The Stovebolt Site Forums The Shop Area Engine Shop TH-400 rebuild question

Wondering if anyone has any advice?

I have a TH-400 with probably no more than 120,000 miles on it. Although it still works fine, a rebuild is in order because 1: it's a project truck, 2: the last time I opened it for filter/fluid there were 2 metal chunks in the pan (about 3/16" slightly curved as if a shaving from something the size of 1/2" pipe) and 3: On sub zero days there's a "turbine" sound in 2nd until it heats up. My question is, when this tranny is rebuilt. Is it good as new or do they just throw in new friction materials? I understand that the main guts are reused - gears, drum, valvebody, etc, etc... But are there bearings/bushings/other things that are just "left in" (like when you swap a cam and the bearings stay in the block) so that for example if you kept rebuilding the trans every 150,000 miles by the time it gets to an aggregate of 900,000 it's going to be junk anyway - or can they just keep being rebuilt indefinatly?

Also, for long sitting periods, winters and the like. Anecdotally I've heard that auto trannys don't like long periods of sitting in the same position because parts of the clutch packs become dried out while others become saturated with fluid. Does anyone have any opinion on this? Are there any negative effects to long storage times?

Jim.

If you have a pro shop rebuild that 400, they will disassemble it and carefully inspect every part in it for proper fit. If there is any doubt about any of the hard parts or bushings they should be replaced. Usually a bushing kit is a very good investment in any transmission job, and if there are chunks breaking off of something it should be replaced. Ask around about shops in your area and ask them how much to disassemble it and to give you an idea what it will take to rebuild it. Like an engine, you really won't know how much until everything is cleaned and checked. Most anyone can throw the frictions and steels in one, but that won't last long if there is anything else that is bad. Get ready, it probably won't be cheap, but a 400 is nearly bullet proff if done right. Good luck

I've been building various automatic transmissions since 1958, when I sat in on a class my father was teaching for local mechanics on the Dual Range Hydramatic used in mid-50's GM cars. The Turbo 400 is one of the toughest transmissions out there, surpassed only by the Torqueflite 727. A good rebuilder will clean and inspect all the parts, and replace whatever is necessary to get it back into good running shape. On a high-mileage trans, replacing bushings is a good idea. Also, inspect the pump gears and housing for wear. Lots of whining noises can come from a worn pump, before the hydraulic pressure is affected. End play is important, determined by the thickness of the thrust washers used during assembly. One of the advantages of the 400 over other transmissions is the center support which locks into the case with a snap ring. Turbo 350's, 200's, etc, don't have that feature. It makes for a much stronger assembly. The 4L60 is the overdrive version of the 400, and it's even better.
Jerry

Thanks or the replies. The 4L60 may be a good idea. I've heard little about them - seems the 700R4? is the common one here. Not sure of 4L60 apps and production numbers, but I could certainly use the O.D. If they're found in the full sized vans then they'll be really cheap here as rotted running gas vans with under 75,000 miles go for about $400 here.

I wonder about attempting the rebuild myself. I'm not that intimidated by the idea - I work on much more complex and high tolerance equipment every day, but worry about the lack of specific experience and "grandaddy feel" for the tranny and what to really look for. I'd have to obviously rely on a very good manual, but there's nothing like the feeling of doing it yourself, Eh? I have the space and time. Does the job consist of (horribly understated) disassembly and parts replacement, or is there shop specific tasks that are simply beyond the scope of D.I.Y. to do it right? For example the bushings or machine work.

Litte, if any machine work is involved, and bushing replacement is pretty simple. There's a lot of "feel" involved in replacing the lip seals on the clutch pistons, and a lot of danger of nicking a seal during assembly and creating an internal pressure leak. Definitely seek out a mentor for the first 50 or so transmissions you build. After that, you're on your own! I have fabricated a bunch of home-made tools to assist in dismantling and reassembling the clutch assemblies, spring compressors, assembly aids for clutch piston seals, etc. The tools are available commercially, and shouldn't cost more than twice what getting the job done professionally should run. Plan on doing several transmissions for pay to recoup your investment if you go that route. One final tip- - - -use LOTS of petroleum jelly during assembly. It's impossible to get the parts too slick! Lube all the clutch plates by soaking in ATF for several minutes prior to assembling the clutch packs.
Jerry

Ditto what Hot Rod said.

I did think the 4L60 was a league of it's own with the 4L80 being the overdrive version of the TH400, they share several components. But I have been wrong many times before.

I think that's correct, the 4L80 is the OD version of the 400. Dang! Once, long ago, I thought I was wrong, but I was mistaken, I think!

Jerry

It sounds like for the most part you're recommending against giving it a go on my own. My experience has been that "machines" don't simply work by "FM" and I'm usually inclined to tear into them with the "worst that will happen is that I'll have to bring it somewhere anyway" attitude. A long while back I tore two Saginaw steering boxes apart in hopes of matching the input shaft I needed to the case/output I had. Went fine and is still in service. On the OTHER hand; Last month doing a Velvet V-drive (Borg Warner boat transmission) re-assembly, another guy showed me how I had a case plug (with a kind of crush sleeve that preloads an idler shaft) too loose. He corrected it by feel and told me that the drive would have killed itself within a few months the way I had it. That's the scary part for me. If I attempted a job like this and it just didn't work, then that's one thing. You can either go back in or cart it to someone else. However if your hard work appears fine but eats itself alive in 5000 miles because (say) a clutch servo piston wasn't applying properly... Well, the kit here is nearly $1000. A shop rebuild is $1300. Know what I mean?

Did some Googlin' and suddenly don't even care about the rebuild anymore as the 4L80E seems to be a beautiful option. I can deal with the "E" no problem, this appears to make them less desirable (and cheaper) anyway and I really like the idea of an O.D. The only thing that I didn't find (yet) immediatly obvious is any issues concerning bolting one to the back of a 292. Moving the crosmember isn't an issue assuming the tail mount is the same "heigh"? and I assume the bellhousing is the same ol' chevy pattern. What about the converter though? My ring gear/converter has 6 metric fasteners that go throught the plate into tapped blocks welded onto the converter. Will the 4L80E converter mate to the original 292 flexplate?

I think it would be prudent to mention the possibilty of metal chips being present in the rad cooler. Some like to replace the unit and other rely on a flush?

I think your gonna need a computer to use those overdrives in an old truck.Mine has about a dozen wires coming out of the valve body. They have kits for the 700r but i don't know about the 4L80 and 4L60.

http://www.tciauto.com/electronics/index.htm

jim......
$1000 for an automatic trans rebuild kit??? I know things are more expensive in Canada (used to live there) but $1000 seems real high. I have rebuilt TH700's, 400's, 350's and a few non GM types and the kits I buy always cost around $60 from my local auto trans parts store (Rayco). Having to buy a band, some bushings, or a rebuilt torque converter can push the cost up to maybe $200.

BTW, how are the Ti Cats doing these days?

Cats won last night. I'm about 1000ft from Ivor Wynn so I didn't get much sleep after 17 hours of work.

yeah, I thought 1K$ was a bit brutal too, but I'm finding it's hard to find much of anything around anymore here. I've needed two seperate bushings for stuff recently, and you just can't get some things. You have to buy an entire assembly or part. Hell, I've tried maybe 30 or 40 carb shops trying to get a VERY common metering rod and seat and all they have is gasket kits. GM doesn't even have them and wants to sell me an entire monojet for $750. (Yeah, right.) Although with such a large difference in the tranny kit ($60 - $1000) something isn't quite right.

Computer for the "E" won't be an issue for me. That kinda thing is my "real" job and I was planning on having to build a custom controller.

You should look into that TCI controller. They're a good company, and they've been around a long time. I got a guided tour of their facilities a few years ago from one of the owners of the company, and I was very impressed. If they're selling it, they have done considerable research and development, and it's probably very reliable.
Jerry

Thanks Jerry, It's not that I have any issue with the company, product, or parting with green but that as an electronics geek I actually LIKE building my own FI/ECM computers and controllers!
Jim.