Drive shaft noise?

[personaltrainer]

Okay so, I'm at a light with the brake pedal depresed, light turns green, when I take my foot off the brake and befor i touch the gas i hear/feel at "thud".

Not a huge noise, but noticable. My mechanic tells me it's play between the driveshaft and the rear end. Says it's common. Any ideas from you guys? Any common/cheap-ish remedies? Is it gonna tear something up? What to do? Thanks for the help.

 

[personaltrainer]

no ideas? someone's gotta have a clue.....

 

[dremu]

Could be slop in the driveshaft's slip. Grease the splines, see if it goes away?

-- A

 

[personaltrainer]

what is to grease? there is only trans fluid in there, no?

I thought this was a common problem - guess no one knows anything about it. thanks

 

[zeroz400]

It helps to know what year vehcile you have, im guessiing now that you have a slipyoke on your tcase and not your driveshaft. Try changing your ujoints if you have not in a while.


Later

 

[personaltrainer]

'86 Jimmy with 350. I'll have a look at the u-joint today but it doesn't seem like that's it - could be though. thanks

 

[LKJR]

yea, check your ujoints

 

[BigOrange90Jimmy]

If it's an 86, then it most likely has a 208. If it's what I think it is, then it's most likely the slip yoke binding on the output shaft. When you brake, then rear end lifts, pulling the slip yoke out of the tcase. While you're sitting there stopped, the brakes are holding this "lifted" position. When you let off the brake, the rear end falls back to it's original position, which causes the slip yoke to bind, release, and give you the noise you describe.

 

[dremu]

what is to grease? there is only trans fluid in there, no?

I thought this was a common problem - guess no one knows anything about it. thanks

Umm, I'm thinking of the splines on the shaft itself -- it's two pieces, as it were, and might even have a grease zerk on it.

Or your tcase may have the slip yoke.

-- A

 

[personaltrainer]

If it's an 86, then it most likely has a 208. If it's what I think it is, then it's most likely the slip yoke binding on the output shaft. When you brake, then rear end lifts, pulling the slip yoke out of the tcase. While you're sitting there stopped, the brakes are holding this "lifted" position. When you let off the brake, the rear end falls back to it's original position, which causes the slip yoke to bind, release, and give you the noise you describe.

That sounds like the mostly scenario to me. I'll get my buddy to stop the truck, while I'm under it, then release the brake. Think I'll be able to see the play in it? or I guess I could put my hand on it (carefully) to see if I can feel the play in it. Also it leaks trans fluid form the rear output shaft seal - I've replaced it and it still leaks. Think this has something to do with the problem?
Supposing it is a 208 and this is the problem - what next? How do I fix this problem? Thanks for the help.

 

[personaltrainer]

Okay. I looked at it while it was acting up and it is def the drive shaft. At the rear output (befor the 1st u joint) it seems to be pulling out of the t-case. Is this normal? Not too far but enough that I can see it. Also it is leaking trans fluid from the same place. Looking back at it - this problem only arose after I replaced the body bushings - adding about 1 inch to the body lift. I bet that one inch was the straw that broke the camel's back.

What do I do now? Can I get a new output shaft that is a bit longer? what to do? Thanks.

 

[imiceman44]

Okay. I looked at it while it was acting up and it is def the drive shaft. At the rear output (befor the 1st u joint) it seems to be pulling out of the t-case. Is this normal? Not too far but enough that I can see it. Also it is leaking trans fluid from the same place. Looking back at it - this problem only arose after I replaced the body bushings - adding about 1 inch to the body lift. I bet that one inch was the straw that broke the camel's back.

What do I do now? Can I get a new output shaft that is a bit longer? what to do? Thanks.

Well it's typical with the slip yoke shafts to get to this point when lifted.
The upand down force on the shaft will tend to push on the output shaft at the Tcase putting some wear and tear on the bronze bushing at the end of the tail housing.
That makes some play wich makes it easier for the shaft tomove up further thus wedging the splines of the slip yoke with the output shaft splines uner load.
That also explains why even after replacing the seal it stillleaks.
You need to first of all change that bushing in the tail housing.
Next check your angles between the tcase and the drive shaft, if it's more than 18-20 degrees, I would try a SYE (slip yoke eliminator) that will eliminate your pressure against the shaft upwards.
If more than 25 degrees try and get a CV driveshaft to aleviate the angles.
These numbers are conservative so you could be fine after you change the bushing but that does need to be changed.
And yes it's exactly what it is, binding under load then releasing when you let off the brakes.

 

[muddog]

this problem only arose after I replaced the body bushings - adding about 1 inch to the body lift. I bet that one inch was the straw that broke the camel's back.

What do I do now? Can I get a new output shaft that is a bit longer? what to do? Thanks.

the body lift is not your problem. Has no affect on drive line geometry or anything.

Not sure if the rear shaft would have it but the front shaft used to ( not sure if they still use it) have a blue coating on the drive shaft splines to provide something other than metal on metal at the slip yoke. May check that.