Drive shaft angle/vibration question
 

Hi all,

I had the frame stretched on my Kenworth T2000. I had 8 feet added to the wheel base and installed a 26' box on the chassis behind the sleeper. A place out in Gurnee, Il area did the frame stretch and driveshaft work. I am questioning the way they did the drive shafts and wanted another opinion. I now have 3 drive shafts that are about 5' long going from the transmission to the front differential. The first one was always there, but then added 2 more to make up for the length added. I haven't measured the angles of them yet but will. The first 2 drive shafts are angling down about 10 degrees or so and the last one angles up just a bit (approximately 5 degrees). All the information I can find has all the drive shafts angling down. I feel a slight vibration now in the floor and shifter when under heavy load and acceleration. When I take my foot off the accelerator pedal it stops immediately. Does anyone see a problem with this drive shaft setup? I am not sure if the last driveshaft going the opposite direction would be causing a vibration or not?

Thanks,
Steve

I'd take it to another shop and have them look at it. I don't know anything about driveshaft stuff but think a good shop will be able to advise.

thanks, I sent volvoman a note as well as he has a drive shaft shop in Rockford by me. Hoping a retired trucker will chime in and have some advice!

Steve

Steve;

I have an Allison driveline manual you will probably find useful for information.

Send me an email to robsautoaffair@gmail.com and I'll get it to you. The size limitation of this site precludes me posting it.

Rob

Look at the angle from the pinion (the flange on the rear end) and the rearmost drive shaft. there should be very little angle here.

If I'm understanding you correctly.... going from front to rear, you have:
1st Drive shaft exits the transmission ---> angles down towards the first carrier bearing
2nd drive shaft exits the first CB ---> angles down towards the 2nd CB
3rd drive shaft exits the 2nd CB ---> angles UP towards the rear end

If this is how your system is it sounds wrong to me! each time you have a joint you want to minimize angles. In an ideal system your pinion should point directly toward your transmission output and the driveshafts should be in a straight line between the two.

Sometimes things will be a bit different from the ideal, however I can't see going down and then back up unless you are going around some really strange stuff on the chassis or perhaps your pinion angle is set wrong. (down)

Some other things to consider:

--You should have your U-Joints all alligned in the same plane, (all of the bearing caps on the large side pointed down)

--How does your pinion angle change through the suspension cycle or under load?(shouldn't be much!) Are there any loose suspension links that allow unwanted movement?

As the other posters noted, you need to minimize all angles on the driveshaft. And normally all the driveshafts would point "down", and in keeping with that the pinion on the rearend would always point "up". I suspect it is the angle from the pinion to the rearmost driveshaft that is giving you the trouble. I'll bet if you put an angle finder on the pinion yoke you will find it is pointing "up" by a few degrees like it should be. You're a racer so you should have an angle finder in your toolbox anyway, and if not they are cheap at Harbor Freight and the like. The solution will probably be to raise each carrier bearing slightly until you have the same angle at each joint. Or you could look at it with the angle finder stuck to the top of each section of driveshaft and calculate the difference between each. For example (and I'm picking these numbers out of the air as an example) the first driveshaft might be at 88 degrees (2 degrees from level) and the next shaft 86 degrees and the last 84 degrees which would also be 2 degrees from the actual pinion angle. The idea is to have the same angle at each joint. Also of note, when I was talking to my driveshaft shop about lengthening my truck he told me the longest shaft they would build would be 54". Not sure if that was due to strength or vibration issues.

Hey Hot rod and Asitool, Yes you interpreted me correctly, my first 2 drive shafts go down and my final one goes up! When I have built chassis for racing this is a no, no, but never did one on a truck so didn't know if you could get away with it or not! I think the fab shop that did the work was too lazy to raise the first 2 carrier bearings and this was the easy route to take. From my understanding you want the difference of the 2 angles from one end to the other to be the opposite of each other within 2 degrees. Mine are within the 2 degrees, its just that the last one is going up. There is nothing in the way that they are avoiding. I will have to try and get them to readjust the angles. Thanks for the info guys.

I also did verify the phasing is correct of the u-joints and yes it is.

sent you a message to let me know your email. i can send you pages out of spicer book. take it back to the shop and have them recheck angles. were they a driveline shop or just truck repair shop. maybe the driveline shop they had sublet driveshaft rebuilding would help. another thing were driveshafts balanced as a assembly or separate? if you want call me and we can check them out for you. just hate to see you pay twice for repairs that should be warranty.

Thanks for the tip. I sent you a message with my contact info, I have misplaced yours, sorry.

I imagine the drive shafts were done separately. My original driveshaft was used, a used one was purchased and installed and they shortened another used one. I am not sold that it is a drive shaft issue other than I have never seen a drive shaft angle up before. The vibration is not terrible and is only felt when under hard acceleration. As soon as your foot is off the throttle the vibration is gone? The vibration is felt mostly in the shifter and maybe a little in the wheel and floor but you have to be looking for it to feel it every where but the shifter. The shifter kind of feels like the handle on a lawnmower. Not a real violent vibration but a fine and consistent one. Not sure how normal or un normal that is???

Thanks for the help.
Steve

I have had the same issue in a 2013 389 pete. The clutch pedal was the culprit.
Sounded like the driveline was going to come apart, but when I placed my fott on pedal it all went away. Adjusted the clutch, no more isuues. Also is the airride valve set correctly? May have been bumped during the stretch.

For me the vibration goes away as soon your foot comes off the throttle. Will check the clutch adjustment out though for sure. I did have problems with the airride valve sticking so have replaced it as well. When I had the truck at CIT, they checked all the angles of the drive line and set the ride height for me. Drive line angles were not ideal. I readjusted them to be in spec at home but didn't seem to effect the vibration at all. I continue to use it but just worry that something is a ticking time ball!