1951 Flathead to C4 drive shaft advice

[Grayble 123]

I’ve finally completed my C4 swap in my ‘51 coupe. My question is: Is it necessary to have a custom built drive shaft made? I have replaced the rearend with a 1975 Maverick rear end.

[TJ]

You really need to talk with a competent driveline service company. These people specialize and they will tell you what you need in the way of a new driveline. Your old driveline will not work as the front yoke will obviously not fit the C-4. The existing tube may not be the correct diameter for the new front yoke and your tube may not be the correct length. Do it once and do it right.

[Grayble 123]

I do have the slip yoke for the C4. I read one of the threads where a couple guys said he used the old drive line. I haven’t measured the length needed for the new shaft yet. But I have contacted a local shop for a price quote.

[paul2748]

If your old shaft is longer tha what you needed, it can be cut down to fit. A shop can attach the correct end for the c4 yoke.

[Grayble 123]

I plan on taking with me if it is longer.

[69a]

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Have you tried fitting your original driveshaft to the Maverick pinion flange. It's a long shot, but stranger things have happened.
Find a Maverick driveshaft and bolt it on, leaving the rest laying on the ground. Put the C4 universal in the back of the transmission and slide it as far in as you can. Set the yokes on both ends so they are horizontal, and measure the distance between the centers of the holes that the universal joint goes in.
Take everything down to your driveshaft man an tell him your measurement does NOT include the clearance needed for installation and operation. I would think it's about 3/8" but let him decide, because he'll be fixing it if it's not right.

[pistonbroke]

Put the yoke in the C4, push it all the way in. Now pull it back 3/4", then with help messure from the center of the U joint cap in the C4 yoke to the center of the U joint cap on the rear end. This is the messurement needed and it should be done with the vehicle sitting in its normal stance. Tim

[rotorwrench]

A good driveshaft shop can quickly fabricate any shaft that you could need. They will even balance it. Dana Spicer u-joints are available in different configurations and sizes. If a person measures a slip yoke and rear axle drive flange for diameters and widths across the yoke surfaces, a size and configuration will become apparent enough that a u-joint can be sourced. If you know what vehicle types and models the yoke and rear axle are from then you have a way to source a u-joint to fit both ends. The drive shaft shops know what knuckles or yokes will be needed to make up a new shaft for a given u-joint type.

[69a]

Originally Posted by pistonbroke

Put the yoke in the C4, push it all the way in. Now pull it back 3/4", then with help messure from the center of the U joint cap in the C4 yoke to the center of the U joint cap on the rear end. This is the messurement needed and it should be done with the vehicle sitting in its normal stance. Tim

3/4" shorter is excessive! The aim is to have maximum engagement of the spline.
You need enough clearance to slip the yokes over the coupling on the pinion, and make sure the spline doesn't bottom out through the suspension travel.
You will be able to see where the tail shaft seal has been running.

[alchemy]

I thought 3/4” sounds too short for clearance. If there are four inches of splines engaged inside, it should be plenty. Best way to make sure you have enough clearance is to cycle the rearend fully up and down, measuring the shortest and longest.

[pistonbroke]

I was told that by Drive shafts unlimited in Olympia Wa. The did anything you could ask for to a drive shaft. In our mustangs and Camaros we would sometimes get a little wheel hop. I you didn't have that extra slip space in there you would tear up your transmission real quick. Especially in an automatic , they really don't like thrust. I wish I had a photo of my racing buddy's C4 after we tried using a third member with a half inch longer yoke. What a mess! Tim