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MG MGB Technical - Gearbox Fill Location - 74B

I've seen comments that on "later models" the gearbox is filled from a hole on the right side as opposed to the dipstick location behind the radio. Do you know when that filler hole was added?

Dan
Dan Hiltz

RB cars have a combined level/filler hole on the side instead of the dipstick, but they still have the rubber bung on the tunnel. A '74' could be either CB or RB although the latter are usually referred to as '74 1/2'.
paulh4

Dan. Clausager's "Original MGB" might have the exact date and vehicle number when the change took place in the notes in the back of the book. On page 84, Clausager notes the same information that Paul has provided. The big thing, to many of us, is that the two transmissions interchange in both the overdrive and non-overdrive models. Relative merits of the overdrives (there were two models) are subject to debate. In fact, many years ago now, Chris Betson and John Twist debated and discussed the relative merits of the two models. Not sure why you asked this question, but if it relates to changing from one style of tranny to a different style, my own preference is for the later, side filler transmission. You have to elevate the vehicle and use some form of pump to refill the transmission when doing an oil change. But, I have found, over 50 years of working on these cars, that refilling the top fill transmission, regardless of how careful I try to be, always gets some oil on the carpeting. Like all personal preferences, someone else might disagree and be completely correct in that belief. It comes down to what works best for you.

Les
Les Bengtson

Well, yes I do disagree as it happens :o) Having one of each I find it far easier to check the level with the dip-stick than having raise the car but keep it level to use the side plug. However topping-up/filling is a different matter, both are a fiddle, and I'd rather have oil on the garage floor than the carpet (which I have managed to avoid).

Would anyone change the gearbox type just for that? I doubt it, we love and live with our cars with all their faults.
paulh4

Last time I needed to fill the gearbox I made this out of some 15mm copper tube, the bottom end fits easily in to the top of the gearbox and a funnel fits tightly into the top. The funnel sits by the steering wheel and filling is easy.


R.A Davis

People do similar for the side-fill with a longer tube down from the engine compartment.
paulh4

I bought this mini pump 3 or 4 years ago & have found it perfectly adequate to refill the gearbox whilst the car is up on axle stands - Unlike a big syringe you can fill the gear box up & easily slow down the flow when the fresh oil starts to drip out of the filler hole & return a little later to top up,once the oil has settled in the gear box. (I know the handbook also says to go for a short run & then recheck the level & top up if required). I measured exactly how much old oil i had drained out (including dropped during overdrive filter changes) & ensured i put back at least as much as i took out & got very close to the specific capacity quoted.
This pump was also useful for changing the diff oil as well.
Obviously my car is side fill only with no dip stick for the gear box.
Cheers,
Charles



Charles9

You certainly have to cycle the gearbox though the gears and switch OD in and out a couple of time after an oil change following experience with both mine, the level drops off the bottom of the dip-stick by quite a way and OD either cycles slowly in and out or doesn't come in at all. Rather than getting the RB down and back up again for topping-up I chose to run both off the ground, safely supported.
paulh4

This thread was discussed between 16/07/2023 and 18/07/2023

MG MGB Technical index

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