vibrations :-(
- Thread starter Jorgenson
- Start date
mrtask
Well-Known Member
I'm no engineer, just a bumbling hobby mechanic, but I would venture that it is indeed a possibility. I put an LT77 in my 3500 and it also has vibration issues at speeds above the UK legal limit. I've also used a DIY rear gearbox support. I'm going to renew the UJs in the prop and driveshafts come spring and see if that makes a difference. I look forward to hearing what work you have to perform to sort out your issues.
roverp480
Active Member
I also wonder if the Propshaft UJ angles are in angular tolerance . They can work at different angles , as do LR Discovery 1/2 , but the angles of the propshaft UJ.s need offsetting to compensate
Hi Jorgenson,
I am a civil/structural engineer with some knowledge of mechanics as it is applied to mechanical engineering. Universal joints are designed and phased to operate at a design angle. This angle can be varied typically at most by 3 degrees. If you exceed that angle, then vibration will undoubtedly result.
I have attached an article that provides some guidance. I would suggest that you have changed their operating relationship with the homemade bracket, which is why you are experiencing vibration.
Connecting Multiple U-Joints | Belden Universal Joints
Ron.
jp928
Well-Known Member
Ron,
Can almost follow that, BUT, as usual, it does not address the case we have on P6s, and many other vehicles, of UJs installed out of phase by design, and to quote Julius sumner miller " why is it so?". I have searched the web for an explanation to no avail. When I got my car I pulled the prop shaft (forget why)and checked the alignment of the arrows, and corrected the alignment. coincidentally it had a 2000 part no. Over a few 100 kms I had no issues, but on one occasion I had a quite severe vibration, at low speeds, only lasting a km or so. No idea what happened - foreign matter in a wheel?
Can almost follow that, BUT, as usual, it does not address the case we have on P6s, and many other vehicles, of UJs installed out of phase by design, and to quote Julius sumner miller " why is it so?". I have searched the web for an explanation to no avail. When I got my car I pulled the prop shaft (forget why)and checked the alignment of the arrows, and corrected the alignment. coincidentally it had a 2000 part no. Over a few 100 kms I had no issues, but on one occasion I had a quite severe vibration, at low speeds, only lasting a km or so. No idea what happened - foreign matter in a wheel?
Gargo
Active Member
I'm shamefully in the same boat, at the same speed. It just seems to be a thing and no-one has fixed it.
When I got the propshaft modified the engineering shop commented that the std Rover Prop UJ were not aligned. They made the new one with aligned UJs.
As Cobra Boy says, check the gearbox flange and the differential flange are parallel.
I just wonder even with the flanges parallel, the propshaft will be in angular acceleration, oscillating relative to the gearbox output shaft. This must be producing a vibration, is that what we are feeling. Is the rearward slope on the engine just too much, for a lengthened shaft?
I want to mount the engine flat and rotate the diff to suit which would reduce the shift angle of the UJs.....
colnerov
Well-Known Member
Hi, As I under stand it the flanges should, as said, be parallel to each other but not directly in line so that the UJ's work. Otherwise they can 'freeze' and seize up and cause vibration. Coil sprung Land Rovers have this problem on their front propshafts because the axle swings through an arc and the shafts are phased 1 and sometimes 2 splines, some even have a double cardan on them.
You may find that one of the shafts have a seized joint in one plane causing your vibration rather than a worn out one.
Colin
You may find that one of the shafts have a seized joint in one plane causing your vibration rather than a worn out one.
Colin
cobraboy
Well-Known Member
When I put in an LT77 to replace an auto I had not driven the car either very far, or very fast. It had been laid up for 34 years with IIRC 80k odd miles.
I carefully measured the height of the auto output flange down from the top of the tunnel and set the LT77 flange the same height. The diff was not meddled with on a two owner car, it had the right spacers.
I had bad vibration at around 60 mph. I measured the flange angles and they were 5 degrees apart, I am confident that they were as Rover installed the drive train.
I raised the gearbox as much as I could, and tilted the diff by making up spacers etc to get to within one degree of equal.
I subsequently ran the car well north of 100mph and it was vibration free.
I would check the propshaft arrows and also search out the diagrams showing the angles of mis alignment set by Rover, it is not beyond the realms of possibility that a propshaft has been rebuilt in the past with new yokes welded on in the wrong orientation.
I carefully measured the height of the auto output flange down from the top of the tunnel and set the LT77 flange the same height. The diff was not meddled with on a two owner car, it had the right spacers.
I had bad vibration at around 60 mph. I measured the flange angles and they were 5 degrees apart, I am confident that they were as Rover installed the drive train.
I raised the gearbox as much as I could, and tilted the diff by making up spacers etc to get to within one degree of equal.
I subsequently ran the car well north of 100mph and it was vibration free.
I would check the propshaft arrows and also search out the diagrams showing the angles of mis alignment set by Rover, it is not beyond the realms of possibility that a propshaft has been rebuilt in the past with new yokes welded on in the wrong orientation.
Gargo
Active Member
Jorgenson
Member
Great drawing, thank you!
As far as I know, there are small arrows or markings on the two drive shaft components. in our p6b with lt 77 a shaft from an automatic has been installed. That's a good thing. The markings also point to each other
.
I modified the mount. i can now adjust the height and lock it with a lock screw and nut.
my plan is to try it out to see if anything changes.
the universal joints are already fixed.
ah... i see that the arrow is also on the drawing!
As far as I know, there are small arrows or markings on the two drive shaft components. in our p6b with lt 77 a shaft from an automatic has been installed. That's a good thing. The markings also point to each other
.I modified the mount. i can now adjust the height and lock it with a lock screw and nut.
my plan is to try it out to see if anything changes.
the universal joints are already fixed.
ah... i see that the arrow is also on the drawing!
Jorgenson
Member
I remember that another mechanic once removed or replaced the diff. Possibly distance discs were left afterwards
Thinking about why it would be necessary to design a phase shift of 144 degrees between the two tailshaft universal joints leads me to surmise that it
I have not found any information either John, even after searching through mechanical engineering journal papers. The only answer to me that seems plausible is the out of phase tailshaft design of 144 degrees is there to cancel a vibration that is somewhere else in the drivetrain, the difference between the two being T/2 where T is the period (assuming the waves are sinusoidal, which they would appear to be). Through the process of superposition, if you take the summation of two waves with equal amplitudes that are exactly separated by T/2 , then the net result is zero, in other words, they cancel. If the Rover's tailshaft had universal joints in phase (instead of out of phase by 144 degrees), then there is no means of cancelling another vibration that exits within the drivetrain. I have no evidence to support this hypothesis, and I don't have the means to test the hypothesis, but to me, on the face of it, it seems possible.
Ron.
I have not found any information either John, even after searching through mechanical engineering journal papers. The only answer to me that seems plausible is the out of phase tailshaft design of 144 degrees is there to cancel a vibration that is somewhere else in the drivetrain, the difference between the two being T/2 where T is the period (assuming the waves are sinusoidal, which they would appear to be). Through the process of superposition, if you take the summation of two waves with equal amplitudes that are exactly separated by T/2 , then the net result is zero, in other words, they cancel. If the Rover's tailshaft had universal joints in phase (instead of out of phase by 144 degrees), then there is no means of cancelling another vibration that exits within the drivetrain. I have no evidence to support this hypothesis, and I don't have the means to test the hypothesis, but to me, on the face of it, it seems possible.
Ron.
John,
T is the period for one complete cycle before it repeats. Your second point is possible. There was a change in the mount design as well, so they all likely contributed to a required adjustment of the phase angle.
Cobraboy,
That just sounds like poor build quality on the assembly line.
Ron.
Vern Klukas
Well-Known Member
I can't recall where exactly, but I've read at least a couple of things saying this was it exactly — Rover had trouble with drivetrain vibrations in the P6 and UJ phasing was part of the solution.
Yours
Vern