Driveshaft question 78 4x4 longbed

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TeamNeptune
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Driveshaft question 78 4x4 longbed

Post #1 by TeamNeptune » Tue Oct 09, 2018 5:37 pm

I have a 1978 f150 Ranger 4x4 long bed with a 300 six I have been working on. It has a 4" lift with 35" tires. Originally it had a 3.50 gear. I mainly use it to pull my boat hear from the Charlottesville va area mostly east. My boat is around 2000lbs and the truck would struggle to keep up speed on some hills. So I decided to go with a set of 4.11's to bring the gearing back closer to stock. I drove the truck for the first time on the highway with the 4.11's and it ran really well up to about 65mph after 65 it would start getting a vibration which was worse if I coasted at that speed. one driveshaft place told me it had reached critical rpm but its hard for me to believe that Ford would build a truck that couldn't safely go 70mph. I am in the 2700 rpm range at 70mph..

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Re: Driveshaft question 78 4x4 longbed

Post #2 by wsa111 » Wed Oct 10, 2018 3:16 pm

First check u-joints for play.
Balance driveshaft.
Make sure the trans output shaft is parallel to the angle of the pinion shaft u-joint flange.
Best of luck.
67 mustang,C-4, with mod. 80 hd, custom 500 cfm carb with annular boosters, hooker headers, dual exh.-X pipe, flowmaster mufflers, HEI dist. Engine 205" .030" over with offset ground crank & 1.65 roller rockers. 9.5 comp., Isky 262 cam.
2003 Ford Lightning daily driver. Recurving Distributors. billythedistributorman@live.com
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Re: Driveshaft question 78 4x4 longbed

Post #3 by TeamNeptune » Thu Oct 11, 2018 5:37 am

Yes thanks. I have some new slipjoint yolks and u-joints on the way. I wasn't sure if I should be considering a larger diameter shaft. I decided to go ahead and repair what I have and see. Hopefully the male spline is not too worn.

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Re: Driveshaft question 78 4x4 longbed

Post #4 by wsa111 » Thu Oct 11, 2018 9:52 am

Check the driveshaft for runout.
Make sure the bushing in the trans extension housing is not worn.
Get the shaft balanced.
67 mustang,C-4, with mod. 80 hd, custom 500 cfm carb with annular boosters, hooker headers, dual exh.-X pipe, flowmaster mufflers, HEI dist. Engine 205" .030" over with offset ground crank & 1.65 roller rockers. 9.5 comp., Isky 262 cam.
2003 Ford Lightning daily driver. Recurving Distributors. billythedistributorman@live.com
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Re: Driveshaft question 78 4x4 longbed

Post #5 by TeamNeptune » Thu Oct 11, 2018 7:44 pm

The shaft comes out at the transfer case. I could not feel any play or movement in that yolk.
I will take it to be balanced after installing the new yolk and new u joints.
Looks like I won't get the parts until the middle of next week but I will post back with my results.
Until then I guess I should get started on getting these 4.11 gears in the front dana 44.
I am trying to decide if I should get a case spreader or not. I have set up several 9" gears but this will be my first dana 44.

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Re: Driveshaft question 78 4x4 longbed

Post #6 by TeamNeptune » Thu Oct 11, 2018 7:51 pm

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Re: Driveshaft question 78 4x4 longbed

Post #7 by bubba22349 » Fri Oct 12, 2018 8:18 am

:hmmm: Have you checked the condition of the driveshafts center support bearing? A worn out or damaged one is a common cause of driveshaft vibration. Good luck :thumbup: :nod:
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I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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Re: Driveshaft question 78 4x4 longbed

Post #8 by B RON CO » Sun Oct 14, 2018 8:46 am

Hi, one of my tricks is to put the truck up on stands and run it in gear. Often you will see what is causing the vibration. Be very careful supporting the truck and when you crawl underneath.
Besides that, as mentioned, the driveshaft angle is different with the lift. If it too severe there are shims for under the spring pads to point the yoke more at the transfer case.
Good luck
B RON CO. Still workin' on it!

1933 Ford Pickup - 59A Flathead V8
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Re: Driveshaft question 78 4x4 longbed

Post #9 by wsa111 » Tue Oct 16, 2018 4:25 pm

If has a two piece driveshaft. Make sure the u-joints are in phase from the front shaft & rear shaft.
67 mustang,C-4, with mod. 80 hd, custom 500 cfm carb with annular boosters, hooker headers, dual exh.-X pipe, flowmaster mufflers, HEI dist. Engine 205" .030" over with offset ground crank & 1.65 roller rockers. 9.5 comp., Isky 262 cam.
2003 Ford Lightning daily driver. Recurving Distributors. billythedistributorman@live.com
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TeamNeptune
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Re: Driveshaft question 78 4x4 longbed

Post #10 by TeamNeptune » Wed Oct 17, 2018 5:05 am

It has a 1 piece driveshaft I think I measured it at 72". That is why one shop was telling me at 2600 rpm it had reached its critical rpm and would start to bow and shake if spun any faster. I get the new yolk for it today but I won't have time to do much until this weekend. I still need to get the front diff. together. The old 3.50 pinion measured the same as the new 4.11 for thickness (it was within .005). I am hoping just transferring the old shims over will give the new one the right depth . I am not sure the math and the factory pinion depth seemed about .030 off . That seems like a lot from just wear.

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