Vibration

[Burdekin]

If it's not happening at multiples of that speed then that points to not a balance issue. I'd look for rubbing, things worn out. Like Adam suggested mounts but maybe also exhaust or something is loose.

[Derek UK]

As you say, it could be your prop out of phase or a U/J. Usually the rear one but you'll have to drop it off the diff to check it properly by moving the joint back and forth over it's full movement. Could also be a split rubber centre bearing mount.
Front wheel out of balance normally felt through the steering wheel. Rear ones less easy to check but you can swap them back and forth front to rear and vice versa.

[packers1712]

All very valid comments, thanks, the car does appear to have had the centre bearing/mount renewed reasonably recently, Also I have had the gearbox out recently too to tackle oil leaks and noticed that when refitting the mount it was under some tension to be able to get all of the fixings back into the floor. Does this indicate a fault?
I have checked that the mount in my car visually resembles the one on Brookhouse's site and it does.
The sump in relationship to the front cross member visually looks to be in the correct position I'm not sure that necessarily signs off the engine mounts as good but they also don't look that old.
Next stop is the prop U/J's then, the front one certainly didn't seem stiff or overly worn when I removed the gearbox but I didn't touch the rear so I'll check that next, thinking about it if the centre bearing has been replaced maybe the phasing wasn't checked, something else to confirm!
Just when I thought I was getting to the bottom of the job list too!

Doug.

[142 Guy]

If you can squeeze your head under the car, with a flashlight it takes about 60 seconds to do a visual check to determine whether you have a u joint phasing problem. Refer to the service manual for a diagram of the correct phasing.

Note that the source of vibration (the forcing function in engineer speak) can be present at all speeds. The amplitude of the forcing function may be relatively small and constant; but, as the frequency of the forcing function changes with speed it may line up with the resonant frequency of some other part of the car which makes the vibration really noticeable. My rear view mirror would buzz like crazy just around 2500 - 3000RPM when I had a brief experiment with 164 engine mounts on my 142. For a historical illumination on the ill effects of the frequency of the forcing function lining up with the resonant frequency of a structure, Google 'Tacoma Narrows bridge collapse'.

An out of phase driveshaft creates a cyclical vibration; but, so would a damaged bearing on a U joint so examination of the U joints for play or binding would also be useful. Tires & wheels out of balance could be a contributor; but, an out of round tire could also be a source of the problem. Switching the tires front to back may alleviate (or change) the problem if the vibration is exciting a resonance is some particular item at the front or back of the car.

[Laird Scooby]

Originally Posted by packers1712

No only between 20-25mph feels like its coming from the rear but I've been done this path before when I've been convinced a fault is front/rear or left/right and when I eventually find the cause its not where I initially thought!
The plan is to change the tyres very soon so when they're done and the wheels are balanced it will eliminate them!

Is the general thought that a vibration at such a low speed isn't prop related?

Doug.

I'm guessing when the gearbox was out, the propshaft centre bearing was unbolted from the floorpan?

If so, crawl underneath and loosen the mounting bolts (4 if memory serves) 1/2 a turn.

Take it for a short drive up to the speed where the vibration occurred and ensure the vibration disappears.
Return home, still driving gently. Crawl under again and tighten the bolts evenly, a little at a time each - DO NOT JACK IT UP TO DO THIS! If really necessary, reverse it onto a pair of ramps but don't jack it.

Once the bolts are tight, take it for a test drive and see if the vibration has gone, sometimes it takes 2 or 3 goes of doing this to eradicate the vibration but usually it's a first time fix.

[packers1712]

Excellent, I'll be trying this at the weekend, thanks!

Doug.

[Laird Scooby]

Let us know how you get on!

[packers1712]

Will do, as best as I remember the centre bearing only has 2 fixings holding a plate that sandwiches the rubber between the floor and it.

Doug.

[swedishandgerman]

This is brilliant and something I'd never thought of!

Originally Posted by Laird Scooby

I'm guessing when the gearbox was out, the propshaft centre bearing was unbolted from the floorpan?

If so, crawl underneath and loosen the mounting bolts (4 if memory serves) 1/2 a turn.

Take it for a short drive up to the speed where the vibration occurred and ensure the vibration disappears.
Return home, still driving gently. Crawl under again and tighten the bolts evenly, a little at a time each - DO NOT JACK IT UP TO DO THIS! If really necessary, reverse it onto a pair of ramps but don't jack it.

Once the bolts are tight, take it for a test drive and see if the vibration has gone, sometimes it takes 2 or 3 goes of doing this to eradicate the vibration but usually it's a first time fix.

[packers1712]

So I tried Dave's loosening off the centre bearing fixings trick but unfortunately with no success having said that I only managed to try it once and he did say it may take a couple of goes so I'll try again when I get chance and report back.
I did get the new tyres fitted and that made no difference so it isn't tyre balance related!
I also noticed that my prop appears to be a "cut and shut", I'm guessing its been made using an existing none O/D prop as the car now has an overdrive box but didn't leave the factory with it! All of this suggests to me that the prop will be the cause, Ill keep you all updated!

Doug.