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MG Midget and Sprite Technical - Inconsistent Brakes

Hi everyone. I am back with a question! :-)

First up, the car is a 1500 with single circuit brakes. Rear cylinders have recently been changed, rear shoes and drums are good, adjusted "right" rear flexi is of braided type. Front calipers had new seals and pistons about five years ago, decent discs and pads fitted one year ago, rubber hoses on the front (for now). Tin type M/C rebuilt with new seals a few years ago.

The problem is the pedal feel is really inconsistent. It has been like that for so long that the double press of the pedal has become habit when driving my MG!

The brakes always work and stop the car well (even on first press) but I have no confidence in them. The feel and force of the first press seems to vary a bit and a quick pump always firms the pedal up. I would really like to sort the problem once and for all.

What are the collective thoughts on the following causes/cures:
1. Swap the front hoses to braided for improved feel? (surely won't cure the actual problem)
2. I recall reading in the archives somewhere that duff caliper seals can pull the pistons back from the discs slightly, causing inconsistent braking, thoughts?
3. I recall reading in the archives that adjusting the rear brakes too tightly caused the rear pistons/fluid to overheat, causing inconsistent braking, thoughts?
4. Duff M/C?
5. I need to bleed everything again? (I have tried this so many times!!)

Thanks everyone,
Malc.

Malcolm Le Chevalier

Hi Malc,
Your numbered points:

5 - was there any air expelled when you've bled them, if not then suggest not that.

Possibly 2 as it seems your brakes are solid with a single pump which would equate to a slight movement caused by the caliper seals closing.

4 - I had this with a relatively new m/c. Swapping the seals did the trick.

Not heard about No 3, it's logical but I don't think you'll have adjusted yours too tightly!
Jeremy MkIII

Malcolm I have almost exactly the same setup. 1500 single circuit. I have new pads and disks, new shoes, braided hoses all round, and tin type M/C rebuilt with new seals last year.

I'm not sure I can add much to the thread other than to say my set up is consistent if not particularly confidence inspiring compared to my modern car.

Brake pedal feel is consistent. The pedal travel goes a fair way towards the floor before you can feel any effect. The last 20% of pedal travel is where braking starts and requires a fair bit of leg strength to do hard braking or an emergency stop.

Like yours an extra pump of the pedal does firm the feel of the brakes, although I dont feel I need to.

There are two types of tin master cylinder, the replacement seal are different. The later replacement type of cylinder can be identified by a groove around the casting where the push rod exits.

C MADGE

Or option 6. There isn't actually anything wrong!

(as a side thought/issue, if I brake too sharply the oil slops forward in the sump and I lose oil pressure, so maybe I don't want to fix the brakes! ha ha! I do plan on adding some baffling to the sump. I put in a longitudinal baffle, but it seems it also needs a transverse one)
Malcolm Le Chevalier

Malcolm
Maybe go back to basics--
Let the handbrake adjustment right off, adjust the rear brakes--then adjust the handbrake
Also check that the pushrod on the master cylinder has a little end clearance when the pedal is right back and that this clearance is the same every time (sticking MC piston)
willy
William Revit

I'm with Willy plus -
1 - piss-poor new rubber hoses or clogged/collapsing/constricting old ones - you want improved braking consistency not just improved pedal feel. I can't remember noticing much difference in feel when I the flex-hoses swapped to Goodridge 12 years ago (fit 'n' forget but you can't squeeze them off if you should want/need to).

2 - Piss-poor parts, hell yes it's possible.

3 - Never seen or heard that, don't know, would you notice much with the rears(?).

4 - Could be duff M/C and/or piss-poor new seals fitted

5 - Not unless you take/change something

(6) - Are your nipples all right, some people have had trouble with theirs.

(7) - Reservoir cap, does it have a hole in it and is the hole fully clear and open.

Nigel Atkins

Just a thought: excessive brake disc runout? This could cause the discs to push the pistons further back into the calipers, so each time you apply the brakes you have to first move the pads back into contact with the discs before the pedal will firm-up and apply braking effort.
Jonathan Severn

Another good thought from Jonathan.

A few typos in my post but I think you'll know what I meant.

I should have put if (7), and guess how I know about (7), you will need to bleed the brakes again. IIRC you're a gravity man like myself, with brake fluid bleeding if not ale.
Nigel Atkins

I don't see how disc runout, or air in the system, or maladjusted rear brakes would give inconsistent braking, surely these defects would act in a consistent manner? Possibly could be dragging caliper dust seals, but I'd replace the front flexihoses, then look at the master cylinder if still not fixed.
David Smith

I was about to say disc run out, but checked and see Jonathon says the same. And I do think this can give variable braking. After running for a mile or more without touching the brakes the disc run out would have kicked the pads further clear than it would after just a few yards. But I also think you get the same effect if your wheel bearings are worn, in which case a bit of severe cornering load might kick the pads out more than just running in a straight line over smooth roads.
GuyW

Disc run out is an interesting shout and something I hadn't thought of.

Over the winter I did a front end rebuild, so I know the wheel bearings are good, but maybe I reassembled the discs onto the hubs "wrong".

It's an easy thing to check. :-)
Malcolm Le Chevalier

Malcolm, if you had disc run out enough to push the pads back you would also have severe brake judder, excessive play in the front wheel bearing will give you this condition, but not disc runout without brake judder
Andy Tilney

ETA: Andy is your hotmail account working?

A combination of minor faults can cause weird effects.

One for me was when after fitting rear cylinders, after a short time but not straight away, the front caliper seemed to be holding then releasing the pads as I braked turned out I must have swapped the brake and clutch reservoir lids and the clutch lid never had its vent hole cut which seemed to highlight other issues including with nipples.

A combination of issues and not rechecking the basics.

I'd checked the brake lid at the start of work and it was clear (well its in the DH so I have to) so I didn't check again and didn't notice I'd swapped lids with the clutch lid when I done a change of clutch reservoir fluid as I had too much fluid left for brake top up but not enough to really do anything else with.
Nigel Atkins

Malc,
I take inconstant pedal feel as soft/harder (rather than judder) is that what you mean?
Nigel Atkins

Yes Nigel.

They always stop the car OK, but the amount of travel and force required at the pedal seems to vary each application. Not hugely, but enough to be disconcerting. A small pump always makes the pedal firmer, but isn't required to make them work effectively.
Malcolm Le Chevalier

So it's not judder on road wheel, steering wheel or brake pedal.

I realise you're thinking of disc to hubs but if you want/need Norm's (shhh, fwb) images with a little more detail put on I done a set for the last installation (and current) just let me know, and apparently the modern made spacers can be oversized and cause problems.
Nigel Atkins

The FWB are fine, let's not go there :-) (It amazes me how they create such fuss and bother. They aren't complicated!)
Malcolm Le Chevalier

"The problem is the pedal feel is really inconsistent. It has been like that for so long that the double press of the pedal has become habit when driving my MG!"

How long is 'so long'?

Has it always been like that since the rebuild, or has it occurred more recently?
Dave O'Neill 2

If it pumps up, my opinion is that there is air in the system. After rebuilding the rear disc calipers, my MGB had a long pedal which pumped up. The brakes worked alright but the pedal travel was about an inch and a half before anything happened. Re-bleeding got a bubble out of both sides and a nice firm pedal resulted. I had been bleeding with a gunsons Eezibleed, but I only got it right when Mrs H sat in the car and shoved the pedal and held it down while I operated the bleed valve. Just like the old days.
Mike Howlett

Run out would cause some judder. I have similar symptoms - no judder, and dab on the pedal before once again with feeling - so to speak. I think there is still air in there - somewhere, and I too have bled a few times. Only other thing I can think of is standard MC piston is incorrectly sized for my larger (Wilwood) front calipers.
Oggers

Malc,

Have you tried pulling the handbrake on, and seeing if the pedal movement is shorter, or can you still 'pump' the pedal? If it is improved, then try adjusting the handbrake up a bit - obviously not to the point where there is any binding!

Richard
Richard Wale

First thing ticked off the list. M/C lid is a vented sort, cleaned last night so vent is clear.
Malcolm Le Chevalier

https://www.youtube.com/watch?v=aXcsDMwiEtA
Nigel Atkins

Hi Malcolm
Sorry I can't add anything to the brake question, but as regards the vanishing oil pressure when braking, I can. I used to suffer this problem years ago when the car was in daily use. Oil and filter changes made no difference but a change of oil pressure relief valve and spring cured the problem.
The springs appeared to be the same length on the bench and the mushroom head of the old valve appeared to be very shiny on one small section. I seem to recall that the parts were not expensive and probably came from Austin Rover stock.

HTH
Alan
A Pritchett

Another couple of things ticked off over the weekend.

1. Braided front hoses on.
2. Everything bled (a lot!).

Pedal seems better on a short run, still not perfect.

Unfortunately I am not 100% confident on the bleeding of the rears. I use a vacuum bleeder, but it keeps sucking in air round the bleed screw threads, making it difficult to determine if the cylinders are bled OK. I might try an eazybleed (spelling?) to try and "push" some fluid thorough to the rears, rather than "sucking" it.

The fronts worked well and are spot on though.

Cheers,
Malcolm.
Malcolm Le Chevalier

Malc,
I thought you favoured gravity or one-man-and-a-jar methods like me - try those, more haste less speed with these suction and not-so-eezibleed methods sometimes.

Plenty of time for teas and pees with gravity and jar methods too and the glamorous assistant is happy to make the tea to avoid being anywhere near the car, everyone is happy.

Grease round your nipples to stop air getting sucked in.
Nigel Atkins

I use an eezibleed pusher system and have never had a problem. But it's important not to use them at too high a pressure, certainly not more than 20psi so let a little air out of the tyre before connecting up. I have never had one let go at the m/c cap either, which is a horror that some have had.

I also always expect to bleed brakes twice. First gets them operating well enough to drive the car safely. Then after a few miles on uneven roads, l will bleed again. This seems to help get those last little air bubbles trapped in fittings and pipe unions as they are shaken free and you get rid of that slight springy feel and get a proper firm pedal.
GuyW

Malcolm, in my experience the vacuum method only works if there is no air in the system. It is fine for simply exchanging fluid in an otherwise fine system. I took out my bleed nipples and smeared grease on the threads which does reduce the amount of bubbles but with the vacuum bleeder there were always some.

I only got mine perfect by utilising the services of my good lady (other assistants are available) and doing the tried and tested method.

Attach clear tube to nipple.
Open nipple a quarter to half a turn.
Assistant pushes pedal firmly to floor and holds it there.
Close nipple and release pedal.
Repeat.
Check fluid level in reservoir frequently.

This got the remaining bubbles out and the pedal recovered to a nice firm action.
Mike Howlett

Guy, I'm surprised at you using new fangled modern equipment over tried and tested traditional manual methods.

I don't push the pedal beyond where I'd normally press it in case the rod gets rough and rubs up the seal the wrong way, probably totally serrate modern made seals and get air in. :)
Nigel Atkins

I use an Eazibleed and its always been fine. I did have a problem on a couple of cars though and found the traditional method as described by Mike helped to solve it. I would add that a quick and firm action on the pedal with the nipple open helped to drive out the less willing bubbles.
Bob Beaumont

That's interesting Bob. I wonder if that's where I've been going wrong. All these years I've believed in stroking the pedal slowly and gently and eventually came to accept that I'm simply crap at bleeding brakes.
Now you've given me hope that I might finally get it! Thanks.
Greybeard

For stubborn air bubbles, I’ve found that two or three rapid pumps of the pedal before cracking open the nipple will often work. Obviously a two-person job.
Dave O'Neill 2

Even more gooder 😎
Greybeard

Grey,

My dad had a garage business in the 50's to 70's and I liked to help out. He always said to push the pedal hard and fast, almost stamping on it.
Bob Beaumont

I'm with you Grey
Slow and steady and don't stirr things up
Bleeding brakes , i rely on gravity if I can
Piece of plastic hose on each bleeder, open them all up, give the pedal a slow pump to start the flow and sit back and watch it bleed itself, keeping the m/cyl topped up-
Brake fluids are colour coded by law now (here anyway) but some are compatible with others and we had two at work blue and clear
If the car had clear in it and we were flushing through, you'd suck the reservoir out fill it with blue and bleed through till the blue came through-easy peasy--done
Next time round you'd use the clear fluid
Some cars get little pockets of air in the calipers and that's a 2 man job
No1 fits the hose and opens the bleeder
No2 smashes the pedal to the floor and holds it there
No1 shuts the bleeder quickly while the fluid is still charging out
No2 very slowly lets the pedal return up
Guaranteed to work--even on Volvos

William Revit

Cheers Willy. Every day is a school day! I like the colour code idea. When I had to change oil in the deck hydraulics on a ship in Australia the same thing made purging easier. We had to get rid of all the castrol oil and use stuff called Royal Purple (really) because the Oz govt reckoned it was better environmentally. The lurid colour made it a cinch.
I've noticed some motorbike calipers were b*****ds for bubble traps so the solution was to unbolt it, jam it with a chunk of plywood and give it a good shake with the nipple pointing up while pumping. Often wondered if the same would be practical for spridgets.
Greybeard

Interesting about the colour coding. It was an idea I had quite a few years ago - there will be a thread in the archives here somewhere, when I was saying that a choice of colours should be made available so one could tell when old fluid had been flushed through with the new colour. I don't believe that at that time any manufacturers were doing so.
GuyW

Grey
Funny, I was having a look at a bottle of Royal Purple engine oil for my VW at the weekend---Interesting colour, makes it look really thick but it was 5w30 syn. so not very thick at all--not cheap though at $90 for 5 litres---reads up good, but they all do don't they
Cheers
willy
William Revit

I read that the thing with the smaller blenders is constancy of product, obviously with the big companies that have matters well under control with having to keep costings down to fractions of a penny for production. The scales with cost accounting with general larger companies is amazing - until it comes to executive pay then numbers are rounded up to large denominations. It helped in the past that they self "regulated" and now of course it's labour market forces. If you say you're worth £10m a year I must be worth £13m, not counting our tens of millions in bonuses and shares of course. Collapse a bank and it's untold future riches as you're a real proven expert, some even deserve a knighthood. Let's pay them a lot more to sort out the mess they put us in.

Whoops,
how are the brakes going. :)
Nigel Atkins

Don't forget to breathe Nigel! :-)

Off on holiday for a few days now, so no further progress, sorry!

Malcolm Le Chevalier

This thread was discussed between 28/02/2019 and 05/03/2019

MG Midget and Sprite Technical index

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