A few driveshaft questions

[83L98blazer]

My 83 K5 blazer originally came with a 700r4 transmission and a np208 but sometime in its life it was converted to a th350 but they still used the original TC. My question is, How much shorter is a th350 then a 700r4? The reason I ask is because they used the stock driveshaft and under any accerleration it vibrates. Now I solved the problem by making some 1" spacers to lower the crossmember but I would really like to just fix the problem right and get some more ground clearence back.

I have an idea but I don't know if it will even work. The other day I was flipping though the pages of my new LMC catalog and saw that they sell a stock cv joint. So I was thinking that when I a 4" lift with shackle flip out back then I could install one of these and then raise my TC back up. This way the CV would add length to the shaft while solving my vibration problems.
How much length will the stock CV add?

Will this even work?

Thanks in advance.

 

[monster man]

The CV overall is about 5". But, if you do the CV on the rear output you need to point your rear pinion up so that the u-joint is at 0 degrees. That usually means rewelding spring perches because to point it up that high will mean a lot of shims. Also, then your whole differential is pointed up and the lubing system in there gets off because the fluid is going to be 45 degrees off, not completely lubign your gear teeth.

 

[83L98blazer]

I always thought that the cv would correct or at least help steep pinion angles.

What about the length of the 2 transmissions?

 

[BlitzK5]

Everything you need to know can be found here:

http://www.4xshaft.com/driveline101.html

 

[pauly383]

I thought in the 80's the shafts were the same length , and the difference was made up in the adapter length . I had a 4 speed/208 shaft next to a 700r4/208 shaft , and they were the same length . You can measure yours and I can measure mine since I have a 700r4 in my DD

Your probably going to want to get an aftermarket CV assembly for the rear shaft , so you can run larger U-JOINTS . The front you can run for a long time with stock Cv and 1310 u-joints , in the front , because you put less miles on the front shaft .

Now you do , like already mentioned want that pinion to point straight at the transfercase , and take the drop off the transfercase .

There are pictures of my angles in my webshots .

 

[83L98blazer]

OK I just had time to read the driveline article and have decided to not go with a CV. But I do want to get my 2 u joint shaft to not vibrate under acceleration at stock height. And when I do a shackle flip in the rear do you think I will need to lengthen the shaft any?

What could make a driveshaft vibrate at stock height under acceleration, but when I dropped the TC down an inch it fixed it? The only thing that has been swapped is the tranny.

 

[monster man]

at stock height, I'm not sure, maybe the u-joints are toasted? They can only handle acertain amount of angle without vibrating, 15 degrees I believe. If they're not within 2 degrees of each other they vibrate.

With my shackle flip I got mondo vibration because it tipped the pinion up, but adding a 6 degree shim fixed that, brought the pinion down to the same angle. Could have gone 4 degrees and they still would have worked well enough, but I'm going to a one piece shaft so they'll be fine then.

 

[tch777]

My bet is bad u-joints or marginal ones. I would change u-joints and balance the drive shaft.

 

[83L98blazer]

Well it has brand new u joints in it, We got the heavy duty joints from Autozone though, if that makes a difference.