The wheels are perfectly balanced, yet I have an uncomfortable vibration which sets in at 2700rpm, on 4th with the T700 gearbox. Not like badly balanced wheels, where the imbalance is typically between 65-85. My problem persits so I kept the speed down during the 350 miles.
I suspect the propshaft, but it is a new, one piece shaft with new UJs and no play when I test it on the lift.
Any suggestions…?
Peder
Is the new propshaft balanced and aligned to within specification for the car?
Balanced, tes, but don’ know what you mean by aligned. It is a one piece prop shaft, which John in TX who sells the box and kit, says is better.
Hi Peder, do you get the same holding the tranny in third past 70mph. Same prop shaft revs but other dynamics are different? Paul
Drive shaft alignment typically has some sort of specification like 4 degrees maximum angle for transmission output and differential input relative to drive shaft axis with car load on the wheels. Depending on the car, this specification may even be down to a one degree variation allowed. Engine, tranny, and rear end mounts all play a role in drive shaft alignment. As another example, an engine may be specified to have a tilt angle of 3 degrees, this specification helps with propellor shaft alignment.
U-joints are used because these angles have variations while the car is moving and bouncing. Vibration of the driveshaft can be felt at highway speeds when alignment is wrong.
Test the car like Paul Breen says, that will check if it is engine or tranny before the output shaft. Sorry I don’t know the propshaft alignment specs for your car.
I understand perfectly what you mean. I think the Mk 7-9 had 2 piece prop shafts from the factory, just like the Mk10/420G, which have the same long wheel base.
I have never read about the alignment settings. Perhaps the engine needs to be tilted down at the rear, by just 1-2 deg, when using a one piece prop shaft…?
I did 350 miles yesterday, mostly on motorways. The vibrations kick in at 67 mph, and by 78 it is pretty unbearable.
With the car on the lift to change brake fluid, I noticed that yhe new, one piece prop shaft has no balance weight…Either it didn´t need it, which I doubt, or the garage that fitted the T700 forgot to send it off to be balanced.
Hello Peder,
I had almost the same issue on my S-type, send the propshaft to a specialist.
Problem were the U-Joints, new joints these days are a lose fit.
Shims were needed under the circlips from the needle bearing cups the get it right.
Only after these were shimmed right he could properly balance the propshaft.
regards,
Peter Jan
Interesting!
On a 140 coming back from CMC, I had a bad UJ on the prop shaft. The UJ was new and had play in it.
But on the Mk9, the new, one piece prop shaft has no play in the UJs😱
I think the lack of balance weight means that the prop is simply not balanced…
Skickat från min iPad
Interesting!
I had a bad, new UJ on a new/shortened prop shaft. This was on an XK that came back from CMC! Again very embarrassing. There was play in the UJ.
But on the Mk9, there are no bad UJs.
I believe the lack of balance weight on the new, one piece prop shaft is the clue to the problem:scream:
One other visual thing to check is whether the UJ’s at each end are aligned correctly. That is the yoke planes on the shaft fixed and splined ends should be parallel.
I’ve been following this with some interest- I don’t have a saloon, but I do have a Jag.
I put a poly transmission mount under my car and wound having to go back to the original rubber mount because of a vibration. I also balanced my driveshaft using two large hose clamps. Smooth ride now!
How did you know how to position the hose clamps? At the diff end?
Are the screws in the hose clamps enough as balance weights?
I can send a PM with the full story if you like. It will be a fairly long explanation, though!
Peder, I don’t need your e-mail address. I’ll just send a forum PM. You might want to delete it…
PM is headed your way!