Driveline Vibration

[IslipMinor]

Ever since its restoration 16 years ago, there has been a slight driveline vibration between about 70mph and 80mph, and it seems to have got worse recently. I had the prop shaft checked for balance twice some while ago, and there does not appear to be any play in the UJ's now.

It has a Toyota T50 gearbox fitted and part of the kit is a new cross-member, and I am wondering if the output end of the gearbox is at the correct height? If it is significantly wrong, lower or higher, it could affect the angle of the engine/gearbox and how well it matches the angle of the diff housing, which should be the same!

Does anyone have the measurement from the underside of the chassis rails up to the centreline of the gearbox output shaft, which I can use to check ours please?

[philthehill]

Richard
No doubt preaching to the converted
The Hotchkiss or Hardy Spicer U/J should be able to cancel out any differences in the angle of the drive train which is constantly changing as the suspension rises and falls. The movement of the suspension will never give an optimum/equal angle either at the gearbox end or diff end.
Even with your gearbox conversion I would not have considered the angle excessive and beyond the capabilities of the U/J.
For comparison - the prop-shaft tube on my Ford gear box conversion is 43mm from the bottom of the large hole in the cross member and the front U/J is 135mm from the front face of the cross member. The rear suspension has been lowered by 2" which makes for a very shallow angle of the drive train.
Professional drive line manufactures give the optimum settings for drive line angles as between 1/2 and 3 1/2 degrees and the front and rear U/J should not be more than 1/2 degree apart at any one time other wise harmonic vibration may start up.
See:- http://www.hurst-drivelines.com/files/U ... 111606.pdf
I wish you luck because even on the Marina/Ital with the split prop-shaft the drive train was not perfect and would sometimes set up a vibration.
Phil

[IslipMinor]

Phil,

It's not the height as such that I am concerned with, it is making sure that the angle the engine/gearbox lies in the bodyshell at is the same as the angle of the diff input shaft. The engine/gearbox tilts down slight towards the rear and the diff nose tilts up slightly at the front - the angle of tilt should be the same! So long as they are, vertical movement of the axle should have no effect on the diff input shaft angle. Unless the lowering has changed it somewhat??

Assuming that it is correct in a standard Minor set up, knowing the vertical height of the gearbox output shaft above a reference point, such as the underside of the chassis legs, will allow me to see if mine is the same, or needs to be adjusted so that it is!

[philthehill]

Richard
The gearbox for all intents and purposes will remain the same but the axle will move in a vertical plane and the nose of the diff will rotate around the axle centre (torque reaction) so whilst the desired static angle of the joints should be as fig 4/5 of the attached link I doubt in reality that they are or ever were.
If you have a Moore and Wright combination square with the adjustable angle gauge you can check the angles using a similar process as described in the attached link to ensure that they are near as dam it the same.
Do you have a U/J on the front of the prop-shaft or rubber doughnut?
If you have a U/J put a suitable socket against the U/J circlip place the adjustable angle gauge on the head of the socket check the angle, move to the rear U/J and check what that one reads and compare the difference. If the difference is great you may have to wedge the axle but in the back of my mind I seem to have read somewhere that you have already wedged the rear axle or altered the diff nose angle! Am I right or am I going nuts?
With an adjustable angle gauge to me it seems quite simple to check the angles of the gearbox and diff though you may disagree.

[katy]

Richard, measured the distance from the bottom of the crossmember (extrapolated out) to the centre of the gearbox output shaft at 3 & 1/4". I didn't measure from the chassis rail as there is an offset at that point. This is on a '61 MM 1000. The crossmember under the chassis rail is 1/16" thickness.
FWIW the output shaft is at aprox 3.5º down and the pinion shaft is basically level.

On this car I notice a gearbox vibration at speed so I'm going to try and source some 3º or 4º caster shims to install at the rear springs to increase the pinion angle and see if that corrects things.

[IslipMinor]

Katy,

Thanks, I will look at ours when I get back from holiday. We are currently in Amsterdam and have the return trip to do on Sunday, complete with a more noticeable vibration than before.

Thinking about what has changed over the last 16 years, I replaced the gearbox to crosssmember mounting (a standard Toyota part) about a year ago, and looking at the T50 fitting kit instructions from 20+ years ago again last week, there is a comment about the Toyota mount being very soft and suggesting a way to restrict any 'bouncing'.

The perception of a worse vibration may be down to the new mounting (I think the old one had a slightly different configuration, so could have been modified?), but there has always been a vibration, so I want to look at the installed angles of engine/gearbox and diff nose to see if that is the cause.