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MG Midget and Sprite Technical - New Member & Rear Brake Problem

Hi,

I am a new member!
I acquired a 1979 midget 1500 a few months ago, which had previously been sitting a shed at the back of a family friends garden for around 10 years.
I have done a load of work on it, and was hoping to have it ready for an MOT tomorrow, but despite some work on them, the rear brakes are still causing me some trouble.

So far I have:
- Replaced the cylinders, which were completely frozen, with new units.
- Replaced the flexible hose with a new one from Goodridge.
- Cleaned out the two rigid pipes that come the T-piece from this (both of which were full of black junk).
- Bled the rear brakes.

When bleeding the rears, a bit more black crud came through, but the fluid is now clear and flowing freely, although according to my helpful assistant it took quite a lot of force, certainly more then when doing the front.
When pressing on the pedal, with the drum off, there is no movement of the shoes, unless the pedal is pressed incredibly hard, and then they move a tiny amount (probably no more then 1mm).
I also noticed that there is quite a lot of free travel on the pedal, at the end of the pedal becomes hard straight away.
Given the parts that have been replaced, I guess the problem is most likely in the pipe to the rear of the car, the "Pressure Differential Warning Actuator", or the master cylinder.
The switch in the "Pressure Differential Warning Actuator" has broken, and I cannot really feel what is going on in there with a screwdriver, but I am getting fluid through to the rear, so I would have thought that the shuttle is centred, and the pipe cannot be blocked (although it certainly is possible).
Any thoughts, this really has me scratching my head, and I am itching to have my first drive!

Thanks,
-- Josh
J Levine

I am sure others will give a more detailed reply but in my view "black crud " is bad news and could be indicative of internal seals breaking up in the master cylinder (you say you changed the cylinders, but I presume you meant only the rear ones?), flexible pipes breaking down internally, and very old and contaminated fluid.

I would send for a new master cylinder and new pipes and flexibles all round.(apart from those already changed)

My car doesn't have the pressure differential thing, so I can't help with that.

Just don't rush to get it on the road and cut corners with the brakes.
A 10 year lay-up is a disaster for brakes so I would advise replace as much as you can and get it right, for your own and others sake.
JB Anderson

Hi Josh,

I'm with JB, the brakes are so important on any car that you should replace as much as possible

Once sorted and MOT'd use the car regularly to sort out wrinkles and for you to get used to the car

Also (yawn from others) if you've not already got a copy get yourself an owners Handbook even if you have other manuals as it will help with your ownership and give you good info missing from other books - (Ref: 0058)http://www.mgocshop.co.uk/catalog/Online_Catalogue_Handbooks_5.html

cheers, Nigel
Nigel Atkins

ditto what they said, but also add the clutch system to the shopping list (master, slave, flex hose)

oh, and radiator hoses (and probably radiator as well).

while you've got the brakes all apart, pull the PWDA and clean it, and replace its o-rings

more rubber fun / parts that may have perished, and will gradually show up when you put the car back into service:
intake valve seals?
rear axle seals (and the gear oil may have broken down, so should be changed, if you haven't already)?
engine front seal?
steering rack boots?


10 years is a very long time for anything rubber, or in contact with fluids, to last.


Norm
Norm Kerr

might be a plan to get rid of the PDWA; earlier Midgets didn't have it, I think it was mainly introduced to meet US legislation.
David Smith

I am with smithy on this, first get rid of the diff switch

Then check the pipe going to the rear, when you break a connection near the M/C do you get free flowing fluid? now check near the wheel cyl, do you get free flowing fluid there? simple checks should be simple solutions. I hope!

Does that model 1500 have a dual line system?
Robert (Bob) Midget Turbo

Thanks for the information, I agree it would be a good idea to replace all the bits in the breaking system, but would like to try to work out where the problem is anyway.

JB - Correct, only the brake cylinders have been replaced thus far. I think that the crud was probably contaminated brake fluid, the rear brake hose seemed OK, and it lined the entire pipe. Seemed to be no similar problem at the front.

Nigel - I followed your advice in a previous thread and picked up both the official handbook and manual, they have been very helpful thus far.

Norm - I have already rebuilt the clutch part, as it wasn't disengaging, turns out it was a ceased clutch, which has now been dealt with. Will certainly take a look at the PWDA. Steering boots are fine, no idea about the engine seal and intake seats, rear axle may well need to be done, it was at the top of my post-MOT todo list, there is some moisture around one of the rear axles.

David & Bob - Any suggestion on the best way of re-plumbing the system if it is removed (presumably a T piece for the front, and straight to the back).

Bob - I seem to have free flowing fluid throughout the rear, hence my confusion, is it possible that fluid can flow, but that pressure is not being generated? Perhaps the master cylinder has failed in such a way that it doesn't externally leak, but stops pressure from being developed on the rear circuit.

Thanks,
-- Josh
J Levine

The MS can certainly fail in that way, which is why I think you really need to change it.
The internal piston seals will pump fluid happily if there is no pressure resistance, but as soon as a resistance is added the seals will give way and allow fluid to bypass the seals. Hence no pressure to operate the brakes.
The crud I suspect is a mixture of partially decomposed master cylinder piston seals and old dirty fluid.
Are the front calipers working OK? After ten years I would expect them to be seized up too..which will give a hard pedal (if the rears were OK) but no brakes!
JB Anderson

As far as I can tell, fronts are working fine, pads have been replaced, and pistons wound back happily.
Also replaced the front flexible hoses, and the fluid was clean.

-- Josh
J Levine

Josh great news you got the owners Handbook you'll find it excellent later when you're using the car and regularly service and maintaining

I'm not sure which manual you mean but I would say that the factory parts catalogue would be very useful to you now, I know there are free parts lists and drawing available on the t'internet by this paper version is very useful to see which order the parts and fixings go - (Ref: 0016) http://www.mgocshop.co.uk/catalog/Online_Catalogue_Parts_Lists_3.html

Good luck
Nigel Atkins

A car of two halves: front brakes fine and fluid clean, rear brakes no go and fluid dirty.

It seems that it may be that warning actuator thing messing up the fluid/pressure delivery to the rear, unless it is a dual line system in which case there will be a seperate hydraulic seal in the MC (other than the one serving the front brakes, which is OK) which could have failed.

I would still be happier having a new MC as they are not too expensive, and find a way to do without that PD warning thing.

It can be a bit of a fiddle getting to the nuts that hold the MC onto the pedal box, but that is typical of a Midget.
If there is a way to make an easy job difficult, a Midget will find it...
JB Anderson

JB - It is a dual circuit system (with tandem MC), so the two halves are pretty separate, I am going to have another go at finding out where the problem is now, I suspect there could still be some air somewhere as well. I will pull the master cylinder later and rebuild/replace, along with the PDWA, which I may remove completely.

Nigel - The manual I was referring to is the "MIDGET 1500 Workshop Manual":
http://www.mgocshop.co.uk/catalog/0018.jpg
I also have a parts catalogue, although this may be from the MGOC, I will check out the one you linked.

Thanks,
-- Josh
J Levine

From what you say, J, it would seem that the MC piston seal that actuates the rear brakes has failed, but the front seal is OK. (assuming the PD thingy-thingy is not causing the problem, and that it is not a diagonally split system).
Please let us know what you eventually find out has been the cause of your problem.
JB Anderson

Josh the Parts Catalogue link I’ve put is to MGOC (other providers may/are available)

As for Workshop Manuals they’re well beyond me but I think I’ve just found another misprint in Haynes

I don’t know much, especially about the 1500, but I do know you bleed a dual circuit different to a single but I suspect so do you

This is an excellent book just about to be reprinted it gives loads of production information and is a lovely book just to look at - http://www.amazon.co.uk/gp/product/1906133336/ref=pd_lpo_k2_dp_sr_1?pf_rd_p=103612307&pf_rd_s=lpo-top-stripe&pf_rd_t=201&pf_rd_i=1870979451&pf_rd_m=A3P5ROKL5A1OLE&pf_rd_r=1HCZ8SC8VNQH8HK99KYH
Nigel Atkins

This thread was discussed between 04/04/2011 and 05/04/2011

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