Strange noise and vibration

[rgh0]

If you have a leak its a component or assembly problem its not due to the oil IMHO... sorry

[JonB]

No need to apologise Rohan, I?ll be happy to prove myself wrong. Recall, however, that I?m hoping a different oil will help with the noise.

Only one way to find out!

[joe7]

OK, I'll join in. As we all know everyone is looking for that silver bullet. Over 30+ years I have used all the various trans fluids and never really noticed much difference.That said, I was discussing trans oil with some BMW track guys and their suggestion was to try Royal Purple 75W90. Not cheap at $23 per qt. I did and am very surprised how much better the shifting is. As a qualifier this is in a newly rebuilt trans.

[2cams70]

try Royal Purple 75W90. Not cheap at $23 per qt.

Note the effect on how the box shifts has nothing to do with whether a synthetic or mineral oil is used or how well the oil protects the transmission. That's more a function of the additive pack that's been used to assist synchronizer action and the oil viscosity. Castrol VMX80 for example is an inexpensive mineral manual transmission oil that has an additive to assist synchronizer action and will noticeably improve shift quality and is a good choice for a normal road car. Of course you don't need these kind of additives in a rear axle oil - they have different requirements which is why LS90 is a good choice for them.

[rgh0]

try Royal Purple 75W90. Not cheap at $23 per qt.

Note the effect on how the box shifts has nothing to do with whether a synthetic or mineral oil is used or how well the oil protects the transmission. That's more a function of the additive pack that's been used to assist synchronizer action and the oil viscosity. Castrol VMX80 for example is an inexpensive mineral manual transmission oil that has an additive to assist synchronizer action and will noticeably improve shift quality and is a good choice for a normal road car. Of course you don't need these kind of additives in a rear axle oil - they have different requirements which is why LS90 is a good choice for them.

Yes agree shift quality is largely determined by additive package and oil viscosity. Synthetic oils have greater viscosity stability over a wider temperature range ( hence they are "thinner" at room temperature) for the same viscosity as mineral oils at operating temperatures. This lower viscosity helps gear changes when the gearbox oil is cold on startup which typically improve when using synthetic oil.

cheers
Rohan

[2cams70]

This lower viscosity helps gear changes when the gearbox oil is cold on startup which typically improve when using synthetic oil.

Castrol VMX80 mineral oil will improve the shift quality across the whole temperature range especially when cold. We have used it to good effect in truck gearboxes to replace the factory fill in order to alleviate customer complaints about poor shifting when cold. I've used it to good effect in car gearboxes too.
Large truck gearboxes really test synchronizer mechanisms because the gears and clutch plate are so large and have so much inertia that it's difficult to speed them up and slow them down. You definitely have to shift with sympathy and not treat the box like it's in a race car!

[sprintsoft]

Thanks to Alan (barker)’s advice earlier in this thread, my transmission resonance issue is now solved.

I removed the propshaft and had both uj’s replaced then balanced. The uj’s had slight wear in them undetectable until removed and on the bench, plus the balance was quite a way out. The net effect was the propshaft was feeding vibrations back into the gearbox.

One other point worth mentioning was that I found when fitting new bolts that have the long shoulder specifically for the rear flange where it connects to the diff, there must be a washer used otherwise the nylock nut could fully tighten onto the shoulder just before fully clamping the two flanges, so you think you have it tight but it’s not.

Iain

[alan.barker]

Hi Lain,
Well done and i am happy to be of help. This is a great forum when we put our heads together
Alan

[alan.barker]

Hi Lain,
well i just stopped being lazy and took some of my own Armchair advice
Removed the Prop Shaft on my 1972 Sprint and changed the UJs. No play felt BUT after removal of UJs in Yokes worn lines found on Needle Roller Journals
So with new UJs + TTR Diff Mounts (Diff was touching Chassis) fingers crossed "Little Lo" should run smooooooth.
I've just patted myself on the back and promised a Glass of "Saint Nicolas de Bourgueil" for Lunch
Bon Appetit
Alan