Measuring for torque tube shortening

C

clo

Member
I need to shorten a 34 torque tube and drive shaft. I know there is the bearing and keeping the speedo gear in its place. I don’t know how far in the drive shaft sits in the u joint. It will be shortened fron the rear of the drive shaft. Where do I take my measurements from? It will need to be shortened about 2’’ to 3’’.
 
not very scientific here, but i have always used this plan. when you look at the end of the shaft in the torque tube, you will see that the straight part of the splines come up to flush with the end of the bell, set a straight edge across the bell you will see it, and rounded end part of the shaft, forward of the splines extends beyond the bell by about an 1/8". so, make your tube fit, then put it together and see how much you need to shorten the shaft
 
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I have someone that can shorten it but i have to give him the measurements. Just want to be right the first time.
 
Just remember to deduct for the pinion and coupler. Dont make the drive shaft the same length as the torque tube.
 
Good advice. When I shortened the '40 rear end for the '32 frame we took the same amount out of the torque tube as we did the drive shaft, and it worked great. For a good overview of the process, check out page 56 of "How to Build a Traditional Ford Hot Rod" by Vern Tardell & Ron Bishop. Don't throw away the cutoff driveshaft or torque tube as they are some of the finest steel I have ever machined, and when I need something that size, that what I use.
 
I like to use the 37 to 40 . With the carrier bearing it gives a nice true surface to dial the shaft in with a 4 jaw chuck.

The torque tube flange i cut off long and machine a register to fit back into the shortened tube
Before you weld the flange on, put the shaft back in and bolt the flange to the rear. Lines it all back up.

You also have to relocate the radius rod lug and make.sure the drain on the flange is in the right spot
 
this subject has always had my interest. the first one i did , a warmed up B motor in an A, with v8 rear, and v8 trans. custom length was determined by me, i used a solid shaft from a later v8 as you can get away with that with the short wheel base. note, the OP has not told us what he is building, and at the time i did not have a mill, so a friend milled the splines back into a solid shaft by hand. he did a fair job, one spline was on the loose side, but it had to be forced in so we thought quite acceptable. the next two i did was for 34 fords with 40 rearends so the shaft and tube must be shortened by 9/16". so, hollow tubes, not a shaft. some of you may remember a long thread i did about 4 years ago with all the issues involved. first, i tried to have my local drive shaft place that makes shafts for everything you can name, weld my parts together. reason is, they do it on a machine that welds as it rotates so very little movement from the heat from welding. they could not do it because the machine is set up with fixtures to grab onto modern u joints, not a shaft. so...as usual i did it my self. in a long lathe, with a dial indicator set up to watch the movement after the first tac, i used the cross feed to push it back to straight, then tac again. long story short, i did everything in my power to keep the ends all straight, and they were not straight when done welding. so, the next lesson was in straightening shafts with help here from Pete, and Lawrie. got that done, then, no place in several hundred miles that could balance it. did that myself too with a static balancer. After about a month long episode here on the barn, Cory taulbert comes in and says he does it all the time, start out with a new tube, 4130 steel, for hollow shafts, and easy peasy according to him. no mention of straight or balanced, but my point is, if it a hollow tube, be sure of who you hire. for a solid shaft, many folks get away with just turning down the shaft until its a press fit into the coupler, and then rosette weld a couple sides, and weld the end. also, be sure the front bearing surface is good before you spend the time and money on a bad shaft
 
Check out “Mart” on this forum. He did a great video covering this recently on his YouTube channel ‘Marts Garage’.


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I measured two factory torque tubes and the corresponding driveshafts. This is for hollow shafts that have an internal spline at the end.
The driveshafts are 70mm shorter than the torque tubes measuring to the edge of the pin hole. The edge of the pin hole is 25mm from the end so the driveshaft is 45mm shorter than the torque tube.
If you are using a solid shaft, you need to consider the splined coupler as part of the shaft and work from the 2nd pin hole where it attaches to the pinion.

Set the length of the torque tube to put the rear end where you want it.
Set the length of the drive shaft at 45mm shorter and you're done.
As stated this is shaft total length, including the splined coupler, if used.

Note: I usually work in inches, but for this job, I found mm to be much simpler.

When I assembled mine up, the speedo gear was in just the right place with a small gap between it and the retaining ring.

This video explains what I am talking about.
https://youtu.be/-mOo2eZX_2U
Mart.
 
Does the bell of the torque tube rest against the inner u joint cover? I would think theres some space for movement.
 
Itn is sandwiched between the inner cover and the clamshell. I've never measured for clearance, but as the forward thrust of the vehicle is through that spherical seating, there is effectively zero clearance between the torque tube bell and the inner spherical cover.
So in simpler words, yes, they do rest together.
 
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Similar to what Mart is saying above, the PIN hole location in the pinion spline for rear end of the drive shaft is one of the critical measuring points.

The centerline location of the speedometer gear is the other critical measuring point on the front end of shaft. ALWAYS cut torque tube at REAR end. The length required of the torque tube will be determined as a result of situating the rear end banjo housing at the desired location, fore/aft. Bolt the bell end of the torque tube to the transmission. Whatever dimension of tube that goes rearward BEYOND the banjo front bolt face is the total amount to shorten torque tube...shortening at REAR of tube.

When re-welding rear of torque tube, make sure the drain-back hole in banjo flange is at the correct, BOTTOM rotation. Also, make sure SPEEDOMETER turtle hole is clocked as necessary for your application. DD
 
clo said:
Does the bell of the torque tube rest against the inner u joint cover? I would think theres some space for movement.
Click to expand...

As Mart says, they rest together, essentially touching each other, with a healthy film of grease between the two for lubrication. DD
 
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