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Renewing fluids in differential, transfer case, swivel housings


Vehicle: 1991 Range Rover Classic with 170K miles primarily ‘round town, no off-road or towing

History: I suspect 30K was done at dealer. Fluids last changed at about 65K by a shop.

I read and was prompted into action.

Additional Goal: increase gas mileage

RR Specified Fluids:
Differentials – 80W EP (Mil-L-2105) 3.6 pints each for front/rear
Swivel Housings – 80W EP 0.7 pints each
Transfer Case – Dextron IID

Differential Fluid Analysis:
I wanted synthetics and found the following.
Redline 75W80 Lightweight Gear Oil (API class GL-5*)
Several Brands 75W90 – Mobil 1, Amsoil 2000, Castol, Neo, Royal Purple, etc.
Several Brands 75W-140

I selected Redline 75W80 as it was thinnest and met 80W spec. I would probably go with 75W90 if I did any off-road or lived in hot climate (I’m in San Jose) and would consider 75W-140 for towing. Amsoil claims best mileage but there may be issues with API certification if vehicle is in warranty. I think it is a cost issue for API testing on smaller brands. There also ‘may’ be an issue with the breather vent cap when changing to synthetic (my 1997 GM needs change out to P/N 12479296). I did not inspect to see if the GM part is usable or research a RR equivalent on late models. *GL-5 rating called for on my Chevy Tahoe using 80W90 mineral gear oil.

Transfer Case Analysis:
I selected Redline “Synthetic ATF” as it met the Dextron IID spec. and is a 100% synthetic. Generally Dextron II has been superceded by Dextron III and is not readily available. Redline also makes a “D4 ATF” version that meets the Dextron III and is claimed to meet upcoming Dextron 4 spec especially for low temp viscosity. ATF D4 is also a full synthetic. Not all “synthetics” are full, some are blend. They also have a “High Temp” version for “heavily loaded vehicles”. I would suggest the D4 ATF for some off-roading or hot climate.

In selecting materials I like to use item available locally in case of any ‘urgent’ need for more. Often I buy online though for best price since I live in high tax state. Redline is available at Napa locally but they didn’t have the 75W80 or know what it was (the Redline brochure does not show 75W80 just says Lightweight).

Purchasing Materials/Tools:
1) I ordered 5 quarts of 75W80 and 2 quarts of above ATF from HBR at $7.75 / quart.
See Cost with shipping $61. This site gave me confidence I would get what I ordered. Other retail sited did not show the 75W80.
2) 0.5” socket adapter for my 3/8” socket set ( all plugs are 0.5”) on differentials and transfer case $4
3) Vavoline hand pump $4 (comes in re-sealable baggy)
4) Permatex Hypolmar for sealing transfer case plugs $6 (usable for gaskets).

1) I drove about 10 miles to warm things up
2) Spray cab cleaner on plugs and clean areas with wire brush
3) I had 2 quart jug which I cut off top and a 1 pint milk bottle. I used these to measure and to inspect fluids coming out.
4) Drained each item. Take out top fill plugs first in case of difficultly. You don’t want to drain first.
5) Swivel housing has three plugs. 16mm fill on top, 0.25” level plug, ~12mm drain plug on bottom (this last plug appeared to be 15/32”, very loose 12mm so I used adjustable to break loose.)
6) Used Hypolmar on transfer case plugs only
7) Refill until fluid reaches fill plug lip or level plug on swivel housing.

See for some pictures on transfer case.

NOTE: I have read NOT TO USE SYNTHETIC during a suitable break-in period for new or rebuilt engines/axiles unless specified by manufacture (eg. Corvett).

Problems: Several plugs very difficult to get out (read as need hammer). A real 0.5” breaker bar would be helpful.

1) Right swivel housing had no oil seepage on outside but had much LESS THAN 1/10th of a pint. No metal particles were found and I probably avoided the destruction of the CV joint by doing this service (it is recommended at 30K intervals, I went 105K.)
2) Left swivel housing HAD oil seepage but had at least 0.5+ pints of fluid.
3) Although transfer case was rated to hold 3.6 pints it really took maybe 3.9 pints.

Follow-up: As expected, I have more than 1.5 pints of the 75W80 left and will re-do the swivel housings after 1000 miles. Gas mileage improvement is expected to be only 1-2% so it will be hard to document. Breather vent cap issue will be re-visited when I work on Chevy Tahoe fluids. I will be watching for seepage on seals.
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