With your videos and the book. I finally built my own TH400. Thank you so much for all your knowledge. I couldn’t be happier it works like a champ and has been holding all the power I can throw at it!!
Just picked a th400 4x4 up last night , plan on using it in my chreokee with a small block 350 until I build a big block, these videos are full of great info
Hi Sean this is Chris from Wisconsin looking forward to doing the do it yourself to my chevelle 1970 454 th400 an old friend of mine helped me do one years ago but I forgot how to do it thank you so much for posting this now I don't have to call him it used to chirp second gear and third gear would hit very hard at 90 mph can't wait to do it to my Chevelle
Great idea on the dip stick mounting trick and not going all the way through. And repurposing the LS motor mount bolt. I'm stealing this! I use a 1/16" npt to plug the hole behind the pump, the tapered sealing makes me feel warm and fuzzy relative to a straight thread although it's probably just as safe.
I just got off the phone with my buddy who is 2 states away I'm going to bring him my 2 speed turbo 400 and have him put a manual valve body in it. And I talked to him about the 3 speed turbo 400 I blew I told him I was going to have him set it up with a trans brake he said he would have to see if he would be able to do it with that case because of some of the modifications he did the first time and what transbrake valve body I bought. If that won't work I'll have to find another case or buy a aftermarket case
Thanks for your awesome videos. What are some suggestions for a THM400 with a harsh reverse. Looks like the Transgo reverse kit just tightens up the reverse band and restricts the feed down to .090. Direct drum has the waved cushion with clearance set at about .050. Direct drum is not dual fed. Thanks for your time. Steve
On the black transmission I see there is a oil pan with oil cooler tubes in it. Does than pan make a difference with cooling or is it for show. Thanks, keep-up the great work.
Shawn can you use a vacuum modulator with out a governor, to control pressure when street driven?? Thanks in advance. Keep doing what you are doing love it.
Hey shawn, i did the first part of the video, on my sons s10 Transmission, it worked good, except i have to stay on the throttle a little to keep 3rd in, i bought a new modulator, adjusted it, same thing, decided to go full manual, pulled it back out, removed the tubes, blocked them, drilled the hole for the governor flow, did not mess with the boost valve but my issue now is it takes off in second, has a nice third but no first, what am I missing?
Loving your channel, Can you tell me if its possible to have a manual/auto shift reverse pattern valve body on my column shifter? I have a 68 full size pontiac and do not want a floor shifter. What do they change to make it reverse shift pattern?
I have a quick question. Rebuilding a th400 for the first time ever (first trans period).... I understand the parts about the 1-2 auto shift when holding 1st gear but why do you only put 2 check balls in? I haven't really found clear answers for that and it wasn't covered in the video. Thanks for your time!
hello thanks for the great info, just wondering about a couple things on the separator plate the 3rd hole you said you drilled .154" will a 5/32" work or should i buy the size you mentioned, also the dual hole you plug.. if every thing internal has not been touched just skip plugging that hole "seal off the direct drum" or should that be done regardless thank you.. in advance hoping to pull mine out next week or so to play with it ..
When doing this to firm up the shifts, would this require upgrading to the 34 element sprag? Or would the stock one suffice with these changes? Thank you
@@mountainsgarage hi Sean thank you for your advice I have an other question which I have I installed a shift kit ,still auto shifting but I installed a case saver eliminating the band servo I removed the 2-3 accumulator and blocked the apply hole do I need to reinstall the accumulator piston or can I leave it out
I rèally love your channel so much information i talked to you awhile back about building a 421 with a stock GM block its pretty much going to be a budget build which rotating assembly do you perfer scat or eagle? And di you like the I beam or H meam rods if you were building it for yourself? I would just like your input on this.
Hello! You can’t go wrong with either brand. For rods there are cheap I beams, then cheap followed by good H beams, then the really good I beams. I am going to finish my 421 shortly, working on the 377 now. Thanks for watching!
Can I do all the mentioned modifications for full manual and retain 2nd gear engine braking? Thank you for all your videos currently building my own th400 based on your videos! Much appreciated.
I’m currently rebuilding a th400 here in Australia everything is super expensive for them I have a 36 tooth sprag and I’m wondering what you mean by grinding the flats do you mean as like a pressure relief sort of thing?
So if you're dual feeding the direct clutch should you drill the 1/16" hole in the drum even if you aren't using a transbrake? Does it hurt to drill it if you're not using a transbrake?
When blocking the 2-3 Accumulator if your not running an intermediate band why would you install the piston in the valvebody again? just curious. I ditch it just wasnt sure if i should stop tossing them in the trash
I e been watching your videos and they are helpful! I have a question I see all the videos with the transmissions out if I need to drop my valvebody only do I have to pull the trans or can I do it with out dropping it?
I've been having trouble with really early shifts at low mph after doing a shift kit and was thinking of just doing a full manual valve body. How does the shifter work exactly with a manual valve body? Just low=1, 2=2, and D=3?
I'm trying to build a short 4x4 T400, can I go manual VB, no governor and 4l80 short output shaft? the 4x4 super short shaft is like a needle in a haystack, any ideas?
Well, you talked me into pulling my '73 TH400 and building it. I have zero experience. I've disassembled and I'm pretty overwhelmed. But anyhow, I have 5 check balls. What might that say about this beauty's history?
Thanks for all the info...when doing the automatic shifting valve body modifications...do I leave the engine braking band out and if so can I still down shift into second on boosted pulls?
Following the video and going with the full manual mods in a early 67 8 bolt with the canister style filter. I'd like to run a deep pan and flat filter/tube. From what I can see, it appears the valve body is solid thru the area where the filter bolt threads in. Is it safe to drill and tap the valve body and if so, what thread is required? Like your style and simple explanations for us guys that haven't cracked open a TH400 since the mid 80's. Cheers.
Thanks! While I have never drilled the 5/16-18 hole in an early valve body, others have. Then you will need the correct length suction tube to match the pan depth, and the correct bolt and spacer to hold the filter. Worse case you will need a later valve body if you mess yours up. Good luck and report back!
@@mountainsgarage I did drill and tap the valve body, and changed to the later filter and pickup as I went with a deep pan. Modified it per your videos for full manual. My bell was cracked so I cut it off and since this is for a Jeep, I fabricated an adapter plate to use a 4L60 bell and spaced the converter as needed. Many thanks for your insight.
Hey. I built my thm400 according to your video. It works well. But at idle I have 185 psi in park 75 psi in reverse 185 in drive, 65 to 75 in second, and 185 in 3rd. But at 1500 rpms they all come up to 185. Is this ok. Or will cause it to fail. The 400 forum seems to think it's gonna fail. Shaun. what do you think? Looking forward to your response.......
So with grinding a flat on the pump valve and plugging the hole by the pump face in case you can plug the modulator and not have extra high pressure all the time and wear out the pump?
You get full line pressure with the modulator plugged. We are only talking 200psi or less, normal hydraulic systems run in the thousands. No issues wearing out the pump that I have ever witnessed in a TH400 with a slight pressure increase. GM’s goal was to make the shifts smooth for the customer at light throttle using the modulator, at full throttle it was full pressure.
I'm having transmission problems. I have a 85 c30 5.7 350 with a TH400. It was running okay. Now I have noises and it shuts down when going up a slope. If someone can give me some tips that be awesome.
Have you saw a reverse man vb in a 400 that has aluminum plate no gaskets and no check balls and the plug to the right of the center support bolt has 3- .081 holes drilled in the plug. I've never seen this exact setup
Doing my first TH400 rebuild shortly for a single turbo 5.3. My core is a 1990, which from your video may be different than the 87 down, do the mods in this video all apply for the 1990 unit? Thanks!
Yes they do. If you install a transbrake it will work fine. If you are using the stock valve body use the correct gasket for the later case. I drill out the rear servo feed either way, it is probably restricted on your case.
@@mountainsgarage thanks, no transbrake, looking for automatic shifts for daily driving and will only manually shift if needed. Sleeper car so keeping the column shifter.
Quick question....do you worry about high fixed line pressure damaging the pump in a street car? I just finished building my first th400 and ground the boost valve and plugged the modulator, along with full manual, dual feed, converter restriction etc... Also using what I assume is the stock spring (no color) and a .065 shim behind the horse shoe. I can't seem to find a clear answer on the possible pump damage. Thanks in advance
Not one worry here. If you poll what I consider the transmission industry leaders they agree there is no correlation. We are talking less than 200 PSI that is regulated and has a relief valve. This is an internet myth told by one guy.
If you're only installing center front and rear bathtub checkballs, why do you suggest a size 1/8" drill for 2nd feed?? You don't have a checkball in the 2nd location and the fluid will no longer be restricted or forced through the 2nd feed hole? won't it go through the checkball hole instead and the feed will be the size of the checkball hole?
Is the 475 stronger for racing or is it just for pulling trucks and stuff ive heard they can be a bit noisy is it worth finding one to have cuz I can get my hands on one right now for cheap low milage motor home big block it was behind
Opinions vary, can’t go wrong with either lower unit as they are very strong in both helical and straight cut. I like that they re usually low mileage like you said.
I want to retain auto features but I want to eliminate the 1-2 safety feature. Is all I have to do is grind the flats on valve and plug the hole in the valve body?
I bought that th475. Im gonna use your videos to look at this trans. I’ll let you know if it has straight cut gears or not. I know you are busy I hate to bother you with stupid questions. Do you have an email address?
Do you happen to have a stock straight cut rear ring gear for a th400? I happened to pick up a th400 that probably broke a drive shaft so the tail of the drum that goes into the bushing in the output shaft is all chewed up.
Never silly. You could definitely command a 2-1 downshift, but beyond that I am not sure. When the solenoid fails the transmission usually doesn’t upshift.
Was just thinking if you put it in second gear and energized the kick down that would hold it in first until you turned it off then it would shift. Thanks for the reply
@@mountainsgarage GM don't make it anymore. I've searched just about everywhere, not available. I want to use it on a truck that I'm working. I have a 6.0 and TH 400 combo, that sensor would make it a lot easier to get the speedo working, and cruise control. Thanks
@@mountainsgarage thank you! I've been searching everywhere for this information. You should make another video just aimed at keeping it from automatically shifting. I was having a hard time trying to figure out if I had to do everything you did in the video or if I just had to gring those flats and plug the hole.
@@mountainsgarage Thanks! Are you far from Alabama? I am needing my Trans repaired and not wanting to take it anywhere near me and have decided do it myself. Been tur ing wrenches for years and figure if someone were reasonably close would bring it. Or just go get a book, kit, and trans stand and take my time. I do love Th400 HD trans, been in my step van 38 yrs. And need the vehicle Thanks for your info on the Tube . Ps any ideas on who to purchase a good kit from
The ASTG manual is handy for stock info, I believe on the DIY TH400 Facebook page there is a link to the PDF. For upgrades the Crankshaft Coalition TH400 page covers mods.
Dear sir, After a while, the kit for my TH400 GM has finally been installed and back on the car. I have a problem because gear changes are unnoticeable and i think that the transmission is ceased up in third gear. I drive at 120km/hour with engine at 3000 rev. Per minute. Even when i change gear with the gear selector in the car, it stays blocked in third. I select "L" or "I" and i may run at 120km/hour!! Do you have please any advice? Thanks a million for your helo Best regards
Hi man you look to have a lot of knowledge on th400 so i give you a shout my man mine is th400 full manual slam gear strong no trouble but shoot oil look to bee from the pan is that a comon thing or the cork rubber would do the job better than rubber only
@@mountainsgarage Ok, sorry you had to buy tampons because your vagina hurts. 4,000.00....thats a looooot, almost as much as my private vacation videos. Just trying to help...Hye, look, your comment made me respond and you got 1 more view and you didn't even have to re-submit it with a greater volume.
Hi Shawn, I want to go full manual and fixed line pressure, but I want to keep the engine braking front band. Do I do all the same mods, just add the band and apply servo in the case? Do all other mods stay the same? I appreciate your help.
@@mountainsgarage I looked at the crankshaft coalition full manual and it's the exact same as your mods. Does your mods shown in this video keep the band? All it says on the crankshaft coalition site is " if using a valve body that uses a band, install it now.". Sorry, I'm not trying to be a pain, I'm kinda disabled and I don't want to have to do it again. I seen another guy on RU-vid say that blocking the third accumulator with a set screw eliminates the band function, so I'm kinda confused.
