700R4 trans problem

My 88 Chevy 1/2-ton(2-wd/305/178kmi) is having some transmission problems, but first a little back-story:

The truck has been in the family since new, my mother had the trans rebuilt about 8-years ago, at around 150kmi, when I died while she was on a road trip. I inherited the truck in '06 and soon after the lockup clutch started acting up due to temp sensor problems(common on 700R4s), but wiring a manual switch to engage it as needed did the trick.

I really didn't drive the truck much until last summer. Soon after the trans started slipping once, I pulled over & found it was low on fluid(presumably due to dry seals), topped it off & started checking it more frequently. I had to top it off a few other times, but for the last 9-months it had been fine.

Fast forward to last week: I felt a little bit of slippage & checked the level when I got home. It was fine. Drove a few more times without problem, but then it started slipping really bad the last time I drove it. Finally had a chance to check the fluid tonight & found it was somehow WAY over-full!!?!?

Is the trans dying?

does trans fluid smell of coolant or do you have trans fluid in the radiator?

Didn't smell coolant on the dipstick, but I'll check the radiator this weekend.

Would I be better off swapping in a TH400 if this is a goner? If so, what other parts need to swap with it?

Sounds like the filter is plugged if the level is high and it's slipping.

Coolant in the trans fluid is easy to spot, don't even have to smell for it. Coolant turns trans fluid to a strawberry Quik color.

If the trans was rebuilt by a trans shop and NOT the dealer, it should have most of the the updates available. This may come down to a simple soft part rebuild, aka: seals, clutches, gaskets, and filter. Probably should bypass the rad cooler for an external, jmo.

Turbo 400 swap would be absolute last resort, IMO. About the only thing going for the swap is that the trans bolts up to the back of the engine. Most everything else is swap over other stuff and fabricate.

I am impressed though as you only have had two transmissions for 178k. Most people I know would be on #4 at least.

Brian

Wow, do they suck that bad??? FWIW, I've flat-towed an old Beetle home once, and a small lawnmower trailer another time, but other than that it hasn't towed anything. Maybe that explains the longevity?(Oh, and both those were with this current trans.)

So, should I just drop & swap the filter and see what happens first?

It was rebuilt by the dealer who sold the truck new. They said a replacement 700R4 was NLA from GM at that time, and offered to swap in a TH400, but they "have a guy" who could rebuild it. I told Mom that it was probably better to keep the 700R4...

it is way better to keep the 700r4 and they do not suck. i personally have never had one let go on me with less than 170k. actually the only other one i had go was 238k. i had one that i pulled with 220k and sold to a guy who put it in something old for overdrive. the early ones had some not so good parts but by 88 they were good.

try to replace filter and see, easier than rebuilding. if it is still bad chances are the rebuilder either went with cheap parts or didnt replace some things that looked ok at the time. i bought a reman engine once where all they did was resurface the lifter bottom and clean them - so my engine came with 4 lifters that were just worn out and would not work with the engine warm.

ACK! Dealership rebuilt. That just means overpriced and under worked repairs, when everything should be replaced.

Looks like to me now with this information, it probably needs a proper full rebuild.

BTW, most of the 700's are dealt with either had burnt out OD or reverse or broke/worn out planets.

Brian

Is it worse when its warmed up? Probably a hairline crack in the input drum. Can't usually see them but the gap increases as it heats up and lets pressure leak past.

Most common causes for slipping and appearing overfull are clogged filter, trashed pump, or some other governor/pressure issue.

Well I picked up the filter & fluid today...and if I drop the pan & find chunks of steel I can probably get a refund if I haven't opened the package.

Call me crazy but id check the cooler flow before even messing with the tranny.

I finally got to spend some time under the truck. I noticed some trans fluid leaking out the hole on the bottom of the bellhousing cover, and some on the cooler lines where they elbow downward(I think one may have a pinhole leak). I disconnected the lines at each end & blew them out gently, the both seemed to flow freely & were full of fluid.

I was surprised there was very little fluid that came out of the cooler, so I blew it out & it also seemed to flow fine. Next I dropped the pan & checked the filter, fluid & filter were nice and clean.

So I'm a little surprised. If the cooler line is leaking, the dipstick wouldn't be reading high unless there was another problem. Adding to my "what next" confusion - I picked up a '93 700R4 yesterday, also out of a 2wd/V8 truck & supposedly good, for $45.

Now I'm not sure which gamble to take. Swapping the trans doesn't seem that tough - if it is a match, and if it is indeed good. But if the problem is the cooler or lines, I wouldn't want to trash a 2nd trans. I don't see anything obvious though pointing at anything other than an internal problem...