th400 power.

[Blown Dually]

Hey all, new to the forum here. Have a question. I've got a 1976 Chevy c30, crew cab, long bed dually. Just dropped in a supercharged 496 making around 850hp. Also, upgraded the rear rubber to 34x18.50r16 Mickey Thompson rubber. Question is this, will my th400, that only has a shift kit installed, ( unknown brand and stage.) hold this kind of power? Its mainly just gonna be a street cruiser, but when i wanna get on it, i don't want tranny all over the road. Thanks for all the help.

Michael.

 

[glockholiday]

I have no facts to back it up but my opinion would be no. Along with the trans build I would also upgrade u-joints and maybe even drive shaft.

It will be fine for cruising around and some smooth accelerations maybe even to full throttle but definitely no hard launches off the line.

 

[1987 GMC Jimmy]

Agreed.

 

[74 Shortbed]

Welcome to the site..

That's a 7500lb truck and a lot to move especially from a dead stop, shift kit speeds up shifts which increases clutch life but that's it does nothing for internal parts, a 400 is a great tranny and would be a shame to destroy it, I highly recommend tearing it down and freshen it up with upgrades to withstand the torque you're motor will put out, torque breaks parts not HP, and with a blower you will have parts breaking torque..

 

[gmachinz]

You need to open that TH400 up again and do an upgrade-a shift improver kit is great but to handle 850, you need to swap out the 16 element intermediate sprag for a 32 element sprag-Hughes makes a good one at a decent price....B&M, TCI etc also supply them. This upgrade basically doubles the holding power of the trans, so while a modestly built TH400 can easily handle 450-500 HP, one with a 32 element sprag can handle 800-1000 HP. Go above that number then we're talking hardened output shafts, etc. That trans will be living on borrowed time the instant you start driving it with that motor until you change that sprag.

 

[Camar068]

Pics Pics Pics Pics!!!

 

[HotRodPC]

I'd agree. For that heavy of a truck and 850hp, you'll need a few upgrades if you're going to be getting all in it. Th400 is good for about 500hp. The internediate sprag mentioned above for sure needs to be done. If you're doing hard launches, probably ought to do the Low Sprag too in the back. That one is a tough one to find. Used only in 64 and 65 OEM and then aftermarket otherwise. The ones I have, I've had them put on a lathe and machined to accept a Torrington roller bearing instead of a thrust washer. Next concern would be the input and output shafts, moreso the input shaft.

 

[74 Shortbed]

Add clutches too, use 6 clutch Cad drum and add one more for 7 clutches.

 

[Rusty Nail]

Wtf

 

[bucket]

Pics Pics Pics Pics!!!

Well said!!!

 

[68post]

?? Crickets !!

 

[HotRodPC]

?? Crickets !!

Just don't step on them and squish them in here. I've been told it's bad luck to squish or kill crickets in the house. You throw them outside instead.

 

[Honky Kong jr]

Then stomp the noisy bastards......and I call bs.

 

[Irishman999]

Might consider upgrading the forward clutch hub that links the forward and direct drum. As far as the sprag upgrade, you can always buy a 4l80 drum and a new clutch off ebay for under 200 bucks. All the 4l80's came with dog bones instead of a roller clutch.

There is also a way to rollorize the output shaft carrier with a torrington bearing out of a th350, I dont have the details yet but i am looking into it.

 

[74 Shortbed]

There is also a way to rollorize the output shaft carrier with a torrington bearing out of a th350, I dont have the details yet but i am looking into it.

Simple, replace thrust washer and backing plate with a th350 pump bearing, it is exact thickness of plate and washer, sink case bushing a few thousands to retain bearing, that's been done forever..