loading.

The chance that the fluid has a significant influence on this is slim at best. A synthetic should thin less as it gets hot and help with converter coupling. There may be some small differnaces between lubes and perhaps an ATF that’s is used and thickened with age works better, however that does not change the root problem of the converter being overworked.

I had this problem myself when I put taller tires on my Turbo Raider. Getting a lockup converter or better gears are the best solutions.

Now if you already have a lockup converter and you are overheating on the highway odds are you have a bad convert clutch or its not being applied. Once the clutch locks the transmission runs very cool.

Finally look at what the factories are going to for gear lubes. My Passat comes factory filled with synthetic gear oil in the transaxle as do most new cars. These guys are not going to spend the extra money for no reason.

That’s my experience.

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87 Raider, 2.6 Turbo-Intercooled, lockup auto tranny, 2.5" mandrel bent exhaust, 2.85 T case, LSD front diff, Torsen rear diff, V6 brakes and front axles, Dual suspension seats = lots of fun.

Edited by Kevin C (07/10/05 12:41 PM)