vibration at speed

[laikathedog]

hello

i have a 3000m with :

rebuilt prop
rebuilt gearbox
rebuilt drive shafts, bearings hubs and UJs
new diff rubbers
refurbed and balanced wheels
diff has new oil and seals but no excessive play

all is perfect… until i get to about 40, a vibration at the rear begins and gets progressively worse, 60 mph is the max i could do yesterday without fear of loosing bits of TVR

i confess that this is pobably the first time i went above 50 for over 6 months ! my commute is town and country, so no A roads or motorway.

where should i start my search for the source of this problem ?

i have been told to unbolt by prop turn it 180 degrees and reconnect… how would this help ?

thanks

Edited by laikathedog on Friday 9th May 21:00

[madsvlund]

If the wheels or driveshafts is out of balance, will it normally vary in amplitude in soft highway bends as the 2 sides in some positions will eliminate each other, and in other will play together. The frequency of the wheels at 60mph will be around 15 HZ (low frequent)
The propshaft rotate at triple rpm as the wheels (50 HZ aprox at 60mph) and due to the low inertia mass, and the higher frequency will that normally feel like a buzz rather than a vibration.

Best way to troubleshoot is to get the car on a 4 point jack (wery solid) and spin the wheels to speed while examining is visually. But be very carefull as it's by nature dangerous with the car running on jacks.

[RCK974X]

It's all about balance and rotating weight....
Turning stuff *might* help, if it happens to offset an out-of-balance bit somewhere else.

You could try any or all of -

Rotating prop shaft at diff end (180 deg).
Rotating prop at gearbox end (a few splines at a time)
Rotating (each) drive shaft at diff. (180 deg)
Rotating each road wheel (90 degrees, one stud, at a time)

If you rebuilt the driveshafts did you put the two halves together back in the same place on the splines ? That can affect the balance too....so could try rotating the driveshaft halves on their splines as well (some have a 'master' spline so can't be rotated, but some don't).

None of this is guaranteed of course, and yes, some of these are a PITA, but I have had success with rotating road wheels a few times on different cars - in fact I tend to mark mine so that I put them back on in the same place.

Do them one at a time to see if there's any improvemnt...

Might be worth checking tyres also in case one has a 'lump' - it can happen when they warm up. Not common, but possible.

The propshaft rotate was a common suggestion when I was a lot younger, so it may have had some success, but I suspect more so on cars with longer propshafts ?

Edited by RCK974X on Friday 9th May 22:22

[GAjon]

Wheels refurbished?

Put the back wheels on the front and try it before you start stripping props and joints.

You never know?

[Grantura MKI]

would check the "clocking" of the u joints on the prop and axles.
Best,
D.

[njhucker]

When you put the gearbox back in did you put the spacers between the alloy cross member and the chassis . If not the output on the gearbox will be at a different angle to the diff input and this will cause a vibration similar to what you are experiencing. The diff and the gearbox should not be in line, but if you draw a line through the pinion and the gearbox shafts they must be parallel.

[RCK974X]

njhucker said:

When you put the gearbox back in did you put the spacers between the alloy cross member and the chassis . If not the output on the gearbox will be at a different angle to the diff input and this will cause a vibration similar to what you are experiencing. The diff and the gearbox should not be in line, but if you draw a line through the pinion and the gearbox shafts they must be parallel.

I agree that's good advice, but just to say I have broken that rule when building kit cars and got away with it, perhaps I was just lucky.

I forgot to say, but as above, swopping the wheels around is also a good idea.

[ausi steve]

I had a similar problem with my 289 Mustang after refitting motor gearbox etc. After trying various remedies a friend said loosen all mount points, raise the engine 25mm or so & drop it quickly, this sometimes realigns all the mounting points that we have slowly carefully worked on in refitting the parts. In my case it also meant loosening the exhaust extractors. Any way it certainly fixed the problem.

[bluezeeland]

think you might want to have a read at the 'tuscan v6 prop lenght thread, some solid advice there !

I too had my car rebuild sort of similar to yours, one of the first things you might want to had done is mark both driveshafts and propshaft, so they went in as initial...
Perhaps a good check of all is required here, as this can be caused by multiple causes, e.i. is the rear suspension all properly bolted up, are the shocks level, has it had a geo, is the diff carrier bolted up correctly and squared up (and so the diff), is the diff 'level' (I found 2 spacers between the forward carrier to diff bolts, effectively making the front flange close to be vertical.

the engine and gearbox combined should be at the right angle, not so much so in the longitudinal sense but in the horizontal (the suggestion about the height of the gearbox-mount is imperative, here)

The propshaft could need a balance, but only after checking the above

Lastly, have the UJ'been installed correctly ? They need to be moveable by hand without to much resistance (can be achieved by 'widening' the yokes, a bit (learned this trick from an old mechanic..))

Have fun, and please report progress !

Frank

[laikathedog]

i have rotated prop 180, no difference

swapped front to rear wheels, bad vibration moved up to 60, but is present at 50 as a thrum.

vibration at 70 is so severe i worried about loosing the doors !

couple of questions:

What are the torque settings on the diff cradle ?, particularly the large vertical bolts through the front bracket

I found no shims on the gearbox or diff when they came out

I have read the prop thread and will be out under the tvr with an angle set and shims later today...

Edited by laikathedog on Saturday 10th May 11:47

[bluezeeland]

Blimey, you have got a problem !

The carrier to diffs are 110 Nm, iirc, the ones going thru the bobins, dunno by head (will have a look)

Think you should check all of above suggestion, working yourselve down the list usually brings the solution......

good luck !

[laikathedog]

I put clinometer on my phone, removed prop and found that there was a 4 degree difference between the gearbox and diff, as i couldnt move gearbox angle, i shimmed the diff front down and now there is a 1 degree difference, severe vibation is now much much better, still present at 70, but as i have been a human dam in the gutter with rainwater pooling around me as waxoyl and rust flakes attempt to blind me i am leaving the tightening of the rear of the diff to get that last degree to another day!

While was under there i checked UJs and bushes with my pry bar with no problems, and no cracks on the diff hanger either

But on a good note the car drives perfectly, the tracking is very slightly out after i changed the front balljoints
But my engine starts every time, and runs really well, gearbox is good and the change to a 15 inch steering wheel means i no longer hanker for power steering, makes it most civilised, but exhaust note puts a stop to that, 650 miles this year so far, most of it in the first three gears!

Edited by laikathedog on Saturday 10th May 16:05

[bluezeeland]

Well done that ! even if you learnt to swim in the proces..........

That same bl**dy rain prevented me from have a hoon in the 3000S, so put new(ish) shocks on the 3000M instead......

keep at it, you will prevail, as the yanks say ()

[TDC-belgium]

laikathedog said:

I put clinometer on my phone, removed prop and found that there was a 4 degree difference between the gearbox and diff, as i couldnt move gearbox angle, i shimmed the diff front down and now there is a 1 degree difference, severe vibation is now much much better, still present at 70, but as i have been a human dam in the gutter with rainwater pooling around me as waxoyl and rust flakes attempt to blind me i am leaving the tightening of the rear of the diff to get that last degree to another day!

While was under there i checked UJs and bushes with my pry bar with no problems, and no cracks on the diff hanger either

But on a good note the car drives perfectly, the tracking is very slightly out after i changed the front balljoints
But my engine starts every time, and runs really well, gearbox is good and the change to a 15 inch steering wheel means i no longer hanker for power steering, makes it most civilised, but exhaust note puts a stop to that, 650 miles this year so far, most of it in the first three gears!

Edited by laikathedog on Saturday 10th May 16:05

Perhaps you should have the propshaft now rebalanced at 3000- 3500rpm
How ever ; check first if both U joints are mounted in the same longitudinal direction: if not a good qualified company must reweld your propshaft again before rebalancing .
And check too if there is no damage on the tube of the propshaft.

[TDC-belgium]

A lot of TVR's with propshaft vibrations last week :-)

[TDC-belgium]

A golden tip : grease all the U joints after every winter with an excellent grease, and some problems can be avoided !