Clackety 3rd Gear Transaxle Noise

[Mark91SE]

I noticed a noise thru my shift boot in 3rd gear. It's a clackety-clack sound kind of like a train going passed you on the railroad tracks. It goes with the speed of the car not the speed of the engine, ie., with the clutch pressed and coasting, it slows down with the speed of the car and is rather loud when rolling down the windows and hearing it reflect off a nearby building wall.
1st and 2nd gear are totally quiet. I think the noise can be heard slightly in 4th and is not there in 5th, but definately in 3rd.
I switched from 6 month old Swepco 201 80W90 gear lube, to Redline MT90 a few months ago to try it. I'm not as happy with the MT90 as I was with the Swepco, as it made my tight 1st gear downshift worse when cold. The Swepco has a higher viscosity based on comparing the specs and talking to both manufacture's reps. So I am going to switch back to Swepco (expensive stuff).
Any other ideas? Thx
- Mark91SE

[cnh1990]

Other than something on your tire it seems rather strange.
Calvin

[windsorlotus]

I switched to MT90 in my 90SE after the clutch hose change out and couldn't be happier. The shifts were smoother with less vibration. Of course the braided line contributed to this but Red Line products are terrific.

SGB

[Mark91SE]

I know... everyone swears by MT90. I can't say I've had bad shifting with it. Though I've missed 2nd gear synchros a couple times (nasty, embarrasing feeling). Also, I switched to MT90 thinking it would help warm tight 1st gear downshifts. I was getting easy 1st downshifts with the Swepco only when cold... then I put MT90 in and 1st downshifts were then hard 'even' when cold.
This is 'after' replacing the red hose with SS and replacing both master and slave cylinders (slave is new aluminum type)... with fresh, well bled Castrol LMA.
I did some pretty thorough research, for not being a specialist in this field. Here's what I found;

Red Line MT90 Synthetic
SAE Grade 75W90
Vis @ 100°C, cSt 14.7
Vis @ 40°C, cSt 89.2

Mobile 1 Synthetic
SAE Grade 75W-90
Vis @ 100°C, cSt 15.2
Vis @ 40°C, cSt 106

Swepco 201 non-synthetic
SAE Grade 80W90
Vis @ 100°C, cSt 15.3
Vis @ 40°C, cSt 151

For reference, the Mobil 1 full synthetic is recommended by Lotus. So you can see, MT90 is the lowest viscosity of all three. My theory is that is why I get tighter 1st downshifts even when cold... because the synchros don't get enough grab due to the lower viscosity of MT90.
This mught also be an issue with the increased noise. I picked up another gallon of Swepco (not cheap), and will be running that comparison/confirmation test soon.
- Mark 91SE

>> Edited by Mark91SE on Wednesday 25th June 17:46

>> Edited by Mark91SE on Wednesday 25th June 17:47

[lotusguy]

Mark,

It's great to see someone do some empirical study instead of just relying on the anecdotal evidence of others.

I have to say though that I'm not with you on your theory about viscosity. MT-90 may well be the 'thinnest' of those gear oils you've researched, but the real issue is the friction coeficient or 'slipperyness', not the viscosity, of the fluid.

The other brands you researched have several additives which make them more 'slippery', not a good thing when it comes to synchros.

Viscosity is an important characteristic, but within limits. The ability to remain stable under heat and pressure and the friction coefficient of the fluid will have a greater effect on the gearbox's operation and 'health' than viscosity. Great approach though, keep up the good work! Happy Motoring! Jim'85TE