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Switching from a TH-350 to A TH-400.


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I'm needing some info on switching from a TH-350 to a TH-400. I know I'll have to move the tranny mount crossmember probably but I'm wandering about puting a 400 yolk on a drive shaft that had a 350 yolk on it. Will they cross over between the two? Another thing is the length of the drive shaft it'self. Are they different lengths between the 350 and 400? If so what does the driveshaft measure for a TH-400? What measureing points on the driveshft do you use? I'm shopping for a tranny and I want a tranny brake real bad but I have found a couple 400's with breaks that were alittle cheaper than the 350's I found with brakes. I was hoping a swap over would be easy.

 

Jon.

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Basically it is an easy swap. The TH400 yoke will fit on your driveline, but you will have to shorten it first. For the length, slip the yoke into the tranny (after you install it) all the way then subtract 1". Don't remember exactly how to determine machinist measurements for driveline length so log on to Dennys Driveline to find this out. That is what I did. You can get a measurement printout from them.

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Hey clock!Once you have the 400 in you measure from the tail shaft of the trans were the yoke slips in. To the rear end were the Ujoint sits.The center half. PS I have a new 400 with shift kit. no brake WITH COVERTER and yoke. Let me know if interested. ROMAN!!!

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Thanks for the input. it seems we have some cotradiction here. George thinks my current driveline end will work??? and Bob thinks it will not work and I need a special u-joint. Ok I'm confused, will the drive shaft end work with the 400 yolk ? And Romans post leads me to another question. Does a 350 converter work on a 400?

 

Roman, I may be interested. Does it have a reverse shift pattern? I was alittle confused about the trans brake and converter. If I read it correctly, it has NO trans brake but Does have the converter. By the way what are you looking to get out of it????

 

Jon.

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They do make different size yokes to fit different size universals. I have several sizes and lengths in my supply. You should be able to measure the universal cups and driveline holes to see. A good driveline shop would have supplies.

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Just a thought. I would check with the machine shop what will shorten your drive shaft before measuring. I have seen different shops that have different meathods. Once again I am showing my over conservativness (if that's a word?). I would hate to bring a shaft home and find out I measured differently than they are used too. Big J

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  • 2 weeks later...

They make 2 different 400 yokes. One uses the larger buick, olds, pontiac, and SS454 u joint, and the other uses the standard chevy u joint. Most chevys, except for 454s and some other death ray engines, and later full size wagons and such, use the smaller, standard joint.

The drive shaft will be shorter. You can shorten the shaft easily. Scribe a line lengthwise on the end you are cutting so the end goes back in the tube in the same spot. Either end will do, as long as no weights are disturbed. Then cut through the weld with a hacksaw or a whizwheel,About 1/16"-1/8". Knock out end. Cut the tube as square as you can. The end is then pressed or knocked back in, making sure to line the scribe mark exactly. The end fits tightly, and should square itself in the tube. Weld the shaft up. You can almost always get by without having to rebalance the shaft.

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They make 2 different 400 yokes. One uses the larger buick, olds, pontiac, and SS454 u joint, and the other uses the standard chevy u joint. Most chevys, except for 454s and some other death ray engines, and later full size wagons and such, use the smaller, standard joint.

The drive shaft will be shorter. You can shorten the shaft easily. Scribe a line lengthwise on the end you are cutting so the end goes back in the tube in the same spot. Either end will do, as long as no weights are disturbed. Then cut through the weld with a hacksaw or a whizwheel,About 1/16"-1/8". Knock out end. Cut the tube as square as you can. The end is then pressed or knocked back in, making sure to line the scribe mark exactly. The end fits tightly, and should square itself in the tube. Weld the shaft up. You can almost always get by without having to rebalance the shaft.

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