Jimmy Transmission Problems

[kodyb87]

My '86 Jimmy is completely stock except for the mildly built crate motor and 33x12.50's on it. The sticker says 3.08 gears and I know it's a 700R tranny. Since I've owned it, it's only seen highway miles back and forth to work. No rocks, no mud, no abuse. About 6 months ago it stopped coming out of first gear and when it would shift, it acted like it wanted to skip straight to third. Took it to the shop and he said it was toast. Bought a new transmission and a about a month later it's doing the same thing. It blew the pan seal so I replaced that, the filter, and all of the ATF. Ran good for about 2 days and then it started acting up again. The confusing part is, some days it shifts like a brand new one. I got in it yesterday morning and had no problems driving it around the neighborhood. Yesterday afternoon when I got home from work, it wouldn't shift out of first. Any suggestions? I can't afford to keep replacing transmissions. Thanks in advance for the help.

[70-K5]

In my opinion you should get rid of the 3.08 gears. With 33's you should be in the 3.73 - 4.10 range for good power and keeping the cruising rpms in the very low 2,000's.

Who did you buy the "new" transmission from and who did the installation?

You say you have a "built" crate motor. Does that mean that you have an upgraded carb too? Do you have the correct linkage to properly hook up the TV cable? Last 700r4 question is, did you set the TV cable properly after installation?

[kodyb87]

All of the transmission work was done at the shop here in town. He's one of the best around but I know that doesn't mean he can't foul up. The 3.08's will be gone as soon as I get the cash to replace them. The motor just has a mild cam, bored .60 over, full tube headers, and an Edlebrock carb. Honestly not sure what carb it is without looking at it. I bought the truck already setup the way it is. He replaced the TV cable and adjusted everything. It ran perfect for the first few weeks but now it's acting up again. I may take it to him today and see what he says. Just looking for some other opinions. Thanks!

[4pilgrim4]

When I bought my 83 diesel the P.O. had installed 31 x 10.50 - 15's on it. The differentials were 3.08's, like yours and it was a real dog, performance wise. Awhile later I scrounged some fair looking mags at a junk yard and had 235 x 70 - 15 Michelins installed at a COSTCO special sale.

That helped a bunch, but when I found a set of 3.73 axles and installed them, performance jumped another notch or so. Then the Banks turbo put it ahead a bunch more.

Through this period I also lost several transmissions, six in total. The local rebuilder just couldn't seem to provide one that would last and ended up doing three on warranty. Then on a winter vacation to southern CA pulling a small camper the transmission went out on I-5 with the Grape Vine ahead of us. I had a small Mexican shop pull the pan, clean out the debris that included a lot of metal, install a new filter and new fluid. It worked, most of the time on an alternate route into LA.

First stop was to visit some friends who had three boys in late teens and early twenties who were into a Chevelle they dragged at a local strip and a couple of Jeeps set up for rock climbing. The recommended a certain shop and I checked in there. The owner check out the max torque and hp via a call to the Banks manufacture which is on the other side of LA, checked the weight of my camper and axle ratio of the Jimmy.

With the transmission out and apart he found the clutches almost like new, but several of the hard parts broken and ground up. Even the case was toast. What it turned out was that GM was a little presumptuous installing that transmission behind a 350 gas or a 6.2 diesel and had upgraded it a lot in later years.

A later transmission was located, rebuilt, some even stronger after-market components installed at my authorization and it has worked flawlessly for at least 15 years, a lot of it pulling the camper. The shift points are more consistent, RPM-wise, and crisper. I could easily afford a newer SUV, but I like this one better.

The point is, perhaps a speed shop rather than a transmission shop might be more aware of the upgrades that should be done on that transmission to give it better longevity. Sorry that it has been so long ago that I have forgotten the details, but I do remember a discussion about a pump that puts out more pressure and a broken planetary gear set that failed because it wasn't getting enough lubrication.