TH350 to TH400 Conversion Yoke question

mcutlass1969 · 01-02-2007, 11:47 AM

Today I am converting a 69 Cutlass S 350 engine/350Tranny to a 455 engine and BOP TH400 tranny. in measuring both tranny's are the same length so the drive shaft length should not be an issue. The issue is the TH400 has a larger gear so that my current yoke on the drive shaft is to small. I called the local O'Railly's and they are lost. I need some info on what would be the best way of getting this resolved.

texasred · 01-02-2007, 11:51 AM

I've always heard you'd have to shorten the driveshaft...

You'll have to snag the output yoke from a junkyard. The yoke isn't BOP specific, though. Any TH-400 will do.

C.J.

mcutlass1969 · 01-02-2007, 12:07 PM

I also have another question. This is the bolts from Flywheel to Torque. On the 350/350 combo it had bolts that threaded directly to the torque. I see this is not the case. I take it that you have to use bolt/nut combo's to put the 2 together? If I am right then are these special bolts to handle the torque

Oldsguy · 01-03-2007, 06:05 AM

That doesn't seem right to me. The flywheel bolts directly onto the torque converter on my Delta with a 455/400 combo.

64Rocket · 01-03-2007, 07:19 AM

Sounds like you have a aftermarket convertor. I would use grade 8 bolts and self locking nuts. Be sure to use small block OLDS motor mounts to the 455. The T-400 IS 4" longer, you will have to shorten the drive shaft.

Gene

texasred · 01-03-2007, 07:29 AM

Quote:

Originally Posted by 64Rocket

Sounds like you have a aftermarket convertor. I would use grade 8 bolts and self locking nuts. Be sure to use small block OLDS motor mounts to the 455. The T-400 IS 4" longer, you will have to shorten the drive shaft.

Gene

Gene,

I just know what I've heard on ROP and elsewhere about the conversion...I thought 350 motor mounts were shorter and you were supposed to use 455 mounts...

C.J.

2blu442 · 01-03-2007, 08:38 AM

My experieces has been if your keeping the metal engine perches from the 350 then use 350 rubber mounts. If you change to the 455 metal perches then use the 455 rubber mounts. The bottom of the engines are the same so they both fit, but where the difference comes in is the exhaust manifolds. I mixed the perch/rubber mounts on a car with headers and the headers wouldn't fit. I had used this engine with these headers in a different car and they fit fine, so it took me a while to figure out what I did wrong! I've made the swap from TH350 to TH400 several times and always had to change the driveline to a shorter one. Check your trannies again to see what they are. They should have both been short tailshaft versions for the A-body car, but if someone put a long tailshaft TH350 in that might make them closer in length, I don't know, I've never compared the TH350 long to the TH400 short tailshafts.

texasred · 01-03-2007, 01:29 PM

Quote:

Originally Posted by 2blu442

My experieces has been if your keeping the metal engine perches from the 350 then use 350 rubber mounts. If you change to the 455 metal perches then use the 455 rubber mounts. The bottom of the engines are the same so they both fit, but where the difference comes in is the exhaust manifolds. I mixed the perch/rubber mounts on a car with headers and the headers wouldn't fit. I had used this engine with these headers in a different car and they fit fine, so it took me a while to figure out what I did wrong! I've made the swap from TH350 to TH400 several times and always had to change the driveline to a shorter one. Check your trannies again to see what they are. They should have both been short tailshaft versions for the A-body car, but if someone put a long tailshaft TH350 in that might make them closer in length, I don't know, I've never compared the TH350 long to the TH400 short tailshafts.

Show me a little smarter today!

Check this out on transmission lengths:
http://www.tciauto.com/Products/TechInfo/trans_dims.asp

C.J.

2blu442 · 01-03-2007, 10:15 PM

Cool Link C.J. I copied that to my hard drive for future reference!

texasred · 01-03-2007, 10:29 PM

There's an awful lot of good stuff on that site!

C.J.

01-02-2007, 11:47 AM	#1 (permalink)
mcutlass1969 Member Join Date: Apr 2006 Posts: 61	TH350 to TH400 Conversion Yoke question Today I am converting a 69 Cutlass S 350 engine/350Tranny to a 455 engine and BOP TH400 tranny. in measuring both tranny's are the same length so the drive shaft length should not be an issue. The issue is the TH400 has a larger gear so that my current yoke on the drive shaft is to small. I called the local O'Railly's and they are lost. I need some info on what would be the best way of getting this resolved.

01-02-2007, 11:51 AM	#2 (permalink)
texasred Super Moderator Join Date: Apr 2004 Location: San Antonio, Texas Posts: 807	I've always heard you'd have to shorten the driveshaft... You'll have to snag the output yoke from a junkyard. The yoke isn't BOP specific, though. Any TH-400 will do. C.J. __________________ Home of the 1971 Cutlass Supreme convertible Super Karate Monkey Death Car.

01-02-2007, 12:07 PM	#3 (permalink)
mcutlass1969 Member Join Date: Apr 2006 Posts: 61	Thanks I also have another question. This is the bolts from Flywheel to Torque. On the 350/350 combo it had bolts that threaded directly to the torque. I see this is not the case. I take it that you have to use bolt/nut combo's to put the 2 together? If I am right then are these special bolts to handle the torque

01-03-2007, 06:05 AM	#4 (permalink)
Oldsguy Administrator Join Date: May 2004 Location: Lees Summit MO Posts: 3,145	That doesn't seem right to me. The flywheel bolts directly onto the torque converter on my Delta with a 455/400 combo. __________________ Dan '77 Cutlass Supreme '46 2 door

01-03-2007, 07:19 AM	#5 (permalink)
64Rocket Member Join Date: Sep 2006 Location: Union City Calif.94587 Posts: 71	Sounds like you have a aftermarket convertor. I would use grade 8 bolts and self locking nuts. Be sure to use small block OLDS motor mounts to the 455. The T-400 IS 4" longer, you will have to shorten the drive shaft. Gene __________________

01-03-2007, 08:38 AM	#7 (permalink)
2blu442 Senior Member Join Date: Sep 2006 Location: Medford, Oregon Posts: 924	Engine swap My experieces has been if your keeping the metal engine perches from the 350 then use 350 rubber mounts. If you change to the 455 metal perches then use the 455 rubber mounts. The bottom of the engines are the same so they both fit, but where the difference comes in is the exhaust manifolds. I mixed the perch/rubber mounts on a car with headers and the headers wouldn't fit. I had used this engine with these headers in a different car and they fit fine, so it took me a while to figure out what I did wrong! I've made the swap from TH350 to TH400 several times and always had to change the driveline to a shorter one. Check your trannies again to see what they are. They should have both been short tailshaft versions for the A-body car, but if someone put a long tailshaft TH350 in that might make them closer in length, I don't know, I've never compared the TH350 long to the TH400 short tailshafts. __________________ 1964 Cutlass Factory 4spd 1965 442 4spd 1967 442 Auto 1967 Cutlass Convertible 1968 442 Auto 1969 442 W30 Auto 1970 442 4spd 1971 Cutlass Flat Top Wagon 1973 Che*vy 3/4 Ton 454/TH400 Tow Vehicle Only the tow vehicle is finished!

01-03-2007, 10:15 PM	#9 (permalink)
2blu442 Senior Member Join Date: Sep 2006 Location: Medford, Oregon Posts: 924	Cool Link C.J. I copied that to my hard drive for future reference! __________________ 1964 Cutlass Factory 4spd 1965 442 4spd 1967 442 Auto 1967 Cutlass Convertible 1968 442 Auto 1969 442 W30 Auto 1970 442 4spd 1971 Cutlass Flat Top Wagon 1973 Che*vy 3/4 Ton 454/TH400 Tow Vehicle Only the tow vehicle is finished!

01-03-2007, 10:29 PM	#10 (permalink)
texasred Super Moderator Join Date: Apr 2004 Location: San Antonio, Texas Posts: 807	There's an awful lot of good stuff on that site! C.J. __________________ Home of the 1971 Cutlass Supreme convertible Super Karate Monkey Death Car.

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