driveline angle

[dhigdon@southerntank]

I'm building a 67 c10 swb. I have a 700r4 and 12 bolt gm rear, 4/6 drop. My driveshaft is at 1.5 degree angle. Seems I read you need at least 3 degress of angle. Is this setup going to be ok?

[Lee H]

Drive line angle will change with the cab, box, etal installed.

[Jason Banks]

I'm not sure the angle of the actual driveshaft is as critical as making sure the angle of the pinion on the differential and the angle of the engine are equal.

I found this page - https://4xshaft.com/blogs/general-te...veshaft-angles
The 2nd video gives a great explanation.

You are going to want to check all this once the whole vehicle is assembled and all the weight is on the suspension.

I'd make sure the back of your transmission is angled down slightly and then adjust the differential with shims once the weight is on. It looks like you are using a factory transmission crossmember that doesn't have much adjustability, other than shimming the transmission up.

[Richard]

The working angle of the ujoint is what matters, not the driveline angle. Driveline angle + trans angle and driveline angle + pinion angle determine working angle at ujoints. Working angle should not be zero, If over 3 degrees it is not really a problem as well. I see problem of people believing both angles should be set the same, not allowing for load at axle. Angles should be equal under load. That is the main reason some experience vibration issues. Angles constantly change while driving. With a modified vehicle the key is finding the sweet spot for average driving conditions.

[72SB]

OP, you want the engine/trans angle and pinon angle to be equal but opposite and ideally not more than 3 degrees each.

Once you get the Truck weight on all 4 tires, you may need to either add shims between trans and mount and/or angled shims on the rear end

If, for example you wind up with 3 degrees down on motor/trans but 2 1/2 up on the diff, doubt you will feel any vibes but you could just put 1/8" shim under trans to make it 2 1/2 degrees also.

[Richard]

Originally Posted by 72SB

OP, you want the engine/trans angle and pinon angle to be equal but opposite and ideally not more than 3 degrees each.

Once you get the Truck weight on all 4 tires, you may need to either add shims between trans and mount and/or angled shims on the rear end

If, for example you wind up with 3 degrees down on motor/trans but 2 1/2 up on the diff, doubt you will feel any vibes but you could just put 1/8" shim under trans to make it 2 1/2 degrees also.

Yes, you want the ujoint angles close to parallel. But that is while driving.
Setting them that way at a static position may cause problems. The pinion will twist up even with a trailing arm or link suspension under the load of driving. That is the point I was trying to convey. Pinion may need 1-3 degrees more operating angle depending on type of suspension to eliminate any vibrations. Just trying to help out. I see many posts about drivetrain woes. The ujoints move in an ellipse. Nothing exact about their operation during suspension movement.

[Keith Seymore]

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[Keith Seymore]

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[Keith Seymore]

Those are from 30+ years ago, but the science hasn't changed.

K

[Richard]

Thank you for posting that information again for people that do not know it. It is important information to know. I am fortunate to know that information and have the knowledge and ability to apply to different situations. There is textbook and application. I stand by my recommendations. I have two GM vehicles that are in stock form. A 2000 truck and 2020 Blazer. I am going to take the time in the near future to measure the working angles on shafts to see if they support textbook or what I see. Worked for over 40 years making adjustments to engineer/textbook specifications to make products work in real life in my career. Custom application.

[Robert Crandall]

Thank you, Mr. Seymore, for posting this. I am preparing a 12 bolt differential from a 1966 C10 to put into my 1950 GMC. It will be a couple of months before I can get to installation, but your information is timely for me.

I made my brackets, and they are not installed. What I think I need to do is place the differential and not welded brackets onto the springs, with the pinion intentionally low, install the u-bolts, and put the weight of the truck on it. Next, jack the pinion up until the angle of the face of the pinion matches the angle of the face of the rear of the transmission. Then tack the brackets in place, remove the differential, and have a real welder complete that welding.

Figures 4-28 and 4-29 show the faces of these end components as being vertical. Mine are angled from vertical. My plan is to make these two angles match.

Will this be correct?

[Keith Seymore]

Originally Posted by Richard

I stand by my recommendations. I have two GM vehicles that are in stock form. A 2000 truck and 2020 Blazer. I am going to take the time in the near future to measure the working angles on shafts to see if they support textbook or what I see. Worked for over 40 years making adjustments to engineer/textbook specifications to make products work in real life in my career. Custom application.

Your posts are exactly correct. My posts were not directed at you; they just were next in line.

I, too, have been fixing other people's mistakes for about 50 years. I wrote those for inclusion in the S/T truck service manuals.

K

[Keith Seymore]

Originally Posted by Robert Crandall

Thank you, Mr. Seymore, for posting this. I am preparing a 12 bolt differential from a 1966 C10 to put into my 1950 GMC. It will be a couple of months before I can get to installation, but your information is timely for me.

I made my brackets, and they are not installed. What I think I need to do is place the differential and not welded brackets onto the springs, with the pinion intentionally low, install the u-bolts, and put the weight of the truck on it. Next, jack the pinion up until the angle of the face of the pinion matches the angle of the face of the rear of the transmission. Then tack the brackets in place, remove the differential, and have a real welder complete that welding.

Figures 4-28 and 4-29 show the faces of these end components as being vertical. Mine are angled from vertical. My plan is to make these two angles match.

Will this be correct?

Yes.

The engine/trans assembly will angle down, approx 3-5 degrees depending on manufacturer. The rear axle should angle up commensurately, but also accounting for any wrap motion during accel/decel.

If you are using leaf springs then you'll want a couple extra degrees windage in there to account for windup during acceleration.

K

[mr48chev]

It can't be done any better than Keith Seymore showed in his posts as far as this goes.

The only real reason the transmission angles down at all is to clear low floor boards.

On AD and TF trucks the stock centerline of the crank and mainshaft in the transmission sit pretty level. On sixes the carb sits level to the head and block. Get into the V8's and they started putting the engine and trans at a slight angle to clear the floorboards in cars and they made the intake manifolds so that the carb sits level . Now we install our engines at an angle to put the carb mounting surface level and that is why all too many guys think you have to set the engine up at an angle for U joints or drive shaft.

Transmission shaft and pinion shaft = parallel is the main concern. Don't listen to the ricky racers down at the spit and whittle club who say you have to have the pinion pointing down at an angle to compensate for torque, They were the ones who were always breaking U joints at the starting line at the drag strip with that nonsense but they are still around giving bad advice.

[Robert Crandall]

Thank you all for this information. This is very helpful to me. I feel that my questions may have hijacked the original poster's question. I hope not, but I do apologize if I did do that.

I am well practiced at seeing things wrong, so, I ask to clarify: Are Mr. Seymore's recommendation in post #13 to add a couple of degrees to the pinion angle and diagram page 3-6 provided by mr48chev in post #14 showing me the same thing? I worry about adding 2 degrees to the wrong direction.

It will be a couple of months before I will be able to make my switch.

Again, thank you all for your help.