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MG MGA - best gear oil to use in '56 MGA


Hey all,

I'm new to the MGA fold, but not new to MGs. I recently picked up a '56 A to keep my '67 B-GT company. Anyhow, the A is in nice condition and was restored about 15 years ago by a British sports car specialist in North Carolina. Presently, I'd consider it a "nicely aged restoration". I had it out for the first time the other week after a long winter hibernation (bought the car last fall) and after a spring tune and valve adjustment and oil change, I wanted to get it out to see what (if any) bugs may be lurking and all I can see is that (1.) there is a gearbox leak - which I think is the rear seal, and is pretty typical, so that will soon be rectified, but one other note of mention is that I was wondering what the best oil to use in it would be. I understand that SAE 30 engine oil is what was recommended from the factory, but perhaps someone has discovered something better? I have Red Line in the 'box of my B-GT and it shifts very nicely, so I was wondering if anyone here might be using Red Line or another equivalent in their MGA? The gearbox seems to shift ok, typically notchy and third gear usually requires a double clutch, but otherwise, everything seems to be tight and in order. Oh, and last but not least, I understand the fill plug/dipstick is accessible from inside the car. Can anyone point me as to exactly where I locate it?

Thanks all in advance!

Cheers,
Aaron
'56 MGA
'67 B-GT
'83 Ferrari 308GTB QV
'89 Mercedes-Benz 560SEL
'94 Mercedes-Benz E320 wagon
'96 Range Rover 4.6HSE


Aaron Greenberg


P.S.

Anyone use Red Line Lightweight Shockproof gear oil? That seems to be the best option for the MGA 'box, as it offers the same viscosity as SAE 30 engine oil.
Aaron Greenberg

Hi Aaron

The filler/dipstick is covered by a flap in the tunnel carpeting in the passenger compartment (LHD car). It is quite well forward near to the heater box outlet (if fitted). Lift the flap to reveal a large rubber grommet. Remove the grommet to reveal the dip stick/filler.

Steve
Steve Gyles


Thank you Steve for the direction on the gearbox filler. As soon as I can get the car back up on my lift, I'll be handling the gearbox service! Is there enough access to get a small funnel up there?

Cheers,
Aaron
Aaron Greenberg

Redline smoothed out the original gearbox on my A, I certainly recommend it.
Russ
Russ Carnes

I tried Redline MTL for a two year test run. I didn't like it immediately and was very happy the day I switched back to 20W50. For full details see here:
http://mgaguru.com/mgtech/gearbox/gt107.htm
Barney Gaylord

Aaron,
Putting the car on a lift will be helpful to drain the gearbox but not to fill it. This must be done from inside the car. I have found a funnel with a long fexible neck to be useful. You have to kind of crawl under the cowl on the passenger side to add oil. Getting the dipstick/plug out can prove interesting. I've found that adding a tie wrap to the handle on the dip stick is helpful in removing and re-installing the dipstick.
Cheers,
Gerry
G T Foster

My 2nd gear synchro was starting to go, so I tried Redline hoping it might improve things a little until I had time to rebuild the gearbox. I couldn't tell any difference from the SAE30 that I had been using.

Jeff Schultz

I think that it is funny that you have a 56 A and 67 B-GT, as this is what I have, along with our 57 ZB. I too accumuated these while living in Ohio also.

As everyone has said, dip stick, which is also the fill hole, is only accessable from inside the Passenger side foot well on the tunnel. You must use a funnel with a fairly long stem to get it into the hole in the trany from the service hole on the tunnel. A flexible funnel would be ok, but I find that a plastic funnel with a long stem, cut to optimal length, works best. The problem you will find is that you must always use a full bottle of oil as you can only lift the bottle to slightly above horizontal when pouring the oil in. You will see what I mean.

As for what to use, the Haynes Manual says to use 20W50. I use Castrol and have not had a problem in 18 years. I also use this in the ZB for about 10 years with no issues.

Dennis, Arizona
rtoys

I put Castrol 20/50W in mine 10 years ago and I have had no problems. MGA's are pretty basic and Redline stuff costs a bunch more.
Bill Haglan


Thanks all for the replies! Barney, that article was quite interesting and informative and after a good read of it, I think I'll try some good old Castrol GTX 20W-50 in the 'box first.

Anyone recall off the top of their head how many quarts the gearbox holds?

Cheers,
Aaron
Aaron Greenberg

Three quarts for the standard gearbox.
Barney Gaylord

Barney

All my references say 4 to 4.5 pints. That's 2 quarts.

Steve
Steve Gyles

I recommend an oil pump rather than a funnel for filling - a big syringe - useful for filling the diff also.
Mike
Mike Ellsmore

4.5 UK pints equale 2.7 US quarts. The conversion is 1 to 1.2 (UK pints to US pints) just like tha gallon.

Chuck
C Schaefer

Chuck

Ah, short changed again. I should have realised! Historically, I wonder where we drifted apart on this one?

Steve
Steve Gyles

Jeff, I also tried Redline to improve after market 2nd syncro. Waste of money, back to multi grade 20/50. All I got was slight weeps turned into leaks. Apparently Redline loses its viscosity when hot, where as the multi grade does not. After market syncros are not the quality of originals, since I did mine ,I now know of three boxes that had to be re-done using good original second hand rings. Maybe some one has used the top gear ring in second and the new ring in top ? ? I may get fed up with the baulky 2nd gear shift and pull the box again. But I live in hope that it may come right, I'll give it another 4 or 5k miles.
Sean
S Sherry


I've had excellent luck with Red Line in my Ferrari in the 75W-90N/S flavor, although obviously MG and Ferrari gearboxes differ quite a lot ;)

I have three quarts of Castrol GTX 20W-50 ready to go into the 'A this week so I'll report back on my results!

Cheers,
Aaron
Aaron Greenberg

To be precise, the MGA gearbox takes 2.56 Litres, 4.5 Imperial Pints, 5.4 US Pints (2.7 US Quarts). Most oil is sold in quarts (in the US), so you have to buy 3 quarts (6 pints).

3rd and 4th synchro rings are same part number and are interchangeable in the 3-synchro gearbox. 3rd and 4th usually don't wear much, 4th even less than 3rd. I often swap 3rd and 4th synchro rings to even out wear and put them back in service. Having parted out a few gearboxes I have spare 3rd and 4th rings, and I have never purchased a new one.

2nd gear synchro ring is a smaller in the 3-synchro gearboxes, wears much more, and needs to be replaced almost every time you open the gearbox. It will last about as long as the laysheft (or graphite clutch release bearing), so there is no lost labor in replacing the 2nd gear synchro ring at same time as the layshaft.

The "improved" steel 2nd gear synchro ring and matching 2nd gear are so expensive that it is cost prohibitive to change from brass to steel synchro ring.

The later MGB 4-synchro gearbox (1968 on) has four identical steel synchro rings. While these may wear for a long time, I came across a broken one recently (on 4th gear even, go figure).
Barney Gaylord

According to my original second edition series MGA Operation Manual, published in Aug of 56, the gearbox capacity is 2 3/4 pints (2.27 liters, 4 3/4 US pints) and the recommended lubricant is the same as the engine which is 30 weight.
James Johanski

I've always been told to use "non-detergent" oil in the gearbox, because the detergents will cause gear crud and metal bits to remain "in suspension" in the oil and muck-up the gears. Non-detergent oil, I was told, permits the crud and metal bits to sink to the bottom of the gearbox. Any truth to this?
M. D.

That would be a "conditional yes", but I use detergent oil in the gearbox anyway, and I think it's just peachy.

Detergent oil does hold dirt in suspension, which is great for circulating systems with an oil filter, like engines and automatic transmissions. Non-detergent oil does allow dirt particles to settle out of suspension to the bottom of the box, but detergent oil may also drop the larger particles when the car is parked (and not pick them up again). Particles small enough to stay in suspension are likely smaller than thickness of the oil film and will not cause general wear. There have also been old tales that detergent oil may foam in a gearbox, which is entirely unfounded.

That said, I have been running 20W50 detergent oil in my MGA gearbox(es) for decades and hundreds of thousands of miles. With non-detergent oil the book specifies to change the gearbox oil every 6000 miles (every second engine oil change), which almost no one does. With good quality modern detergent oil I change oil in gearbox and differential every 12,000 miles (whether it needs it or not). Gear wear is nearly negligable (except for my intentionally inflicted ham-fisted chips on corners of 1st gear when downshifting in motion). The gearcase stays fairly clean inside, where non-detergent oil usually accumulates mud in the bottom of the case and might eventually clog up some oil passages.

I change a layshaft and 2nd gear synchro ring at about 80,000 mile intervals (if I don't break any gear teeth earlier), but I think that will be about the same regardless of what oil you might use (even synthetic oil). I drive it hard , and I'm fussy about the 2nd gear synchro working well at all times. Other people who drive more casually might go longer before changing the 2nd gear synchro ring or layshaft.
Barney Gaylord

I guess someone should say the 2.7 US pints is the capacity of the rear axle, not the gearbox.
Barney Gaylord

Barney, as you are luckly enough to have good original spare 2nd gear syncros, I guess that's why you haven't had a problem. I would welcome any advice as to where there is a source of new rings that are up to standard. I have no recollection of problem 2nd gears in Mowog gearboxes as fittd to all 4 speed Morris, Wolsley, MG, cars from the late '30 to early fifties. So all the technical stuff about exact clearances etc.,just don't hold up. If the syncro ring is not up to standard nothing will fix it. Ditto all fancy oils. Straight 30 will still work ok but the more advanced 20/50 will hold up better cold and hot. It's all down to that little brass ring !
S Sherry

I stand corrected. My post read 2 3/4 pints for the gearbox and should have said 4 pints. 2 3/4 pints is for the rear axle as Barney has stated.
James Johanski

I have never had a spare 2nd gear synchro ring except to buy them new, and I have bought a lot of those. They do wear out faster than we would like, but that doesn't mean the new ones are defective or poor quality. It's just the nature of the beast. They don't wear out in the cone surface, just the three three outer ears.
Barney Gaylord

Barry, maybe there are more than one manufactuers of the syncro rings. I don't know where the rings in the Australian mrrket are sourced from. Eg., I know one of our major suppliers sourses their trim kits and convertible tops from the USA because of their superior quality. Maybe that's the answer. ?
S Sherry

Steve,
It all started with the difference between the volume of a gallon of wine and the volume of a gallon of beer in the middle ages!
Peter.
P. Tilbury

This thread was discussed between 14/04/2009 and 18/04/2009

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