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ATF in BN2 gearbox/Overdrive

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mbrooks

mbrooks

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I've cut-&-pasted below an old email from Dave Russell I found on a search. Since moving to Milano Italy I do not have the nice big double garage to do work on the BN2. Cutting a long story short, I recently had some work done by a mechanic I met through the Healey club in Milano. He's done some good work, but insisted on refilling the gearbox/overdrive with ATF. Since then, when everything is up to temperature, and with the O/D switched on, the O/D drops out on its own if I accelerate hard. Note that the throttle switch is completely bypassed - only the toggle switch on the dash and the gearbox switch [the one that allows 3rd/4th only] are in circuit.

I suspect that the lower viscosity ATF is causing O/D clutch slip due to lower hydraulic pressure, but I would really welcome some second opinions.

Rgds

Mike Brooks

--

----------------------------------------------------------

[Old posting by Dave]

Bob,
This is one case where shooting from the hip doesn't work. A lot of people get fooled by the two different rating temperatures of gear oil & engine oil. Gear oil viscosity is usually rated at 100 degrees F. Motor oil viscosity is rated at 212 degrees F. Thus the viscosity of SAE 75W-90 gear oil is roughly equivalent to SAE 10W-50 engine oil.

A lot of people are having very good results with Redline MTL which is rated 75W-80 & Redline MT-90 which is rated 75W-90. These oils are rated GL-4 which means they don't have the sulfur compounds that destroy bronze synchronizers as do the GL-5 rated oils with sulfur which is needed for the higher contact pressures in hypoid axles.

These Redline oils are compounded to have a higher friction coefficient which enhances the synchro ring "grabbing" & usually results in quicker & easier shifting. A "good" motor oil is actually too slick for the synchros to work at optimum. As are "slick" additives. The Laycock overdrive clutches also benefit from a less slick oil.

BTW - ATF oils are usually rated around 5W-20 on the engine scale. Not too far off from the SU carb recommended 20 wt.
D
 
Mike, as far as I know ATF is absolutely NOT the right stuff to use in your gearbox and overdrive. You can use engine oil 20W50 or, as I heard from many others, MT90 from Redline, which is not available in Germany. I think I've seen it advertised on an Italian website, but don't ask me where...

These bloody Italians, first kicked us Germans out of the soccer world championship, now they fill your gearbox with strange stuff /ubbthreads/images/graemlins/hammer.gif /ubbthreads/images/graemlins/wink.gif
 
Hi Mike,Just use a good single viscosity motor oil and you will do fine.--Fwiw--Keoke
 
Hi Mike,
As you suspect, ATF is a bit thin, especially if the OD pump, accumulator seals, & operating piston seals are less than PERFECT. The hydraulic system just won't hold pressure. Additionally, ATF comes in two varities. The old GM spec for Dextron was slicker than the Ford type F oil, so the problem might be even worse if the slick ATF were used. No matter, as ATF is just too thin for OD use.

Original factory specs called for a straight 30 motor oil. Many folks have good luck with a 20-50 motor oil which holds viscosity a little better than straight 30 weight. Either should work ok for you. Just don't use an oil which contains super slick additives. The RL oil works a little better, but if it is not available, no big problem.

As a note of interest, I believe the Triumph factory recommended a 90 weight GL-4 type gear oil for use with the very same type of OD.

There is sometimes a controversey over detergent vs non-detergent oils but I have never found a real problem with using a detergent type oil, which most commonly available motor oils are.
D
 
Thanks to Rick, Keoke and Dave for their responses. I will get the ATF changed out for something heavier. I've found the Italian rep for Redline on the web so I will try them first.

Regarding Dave's note on the Triumph recommendations, I have a Triumph Dolomite Sprint engine in a special I built a few years ago. And yes, they recommend 90 weight gear oil in the gearbox and therefore the O/D. BTW, since that engine was I think not available in the US, and in case anyone is interested, it is a 16 valve version of the 2litre TR7 engine.

Rgds

Mike Brooks
 
Triumph recommended ATF in the 5 speed gear box in the 7 and 8. The gear type they put in the 5 speed could not stand up to the oil in the cold weather. I doubted this but talked to many experts and they all recommended it and over the past 5 years have had no trouble
 
[ QUOTE ]
Using ATF, would you not get "foaming" ocurring also,?

[/ QUOTE ]
I doubt it. I can't think of any application capable of causing more foaming than an auto transmission & torque converter. ATF is especially resistant to foam.
D
 
Thanks Dave, never thought along those lines, was always of the opine that because it felt thinner it would foam easier!, one learns something new here all the time!
 
Zblu,

I am fairly sure that the TR7 and 8 used the same gearbox as the Rover 2300/2600/3500. I used to have a 2600 and it was a pig to change gear in cold weather, until the gearbox warmed up. Hence the recommendation for ATF maybe. Another thing that interested me a few years ago - Vauxhall in UK, in the 90's sometime, started putting ATF in their 5-speeds as well as their autos. I wondered at the time if it was to make things easier on the production line. In my opinion 75/90 gear oil gave a smoother gear change. I know that because I changed out ATF for 75/90 in two Vauxhalls I had.

Sorry we're a bit off topic here..........

Mike
 
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