Last October I had the limited-slip clutch pack replaced on my F-250 10.5 rear end and had the mechanic use Royal Purple max gear oil.

Yesterday I dropped off the truck so that he could check the limited-slip clutch pack and maybe add a larger shim so that it grabs better (it was acting more like an open diff in snowy conditions).

Today he called me and said I need to come look at it, that the gears looked like they were being eaten away by the gear oil due to a chemical reaction. The gears were normal back in Oct on the prior service date.

I don't drive the truck much and the areas of the gears that were submersed in the gear oil are deeply pitted / corroded and less metal thickness. There are also some areas on the bearings. Here are some pics. Anyone seen this before or have any ideas?

 

Water got in and rusted while sitting.

 

^^x2

 

^^x3

 

That was my exact thought but the mechanic who took it apart and another guy there said the oil line in the diff housing matches up with the gears where the damaged area would have been under the fluid level. Also no signs of water mixed in with the gear oil.

 

The moisture has been homogenized into the oil from driving. The slight detergent in the oil will encapsulate the water and hold it. Clean everything, replace damaged bearings and washout the case. Also check the vent, it could be clogged and the check valve, if it has one. Then refill with premium fluid and drive the hell out of it until the case feels hot.

 

Thanks, will do.

Also, I've ordered a Detroit TrueTrac Limited Slip and I'm trying to find a new 4.30 ratio ring & pinion but having trouble. The mechanic thinks the corroded gear area will lead to failure.

 

Depends upon the depth of the scar area.

 

The damage is due to water condensed in the lube while the vehicle sitting; unused, for a long period of time. I see a lot of wear on the ring gear. This is an indicator that perhaps the lube at some point in time did not contain GL-5 additive. GL-5 is the protection package that resists wear of hypoid gear to pinion mesh. Never use any gear oil in hypoid (bevel) ring and pinion applications, unless it contains GL-5 additive.

 

The Royal Purple gear oil bottle says GL-4 and GL-5 approved, but I don't know what was in it previously when Ford serviced it in the past, before the current gear oil.

I was not aware of the GL-5 rating requirement, but I will make sure the gear oil used will have it.

I appreciate everyone's input.

 

If you are going to put a TrueTrac in it, use the lube recommended by Eaton - which I believe is non-synthetic 80W90.

 

I knew Eaton recommends non-synthetic without friction modifier but I didn't know the oil weight, thanks.