th350 to th400 swap questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

MylilBowTie · 08-03-2003, 01:13 PM

I have some questions about a transmission swap. I currently have a TH350 (9inch tailshaft) that has been rebuilt no less that 8 times in six months time including rebuild time about one work week each time. So I bought a TH400 with bolt on yoke inch tailshaft. I found out that it came out of a 1984 G20 van. Supposed to have been rebuilt and good to go. I have started to think what all has to be done to get this switched over to the TH400. I have a one piece driveshaft now that is stock length for TH350 nine inch tailshaft with an 8ft bed. What I'm wondering is can I use a one piece driveshaft with a slip yoke 33 spine (TH400) and not have any problems or issues with it? I know its a little short if I use it but I would have it lengthened. I know a little bit about two piece driveshafts but never messed with a two piece driveshaft. If I have to use a two piece all I need to do is buy it and drill tap two bolts for the carrier and be done with it. I might already have the bolt holes there but I don't think I do. Cross member has to be moved back I know that.

TH350 is 30 11/16 long - TH400 is 28 3/8 long. Using a one piece, if I done it right I would need a 2 5/16 longer driveshaft right? I rather use a one piece but if its cheaper to buy the two piece I will use that. Pricing slip yoke for TH400 is 75.00 -130.00. Plus I will have to have driveshaft lengthened and balanced. I have yet to call how much that will run me. Plus that would be a good time to get the bigger TH400 ujoints installed.

The other thing I was thinking about is the u-joints the TH400 are bigger than the TH350. I know I can get a u-joints that have TH400 one side and TH350 other. But I would like to have front and back the same size. Would the TH400 u-joints fit in the rear yoke? Im lost as to what the different sizes and all that are.

Has anybody run the Lokar Kickdown kit for the TH400? Looks to be a lot better setup than the B&M switch.

87 STEPPER · 08-03-2003, 01:55 PM

Get the trany in first then get under there and see what you end up with then get some good measurements and go from there.

I dont see any problem's running approx 2" longer 1 piece drive shaft.

As for the u-joiunt i'd go with what ever it takes to make it work and don't worry about it unless your engine is producing 500HP.

Dont know any thing about the lokar down shift kit.

This was my 333rd post on the 3rd

AirMale · 08-03-2003, 07:35 PM

1. Install Turbo-400
2. Call Denny's Driveshaft. They will help you get a driveshaft for your truck with the slip-yoke allready mounted. 1-716-875-6640 tech or www.dennysdriveshaft.com
3. Don't forget the pics

MylilBowTie · 08-04-2003, 07:41 AM

I would like to get a custom driveshaft like that but those are 260-300. If I had that much money Id be all for it but I can get my TH400 rebuilt for that. I may have to do that still don't know yet.

So I'm going to call around today and price getting my driveshaft lengthened and balanced. Also call around the local boneyards and see what I can scratch up a two piece for.

I just want a one piece because they look better and don't have to mess with that stupid center carrier thing. But if I can a two piece I will settle for it right now and then get the Dennys Driveshaft with the 1350 u-joints.

Thanks guys

**swervin ervin** · 08-04-2003, 10:20 AM

Well, funny thing to me is my 79 SWB Big 10 came stock with a TH400. It has a 2 pc drive shaft. It's a SWB, what does it need a 2 piece shaft for?

Are all Big 10's this way?

MylilBowTie · 08-04-2003, 01:31 PM

It has a bolt on yoke. If I use my one piece I would have to get a slip on yoke. I cant do that because my driveshaft is to short if I go that route. I will have to have a new driveshaft made. Unless I can find one. I called around today and all the boneyards didnt wanna really mess with it after I told them what I was doing (th350 to th400). So if I could find one that would fit that would be great but that isn't all that likely. Today might have been a bad to call around the boneyard something about its been pouring all day.

lol

So here is what Im left with. Put the th400 in the truck, measure it, find out how much the driveshaft is going to cost. Or look a little harder and see what I can find in the way of a driveshaft that will fit. If I have to get a custom one Im going with the 1350 u-joints both ends.

Anything over 72 inches has to have a two piece driveshaft legally. Im not sure if its nation wide or just Ohio but that is what a good local shop said. That is person at a shop that I have talked to that was willing to help and explain everything.

Im not really sure why the two piece in the swb truck?? Long beds I have seen both but mainly one piece.

79BIG10 · 08-04-2003, 05:32 PM

Quote:

Originally posted by swervin ervin
Well, funny thing to me is my 79 SWB Big 10 came stock with a TH400. It has a 2 pc drive shaft. It's a SWB, what does it need a 2 piece shaft for?

Are all Big 10's this way?

My Big 10 came with TH350 and one piece shaft. I'm wondering if SWB came with 2 piece?

08-03-2003, 01:13 PM	#1
MylilBowTie Right turn Clyde Join Date: Nov 2002 Location: Cincinnati, Ohio Posts: 2,911	th350 to th400 swap questions I have some questions about a transmission swap. I currently have a TH350 (9inch tailshaft) that has been rebuilt no less that 8 times in six months time including rebuild time about one work week each time. So I bought a TH400 with bolt on yoke inch tailshaft. I found out that it came out of a 1984 G20 van. Supposed to have been rebuilt and good to go. I have started to think what all has to be done to get this switched over to the TH400. I have a one piece driveshaft now that is stock length for TH350 nine inch tailshaft with an 8ft bed. What I'm wondering is can I use a one piece driveshaft with a slip yoke 33 spine (TH400) and not have any problems or issues with it? I know its a little short if I use it but I would have it lengthened. I know a little bit about two piece driveshafts but never messed with a two piece driveshaft. If I have to use a two piece all I need to do is buy it and drill tap two bolts for the carrier and be done with it. I might already have the bolt holes there but I don't think I do. Cross member has to be moved back I know that. TH350 is 30 11/16 long - TH400 is 28 3/8 long. Using a one piece, if I done it right I would need a 2 5/16 longer driveshaft right? I rather use a one piece but if its cheaper to buy the two piece I will use that. Pricing slip yoke for TH400 is 75.00 -130.00. Plus I will have to have driveshaft lengthened and balanced. I have yet to call how much that will run me. Plus that would be a good time to get the bigger TH400 ujoints installed. The other thing I was thinking about is the u-joints the TH400 are bigger than the TH350. I know I can get a u-joints that have TH400 one side and TH350 other. But I would like to have front and back the same size. Would the TH400 u-joints fit in the rear yoke? Im lost as to what the different sizes and all that are. Has anybody run the Lokar Kickdown kit for the TH400? Looks to be a lot better setup than the B&M switch. __________________ 1974 C25 LWB: 454 4bbl Carb / TH400 / 3.73 1992 Camaro RS 305 TBI Last edited by MylilBowTie; 08-03-2003 at 01:23 PM.

08-03-2003, 01:55 PM	#2
87 STEPPER STILL PLAYS WITH TRUX Join Date: Nov 2002 Location: Melbourne, Fla. Posts: 2,764	Get the trany in first then get under there and see what you end up with then get some good measurements and go from there. I dont see any problem's running approx 2" longer 1 piece drive shaft. As for the u-joiunt i'd go with what ever it takes to make it work and don't worry about it unless your engine is producing 500HP. Dont know any thing about the lokar down shift kit. This was my 333rd post on the 3rd __________________ ~~Bruce~~ MY 87 STEPPER MY 99 2D/WD TAHOE Last edited by 87 STEPPER; 08-03-2003 at 01:58 PM.

08-03-2003, 07:35 PM	#3
AirMale Senior Member Join Date: Jan 2003 Location: Atlantic City, NJ Posts: 1,073	1. Install Turbo-400 2. Call Denny's Driveshaft. They will help you get a driveshaft for your truck with the slip-yoke allready mounted. 1-716-875-6640 tech or www.dennysdriveshaft.com 3. Don't forget the pics __________________ 86 SWB 9.0 LITER T-400-OD 4.11 eaton-4/5 drop Best 1/4 12.51 @112mph no traction

08-04-2003, 10:20 AM	#5
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Well, funny thing to me is my 79 SWB Big 10 came stock with a TH400. It has a 2 pc drive shaft. It's a SWB, what does it need a 2 piece shaft for? Are all Big 10's this way? __________________ Mike 1985 Chevy C-10

08-04-2003, 01:31 PM	#6
MylilBowTie Right turn Clyde Join Date: Nov 2002 Location: Cincinnati, Ohio Posts: 2,911	It has a bolt on yoke. If I use my one piece I would have to get a slip on yoke. I cant do that because my driveshaft is to short if I go that route. I will have to have a new driveshaft made. Unless I can find one. I called around today and all the boneyards didnt wanna really mess with it after I told them what I was doing (th350 to th400). So if I could find one that would fit that would be great but that isn't all that likely. Today might have been a bad to call around the boneyard something about its been pouring all day. lol So here is what Im left with. Put the th400 in the truck, measure it, find out how much the driveshaft is going to cost. Or look a little harder and see what I can find in the way of a driveshaft that will fit. If I have to get a custom one Im going with the 1350 u-joints both ends. Anything over 72 inches has to have a two piece driveshaft legally. Im not sure if its nation wide or just Ohio but that is what a good local shop said. That is person at a shop that I have talked to that was willing to help and explain everything. Im not really sure why the two piece in the swb truck?? Long beds I have seen both but mainly one piece. Last edited by MylilBowTie; 08-04-2003 at 01:37 PM.

08-04-2003, 07:41 AM	#4
MylilBowTie Right turn Clyde Join Date: Nov 2002 Location: Cincinnati, Ohio Posts: 2,911	I would like to get a custom driveshaft like that but those are 260-300. If I had that much money Id be all for it but I can get my TH400 rebuilt for that. I may have to do that still don't know yet. So I'm going to call around today and price getting my driveshaft lengthened and balanced. Also call around the local boneyards and see what I can scratch up a two piece for. I just want a one piece because they look better and don't have to mess with that stupid center carrier thing. But if I can a two piece I will settle for it right now and then get the Dennys Driveshaft with the 1350 u-joints. Thanks guys



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