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MG MGB Technical - rear brakes

Where can I find full details of fitting MGF rear disc setup to an MGBGT with tube axle.
Any help appreciated


Jim
jim soutar

Google?
paulh4

try this Jim

http://mgparts.co.nz/josephs-rear-disc-brake-conversion/
S P Brown

SP, that looks like a really interesting conversion
and I quite like the idea of fitting the MGF rear calipers to my MGA.

From the pictures I couldn't quite make out how the caliper fitted to the axle, do you know if you need to make or buy a special caliper adaptor-plate to make them fit?

Cheers
Colyn
Colyn Firth

Colyn,
why not contact Paul, remember the time difference though. Unless I've got false memory again Paul used to post on the midget & Sprite forums here.

Scroll down this page for email and phone contacts -
http://mgparts.co.nz/contact-us/

Nigel Atkins

Thanks Nigel
I have sent Paul an email and I will let you know what I find out.
Cheers
Colyn
Colyn Firth

Thanks Colyn but don't worry about me as I have enough trouble with standard brakes and wouldn't be capable of conversion work.

Anyway I'm very light on my brakes, I can't afford to lose any moment, I use the expensive petrols, those top oil company executives barely have two yachts to rub together so need my help.
Nigel Atkins


I know the MGA rear drums are pretty good as standard and the car doesn't really need disc brakes on the back.

However, I must admit that I really like the idea of rear brakes that are self-adjusting.

Whether or not I decide to fit them kind of depends on how how it would affect the front / rear brake balance and also on how difficult / expensive the job would be.

I have been toying with the idea of uprating the front brakes by fitting 3 or 4-pot calipers and if I did, the rear disc conversion would then make a lot more sense.

Cheers
Colyn
Colyn Firth

Colyn, I love the idea of going to the ragged edge of experimentation, but is this a solution looking for a problem? As I think you've observed, the front braking would have to be uprated a fair amount to balance the enhanced rear braking performance. If you could achieve this then you'd be limited by the grip of the tyres. As standard, the majority of the braking effort is on the front wheels and the racing chaps reduce braking effort at the rear still further, by reducing the size of the rear wheel cylinders (BMC Mini Cooper items?), presumably to change the brake bias. Plus you'll have traded off manual brake adjusters (a plus feature in my book) for potentially seized brake calipers!
Peter Allen

I still exist, but between being flat out with work and for some reason not being able to get onto the BBS simply (have to go back through internet history and get in from there) I haven't been as active lately.
But still as interested!

Here is some more detail about what I have done, most should be self explanatory. Feel welcome to seek clarification.

I have to say that one of the primary motivations for going to discs was no longer having to crawl under the car on wet roads after every special stage to adjust the shoes! Having said that, the catalyst was frying the linings off the shoes completely on one very fast special stage and finishing with front brakes only (virtues of dual circuit). Rallying is a lot tougher on rear brakes, as the car is tail heavy by the time a co-driver and bolted down tool kit are added, coupled with less weight transfer on gravel surfaces requiring more rear braking effort, and more rear bias again to allow the back of the car to flick out when setting up for corners.
Racing has the reverse effect of course, with sticky tarmac tyres providing even more weight transfer than standard and reducing the contribution required of rear brakes accordingly.

But having done the change, the brakes feel soooo much better, with a firmer and consistent pedal height. And I can be a lazy old fella and not chat at the end of a special rather than crawl under and adjust things.

Respondng to Peter's thoughts:
Calipers never seize if maintained, and the required maintenance is simple.
Where brakes aren't maintained or have been left idle, we find drum brake cylinders seize much more frequently than calipers.

Agree front/rear balance is very important, abut whenever brakes are modified, even by uprating linings, this should be checked.
There are two key factors here which shouldn't be confused: Braking power is all about how much heat the brakes can dissipate. Discs have higher braking power than drums. Brake grip is quite different. Typically, standard friction material has high grip but fades away, whereas competion linings have low grip (and so require higher pedal pressure) but don't fade any where near as much.
Usually, disc brakes have higher power than drums, so can handle repeated stops better, but lower grip than drums (due to a lack of self-servo action) and so require greater pedal pressures.
What affects brake balance is primarily the grip, not the braking power. So when discs are fitted to the rear the usual effect is a balance transfer to the front, not the rear.
With the original disc front/drum rear set-up, uprating the linings can have a significant change in front to rear balance as the drum dinings can have quite different characteristics to disc.



Paul Walbran

Thanks Paul
I sent you an email through your website to ask you about this which you can now ignore as you have now fully answered my question.

It doesn't look to be so difficult to do this conversion but as you and Peter say, it may be a step too far for road use, even though in my case, that does get pretty heavy right-footed. :^)

I still like the idea of self-adjusting rear brakes though, I don't have to re-adjust them quite so often as the rally guys do.

I find that my brake pedal movement does go a bit long after a long trip through the mountains for example and I have to re-adjust the rear brake shoes to get it back. An awkward job on an MGA because you have take the wheel off to get to the adjuster through the hole in the rear drum.

Maybe there lies another option, just fit MGB brakes and backplates to my MGA (if they are compatible)

Cheers
Colyn
Colyn Firth

FWIW although MGB banjo axle drums have the hole the adjuster sticks out the back as on the Salisbury axle, and is possible to adjust with the wheels on the ground as I found once with smoking brakes. The process of converting MGA to MGB is described here https://mgaguru.com/mgtech/brakes/bt204.htm.

MGC rear brakes were self-adjusting, on the Salisbury axle.
paulh4

Hi Guys
Lots of interesting ideas there. Thank you. Personally Im really looking for a way to auto adjust the rears. I dont like the way pedal travel increases so quickly and the brakes seem to loose power at the same time. Readajust and all is well. Maintaining correct adjustment would cure the problem as I see it.
I run V8 discs and four pot alloy calipers on the front, and standard drum rears, so the idea was to use self adjusting F setup
No competiton use anymore its just a 1950c supercharged road car.

jim
jim soutar

Can't speak for that set-up but the only time I adjust mine is part of the strip, clean, lubricate and reassemble each year. Having to keep adjusting implies the shoes are wearing down, but I've replaced shoes on mine once in 30 years and 25 years at most. Either that or the adjuster mechanism is worn and stepping back.
paulh4

I'd second that: only at each annual service. As I back off the adjuster to remove the drum, it's difficult to tell if on replacement it is different from how it was originally. However the last few times (all I can remember!) it didn't appear to "need" adjusting.
Michael Beswick

Jim,
I'm interested in fitting self adjusting rear brakes, probably for exactly the same reasons as you. I have a 1950 cc engine in my MGA which I tend to make the best of and so my brakes tend to take a bit of a hammering and I do adjust quite regularly as I like to keep the pedal to feeling solid.

I have looked up the MGC rear self adjusting brakes and although it does look do-able, it seems like a lot more modifications and parts would be needed to convert. This is the link.

https://www.mgexp.com/forum/mgb-and-gt-forum.1/self-adjusting-drum-brakes.3751081/page-2

The MGF rear-disc conversion looks a lot simpler but you would probably need to fit either a rear brake pressure limiter or an adjustable front/rear balance set up to prevent the rear brakes from locking up.

On the subject of brakes, I have fitted Mintex 1144 material to both front discs and rear drums and they are superb.

Cheers
Colyn

Colyn Firth

Hi.. I can*t explain the different adjustment regimes between cars but my rears need adjusting after every 2/300mls or so. Its only a notch each side that makes such a difference to pedal travel and feel. I obviously need to do more reseach but the original rear drums are massive for size of car and very heavy, the MGF discs are on the small side so the balance factor should be easy to control with an adjustable balance valve as per comp cars.

Jim
jim soutar

Personally I wouldn't countenance self adjusting drum brakes. On the cars I have had that used these things they were a complete pain. Even if the adjuster works as it should, and they often don't, they make getting the drums off really difficult because you can't back them off externally.

If you are going to change, a small disc brake would seem ideal. My MGB GT with a V8 conversion has Hoyle brakes and suspension. So the front discs are 4-pot with ventilated discs and large pads, while the rears are from the Ford Sierra. The balance is fine with no tendency for the rears to be overpowered. No balance valve is necessary.
Mike Howlett

Jim,
"I run V8 discs and four pot alloy calipers on the front,"

Presumably this is the cause. For the rears to need (more) adjusting, they must be wearing more-ie used more.
Michael Beswick

Michael, Just a little puzzled , are you suggesting the front brakes are inadequate and the rears are having to make up for that or that the rears are keeping up with the fronts? Visually the rear linings never look to be wearing exessively yet the need for constant adjustment is always there. Jim
jim soutar

If they are not obviously wearing then the adjuster must be backing-off somehow, needing adjustment every 2-300 miles is very wrong in my experience. I realise one click is only a quarter of the fine thread pitch, but even so that's one full turn every thousand miles.

Even when I was doing 10-15k per year in my V8 for several years they didn't need adjusting between annual service or replacing at all, although that was road miles not rallying or the like.
paulh4

Jim If the rears are not wearing then the adjustment mechanism must be at fault, as Paul says. Only if they were wearing (more than "usual") would it be related to what was fitted at the front.
Michael Beswick

This thread was discussed between 27/02/2019 and 04/03/2019

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