Driveshaft - transmission tail piece
 

About how long is the front section of the driveshaft (tail piece/yoke) that inserts into the transmission?

After centering my wheels in the wheel wells and mounting the new lowering but multi-leaf springs and getting the axle bracket lined up with the springs center bolt, my yoke/tail piece is out of the transmission a smidge more that it was with the mono spring that were on the truck from the previous owner.

How much yoke shaft sticking out of the transmission is too much?

Re: Driveshaft - transmission tail piece
 

you really gotta post a pic. some slip yokes are longer than others. somebody here may have the knowledge but maybe won't be inclined to research what you are running for a transmission so they will carry on to the next posting. a pic and some better info would help
after doing all that work and change you should block the truck up on it's frame and run the suspension through a full suspension run, from one end to the other, just to make sure the driveshaft is gonna stay where it is and also so it doesn't bottom out on the yoke or the shocks. yup, I know, its easy to do the suspension hung but not that easy to do a full jounce. taking a chance is just that, chancy.

Re: Driveshaft - transmission tail piece
 

Good points! Virtually everything on this truck is non-stock (engine, transmission, rear axle/diff, etc. The engine is a 1959 261 cu/in inline six, the transmission appears to be a GM 4-speed, and the rear/diff is a Hallibrand quick change.

Here are two photos of both the transmission and the yoke. Given all the custom aspects of the truck and the fact that now the wheels are centered in the wheel well, I may ultimately need to have the drive shaft lengthened if the yoke is pulled out too far. There is approximately 2 inches of the yoke showing.

Attachment 2236589

Attachment 2236588

Re: Driveshaft - transmission tail piece
 

personally I wouldn't trust that. if the front of the driveshaft comes out of the trans it can make a real mess under the truck and if the fuel tank is also under there it could be a really bad day for you.
like said though, do the full suspension travel and take dimensions on that yoke each time. then you will have a good idea of how much change you will need in the shaft length as well as if the shocks bottom before the suspension hits the jounce stops, etc. for leaf spring suspension also factor in a bit for spring wrap which can cause the pinion angle to change.

Re: Driveshaft - transmission tail piece
 

Again, all good points. Once the truck goes from being a roller to a driver, I will 1) test the suspension travel and its effect on the drive shaft, just the way I did when I lifted my Jeep. 2) decide on the length necessary to add to the drive shaft (after I find a qualified drive shaft shop to lengthen and balance it. Fortunately, the fuel tank is behind the diff and out of the way of a flailing drive shaft. Obviously, more work to be done.

Re: Driveshaft - transmission tail piece
 

if you get a dimension for the new driveshaft you could also check if an OEM vehicle shaft is kicking around that would be the right length. might save you some bucks but tke you some time.

Re: Driveshaft - transmission tail piece
 

when you gat the shaft off slipit all the way into the trans and get that dimension as well, so you know the absolute bottom out dimension.

Re: Driveshaft - transmission tail piece
 

I'll probably pull the drive shaft out later this week to get its current measurement. I just found a decent drive shaft shop a few miles from my home. I'll call them in the morning to see what their quote it on working on this one, then go from there. Thank you.

Re: Driveshaft - transmission tail piece
 

The way it is now it will probably knock the tailshaft bushing out in a couple hundred miles just like mine did on the way to the Street rod Nationals in Tulsa in 1973. I had the same issue, when I put my wheels back where they were centered in the wheel well my driveshaft was too short.

If you look real close the seal used to ride pretty close to where I put the arrows.

If you know Bob Davis who used to teach Auto mechanics at TSTI in Waco and at least used to be heavy into early F100 trucks you can ask him about helping me change the tailshaft on the trans in a wrecking yard in Marietta OK in 1973. That was after I burned out my coil crossing the red river.

Re: Driveshaft - transmission tail piece
 

When I was struggling with the leaf springs today, at one point the yoke was all the way in, but the wheels looked awful in the wheel wells, almost scraping the front edge. It was obvious that wasn't going to work, so I changed up the spring mounts and the earlier photo is the end result. Wheels look great, leaf springs fit properly, yoke is too far out......go figure.

Re: Driveshaft - transmission tail piece
 

Bingo. You are right on the money. Where you placed your arrows is exactly where the yoke was with the mono springs. When I tried to place the axle using the yoke as a guide, the axle/wheels looked ridiculously too far forward in the wheel well. It looks like a lengthened drive shaft and/or new drive shaft is in the cards for me.......

Re: Driveshaft - transmission tail piece
 

I concur, that is sticking out too far.

this table might be useful:
https://www.demandaam.com/technical-...l-of-materials

I had a driveline place make a new driveshaft about 5 years ago and it was not that horrible, 350 ish Canadian as I recall. That is a lot cheaper than hating the way your wheels look in your fenders every time you walk up to your truck.

Re: Driveshaft - transmission tail piece
 

If you can find another shaft that's too long it may be cheaper to shorten that than retube yours.

I’ll know more once I take the drive shaft off and get a measurement. I’ll be calling a shop tomorrow to get a price quote to add some length and balance. If buying a new one is cheaper, I’ll be going that route for sure.
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Re: Driveshaft - transmission tail piece
 

Making the driveshaft is the last thing I ever did.
With everything mounted up and sitting at ride height then you can get an accurate measurement. Add some fuel to the tank too or the fuel tanks full weight in the box. Barbell weights help in that.
Rule of thumb was push the yoke in all the way and then pull it out 1 inch.

Re: Driveshaft - transmission tail piece
 

Yikes! I wouldn't drive that one foot. If it failed i wonder which way the forward end go? Up on down?

Re: Driveshaft - transmission tail piece
 

I had the same problem When I installed the Flatout crossmember and changed the motor mounts the yolk didn't have enough engagement with the TH350 trans. I replaced the 4'' yolk with a longer yolk, I believe 6'' yolk from Summit. I don't know if this is another option or if I was just lucky it worked out.

Re: Driveshaft - transmission tail piece
 

I just finished the final installation of the leaf springs and removal of the drive shaft (but not before a number of measurements). Once the leaf springs were fully installed and tightened, I found almost 2 1/2 inches of the transmission yoke showing, out of a total 4 inch length of the insert section) when previously there was about 3/4 inch showing.

Based on measurements of the drive shaft, I need to have the shaft lengthened about 1 to 1 1/2 inches. I counted the splines on the transmission yoke at 27 and see longer yokes at both Summit and Speedway at a fraction of the cost of lengthening the driveshaft (best quote this morning is $300-395). I may consider this route. Thanks.

Re: Driveshaft - transmission tail piece
 

longer yoke could / might lead to vibration or bushing wear.
At some point an unsupported shaft starts to rotate off centre

I would not run a longer yoke with the stickout you show on a LS swap pushing a $5,000 t56 magnum, but would probably give it a shot on a 235 twisting a $75 Saginaw 3 speed

Re: Driveshaft - transmission tail piece
 

Attachment 2236944

Wheel centered with lowering but multi-leaf springs. Also 1 1/4" wheel spacer/adapter installed. Wheel rotates clear of the caliper and is clear of the wheel well.

Re: Driveshaft - transmission tail piece
 

How’s your pinion angle?
Or what’s your pinion angle?

Re: Driveshaft - transmission tail piece
 

I've been told that I"m incorrectly measuring the pinion angle with my gauge. Given that the driveshaft is currently off, how would you suggest I measure the pinion angle. When I put by magnetic gauge on the output yoke of the differential, it is showing 0 degrees. When I put the gauge on the output shaft of the transmission it is between 2 and 3 degrees.

Re: Driveshaft - transmission tail piece
 

Depends on the measuring tool you have.
Put it on the yoke ear or the yoke face.
With 2-3 down on the trans and at zero on the pinion you should be fine. The rear end tends to climb (rotate) upwards a couple degrees making them equal. Leaf sprung does that, coil spring doesn’t.

Re: Driveshaft - transmission tail piece
 

This is what I used. Disregard this measurement, its from a prior test. Just wanted to show what I used.

Attachment 2236967

Re: Driveshaft - transmission tail piece
 

that angle may change slightly with a longer shaft due to the trans end going further forward. should be a minor cange though