Tranny fluid recommendation for vintage MGB w/overdrive

[HardbodyLoyalist]

I'm in the process of resurrecting my fiance's 1968 MGB.

This car has a 4-spd manual with electronic overdrive. It has synchromeshed gears on 2-3-4 and the overdrive has a wet clutch arrangement. The manual calls for 20W-50 motor oil.

I HATE the idea of running motor oil in this tranny. Yes, hundreds of thousands of MGB trannies have run just fine on this, but I think we all can agree that there is NO WAY 20W-50 oils have the shear stability to handle 10-20k mi drain intervals in this application.

The tranny fluid is a pita to change and I really don't want to do it at every oil change.

On the various MGB boards, lots of posters have claimed success with MT-90, but ONLY on non-overdrive trannies. With the overdrive units, it causes slipping. The same has been reported with synthetic 50 wt motor oils.

Also, these units are full of yellow metals, so anything GL-5 is out of the question.

Thus, it looks as though I need a shear-stable GL-4 90 wt. dino with as little friction modifier as possible.

Any ideas?

 

[MolaKule]

Check this one out:

http://www.specialtyformulations.com/index_files/Page675.htm

 

[TR3-2001SE]

My transmission seemed to reach 100,000 with out much of a problem with standard 30w non-deterent on my TR3. This is what was recomended in my 1960 owners manual and workshop manual. It was only changed once at 100,000 and I just changed it again at 130,000 and no problelms. My TR3 does not have overdrive but I would still use what they recomend or 30wt. A 30w motor oil viscosity is equilivent to an 80-85 weight transmission fluid. Check the oil viscosity chart on the first page of this fourm. They made no mention of non-detergent but I believe it makes sence in a transmission. Why would you need detergency in a sealed system. Anything else and you are asking for trouble.

 

[HardbodyLoyalist]

Thanks, Molekule. I was hoping you'd weigh in.

I'm willing to give your product a try. If it causes slipping in the OD unit, I guess I could just drain it and use it in my Nissan -- should work quite well there.

I have a question for you, though...

This car also has shocks that must be periodically refilled with fluid. A lot of people use motorcycle fork oil for this, but I was wondering if you think your hydraulic jack oil might be suitable. I believe the chief requirement is that the oil be highly resistant to foaming.

 

[HardbodyLoyalist]

In response to TR3:

I REALLY hope you're right about the oil in these things lasting 100,000 miles. The B has 79,000 on the clock. When I asked my fiancee for a "ballpark" figure on how long the fluid had been in there, her response was:

As for the non-detergent issue, apparently lots and lots of owners run 20W-50 (with some specific fixation on Castrol, for whatever reason), so I would assume it's not a problem.

I think what I might do is run some 20W-50 for a few thousand miles and then pull it for a UOA to get an idea of just how bad the shear/wear#s look. If the numbers look awful, I'll start some experimentation. If the numbers look decent, I'll just have to somehow learn to sleep at night knowing I have motor oil in that tranny.

 

[widman]

Obviously you have lots of good choices in the real world. Down here when we have to deal with wet clutches one of my first choices is a CAT TO-4 trans fluid, either in a SAE 30, a SAE 50, or SAE 60. SAE 50 is the midrange of a SAE 90 Gear Oil.

 

[Doug Hillary]

Hi,
I have had excellent results from using Castrol's Syndrive 50E in NON OD BMC gearboxes
It should be OK in the OD series too - Castrol would advise accordingly

Regards
Doug
MY02 Subaru Outback 2.5 manual (Delvac 1)
MY98 BMW Z3 2.8 manual (Delvac 1)
MY89 Porsche 928 S4 Auto (Delvac 1)