Transmission lengths for std to auto swap ('72 highboy)

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carnuck
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Transmission lengths for std to auto swap ('72 highboy)

Post by carnuck »

C6 with fixed output (for FE motor) length compared to 4 speed std. Bell housing edge to center of the ujoint.

I need to know if I need a different length driveshaft. if I switch to auto.
Ks Highboy
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Re: Transmission lengths for std to auto swap ('72 highboy)

Post by Ks Highboy »

If your just wanting to swap in a C6 in place of your 4speed I think you just need to find a truck C6 with the short tailshaft. Problem is, you need the tailshaft housing from a C6 that came out of a 4x4 so you will have the proper bolt holes for your transfer case shifter. There were not alot of C6 highboys made.
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carnuck
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Re: Transmission lengths for std to auto swap ('72 highboy)

Post by carnuck »

I found a C6 for $200 locally then ran against a wall. We have to sell our place due to health issues costing our jobs and I haven't the time, or money to fix it now so I'm taking the LPG system off and selling it as is. It'll be posted shortly.
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Re: Transmission lengths for std to auto swap ('72 highboy)

Post by Tpdaniels »

Sorry about your problems, I decided to address your question in case anyone else might be considering the switch. I switched my 72 Highboy from a 4 speed to a C-6 automatic, I used a C-6 with a short tail shaft, then after looking for months I found a mid 70' F-250 4X4 tail shaft to switch on to it. It is a direct bolt on that corrects a few problems, it has the correct bolt locations for your 4WD shifter to connect to and it has the speedometer cable hole blocked off, you don't need it as your speedometer cable hooks up to the transfer case. You question was about driveshaft length, the original one that goes between the transmission and transfer case is to long and will need to be shortened to work properly. Here are a few other things you need to know, your rear cross member and rear transmission mount will work with the automatic but you will have to move it back slightly for it to work. Just cut off the mounting rivets and drill new holes and remount with grade eight bolts.
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Re: Transmission lengths for std to auto swap ('72 highboy)

Post by dave1972 »

Exactly what tpdaniels said. I found c6 out of a dent side hiboy so it had the correct tail housing. Then move the cross member back about an 1 1/2 if I remember correctly. Rear tranny mount sits on cross member perfectly.
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