LUVTruck.com

Today I finished putting in my new replacement transmission for my 1982 LUV 2WD diesel. The transmission isn't "new", but is a used 5-speed manual that was hard to shift into a few gears using the shifter. Had the trans took apart and put back together by my local transmission shop and shifted fine after put back together. The actual internals looked very good with what looked to me as less than 50,000 miles. Now that I have it assembled in the truck I am debating on what engine oil to use for the transmission fluid. According to my 1982 Chevrolet LUV workshop manual the 5-speed manual transmission uses 5W-30SF weight engine oil. What I want to ask is will running a synthetic engine oil in the transmission help to make the internal parts last longer? My last transmission went about 90,000-100,000 miles on just regular engine oil and I did treat it right and didn't ruffhouse it. That was the transmission I just pulled out and it has over 300,000 miles on it with one rebuild already. But this trans I just put in my truck today seems to be in great shape and I want to make it last for at least 140,000 miles. So I think going to the synthetic engine oil will really help lubricate this trans for a good amount of miles to come. What are some suggestions for me to consider? Thanks and I appreciate any reply.

LUVdiesel--

I have been using synthetics in my two Isuzu P'ups for about 10 years and
don't really know if I have had any trouble related to lubrication.

I say 'don't know' because the Isuzu trannys like to wear out some of their bearings at about 75k to 150k miles with or without synthetics. The big input shaft bearing seems to be the one most likely to fail although I have had others go too. I have rebuilt 3 of these and one of my friends rebuilt his.

Still, I think the synthetics have the edge over regular engine oil. And, since the synthetics tend to have an improved viscosity index, they remain thinner at cold temperatures. This makes the tranny easier to shift when cold.

I have used either 5- 50 or 10- 40 weight in the trannys.

I have also been using a synthetic gear lube in the differentials, 75-80 weight, with never any differential trouble.

I find it strange that Isuzu's engines last for several hundred thousand miles without too much trouble but the trannys have a much shorter life.

Paul

Here is a photo just for entertainment:

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'84 Isuzu diesel P'up

Paul, thanks for the suggestion on the synthetic engine oil, really helps me out when I get an opinion from another member about something like this. Even before I asked this question I was sure in my mind I was going to run a synthetic engine oil. I really think it will help me down the road with a more reliable transmission. For these trucks, you are exactly right about the transmission having a much shorter life than the engine. The engine is the great thing about a LUV/PUP, but the transmissions may be said to be the weak links in the trucks. The transmission I just put in yesterday will be the 3rd transmission in the truck since it was new in 1982. But of course I am on the original engine with about 225,000 miles and absolutely no problems with it. Also, thanks for posting up the picture of the 1985 Isuzu 5-speed trans. That is a great shot of the internals in the trans.

The T5 Borg Warner used in my S10 uses auto tranny fluid, and they seem to last reasonably well. My guess is the longer life comes from a better tranny design, but who knows? The first transmission I had was a pig to shift, and I come to find out someone filled it with gear oil, a no-no with these ones. Ruined the syncros and a couple of bearings. The next transmission was fine.

My own vote is to use the synthetic engine oil. For the small extra expense, it would be well worth it.

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Bona Fide diesel fanatic.
1994 Chev S10 Ext Cab Isuzu Diesel 5spd
Kubota B6100 HST diesel