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TH 400 Pontiac Transmission Build or not to Build Myself?
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I picked up a full rebuild kit for my TH 400 Pontiac Trans., but I had to buy the Thrust Washers from another vender because they were not included in their kit. I ordered the 3 Torrington Bearings too. I ordered the Rear case output shaft bushing kit that uses a Torrington also and came with 8 shims.
I bought a Gear for the Trans. oil pump as a precaution. I want to make sure that I get all the Thrust Loads correct as I build up my TH 400. Not until I open it up will I know if I need any hard parts inside. I have done my best to acquire as much info. off the Internet to solve any problems. If anyone is Interested in building this Th400 Trans. I will pay a fair Price to assemble the Trans. and I will purchase all the parts. You must Live in the south Florida area like Broward, Palm Beach or Dade County, so I can deliver the Trans. to you. Also, I have the tools to build the Trans. here at my home so you can come here to assemble the Trans. My roommate will assist, and he will install the Trans. in the vehicle. If anyone knows a Trans. Mechanic that can handle this job let them know I have a side Job for them. Mike: can be reached at crpt428@yahoo.com. P. S. If I must build it myself (with my roommate) Than it would be nice to have someone to ask questions as they come up. Mike out. |
The TH400 is probably "the" easiest-to-overhaul automatic there is. All the clutches in the front, all the gears in the back, and no pistons in the case. Maybe the worst part of the whole assembly is getting the forward clutch to engage with all the direct-clutch plates.
Make sure the one-way clutches go back together correctly--spinning one way, locking the other way, but both ways CORRECT DIRECTION. I'd install a TransGo shift kit. Be prepared to MAYBE install a governor tuning kit once the trans is back in the vehicle and tested. The ones I build, I plug a certain hole in the valve body, and leave out a seal in the Direct clutch, so that both chambers of the Direct clutch piston apply area are used--more surface area, firmer hold on the clutches. "I guess" the same thing can be done by leaving off a sealing ring on one of the shafts...but I've never researched that. |
I too have been reading all the different ways to rebuild this Trans. However, keep it simple this is my first one I am doing. Those people racing are making Manual shift and Trans. braking, I am just looking to build this one above stock with the Torrington Bearings. I had damaged my Torque converter and replaced it with Hughes recommendation unit. I got reverse but no forward gear and the 1-2-3 gears have low pressure.
I think I ran it too long testing and tuning it as I went through all the easy stuff like Replacing the oil Filter, R+R the valve body, detent Solenoid, Governor, Vacuum Modulator, Pump Regulator and Boost system, Servo's front and back with their perspective Accumulators. I feel by running the Torque Converter with a leak and a bad bushing for an additional 300 miles put the Trans. over the edge. The low pressure caught up with me. Sometimes I was making progress then one day I just made it home as forward gave out. So, I install the new Hughes T.C., and I still don't have forward, why? By the way I cleaned the small Governor Screen and flushed out the Trans. and the Radiator and the remote cooler too. I added Trans fix and that got me the 300 miles, I think. I would go out 50 miles and come back. I did this 3 times, and the last time coming home was like being in second gear. What I need here is a forum member who knows Transmissions like a pro and better is that pro. Please help I am at wits end here. The last resort is me building this trans., I am not afraid too but if some here in south Florida wants a side job, let me know. Even a Trans. tech would be better than me and he could come here to build it and my roommate will install it back into the car. Soon I will have to take it apart to see inside for myself what is wrong, but I still want a pro to reassemble it. |
Pro TH400/4L80 hack: inspect the Center-Support for SunGear Shaft-to-babbit Bushing play. Any play means a new $10 bushing is needed.
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"Even a Trans. tech would be better than me and he could come here to build it and my roommate will install it back into the car. Soon I will have to take it apart to see inside for myself what is wrong, but I still want a pro to reassemble it."
IF you are going to hire the work done leave it together. The standing labor rate here is $60 per hour, $70 if you watch. $80 if you help and $100 if you tried first and couldn't! Don't deliver a "basket case" to someone to put the jigsaw puzzle back together. There is no guarantee it was done correctly the first time. An experienced builder wants to take it apart and study the assembly, checking each part as he goes to look for correct assembly, correct parts used, problems and reasons it wasn't working well/failed. They do not want a bare case and a box full of parts and deal with all that drama. Sure, some have the expertise to build it from scratch but it's ALWAYS better to do the entire job vs starting in the middle someplace and/or going in behind someone else who couldn't complete the work....FWIW........ |
[QUOTE=Half-Inch Stud;6316633] Pro TH400/4L80 hack: inspect the Center-Support for Sun Gear Shaft-to-Babbit Bushing play. Any play means a new $10 Bushing is needed.
I plan on R+R-Ing all the Bushings, while I am in there, "why is that particular area your diagnostic"? So, I can learn something please. Mike out. P.S., Cliff, I recognize your name all over Forums and Internet. You wrote the book on TH 400 Transmissions. Now that I have a reliable source, could you explain "why I lost all the Forward Gears please"? I have been following people like you for the past 10 years as I have been working on this second-hand Project and learned a lot of valuable information and I would like to thank you. I own a 1979 Pontiac Trans Am with a 1967 Pontiac 428 ci HO Engine with a 1966 Rochester Tri-Power 2bbl carbs over the 1966 GTO Intake Manifold made of cast Steel. The TH 400 is backed with a Gear Vendor unit and a B+M Shifter. All was well, until I ran over A root under a paver driveway and because the car has been lowered this event destroyed the Bushings in the old T.C, I must be careful going over speed bumps. This event that damaged the Torque Converter was unforeseen and costly. Mike out. |
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Never tried them or saw the need for an upgrade in that area. There are a few places in the TH350 and TH400 to use a wider bearing and I suggest that upgrade where it applies. The OEM long center support bushing had a babbit coating and many would show considerable erosion of the material in really high mileage units. A coated or harder surface bearing wouldn't be a bad idea in that location....IMHO.
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I won,t run a offshore center support. It has to be GM or say Clevite on it.
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You have reverse, but no forward gears?
I suspect Forward clutch seal, or a leak in the oil circuit supplying the Forward clutch. |
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Story: Some fella's Chevy truck/van with a 4L80 lost drive ( maybe 2nd too), and drove 1/2 hour home. It failed spectacularly near the home and the 4L80 was sold to a coworker who asked me to go through it. Could be a JEEP enthusiast..read on. Well, the FWD & Direct Drums were cooked black, the Center-support cooked, and the rearmost Planetaries went nuclear and reverted to weld fragments. Ya know, the fella wanted as much reused as possible because he is a Jeep guy, (it's a JEEP thing) so i restored the drums, center support, but for sure anything to do with the planetary section was replaced. The 4L80 is all together and waiting install to an on/offroad JEEP. FWD pack is fed thru the Front Pump and determines being out of Neutral, thus Drive. Direct Pack determines 3rd gear, and Reverse. Fed via the Center-Support seal rings. Intermediate Pack within the CenterSupport determines 2nd Gear, Fed via the Center Support MOUNT. Study of fluid passages is one tingk, yet the study of the "3-or-4" CenSupport Seal rings running off-concentric on the DirectPack- CenterSupport sleeving reveals great concern to all involved. You know, some racers and Street folks describe a vibration in drive at 60 mph or so, or the top-end, big-end of the track, and i tink that can trace back to a Direct Pack + FWD Pack running untrue relative to the Center Support via the bushing clearance went from slip-fit to 10 or 20 mils. Exciting times are prevented by the loss of fluid pressure to the Direct Pack to encourage a rebuild. |
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Mikes answer to this: Had I known as much now as then, when I destroyed my Torque Converter, plus if I knew it was the T.C that was affected then, I would have driven home in what seemed to be second gear and dismantled the Trans. right away. The problem is I knew nothing in the beginning. So, I drive 300 more miles testing and tuning while reading all about Transmission 101. Now, I fear the worst in that after reading your posts, I damaged Hard Parts within the Trans. Well, I will have to see, I will give some time to see if any one local will build my Trans. but I am not holding my breath waiting for him. Currently, I have the main rebuild kit and I am waiting for four more additional parts, that did not come in the main kit that are needed to rebuild this TH 400. The weather up North is slowing down deliveries or so I am told by UPS. In the meantime, your valuable input, will give me an idea of what to look for while were into this Trans. So, thank you for all your advice and if anyone has any more input, I am all ears. Mike out. |
The converter is the TH400 canary: the stock Converter sprag splines can loosen and send grit into the TH400. Also when the converter makes a chimey cowbell ring upon pullaway the end is near.
The TH400 guts usually survive a conveter gone bad, but the fluid would be milky-pink, not red. The parts cleaning can be a challenge for a milky-pink situation. |
Tradermike,
Since your torque converter was damaged by impact, this will not be a normal rebuild. Depending how badly the hard parts have damaged you might be better off finding a core to rebuild. Also double check run out on the flexplate before installing your rebuilt transmission with new converter. |
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Mikes, Reply: I bought a remote Transmission Filter, Should I install it before the Radiator Heat Exchanger and next is the Remote air-cooled Oil Cooler?? This should keep debris out of them in the future, in the event I have trouble in the future. |
Well that sounds good and correct, however i never did that even though wanted such a filter when i had a converter go pink fluid on me in the mid-80s.
Solution is to invest in a good converter, then the remote filter is rendered moot. As for gray silt and cluch debris i recommend the fabric filter in the rebuild, then after about 300 miles remove and replace with the screen filter. |
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look into the filter inlet to witness a stiff fabric or a screen.
The "stiction" is usually powdered metals and clutch friction powders, from normal wear. Drawnback to dirty fluid is an eventual clogged fabric filter. Story: i drove a cooked TH400 (in a GTO i bought) where the fluid was burnt dark brown with pepper specs and sure smelled burnt. Even went drag-racing to get performance data before swapping engine/trans. Well the FWD frictions were burnt and Direct clutches were completely burnt down to the metal yet the TH400 behaved as if it was fine. The rebuild went just fine, and surely got my re-programming to avoid burning anything but tires. |
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