To Rebuild or not to Rebuild TH400

[4bogginchevys]

Ridiculous, Here I can buy a HD 400 for 700 w/exchange....you could fly here, pick one off the shelf, take it to UPS, and fly home for cheaper than than some of those quotes! I'd say e-bay. Shipping is only 100.00 from just about anywhere within the continent. Good luck

 

[Coal Cracker]

I've rebuilt all types of GM transmissions, and agree that the 400 is one of the most durable trannies , I will run nothing less during a demo derby. The 400 is a snap to rebuild, you can get kits with or without steels, my advice get yourself a th400 trans rebuild book, and look it over, there are plenty available on amazon.

pull it apart first and look for blueing, charring on the steels, it will be visible you won't have to look hard, minor wear is ok and you'd be bettrer off using the old steels, to maintain a proper clutch pack thickness.

the only specialty tool you'll need is a clutch pack compressor, you can pick one up fairly cheap on ebay.

Then order a seal kit, reman torque converter ( I like Dacco's ) dont get a trailering converter or a high stall, stick with a stock stall.

also order up a modulator, and a shift kit if you'd like. I like the trans go Gil younger kit, I'ts not teeth shattering hard, like a b+m but it's more a shift improver kit.

Allmost forgot, when you pull the pump off the case look at the pump ring and make shure that there's no deep wear gouges, a book will tell you what feeler guage to use to check, I'm sick as a dog right now, and can't remember what thickness is needed.

Once you're stripped down, take the case to a car wash, and clean, clean , AND CLEAN MORE, leanliness is a good key to putting a trans together.

It looks intimitatingbut I pulled one apart at 16 and it's still taking 455 abuse in my GS.


What are the symptoms, you may not need a rebuild???

A good trans part source is Transtar Industries, I know they have locations all over the us, I deal with their Lancaster Pa. branch, and they ups me the parts.

 

[Amtracker]

Well that's the thing... I don't work on this myself, so I don't really know what I'm looking at. Someone will have to work on it for me.

This was my daily driver. When I put the the vehicle in Drive, it won't move immediately, but eventually it will move slowly. The engine is revving, but I am not flooring the pedal. I'm afraid to. So, it will go, but it will only go up to about 35mph, 40 tops.

Does the TH400 have Overdrive? I don't think it does.

I've rebuilt all types of GM transmissions, and agree that the 400 is one of the most durable trannies , I will run nothing less during a demo derby. The 400 is a snap to rebuild, you can get kits with or without steels, my advice get yourself a th400 trans rebuild book, and look it over, there are plenty available on amazon.

pull it apart first and look for blueing, charring on the steels, it will be visible you won't have to look hard, minor wear is ok and you'd be bettrer off using the old steels, to maintain a proper clutch pack thickness.

the only specialty tool you'll need is a clutch pack compressor, you can pick one up fairly cheap on ebay.

Then order a seal kit, reman torque converter ( I like Dacco's ) dont get a trailering converter or a high stall, stick with a stock stall.

also order up a modulator, and a shift kit if you'd like. I like the trans go Gil younger kit, I'ts not teeth shattering hard, like a b+m but it's more a shift improver kit.

Allmost forgot, when you pull the pump off the case look at the pump ring and make shure that there's no deep wear gouges, a book will tell you what feeler guage to use to check, I'm sick as a dog right now, and can't remember what thickness is needed.

Once you're stripped down, take the case to a car wash, and clean, clean , AND CLEAN MORE, leanliness is a good key to putting a trans together.

It looks intimitatingbut I pulled one apart at 16 and it's still taking 455 abuse in my GS.


What are the symptoms, you may not need a rebuild???

A good trans part source is Transtar Industries, I know they have locations all over the us, I deal with their Lancaster Pa. branch, and they ups me the parts.

 

[akonitony]

I'm not trying to be a know-it-all, and most people who do know me will agree I'm not the absolute sharpest knife in the drawer, but in the instructions for the Transgo kit, Gil highly recommends to replace the steels with every rebuild even if they look ok. His reasoning is the TH400 is very hard on the steels.
TH400s are three-speed autos without overdrive. Don't worry abouit any questions you might have. I remember my first build on a TH350 way back when the dead sea was only sick. The guy in the stall next to me helped me pull it out by giving me verbal directions while he worked on his own car - we were in the army garage where you can borrow tools and all. Anyway, the conversation went something like this:
Guy: First you need to pull off the flexplate cover.
Me: Right! What's a flexplate cover?
Guy: Next you need to take out your TC bolts.
Me: Right! What are TC bolts?
Guy: now drop your crossmember.
Me: Right! What's a crossmember?
Guy: Now take out your bellhousing bolts.
Me: Right! Where is the bell located?
Anyway, you get the picture. The only way you will ever learn is to dive in or at least wade a little. I once saw a sign that pretty much made perfect sense to me: 90% of what I have learned came from making mistakes. You can take apart one of these transmissions with a metric socket set and a pair of snapring pliers. The pump can be a little tricky if you don't have the puller for it. I once bumped it out by attaching a chain run through the hole of a 12-pound sledge hammer head, and using that like a slide hammer. The center support bolt can be a little tricky in that you will need a very thin-walled 10mm 12-point socket, and when you reinstall it, tou need to preload the support against the case lugs with a screwdriver as you torque the bolt, or it can damage the case later under high-torque loads.
Get you an ATSG book off ebay for about $15, and look it over. If it seems like rocket science, then maybe you might want to consider having someone else build it and ask if you can watch. Lastly, I wouldn't rev it if it is not engaging firmly as all you are doing is making things worse. if you do rebuild it, a good rule of thumb when inspecting surfaces is to drag your fingernail over it, and if it catches a groove, the part is more than likely needing to be replaced.
Hope this helps.

 

[wallew]

Call your local police force and ask to speak to whoever is in charge of their cruisers. Then ask that person who rebuilds their transmissions. If it's a shop that does everything transmission then they're usually pretty good. Cop cars see a lot of trans abuse so the shops that do their work usually know their stuff.

Sorry to bring this one back up from the dead. BUT if contacting your local PD is not an option, CALL YOUR LOCAL CAB COMPANY.

They drive the same cars, 24x7 and are AT LEAST as hard on them as the police are.

So, call your local cab company and ask to speak to a mechanic (explaining nicely all the while) and find out who THEY use to rebuild their trannys.

If they use a local company, go check them out.

And I've been researching and I have a spare TH400 and I'm going to rebuild it late this fall, early this winter. I also have an NP208 rebuild on the schedule. And if I get REALLY ambitious, I'll take a swipe at my 6.2L in the can for a rebuild.

One step at a time. Rebuilding it all teaches me so much, I figure the education alone is worth the extra time.

And hey, I've got three CUCV's. So there should at least be ONE of them running at all times. And that's why I have the spares that I want to rebuild and then just tuck away against the day I have a failure. Because with three CUCV's, sooner or later I'm gonna need those rebuilt drive train parts.

 

[bronconut]

so i went and found the video i bought to rebuild chev trans, but its only for the th350. Its pretty good at walking you thru a rebuild, dont know how similar the 350 and 400 are, but if you would like i can try and find a way to download a vhs, other wise there might be a video out there some place.

 

[akonitony]

The TH400 is easier to build than a TH350, IMHO, in that the low/reverse piston on the TH350, which is the same exact piece in the 700R4 BTW, requires a special compressor tool to remove the snap ring holding it in place. That snap ring is sometimes tricky to put back in for the beginner. Probably the most difficult part on the TH400 would be the center support. They make a tool for holding it when you drop it into place, but I use a rag and then make sure there are is no lint left on the end of the splines when I am done. It is also important to preload the support against the case lugs while tightening the support bolt. Overall, the TH400 is the easiest trans to rebuild of them all. Just go to ebay and order an ATRA rebuild book here:

TH400 / TH 400 ATSG SERVICE / REBUILD MANUAL OVERHAUL: eBay Motors (item 7999945396 end time Sep-16-10 12:18:51 PDT)

 

[Chevybrit]

Resurrecting this again .. I maybe needing to rebuild my TH400 and if so I'll be doing it myself

This looked very helpful and as some of the inks on this thread are dead.. it might be useful in the future

Tear down Pt1
https://www.youtube.com/watch?v=IA22ibPoccQ
Rebuild Pt2
https://www.youtube.com/watch?v=ojgdV9TCBNc

 

[Chevybrit]

Rebuild vid is incomplete but have found this one with instructions although the audio is a little thin..

https://www.youtube.com/watch?v=clv7Q6KmEWc

Rebuild KITS
Is this a good deal then?

http://www.onlinetransmissionparts.com/MRK3400A-UT-p/mrk3400a-ut.htm

 

[rustystud]

Rebuild vid is incomplete but have found this one with instructions although the audio is a little thin..

https://www.youtube.com/watch?v=clv7Q6KmEWc

Rebuild KITS
Is this a good deal then?

http://www.onlinetransmissionparts.com/MRK3400A-UT-p/mrk3400a-ut.htm

I use "onlinetransmissionparts.com a lot. Good company. As far as getting the "good parts" though you will need to go elsewere.

 

[Chevybrit]

I use "onlinetransmissionparts.com a lot. Good company. As far as getting the "good parts" though you will need to go elsewere.

Pray Tell? What are the GOOD parts that thou speakest of??

 

[Chevybrit]

Rusty, the oil pan shape is different in that kit from online transmissions.. ours has the rectangular one. Is this model called something different or are there many different TH400's??

 

[rustystud]

Rusty, the oil pan shape is different in that kit from online transmissions.. ours has the rectangular one. Is this model called something different or are there many different TH400's??

All TH400's use that odd trapezoidal shape oil pan. If the one your looking at is square then it is most likely a TH700R4 or even a TH350. Now there are 3 different TH400 pans but the differences are just the "dimples" in the pan. Also the depth of the pans can be different but never the overall shape.

 

[rustystud]

Pray Tell? What are the GOOD parts that thou speakest of??

Kolene Steels, high performance fiber clutches, Kevlar bands, Torrington bearing upgrades, bushing upgrades and so on. Also "Sonnex" sells really good valve upgrades like there main pressure regulator valve and spring.
Just go to "COAN Racing" parts and check out what is available for the TH400. That is just one store I use. There are several others that sell HI-PO transmission parts.

 

[Chevybrit]

So I answered (A) and went ahead and rebuilt my TH400 ... I found a few more good Utube resources to help prep me first. Once i'd watched them all I pretty much knew all the pieces by name and the basic functions of them. Taking it apart was much less of an ordeal when you know what to expect. I did spot my issue almost immediately.
The front accumulator piston was cracked (it was the plastic type) and hence the pressure was insufficient for the 3rd gear shift. I got a seal kit from onlinetransmissionparts.com
so the cost of the rebuild including steel/gasket kit, oil/filter and cleaning products was $260.

 

[Chevybrit]

If anyone is interested here are the other links on Utube along with the ones I posted above.. I'd say the biggest issue is not to be intimidated..In the end its just nuts and bolts.
You can see I used an 8x4 board up on saw horses and I laid out every piece as it was dismantled. Pump-forward clutch- inter clutch etc etc including the snap rings. I then disassembled each item separately and laid it back up on the table ready for final assembly. I found the manual very vague as to the positioning of things like the snap rings which are crucial and the lining up of the items when installing back in the case. The videos at least for me, bring it all to life.

https://www.youtube.com/watch?v=nkN-5OL-DuA&index=2&list=PLAqmfyCcPJ7I6EPWkbfueRypIvk5kFS-V

There are 14 parts and all are worth watching.

https://www.youtube.com/watch?v=_TMFibSiwVw

There are 2 parts to this strip and build and there are shots in this one which offers different views that can be very helpful if your looking at something specific (which you will at some point) Also combining them will help you look for damage and how to spot it Ie case damage or modification which someone might have done to the valve body assembly (common).
Great feeling to have got this far into the CUCV and its up and running great!

Hope this helps..

 

[rustystud]

If anyone is interested here are the other links on Utube along with the ones I posted above.. I'd say the biggest issue is not to be intimidated..In the end its just nuts and bolts.
You can see I used an 8x4 board up on saw horses and I laid out every piece as it was dismantled. Pump-forward clutch- inter clutch etc etc including the snap rings. I then disassembled each item separately and laid it back up on the table ready for final assembly. I found the manual very vague as to the positioning of things like the snap rings which are crucial and the lining up of the items when installing back in the case. The videos at least for me, bring it all to life.

https://www.youtube.com/watch?v=nkN-5OL-DuA&index=2&list=PLAqmfyCcPJ7I6EPWkbfueRypIvk5kFS-V

There are 14 parts and all are worth watching.

https://www.youtube.com/watch?v=_TMFibSiwVw

There are 2 parts to this strip and build and there are shots in this one which offers different views that can be very helpful if your looking at something specific (which you will at some point) Also combining them will help you look for damage and how to spot it Ie case damage or modification which someone might have done to the valve body assembly (common).
Great feeling to have got this far into the CUCV and its up and running great!

Hope this helps..

Good job ! You can buy "aluminum" accumulators if you so desire. That way you never have to worry about it cracking again.

 

[Chevybrit]

$10
http://www.ebay.com/itm/TH400-Valve...ash=item20f64196f7:g:u94AAOSw8d9U2VZM&vxp=mtr