2. GM TH400 Rebuild: Front Pump and Drums

[@TheEinart]

Really like your video quality, good camera, sound, and good spec talking. Keep posting 😃

[@nickstransmissions]

Thanks, man and will do.

[@6xcchamber971]

Nike in your other video it appeared that you used Allison clutches, is this correct and if so where can we purchase them? Great job!

[@nickstransmissions]

Thanks, man - appreciate the kind words...Can you specify which video? I don't build Allisons (yet) so don't recall using Allison clutches in anything but perhaps I did without realizing that they were also Allison-spec. -Nick

[@alaskasquarebodyrescue2125]

Thanks for the great vids, Your careful attention to & clearly explaining the details is very helpful, for us less experienced builders! I am building a TH400 for my gas engine square body Chevy. My donor tranny was originally out of a diesel pickup and I am having trouble finding out what I need to change, when installing into my gas engine pickup. Some thought the governor, valve body and input shaft for the diesel converter were all different but not really sure? Are you familiar with this, Any insights would be very helpful!

[@nickstransmissions]

You're welcome! Diesel vs Gas: 1) Governor - purchase a new one for a gas engine 2) Vacuum modulator - purchase one for a gas engine 3) Torque converter - purchase a factory high stall (one row of slashes on the converter body instead of two) or an aftermarket high stall if your engine's cam manufacturer recommends a higher stall speed for your cam's grind 4) Kick down solenoid - purchase a new one if yours did not come w/one 5) Valve body - should be fine as is, assuming nothing is wrong with it AFAIK, those are the only meaningful differences between a diesel and gas engine application. Couple other things I would suggest: A) Determine intermediate roller clutch on the direct drum. If it's an 8-roller style one -way clutch, I'd recommend replacing that drum with one from an earlier TH400 that took a 16-element dogbone style sprag (replace the sprag itself w/the Borg Warner 34 element HD sprag) or retro a 97+ 4L80E direct drum w/the same BW 34-element HD sprag. B) Inspect the forward hub - replace w/a billet rollerized one if damaged or if your truck has 500+ HP and/or will see 5,000 rpms or more on a frequent basis.

[@alaskasquarebodyrescue2125]

@@nickstransmissions Thank you for the reply and the good info!

[@ijteague]

Do the pistons come in different thicknesses? I tore one apart and it has a dished steel at the bottom where the wave plate would go. If I replace to a wave plate, I am way off on the play. I have way too much even with all thick steels.

[@nickstransmissions]

Hi Jason, which drum are you seeing the dished steel (sounds like you are describing an early 4l80e bellville style cushion plate)? Ill have to double check my notes/info to confirm/deny this definitively but I believe they’re all the same height/thickness in most applications except for a few that received one more clutch and steel in the direct drum.

[@ijteague]

@@nickstransmissions I am rebuilding a TH400. its a 1989 according to the plate attached to the side. both drums had one at the bottom instead of a wave plate. Can I put a flat steel on the wave plate then a friction? If I do that ill get my desired play as I been trying all combinations.

[@nickstransmissions]

Yea someone put those early 4l80e belleville plates in the drums. Yep, place a flat steel on top of the waved th400 steel and go clutch-steel-clutch until they are all installed. Directs take .090 thick steels while forwards are .077 IIRC.

[@skutahuniai4830]

Minor critique but you have the ends of the snapring on the direct drum on a retainer rather than the ends being between retainers.

[@nickstransmissions]

Thanks for pointing it out To be honest I’ve assembled countless transmissions before i started checking the orientation of the snap rings holding return spring assemblies so occasionally one slips through. It should be fine - I’ve actually never had one come back due to the snap ring popping out. That said, the optimal position for the ends is between the locking bosses, as you’ve pointed out. Thanks again for watching!

[@skutahuniai4830]

@@nickstransmissions 👍

[@designsinorbit]

I have a great question for ya... I'm installing a 2500 stall converter and it's going to be really close as to whether I'll be able to hold an idle. The manufacturer said it's probably OK but couldn't guarantee it. My question is- might there be something I could do to the TH400, while I have it on the bench, that would help the situation?

[@nickstransmissions]

Nothing to the TH400 itself but if your cam is big enough, you will likely need an auxiliary vacuum pump to ensure you can supply enough vacuum to the brake system and modulator on the transmission. Otherwise neither system will function correctly (brakes obviously being the much more important of the two).

[@6xcchamber971]

Would you not keep the centre drum seal out if you are dual feeding it?

[@nickstransmissions]

Yep, which is what I did in the video starting at roughly 27:10 Are you watching it on your phone? Asking as I just watched it on mine and it does look like there's a seal in there (I had to zoom in to tell there wasn't) but after checking the vid on my computer it's clearly left out and I do talk through leaving it out starting at the 27:10 mark.

[@6xcchamber971]

I meant on both drums! Thank you!@@nickstransmissions

[@nickstransmissions]

You're welcome, man...Forward drum center seal has nothing to do with dual feeding. It's intended to soften engagement into drive. You can leave it in or out...

[@6xcchamber971]

Thanks!!!!!!@@nickstransmissions

[@johnnybrigham8154]

Nice job on pump what brand clamp are you useing? Very nice work jb.

[@nickstransmissions]

Dont recall the brand but bought it off ebay several years ago. A very large hose clamp can also be used but the specialty tool is more efficient.

[@johnnybrigham8154]

@@nickstransmissions hi again johnny here I cant find even one pump alinment tool with knob on ebay would you remember the seller? Or have the link thank you.

[@nickstransmissions]

I also just checked eBay and only see the alignment tools with the wing nut; same with Amazon and a general G-search. Unfortunately I don't recall the seller as I've had that tool for at least five years (probably longer).

[@johnnybrigham8154]

@@nickstransmissions ok thx theres no name on it any were? Can you please help and send them 3/8 cup plugs 4 pls you do nice work thank you jb.

[@nickstransmissions]

Thanks JB…there’s no identifying marks on the tool. Not sure what you are trying to say regarding the cup plugs…

[@designsinorbit]

Do you think this is an upgrade that needs to happen for a 575hp car?

[@nickstransmissions]

Depends on how it's going to be driven. If like it's stolen and on a reg basis, then yes. If only raced occasionally but otherwise a cruiser (and you're we're talking 575 horsepower at the crank, not the wheels) then you may be able to get by with a 4L65/70 drum with the factory induction-hardened input shaft with the Sonnax internal reinforcement kit.

[@designsinorbit]

@@nickstransmissions Woh. So you're saying if I beat on this occasionally I need a different drum, input shaft, and a reinforcement kit?

[@nickstransmissions]

Im sorry - ive been answering lots of questions about my 4L60e high performance vids and was thinking that's what you were working with but just realized you're asking about a TH400, lol. So no, you do not need anything of the sort for a th400 at less than 650-700 assuming full race. Beyond 700 i would suggest a billet input shaft for the th400 and beyond 900, a full up billet drum/shaft and lots of other things. Dual feeding the direct clutch, billet forward hub, sonnax boost valve, rollerize rear case and 34 element sprag, small .045-.055 bleed hole in dir drum for 5000+ rpms, blocking the 2-3 accumulator and drilling the separator plate per your stall speed and use is sufficient for a sub-600 hp application. Sorry for the confusion

[@nickstransmissions]

Did my clarifying response help at all?

[@designsinorbit]

@@nickstransmissions Oh sorry... KZbin didn't inform me you responded on that last message. Anyhow, yes, thank you for the clarification. I will need to research each one of your suggestions except for the rollerizing which I've got down.