tailshafted
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Post Fiend
Joined: Sep 2004
Posts: 5,231
Likes: 1
From: Near Fresno, California
tailshafted
I am installing an efi 300 I6 with a C6 out of a 86 F100 shorty into my 1972 F250 longwheel base truck. The truck originally had a 390FE/C6.
The tailshafts are different between the two transmissions. The later model (out of a '86 F100 short wheelbase truck) has a splined tail and a single driveshaft, while the F250 has a Ujoint saddle and a two-piece driveshaft with a carrier bearing.
I did a search on this forum and found that the tailshafts should interchange, but the entire transmission has to be dismantled to do this.
Is this correct?
If I had wanted to get involved with a tranny rebuild I would have stayed with the 390.
Also, What if I had the front shaft of the two-piece driveshaft cut and the spline from the 87 grafted on it? Would this work?
The tailshafts are different between the two transmissions. The later model (out of a '86 F100 short wheelbase truck) has a splined tail and a single driveshaft, while the F250 has a Ujoint saddle and a two-piece driveshaft with a carrier bearing.
I did a search on this forum and found that the tailshafts should interchange, but the entire transmission has to be dismantled to do this.
Is this correct?If I had wanted to get involved with a tranny rebuild I would have stayed with the 390.
Also, What if I had the front shaft of the two-piece driveshaft cut and the spline from the 87 grafted on it? Would this work?
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Post Fiend
Joined: Dec 2003
Posts: 6,658
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From: "Islander"
Yup you would have to disassemble the C-6 completely to change out the output shaft as well the tail housing. Trucks used a iron housing with ball bearing vs bushing and slip yoke on passenger cars and 1/2 ton trucks.
.....=o&o>.....
.....=o&o>.....
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Post Fiend
Joined: Sep 2004
Posts: 5,231
Likes: 1
From: Near Fresno, California
Damn, Beemer, it is enough to break your heart. Nothing about this swap has gone right. Worse, I no longer need or want a 3/4 ton truck - too heavy and too much gas.
Both the original engine and transmission need rebuilt - if I had wanted to go through a transmission I would have stayed stock. I am about ready to load all the orginal parts into the box and call the junk man.
But it is a clean, rust free truck with new steering and brakes.
Given that it is being pushed by a six, do you think the slip joint and bushing would stand up to use? I don't want to junk it up but I could have the jack shaft shortened and use the long tailshaft with a slip yoke.
Both the original engine and transmission need rebuilt - if I had wanted to go through a transmission I would have stayed stock. I am about ready to load all the orginal parts into the box and call the junk man.
But it is a clean, rust free truck with new steering and brakes.
Given that it is being pushed by a six, do you think the slip joint and bushing would stand up to use? I don't want to junk it up but I could have the jack shaft shortened and use the long tailshaft with a slip yoke.
Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
I would run it like a F100 with a one piece driveshaft and slip joint then be done. To have two slip joints will cause the center support bearing to center the driveshaft and that rubber cushion would fail. The driveshaft length might have to be altered. For you and other FTE members with 3/4 ton trucks I would get a spare truck not passenger car C-6 trans from a Pick-n-Pull or other yard and store it as they will be getting scarce in the future.
As far as extra weight of a 3/4 over 1/2 ton you won't notice fuel mileage difference that much to worry.
.....=o&o>.....
As far as extra weight of a 3/4 over 1/2 ton you won't notice fuel mileage difference that much to worry.
.....=o&o>.....
Last edited by "Beemer Nut"; Jun 3, 2006 at 01:35 AM.
Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
I didn't do anything.
As far as a hard ride in a 3/4 vs 1/2 ton 80% will come from the back suspension.
My 68 CS with 6,900 gvw acted like no suspension and hurt me as I drive 99% of the time empty.
I disassembled the leafs, flap wheel polished and dressed where shorter spring ends dig in the longer leafs then coated with DuPont's # 521 dry film moly spray. 7 years later still with a softer ride with a full spring pack.
Gearing may be lower on 3/4's, bad on fuel bill. I got lucky as the 68 CS has 3.54's and I run 12.00 x 33 x 16.5 in the rear.
If you start work on the 59 parts will show up for the 3/4 ton, it never fails to happen.
.....=o&o>.....
As far as a hard ride in a 3/4 vs 1/2 ton 80% will come from the back suspension.
My 68 CS with 6,900 gvw acted like no suspension and hurt me as I drive 99% of the time empty.
I disassembled the leafs, flap wheel polished and dressed where shorter spring ends dig in the longer leafs then coated with DuPont's # 521 dry film moly spray. 7 years later still with a softer ride with a full spring pack.
Gearing may be lower on 3/4's, bad on fuel bill. I got lucky as the 68 CS has 3.54's and I run 12.00 x 33 x 16.5 in the rear.
If you start work on the 59 parts will show up for the 3/4 ton, it never fails to happen.
.....=o&o>.....
Last edited by "Beemer Nut"; Jun 3, 2006 at 02:41 AM.
Senior User
Joined: Oct 2001
Posts: 258
Likes: 1
From: Central Virginia
The oil pan on the 6 cyl. will not work in the 72 truck front crossmember. The 72 uses a front sump and the 86 is a rear sump. I think this swap will likely be too much trouble for what you will get out of it (just my 2cents).
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Post Fiend
Joined: Sep 2004
Posts: 5,231
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From: Near Fresno, California
Thanks, Ken. The 300 was sold in this vintage truck so there has to be a way to make it work - however, I am going to sit it aside for a while and reconsider just what to do. With gas at $3.30 a gallon I do not want to build a 10 MPG truck. And, like I said, I no longer need anything this stout.
It would have been fun to play around with the efi, but I really want to get my other project on the road.
It would have been fun to play around with the efi, but I really want to get my other project on the road.
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Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
Working on ther 59 will allow more time for deep thinking on what to do with the other truck, it'll come to you around 3:00AM some morning unless free parts appear at your garage.
The 59 is one cool looking truck, "GIT-R-DONE".
.....=o&o>.....
The 59 is one cool looking truck, "GIT-R-DONE".
.....=o&o>.....
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