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MG MGA - Rear brake balance

I took my car for its MOT test recently and it passed ok, I know I don't have to do this these days, but do I like to have another "real mechanic" look it over once a year.

During the brake test he said that there was some rear brake imbalance but it wouldn't prevent the car from passing its MOT.

So when I asked him just how much brake imbalance there was, he told there was 100 kilos difference in brake effort between the two sides!

I have to admit that I was surprised to say the least, I had noticed a very slight "wriggle" from the rear of the car when I brake hard but otherwise the brakes have been excellent.

The pedal is always absolutely solid and needs no pumping up, the drums were replaced a couple of years ago that alone really improved the brake pedal and there were no signs of oil leaks back then.

Now that the car is more or less off the road for the winter I plan to take the drums off to have a good look at the brakes to see if anything stands out.

I have looked for posts on this subject in the archive but there isn't so much there.

Dominic Clancy tells me that years ago, he had similar problems with his MGA and in the end, he took the car to an expert who set them up for him.

I would like to see if I can fix it myself and so, before I go the same route as Dominic, does anyone have any pointers?

Cheers
Colyn
Colyn Firth

Could be that the arc of the brake shoes is not equal between the two sides; I had this issue many, many years ago. Solution was to get a new set of shoes and then I had to have them shaved a bit to match the curvature of the drum.
Nick Kopernik

Colyn

Was that on the foot pedal or handbrake? I am sort of guessing foot pedal from the way you described it.

Following on from what Nick says may be worth first swapping the shoes from one side to the other to see if the imbalance transfers with them.

Steve
Steve Gyles

Hi Colyn

That sounds like a big difference but it might make it easier to diagnose. As Steve says is hand, foot or both?

Did you by any chance note the front brake readings as I would be curious to know how discs compare with drums for which I have my readings

I hope you haven’t been impacted by the floods in your area.

Paul
Paul Dean

As Colyn reports, I always had problems with the balance of the rear brakes. the right rear is repeatedly under the force of the left. Last year I gave up and took it to a workshop who fixed the issue to the point that the safety inspection was successful. They said the issue was the mismatch of the shoe arc to the drum, even though swapping the entire shoe and drum had not changed the behaviour of the brakes. I haven't taken it apart to inspect anything (yet) but was just happy to get the certificate for another six years - even though it cost me 800 CHF (700€, 800 USD) for the half day workshop fees - they didn't need any new parts...

The shoes and drums were all from Moss Europe a few years ago, but it has been a recurring issue in all the time I have owned the car (since 1988...)

There is no oil leak in the hub, as I speedisleeved them both and replaced the seals about six year ago.
Dominic Clancy

Hi Colyn

The MOT test allowance is that the brake effort side to side must be within 70% of the maximum effort on the axle. From memory, my rear brake effort is usually around 150kgf. The fronts are usually 190/200Kgf. If you have a 100Kgf difference I cannot believe it is within the spec. limit of 70%. You would have to have a max effort of more than 333KGf on one side which is huge.
My MOT tester allows me to stay with the car during the test and lets me have a look underneath and help with the controls. I always find it really helpful as they often spot something that I haven't noticed even though its not a fail problem. My left rear has always, for 40+ years, locked up before the right rear.

John
John Francis

Common causes of rear brake issues include --
Seized slider in the backing plate
Rear shoes mixed up and in wrong positions as in fitted as trailing shoes instead of leading-some people look at the book and do it not realising it is reverse on the other side--so one side is correct the other back to front=and
Brake adjustment--don't know how many times i've come accross the rears that have been adjusted up without the handbrake adjustment let off to do it properly
William Revit

Hi Willi

None of those applied to my car. Will have a look to see what they did on Saturday as I want to check all the U bolts anyway.
Dominic Clancy

Thanks everyone, sorry for the delay in responding but I have been away from home since I first posted this.

I may have got it wrong with the exact figure for the brake imbalance but I do recall being told that, although it was a large imbalance, it was still within acceptable limits.

The difference was recorded when I applied the foot brakes, the handbrake passed its test also but I never thought to ask the tester for the figures for it.

I am due to take my MG3 for its MOT next week and so, whilst I am there, I will ask him if he has recorded the readings for the MGA and let you know.

Some good advice here guys, I hadn't considered that you have to back off the handbrake adjuster before adjusting up the brake shoes.

I will be starting the rear brake strip-down in a week or two, I have a job to do on the cylinder head first before I can begin. I will let you know how I get on.

Paul, thanks for asking about the flooding, we were lucky this time and we have not flooded, back in 2007 we were not so fortunate and we got a foot of water through the house and garage. It caused thousands of pounds of damage but we had good insurance cover, thank goodness.
In 2007 I was fortunate in that my MGA was a month or two late in delivery from Bob West and if it had arrived on time, it would have been half submerged in my garage.

Our house is between Toll Bar and Fishlake which are both flooded and so we are very lucky.

Cheers
Colyn
Colyn Firth

This thread was discussed between 11/11/2019 and 12/11/2019

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