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MG MGB GT V8 Factory Originals Technical - Gearbox Oil for V8

Hi folks

This site is a fantastic source of information. Thanks to everyone involved.

I've had a search in the archive, but I can't find the answer to the following:

I've just bought a '77 roadster V8 conversion. It has a 4+o/d box. I assume it's the original. I note that the recommended lubricant for the V8 is EP90 and for the four-pot is 20W-50. Is the 'box different? Do I need to determine the gearbox type to decide what oil to use? Or do I just go ahead and use EP90?

Thanks.

P.S. Brace yourselves for a flurry of equally dim questions in the near future.
Nick Wilson

Hi Nick.
I am lucky enough to have 2 V8 roadster conversions. One has an ex-factory V8 gearbox (basically a modified MGC gearbox), the other a standard 4-synchro MGB gearbox, and I use EP90 in both 'boxes. I know the manual says the standard B box should have 20/50 oil, and apparently using EP90 can cause excessive wear, but after 18 months in regular use covering approx 15,000 miles (its my wife's everyday transport) I have not noticed anything untoward. The overdrive works every time, and the whole thing is a lot quieter as well. As to identifying the two boxes, the std B box has a dipstick on the top of the casing and is accessed through the top of the tunnel, behind the radio console. The factory V8 box doesnt have this dipstick, just a filler point on the side of the casing, accessed from under the car. Hope this helps.
Dave Pollard

I have a Factory V-8 that calls for 90WEP gear oil in the gearbox. I had a problem with notchiness and stiffness in the gearlever when the car was cold, so I switched to 20/50, as is recommended for the 4-cylinder cars. No more problems. I have heard that the factory recommended 90W for a year or so in the 1970s, but switched back to 20/50 to cure the problems with cold operation.

After much cogitation and discussions with Red Line tech guys, I have decided to use Red Line MT 90 synthetic gearbox lube in my car when it is back on the road after restoration. This lube seems compatible with the LH overdrive, and has the additional advantage of improved shear strength under load. The MT 90, unlike normal GL-5 EP90, does not have anti-friction properties which would harm the overdrive clutch.

I'll let everyone know how it goes in a year or so.

Cheers,
Paul Kile
Paul Kile

Paul I used the redline mtl in my SHO tranny and began to get bearing noise after 20,000 miles. A little 90 added to the tranny and it went away. I've read several reports of users reporting apparent increased wear with the mtl product. I think a blend of MTL with some 90 to maintain the hi ep lubrication qualities is advisable.
Barry
Barry Parkinson

Barry,
Thanks for the info. I plan to use Red Line MT90 rather than MTL in the gearbox. This has the viscosity of 90W EP. I think the MTL is suited for trannys that call for 75W/80 gear oil. You might try MT90 in your gearbox the next time around, you might not have to blend it with regular 90W.

Cheers,
Paul Kile
Paul Kile

Hi guys,

I've got a factory V8 and recently changed the G'box oil and cleaned the magnets. then a month later experienced the O/D cutting out on the steep down hill sections of a long motorway run. I assumed that this meant that I was getting insufficient oil at the back of the gearbox and hence the oil pump wasnt able to produce oil pressure to keep the O/D engaged. Diagnosis - low oil; but I just changed the oil. Second possible diagnosis - I didnt put enough oil in; but the stuff was overflowing from the side filler hole. Could it be because the high viscosity 90 wt oil is not flowing fast enough to the back of the box when I go down a steep hill? I'm not trying to hijack your thread Nick, I was just wondering if anybody else had had this problem with 90 wt oil in an MG 'box? My only other thought was that the 'box needs to be topped up a second time once it's been run and the oil flows through into the O/D unit, but this wasn't in the manual anywhere

Philip

Philip Shingler

90wt oil is quite viscous - when I changed the rear axle the timing was such that I filled it at the end of one day, then checked it at the beginning of the next day before its first run. I was surprised how much more oil went in.

I.e. try topping up again.

PaulH.
Paul Hunt

I've been running a conversion with a rover LT77 gearbox for some time and initially ran EP90. Advice from rover suggested that I should use AFT which I have done for the last 4 years. Twelve months ago I had a failure due to extreme wear of the 3rd/4th synchro hub and selector fork. This box was replaced with a rebuilt unit and the replacement has just failed, cause not yet know but there is a good deal of swarf in the oil.

I have temperature records for races from the start of the year ( if I'd looked more closely at them I might have changed it earlier ) and have seen 130 C during races at silverstone international weekend. What I can't findout is if that is enough to degrade the oil.

I'll keep a close eye on things this weekend at cadwell park and report back next week.

Has anyone got experience of using Castrol SMX, this is supposed to be the current Land Rover recommendation.

Dave
Dave Brooke

Phillip, one thing regarding the cutting out that you are experiencing. I too had this problem, and had a devil of a time finding the solution. After all the usual efforts, I went for a total rebuild. Duriing the rebuild I found a small chip lodged in the ball check valve in the pump circuit. The irony? I could have found the small metal chip without even pulling the transmission. It was accessable from the drain pan!!
Chris Jones

This thread was discussed between 21/07/2000 and 28/07/2000

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