I'm looking at having a TH400 tranny rebuilt and was curious if the stock tranny will STAY in first when put in first gear(ie for using engine compression while crawling).

If it is not a stock feature, is there a kit or the like for this feature? I just want first gear that way... not EVERY gear: ie putting it into 2nd or drive will act normal.

Thanks in advance,
John

BTW, I did a search and didn't find what I wanted :(

Be sure to mention this to your tranny guy, it can be done with stock parts, and is a common problem in mid to late seventies TH400's, mainly car trannies with mushy shifting. I think it's the governor, but I can't remember, I had my buddy rebuild a TH400 for another friend, he told me what all he had to do to it but it sounded like the teacher on Charlie Browne, in one ear and out the other, I'm a manual trans kinda guy, so I don't pay attention to all the slush-box mumbo jumbo.

There are some aftermarket shift kits that have that feature as well. Just in case you haven't gotten a kit yet. B&M transpack is one.

Originally posted by 4Bangler
late seventies TH400's, mainly car trannies with mushy shifting.


clutch disk

they left one disk out so it shifts "Smoth" insted of geting a bit of shift shock

Originally posted by Lil'John
I'm looking at having a TH400 tranny rebuilt and was curious if the stock tranny will STAY in first when put in first gear(ie for using engine compression while crawling).

If it is not a stock feature, is there a kit or the like for this feature? I just want first gear that way... not EVERY gear: ie putting it into 2nd or drive will act normal.

Thanks in advance,
John

BTW, I did a search and didn't find what I wanted :(

The answer is yes . . . A stock TH400 will stay in low if that's where you put the shifter. If you put the shifter in 2, that's where it stays. D for Drag gets you a 2-3 upshift. If your trans is stock and doesn't do all of the above, it's broke.

Originally posted by Rockcrusher


The answer is yes . . . A stock TH400 will stay in low if that's where you put the shifter.

you are wrong. there was a thread on this a while back and a th400 will shift from 1st to 2nd with the shifter in 1st. how do i know? i run one. now granted you have to have the motor rapped out pretty good to get it to shift but it will shift.

lil'john, i am not sure when you think it will shift but the rpm's have to be reved up really high to get it to shift from 1st to 2nd while the shifter is in 1st gear. while wheeling i have never had it happen. i don't get the rpm's anywhere near the range they need to be in in order to make it shift. i can make it happen by putting the shifter in the 1st position and just nailing the hell out of it but it doesn't do it under any type of rock crawling situation.

Originally posted by High5
lil'john, i am not sure when you think it will shift but the rpm's have to be reved up really high to get it to shift from 1st to 2nd while the shifter is in 1st gear. while wheeling i have never had it happen. i don't get the rpm's anywhere near the range they need to be in in order to make it shift. i can make it happen by putting the shifter in the 1st position and just nailing the hell out of it but it doesn't do it under any type of rock crawling situation.

Let's just say I want to finally own an auto that works as expected:p I've had the joy of owning a 700r4 equiped rig that ate them like no tomorrow(best I got was 25k miles out of one). Even when locked in first, on occasion it would jump out to second even in engine compression situations:(

I don't currently have the TH400 tranny in hand so I don't know if it is good or not... but I know for a fact that I'm going to have to change the output shaft on it to a 4wd version. So, I'll send the sucker out for a full rebuild and not worry about it.

I was hoping the answer would be it is a stock feature but I'll put a kit in it if needed... I just HATE the thought of having it "custom" done because if I got used to it, I'd be stuck going to the same shop:(

And for the record, I'm not a big autotranny fan since my 700r4 experience:p But in this case, I really don't have much of a choice:(

Nope, not custom. Just modify the 1-2 shift valve. If you buy the B&M transpak, it will show you how to do it. They include a different valve too so you do not have to grind your valve. Either way, the "fix" will be in your valve body, so if you have to get it rebuilt, the valve body does not change :) If you want to, look up TCI instructions on there web site and in it, buried toward the end, are the mods for the DIY'er. You will need a small brass plug though which comes in there kits and the B&M kits too. Otherwise, you don't need any stinking kits :flipoff2: :)

Sounds like a manual valve body for number 1 would do what you want...just go full manual and shift it yourself...kinda the auto...manual set-up...that way you can lock it in and forget it for the steep drop on lion back that eat's auto's....

Originally posted by mnstr_fx
Nope, not custom. Just modify the 1-2 shift valve. If you buy the B&M transpak, it will show you how to do it. They include a different valve too so you do not have to grind your valve. Either way, the "fix" will be in your valve body, so if you have to get it rebuilt, the valve body does not change :) If you want to, look up TCI instructions on there web site and in it, buried toward the end, are the mods for the DIY'er. You will need a small brass plug though which comes in there kits and the B&M kits too. Otherwise, you don't need any stinking kits :flipoff2: :)

This newbie knows it. ;)

Originally posted by High5


you are wrong. there was a thread on this a while back and a th400 will shift from 1st to 2nd with the shifter in 1st. how do i know? i run one. now granted you have to have the motor rapped out pretty good to get it to shift but it will shift.

lil'john, i am not sure when you think it will shift but the rpm's have to be reved up really high to get it to shift from 1st to 2nd while the shifter is in 1st gear. while wheeling i have never had it happen. i don't get the rpm's anywhere near the range they need to be in in order to make it shift. i can make it happen by putting the shifter in the 1st position and just nailing the hell out of it but it doesn't do it under any type of rock crawling situation.

At what RPM will it shift? I have 2 rigs with TH400's. My Jeepster with a 225 V6 which I've run up to about 3500 and my Willys wagon with an AMC 360 to around 4500. Neither one will auto shift to 2nd if I have the shifter in the low detent. Same thing coming down a hill . . . neither one has ever upshifted on me. So far as I know both are stock units.

I have a TH400 that was built by a friend of mine who retired from building race car trannies and it has never upshifted when locked in first gear, Its seen extremely high RPM's in the low range in mud a time or two and some very steep descents and has never budged. If you have a shift kit installed and extra clutches added talk this over with your tranny builder first. Mine is built with extra clutches, a B&M stage II, and a lowered gear set and when it shifts even behind my I-6 it slams you back and especially in the low side. When it shifts at 2250 from 1st to 2nd it will bark my 34" TSL's on gravel with 3.73 axle gears.

John

Originally posted by Rockcrusher


At what RPM will it shift? I have 2 rigs with TH400's. My Jeepster with a 225 V6 which I've run up to about 3500 and my Willys wagon with an AMC 360 to around 4500. Neither one will auto shift to 2nd if I have the shifter in the low detent. Same thing coming down a hill . . . neither one has ever upshifted on me. So far as I know both are stock units.

i am not really sure. my tach has crapped out so i am of no help. i believe that someone said in the other post that it was at like 5500 but i could be wrong so don't take my word for it. it is way up there though.

Originally posted by High5


i am not really sure. my tach has crapped out so i am of no help. i believe that someone said in the other post that it was at like 5500 but i could be wrong so don't take my word for it. it is way up there though.

Thanks High5

The 225 is limited at 3500 and the 360's valves float at 5100 so I can probably live with my stock transmissions. In real life neither rig probably ever exceeds 3K mainly 'cause I don't want to test the "Big Bang" theory.

The TH400 will upshift (with the shifter in 1st) to second around 5500 rpm, it is the governor that causes it.