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Old 03-15-2002, 01:34 PM   #1
timmy
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Question TH-400 conversion

I'm wanting convert my truck from a 3spd to a th-400. I've done an auto conversion before but it was a th-350. the question is the truck is a SWB, and has a 2pc driveshaft. Do i need to get a slip yoke or can i use the short one thats a bolt in version but not bolt it in and pull it out a little for sliding purposes

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Old 03-15-2002, 01:52 PM   #2
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if its a bolt on output yoke then thats a giveaway sign that its out of a truck, how long is the overall length of the trans ? 34 or 29 ?
youll need to use a slip yoke version output yoke, from a donor car and weld that yoke onto your shaft, and adjust length of the shaft with cutter and welder and balance it, hopefully the tranny is long enough that you can make a one piece shaft out of a shaft out of a donor vehicle lie a 73-up truck with same axle as you have then you only have to change one end of the shaft still.(front)
you use a 67-72 auto trans member, and make sure the out put of the tranny is perfectly aligned with the pinion of the rear axle, or.... problems..
you know the rest, rad swap cooler lines linkage, can use 73-up if you dril the two holes for it in the top side of frame rail straight across from tranny shift shaft

good luck !
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Old 03-15-2002, 04:16 PM   #3
one legged lance
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What happens if the output of the trans isn't perfectly lined up with the diff????? And is that horz or vert????
I just put a 700r4 in this week and eyeballed it but didn't check for pefect.
Thx,
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Old 03-15-2002, 09:01 PM   #4
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A short tail 400T will be 11/16" longer than you saginaw 3spd,or a short tail 350T. this will requier cutting the shaft,& the crossmember will mount in a different place....but the holes should be in the frame. when you set the slip yolk up,& measure shaft lenght......slide it all the way in to bottom,mark it with a grease pencil,then pull it out 3/4-7/8". That is what you need for slip clearance....measure the shaft from that point. A link to dimentions.... http://www.tciauto.com/tech_info/trans_dims.htm
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Old 03-16-2002, 06:50 PM   #5
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I made a TH350 swap to a TH400 in my 72 C-10 and had to get a different cross member,also shortend my 2-piece drive shaft "1"inch on the front half.To balance it I drilled 2 small holes 180 degrees from one another,one at each end and put 1/2 a quart of 30 wt oil in it then plugged the holes with sheet metal screws and silicon,perfect fluid balance.


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Old 03-21-2002, 12:04 AM   #6
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ttt

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Formerly know as: "GMC Under Construction" Current project: 1967 GMC shortbed/fleetside, 350/700R4, air bag suspension. Other vehicle of interest: 1957 Chevy Bel-Air 4dr hard top, 283/powerglide, lowered 3-1/2" in front and 2 inches in the rear.

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Old 03-21-2002, 01:29 AM   #7
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You have issues to resolve wormy, er timmy!
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Old 03-21-2002, 01:53 AM   #8
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krossfiretim@aol.com
mail time I just logged on AOL and his address is ligit we may have to get a letter campain together..........

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[This message has been edited by jostrans68 (edited March 21, 2002).]
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Old 03-21-2002, 07:41 AM   #9
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take care of other stuff first!
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Old 03-21-2002, 07:57 AM   #10
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he has mail
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Old 03-21-2002, 11:56 AM   #11
Jesse 67 c-10
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Never heard of using oil to balance a drive shaft, does it work pretty good? would 10w-30 work? I have to shorten my driveshaft 4" from my 5 speed swap so I may try this. Cool idea!
Jesse

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Old 03-21-2002, 12:23 PM   #12
Fast68Chevy
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it depends on what th400 he is swapping to, some are 34" long ans some are 29 long, it depend son year and application, typically all the newer ones like late 70s and early 80s and up are 29"
the early 70s ones like int he big cars are 34"
you do not need a different crossmember, 67-72 trucks only have one version of auto crossmember, no matter what tranny, putting a newer tranny in 67-72 may require you to drill hole in between the existing two holes for the tranny mount to the xmember sine most all newer trannies use single stud style of mount unlike trucks did back then,

you cant use a bolt on yoke for the tranny poutput tail unless you have a lsip join style driveshaft, or you iwl have bg problems when you load down truck or go over bumps in road

one legged lance, i was talking about horizontal alignment, if the driveshaft doesnt go back straigh back to the axle pinion gear stib perfectly straight and if its off by too much then you can end up with broken mount or mounts and broken tranny bell housing because of the forcew of the drivetrain trying to straighten out when you put torque on it, IE when you drive.

and i dont reccommend drilling holes in a driveshaft, i owuld take shaft to a shop to have it balanced on machine, removing any metal by drilling holes in it is not what you should do, IMO


good luck


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Old 03-21-2002, 12:38 PM   #13
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Pay your bills Timmy..... It's not fare to take the money and run.
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