i've never rebuilt an automatic trans, but now is the time. it is in operational condition, but i want to open it up and check things out.
first, what's a good manual that would be suitable for a first timer, and second, what usually goes wrong and how is the condition of these parts checked without road testing? wish me luck!

 

http://video.boxwrench.net/transmiss...amatic-400.htm

 

Rebuilding an automatic transmission properly is not something you do well the first time out using a manual. If you are a 'seasoned' mechanic with lots of tools and experience on engines/differentials/accessories, you might have a decent shot at being successful with your first try. But, there are so many details to take into account and critical disassemblies/reassemblies of sub-assemblies in that mechanism that you have better odds of having a significant problem than succeeding. Now, if you have someone who is experienced to work with you or to advise you, your odds of success will increase.

If you were to ask for a recommendation whether you should rebuild it yourself or drop off your tranny at a reputable shop for rebuild, I would offer that you should go for the rebuild....hands down!!!

Good luck, either way...

 

*Normal* rebuilds on T-400 aren't too bad.

The things to pay attention to are obviously the soft clutch linings and seals. Keep all the old steels until it is completely done. Some trans have *wave* plates in the clutch packs that soften the shifts. Replace those with a regular steel one. You'll need to ck the manual for the clearances in the packs..but tighter is better..right before they drag. Like .020" or so.

You'll need to ck all the bushings internally (or just replace). You'll need a good bushing driver set.

Ck the sprag assy closely and if you're going to use it hard at all...I'd install the 34(?-can't remember exact count) element sprag vs the stock one with 16 or so. Pay attention to the orientation of the sprag assy's. They are designed to spin one way and lock the other. They can be flipped and things don't work too well that way.

The band assy is typcally in decent shape..but many kits come with one anyway. Do some reading on lining materials. Stock stuff will take a lot of abuse..but there is tougher if needed. The lower end gearsets typically have no issues..just again...ck the bushings in the case.

Replacing all the lip seals is pretty simple. They make special little tools.but you can use a feeler gauge, a thin flexible butter knife or whatever works best for you. Some look like a paperclip looped to make a piece to compress the seal as you install the piston. you just slowly work your way around it until it drops in. You'll use air pressure to test the clutch pack operation during assy.

You'll need a spring compressor. The one I have works great. It's a universal sort of tool that is basically two long legs made of slightly bendable shafts that lock into the upper snap ring groove of the clutch pack and a screw **** at the top to compress the pistons to install the c-clips over the sprign retainers.

You'll want to take the pump assy apart to replace the pump bushing for sure(causes mystery front seal leaks if worn) and ck the gears and housing. Typically OK..but you have to ck for scoring. You have to align the two pump halves before tightening the bolts. A couple of long hose clamps joined together that wrap aaround the pump and aligns the halves is cheap and works perfectly.

Replace front and rear seals and if there is an O ring on the output shaft..make sure to replace it also.

I'd install a *street strip* shift kit. No need to take valvebody all apart during rebuild. Just install the shift kit while you're there. Simple ones from B&M etc work great.

Ck modulator real close. If there is any trans fluid showing at the vacuum port-replace it. Get an adjustable one (usually smaller) so you can play with it.

Be very careful with the governor assy. Slip it out, wash it off and ck operation. Work the weights while looking at the internal piston move through the visible slot. If all is free...carefully bag it up and leave it alone until ready to install. Soak it with trans fluid before storing it. They don't like dirt.

There are some real simple tricks to making a T-400 into an animal. You can leave the middle seal out of the direct/reverse clutch pack, plug a hole in the case and leave off a couple of shaft rings and that sucker will go into high gear with a killer feel and hold a lot more power because it will use the whole piston to apply it instead of just half of it. Once you get those parts in your hand you'll see what I mean. Now it's also going to hit reverse hard...but it really helps high powered stuff.

There's more...but this will get you thinking. Other than a compressor, the lip seal tool, an air supply and the bushing drivers...there's not a lot you'll need to get back in business.

For a book..I'd ck one of the halfprice bookstores. There are always great OEM manuals that technicians give up. Grab a drivetrain manual from even back in the 70-80's even for a pickup truck or something. It will have great picks, specs etc and flow charts. The nest there is!

JIM

 

get this video and all the tools needed like spring compressors and bushing drivers...

http://www.technicalvideos.com/video...smission.phtml

take your time ask questions....keep everything in order that it was taken apart and clean, clean, clean everything!

 

And that list of 'detailed stuff' is just the beginning. Every rebuild kit you buy will have tons of special instructions for whatever "vintage" transmission you have. Then you have to build all the clutch packs with correct clearances; and you have to completely disassemble the valve body and clean/check/reassemble everything exactly as it needs to be. Then, yada...yada...yada.... It goes on and on.

For the "pros" that do this kind of work day in and day out, it's no big deal. But, the learning curve on rebuilding auto trannies is very large and very long. Good luck to you if you go ahead with the rebuild. But you will be money, time, and grief ahead by having it done for you. Just remove it from the car, take it to the rebuilder, go pick it up and write a check, and put it back in the car and enjoy.

 

^^^ very good info^^^

 

Well...you CAN do it that way...just like dropping it off somewhere to get a new crate motor installed.

But I've always enjoyed learning how stuff works and knowing I can fix it. Now...I did do this stuff for a living at one time. When I was just getting started, I would pull auto transmissions out during the day and my boss would build them at night. I stayed with him after work to learn how they worked and soon I was having another guy pulling them for me and I was doing the building. It was cool to not be scared of them!

Just about everything inside a T-400 is to calm down the shifts. You can make them insane by defeating some of those features. I built one for myself once after dissecting the OEM manual flow charts that was getting 3rd gear rubber on part throttle shifts. Oops! Had to go back in tame it down some.

The T-400 is one of the best ones to learn on. They are pretty forgiving and don't usually wear out a bunch of stuff. Just study what to inspect and go at it. If you can assemble and engine, you can do an automatic. Remember, it was working fine at one time...you're not boring/milling and changing anywhere near as many parts in an auto as you do an engine build.

The first time you run it through the gears will be a fantastic feeling if you build it yourself! (assuming it works...if not..you'll definitely know how it works when you do it the 2nd time!). You'll have a skill that most of your buddies don't have.

JIM

 

thanks for the info. i'm going to give it a try.
can i use a regular engine stand to support the trans, or is there a special stand i need?

 

They make some that attach to the pan bolt holes and hang off a workbench. You're going to need to be able to get into it from the bellhousing area so it's tough unless you buy/build some sort of adapter to attach to center part. The dealers had a big *C* deal that encircled the trans at the center area.

You'll need the trans standing up on its end to *load* the guts into it. So that means it needs to be up off the ground so the tailshaft can protrude. I've done it with a hole cut in a table and I've used an old empty Muncie trans case also in a pinch. They balance pretty easily on end. Once all the insides are in place, you can lay it on a workbench and install valve body etc.

JIM

 

OK. If you're going to go for it, you will need some a way to fixture the tranny by standing it upright with the tailshaft down. That way you can disassemble from the bell housing down to the tailshaft. You will need lots for clean workspace...probably about 30-40 square feet of area so you can lay things out in an orderly fashion. You will need a way to wash everything down. Mineral spirits is the preferable fluid; you'll need about 3 gallons, unless you have a recirculating pump and filter setup. Petroleum jelly to lube the new seals, O-rings, bushings, journals. A bunch of lint-free cardboard or fiberboard bowls to put loose parts in until they are needed. Snapring pliers, ice pick, depth micrometer (or vernier caliper), a small press to compress clutch packs, and the usual assortment of general purpose tools.

Buy a good quality rebuild kit and a good transmission rebuild book. If you can find a copy of the Chevrolet Chassis Overhaul Manual for the year that trans/vehicle was build, it will have all the disassembly/reassembly info you need. I highly recommend that you find that manual and read through it before you make a final decision.

I applaud your "pluck" and sincerely hope it goes well. Good luck.

 

I've rebuilt a few by standing them in a 30 gallon barrel. Not real handy, but it works. I have the GM fixture for mounting the trans on the bench too.
ATSG has a really good manual to accompany the GM manual.

I'm a fan of the Trans-Go shift kits. Cheaper than the B&M kits (due mostly to the name branding I think).
Kolene steels, Alto clutches and kevlar bands- all run up the cost, and improve the durability.
AS 427Hotrod mentioned- the sprag is one spot that needs to be worked- the 34 element sprag is the stout one.
Read the books, keep it really clean, and proceed slowly. You can check the clutch packs as you build them with a rubber tip air gun and VERY low (5 PSI) air pressure.
If you want to get real crazy, find a rear planetary set from a motor home- straight cut gears- noisy, but really stout.