I have encounter premature prop shaft failure (bearing failure on spider)initial accessment suggested that the big angle of deflection (17degrees_shaft max of 23 degrees)had caused the seal of the needle bearing to fail 1st and as a result debries enters and bearing siezed. I am aware that by reducing the angle or deflection, reducing the speed the failure can be averted and also the bearing is likely to be the component to fail 1st in such cases. Is there anyone out there who had experiences in such problem and manage to find a solution by doing something to the bearing?
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Prop Shaft Failure due to big angle of deflection..
- Thread starter Blurr
- Start date
GregLocock
Automotive
Coo. No. I have seen UJs on PTO shafts at 30 degrees so it is possible. Check out the torque capability for your UJ at the load and speed you encounter.
Cheers
Greg Locock
Cheers
Greg Locock
- Thread starter
- #4
A UJ is subjected to constant cyclical acceleration and deceleration when deflected from a straight driveline. The larger the angle, the worse it gets. This causes high stresses on the bearings. One way of alleviating this is to have two UJs on the shaft, as is the normal thing to do. Is this the case here? If not you need a CV joint instead.
I used to own a Triumph Spitfire that was designed with a fixed diff and a single UJ on the inner end of the rear driveshafts. It used to eat UJs so often that I used to keep a spare in my garage and I could strip the rear suspension and change one in a couple of hours. It wasn't until years later that I realised that the design was flawed, not that we owners could do anything about it.
I used to own a Triumph Spitfire that was designed with a fixed diff and a single UJ on the inner end of the rear driveshafts. It used to eat UJs so often that I used to keep a spare in my garage and I could strip the rear suspension and change one in a couple of hours. It wasn't until years later that I realised that the design was flawed, not that we owners could do anything about it.
- Thread starter
- #6
Yup both ends of the shaft are using UJs . I understand CVs will prolong the life of the bearing/shaft life. The problem here is that the limited space i have inbetween the axle and the hub (350mm) I have yet to find one shaft with CVs that can fit into the space. Any recommendations?
Can the components be re-aligned so the change in angle is +/- 11.5 instead of 23 degrees?
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1 - I'd get professional manufacturer's analysis of a well used joint
2 - Get evaluation of your application direct from a premium U-joint manufacturer's engineering department, and Kluber lubricants. They will want to know how hot the joint is when running at high speeds.
3 - Rebuild with Premium joints and Kluber grease
4 - Relubricate at something like 1/4 failure interval
--------------------
From SAE AE-7 max >>suggested<< speed for Cardan joint at 20 degrees is about 800 rpm, as limited by max angular acceleration of 1500 rad/sec2. This angular acceleration results from the 2X up and down speed variation inherent between input and output speed. With large driver/driven components, Phasing the 2 joints, and keeping the input and output shafts parallel means the only extra joint forces would result from accelerating/decelerating the intermediate shaft mass.
As I look at typical u-joints it looks to me like centrixxxal force would tend to keep grease in a joint. Can you see an indication of greasy mess in-line with the joit after a hi-speed run?
With all due respect to your shaft maker, and all other honest and experienced craftspeople, I would be REAL interested in the joint manufacturers evaluation of a well used but not yet badly failed joint.
Are the joints made by a well known manufacturer? If not, I'd certainly try again with premium joints. Bargain ball/roller bearings are sometimes tragically deficient in material quality, heat treat quality, or journal surface finish, or uniformity of ball/roller diameter.
How are you allowing for plunge, or axial growth? It seems like you probably need a spline in there somewhere.
Grease base oil gets oxidized by heat, and torn up by the shearing of roller action. The higher the rpm (oscillation in the U-joint rollers) the shorter the grease life. Bearing life can not be greater than grease life. There are synthetic greases that have vastly improved life at high speeds. An alternative is to re-grease the bearing more frequently.
---------------
1 - I'd get professional manufacturer's analysis of a well used joint
2 - Get evaluation of your application direct from a premium U-joint manufacturer's engineering department, and Kluber lubricants. They will want to know how hot the joint is when running at high speeds.
3 - Rebuild with Premium joints and Kluber grease
4 - Relubricate at something like 1/4 failure interval
--------------------
From SAE AE-7 max >>suggested<< speed for Cardan joint at 20 degrees is about 800 rpm, as limited by max angular acceleration of 1500 rad/sec2. This angular acceleration results from the 2X up and down speed variation inherent between input and output speed. With large driver/driven components, Phasing the 2 joints, and keeping the input and output shafts parallel means the only extra joint forces would result from accelerating/decelerating the intermediate shaft mass.
As I look at typical u-joints it looks to me like centrixxxal force would tend to keep grease in a joint. Can you see an indication of greasy mess in-line with the joit after a hi-speed run?
With all due respect to your shaft maker, and all other honest and experienced craftspeople, I would be REAL interested in the joint manufacturers evaluation of a well used but not yet badly failed joint.
Are the joints made by a well known manufacturer? If not, I'd certainly try again with premium joints. Bargain ball/roller bearings are sometimes tragically deficient in material quality, heat treat quality, or journal surface finish, or uniformity of ball/roller diameter.
How are you allowing for plunge, or axial growth? It seems like you probably need a spline in there somewhere.
Grease base oil gets oxidized by heat, and torn up by the shearing of roller action. The higher the rpm (oscillation in the U-joint rollers) the shorter the grease life. Bearing life can not be greater than grease life. There are synthetic greases that have vastly improved life at high speeds. An alternative is to re-grease the bearing more frequently.
You didn't describe the rest of your setup. Can you repositioning the differential/axle/etc? A high angle of deflection can often be reduced by the simple use of shims.
otherwise:
...use a double cardan joint. If you can't find a shorter driveshaft, then modify yours. Cut, weld the flange, and balance (if needed). If you want longevity, there isn't much you can do to your current setup.
As usual, check the obvious: Are the u-joints properly greased and maintained. Is there a grease fitting..?
Was the spider pre-greased and installed properly?
otherwise:
...use a double cardan joint. If you can't find a shorter driveshaft, then modify yours. Cut, weld the flange, and balance (if needed). If you want longevity, there isn't much you can do to your current setup.
As usual, check the obvious: Are the u-joints properly greased and maintained. Is there a grease fitting..?
Was the spider pre-greased and installed properly?
What make and model car do you have? For a live axle car the Ginetta G.4 has about the shortest drive shaft I've seen and with +/- 2" of suspension travel youe at +/- 11.9 deg but then both the engine and the drive shaft are at angles in 2 different planes. Never had a problem and at max it is probably closee to 20 deg at full bump.
- Thread starter
- #12
Its a heavy duty track type vehicle.
Unfortunately the config of the axle and hub could not be changed. Yes, the shaft (ELBE shaft) is splined...the original spiders are non maintainable ones, currently am trying to use the maintainable ones hopefully these could help. Anyone know of any brands/type shafts (2100Nm) with CV & flange that are within 350 mm? Thanks !!
Unfortunately the config of the axle and hub could not be changed. Yes, the shaft (ELBE shaft) is splined...the original spiders are non maintainable ones, currently am trying to use the maintainable ones hopefully these could help. Anyone know of any brands/type shafts (2100Nm) with CV & flange that are within 350 mm? Thanks !!
Oooh, tracks... Whats the torque transfer like? What I mean is, is the torque constant and smooth or does is peak up and down with bad reversals? I would imagine a metal track would be anything but smooth along a hard surface. I would imagine such vibration would play havoc with the spiders & brngs. You may have to up-rate the UJ for the higher peak torques.
Might be an idea to try and get away from rigid joints and look at donuts or other such flexible couplings. Having said that, trying to get a flexi-joint to cope with such a high angle of deflection and what I'm guessing will be high torque loads will prove difficult.
Well, good luck!
Might be an idea to try and get away from rigid joints and look at donuts or other such flexible couplings. Having said that, trying to get a flexi-joint to cope with such a high angle of deflection and what I'm guessing will be high torque loads will prove difficult.
Well, good luck!
- this may be useful
Contact Jesse at this site, he is in the know about fabricating drivelines. He is not an engineering type, he is a hands-on type who built his reputation in the 4wd crowd. He has built some interesting custom shafts in the past.
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