Vibrations over 40!

[paul83]

Hi,

 

I'm struggling with this one! Car running Ok, then laid up for 2 months. Just installed forged pistons on my TR6 and:

 

When I exceed 40mph there are very strong vibrations (that make the car impossible to drive),

The vibrations are a bit stronger under power, but not much.

Vibrations not affected by which gear selected, or free-wheeling in neutral or if clutch fully engaged.

Vibration not affected by engine rpm.

 

To track down the source of the problem, I checked the transmission - and have now fully rebuilt the differential (which had a broken pinion gear) and replaced all of the universal joints (a few of which were broken or on the way out). This has noticeably firmed up the response from a standing start, but had no impact on the vibration problem.

 

There is no clunking in the gearbox.

 

The front and rear wheel bearings seem fine.

 

Where and how do I look next?

 

Thanks,

 

Paul

Edited March 24, 2016 by paul83

[Andy Moltu]

One of the U/Js?

[Austin Branson]

+1 for the uj's. My car had been fitted with re-built driveshafts just before I bought it, and I got a vibration over 70mph. Eventually one of the uj's failed, and once replaced the vibration disappeared. Good luck, let us know how you get on. Austin

[TriumphV8]

Wire wheels, bad tires or UJ from the drive shafts.

The Finishbalancer for balancing wheels at the car

is the remedy to identify the culprit.

[John390]

Possible flat spots on tyres after standing and not being used? Check to see if the wheels need balancing as well.

 

 

Cheers John

[oldtuckunder]

prop shaft out of balance would match the symptoms of speed related vibration?

 

Alan

[Peter Cobbold]

Telescopic shocker set too hard ? gives a bouncing sensation, a couple of cycles per second.

[John Bracher]

I once had a car with a similar problem.

After a load of inspection it turned out to be an engine mount, causing the whole drivetrain to cant over during movement.

 

Also, check the propshaft hasn't lost any balance weights.

These are sometimes only a bit of steel tack welded on, so can fall off??

[Bill Bourne]

Or / and the gearbox mount - they don't last long if they have soaked in oil from an oil leak..

 

best Bill

[RogerH]

I was thinking about this vibration over 40 lark.

 

How many forumites out there actually vibrate - 40 or not.

 

At 61 I started to squeak; but a new right hip sorted that one.

 

And my neck has a sort of scruntching sound every now and then

 

Will I survive

 

Roger

[peejay4A]

Nurse!

[paul83]

Hi All,

 

Thanks for the guidance (and the smile Roger - I think you'll survive!).

 

I reinspected the propshaft and hey presto, I had not aligned it correctly when reassembling, so it was not balanced. Newbie mistake! Also, one of the holes in the one of the yokes had worn so that the uj is able to oscillate (even though the uj bearings are sound and it is fitted correctly). So time for a new yoke...

 

It tuns out that although the forged pistons do not have a front, they do have a very slight asymmetry to the left/ right - the manufacturer's logo is raised and to one side (left or right, not front/ back) thus they have a very small weight imbalance. So I need to ensure that all 6 are positioned the same way...

 

I also checked the gearbox mounting and engine mountings, and had all four wheels rebalanced/ checked - all Ok.

 

Paul