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Discussion in '1982-Present GM Diesel' started by USAJon, Jan 13, 2007.
go pick one out of a junk yard. probably going to be in good enough shape to run for a while and only spend a few bucks
Have you ever rebuilt a motor?
rebuilding a motor = easy.
rebuilding an auto tranny and keeping it running = difficult
Not even close... Dodge 727 and GM TH350/TH400/700R4 are all easy to rebuild. They require no more skill than a basic engine rebuild requires. When you start getting into the newer, electronic controlled trannies it starts coming down to a good knowledge base on what should be replaced that may not look like it failed (like electronic solenoid packs on the E4OD Ford tranny). Heck a Dodge 727 can be rebuilt with 2 or 3 different size sockets and a couple screwdrivers. GM trannies call out a few special tools, but they are so simple you can make them yourself with a little effort. I've never heard of a BS being required to rebuild a transmission
Also the most important things I can tell you about rebuilding a tranny... Have plenty of clean and clear work bench space. Lay out the transmission parts in order when you take it apart. And buy a good shop manual from the factory if possible that will walk you thru step by step.
I am pretty well mechanically inclined, but even with a manual my 400 only lasted 3 weeks after i rebuilt it. Had it rebuilt by someone else and asked what was done wrong and got told, "whoever rebuilt that messed up a bunch of stuff." I don't claim to be be ASE or anything, but I am more than capable of taking something apart and putting it back the same way. Still don't know what the hell I did wrong.
I have no mechanical training at all and have successfully rebuilt a 350 V8, a 700R4, a dodge 727 and after a second try a Ford E4OD. When it came time for the E4OD it took a good tranny shop that was willing to give me some tips. I just made sure to buy my parts from them since it makes it easier to ask them questions while I was in there spending money.
The stall rating is different between gas/diesel but that is about it. The governor is also different on the diesel tranny but you can change that out from the old one.
The governor is behind one of the tin covers on the side of the tranny. It is a set of weights mounted on a geared shaft. The faster it spins the farther the weights are pushed out against a spring.
I agree on AT rebuilding, it's easy if you are observant.
I rebuilt a few th350's, and I will be doing a th400 soon.
the first tranny I rebuilt, I took it appart, got new rebuild kit, put it together with the new parts replacing the old ones in the reverse order I took them out, had no manual or nothing, just a video cam filming me take it apart so I can look at it if I forgot anything.
It worked for years and sold it still running great.
I have heard of this and seen some guys do it--but the converter is easily damaged by drilling the hole,if the drill hits one of the internal fins inside of it..also,the ones I have seen drilled and plugged used special Pop rivets to seal the hole,not a pipe plug,and 90% of them leaked after reinstalling into the vehicle..
The only converters I see that pan out this way are Ford ones that had a factory drain plug--GM never seems to use a drain plug factory..I'd bring the converter to someone with a flushing machine that spins it while pumping ATF under pressure to clean it out thouroghly...drilling it and draining it most likely wont get all the crud out,and will probably lead to headaches later..
If the converter is suspected to be defective,I'd just buy a new one,it's not a good idea to re-use one that was in a blown tranny, or suspected of being defective or damaged,it'll ruin the rest of the tranny in short order..
If you drill right at the weld line you can't hit a fin, the best way to clean it though is to cut it open and clean it and inspect it then reassemble
My TC broke the pilot plate off so I took it to Shift management inc where I got it, and instead of just welding it back they chose to cut it open, inspect, and reweld, the tranny had 3000 miles on it and they wanted o see how it looked at that point.
Doesn't sound promising..
Some tranny's get a stuck servo,and that can cause reverse to go out..but its not that common on GM trannys...usually reverse goes away first on a TH350 when its cooked..
But the way you say its "under load" and trying to drive in neutral or park ,sounds like an internal problem,like the valve body gasket being torn or has a peice missing,or perhaps the tranny's case itself has an internal leak between passageways,that allows pressure to be applied to a clutch that should not be engauged..valves in the valve body itself sticking could be the culprit too..
There is a rats maize of passages the valve body bolts up against,and if any are cracked,it usually feels like a "trans brake" when you accelerate,like its fighting itself--maybe yours is letting the pressure that should be going to the reverse curcuit go to one of the forward gears oil curcuit??...better make sure the case is worth re-using before rebuilding it!..
At any rate,it definately needs to come apart and be rebuilt..its unlikely you can fix this "in the truck",or by adding some of the miracle in a can stuff..I have used brake fluid sucessfully to soften up hard seals, and get a few more miles out of worn tranny's,but they never last long..
ive got a friend selling a th400 with 78k miles for $300. hes located in northern VA, he can meet or deliever. pm me if interested
If you going through the trouble of rebuilding the tranny just go ahead and change the convertor. They cheap enough. Its worth my time to do it once instead of having to pull it again when the it fails.
GM trannies (350-400) use the same clutch pak for reverse and 3rd/high. Called the reverse high clutch. So you lose part of 3rd, may not notice it, but ALL of reverse. Very common problem. I'm pretty rusty on this stuff, but I do know that a few elements do double duty. So don't find fault with my blurb, I'm not sure about the exact terminology. Maybe the 350 has the reverse high clutch, or overun band... Sheesh, I'm BAD!
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