driveshaft angle should be around 4deg downward and the tailshaft offset the same as the front crank offset (engine sticking straight back)

 

TT- I know that you have all the theory. I might have dive shaft over 9000 rpm some day so I set the driveshaft nearly straight. thinking that it would work the best. I was wrong. By dropping the tail shaft i increased the angle and the vibration dropped immensly.

U-joint Operating Angle:
This is the angle formed between the two yokes connected by a cross and bearings. It may be a simple or compound angle, depending on the geometry of the driveshaft. While u-joints can operate at fairly high angles (usually up to 30°), the speed at which the shaft moves provides a practical limit to the angle as follows:
SHAFT RPM OPERATING ANGLE
5000 3.25°
4500 3.67°
4000 4.25°
3500 5.00°
3000 5.83°
2500 7.00°
2000 8.67°
1500 11.5°

This table is based upon the joint at rated load and life. Going above the rated load or angle will decrease the u-joints life. As a general rule of thumb, for each doubling of the operating angle, RPM, or load, the lifetime of the joint is decreased by half. Rated lifetimes are on the order of 3000 hours.
In the typical off-road vehicle, a suspension lift is done to increase clearance and allow larger tires to be installed. To compensate for the larger diameter, lower gears are installed in the axles. Lets see what this does for the drive shaft, the lift increases the angle of the shaft and the lower gears means the shaft has to spin faster for a given axle speed, both things are working in the wrong direction on this chart. No wonder, driveshaft problems are common in vehicles modified for off-road use.

 

Did you ever measure the pinion angle? IT's probably aroudn 4 deg upward so you have to set your trans yoke to 4 deg down in that case. If you shim the tranny you have to shim the pinion also to the opposite angle.


Even with those angles, you're always stuck with a minimum angle. With the crank (seen from the side) aiming straight at the diff you will always have the engine offset vs. pinion offset creating an angle . The shorter your driveshaft the bigger the angle.

 

I don't have a way to measure my angles yet. When originally installed the good rearend I also went with a poly snubber shim to keep it from moving very much. Let's just call it 4 degrees up. When i dropped the tail shaft down it might have given the crank/tranny centerline a 4 degree down. I'm going to machine another aluminum block spacer to bring it down another 1/4 inch and retest.

 

Why not get a protractor? They are cheap

 

I was thinking about barrowing a super laser digital gismo with a magnetic base

 

Gkull,

I realize this is a very old thread, but I am having this same problem with my Tremic and I would like to know if you ever solved your problem. Is yes, what did you do?

Mine was installed over 5 years ago and was perfect for about 4 years. Now I have a vibration just as you describe and a very loud rattle in the rear of the Tremic that sounds like something has fallen out. The transmission still shifts fine.

Dejavet

 

This and what twin turbo said is the fix. Our rear end input is really not easy to adjust unless you were to shave or space the snubber arm.

So the fix is to put in or take away rear tail shaft to cross member spacers to match the angle of the rear end. I used big washers to make up and down changes and when I was happy I machined a solid aluminum spacer with an 1/8th inch hard rubber isolator. I also moved my tail shaft over about a 1/2 inch

Boy this is old - how time flys! My tremic is still working fine and I drove over 1200 miles on the weekend of April 28th and 29th

 

Gkull, Thanks for your response. I have not looked at this for a while as I thought you would not respond to such an old thread. I am deep into troubleshooting this problem on my 65. I measured my angles and they appear to be well in speck, but I am willing to try anything. I am not clear exactly where you place washers (spacers) to change the angle of the differential. The Differential is bolted directly to the frame. How can you change the angle when the Diff is essentially part of the frame?

Thanks for your help
Dejavet

 

I also had a vibtration issue and placed a tapered plate between diff and crossmember to provide matching (opposite)angle for pinion angle.

The plate has to be fitted between the diff and the crossmember where it mounts.
The diff has to be dropped out to do this

 

Now I understand. Thanks for your response. I am still working through options and I may try that one.

Dejavet

 

Dejavet, you missed what i posted. I also drilled out the tranny tail shaft cross member mount to adjust left and right,

 

Gkull, I also slotted the transmission mounting holes to move mine about 1/2 inch to the left. The installation instructions said to do this if your shifter was too close to the edge of the hole in the tunnel.

I have decided to pull the transmission and find where the rattle is coming from. I have to pull the engine with the transmission because with a fixed cross member it will be the easiest way. I am beginning to believe the source of my vibration is the engine or the clutch, but I need to find the rattle as well.

Thanks for your help.

Dejavet

Thanks for your help.

 

some guys on here home made removeable cross members. The just cut off each side and welded a flat plates with 4 lbolt holes. Much easier than R&R of the motor and tranny

 

I saw that, but I am not equipped to do cutting and welding, especially with the body on. I expect that some time down the road I will pull the body off to freshen things up. When I do that I will make a removable cross member.

 

I'd drive it to a welding shop and take a SawZall to it.