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MG Midget and Sprite Technical - master cylinder woes

Okay, I'm very frustrated. I've rebuilt my 3/4" m/c several times. Light honing. Feels fine to me. Last time I found the main seal on the brake side had a funny wear pattern and a hole.
Here's the possibilities as I see them:
I'm honing with too fine a stone and "polishing the bore" too much.
The bore is really too crappy to seal and I'm too inexperienced to realize it.
One bent push rod is causing the piston to push "crooked" and not seal well. (see picture) Would maybe explain the funny wear on the seal I took out (which had very little time on it, like 50 miles).
Do I:
get the 3/4" sleeved
test out a 7/8" (from a buddy) or is that just a no-no?
rehone, mess with push rods

The thing is running great after full tune up. Better than ever, I'm stoked but I can't stop and that's not good.



J Van Dyke

When mine went out, I bought a new one. Sorry, but I no longer want to experiment with brakes. Just not worth it.

Don
don g

You can't buy new 3/4" bore masters. I'd buy a 7/8" if I knew it'd work alright. I'll test my friend's spare, if it works than I'll call it good. Still want to know what's wrong this thing though.
You're right about brakes. Not the place to skimp.
J Van Dyke

welcome to midget ownership, I have SOOOOOOoooooo been where your at.

I ended up throwing in the towel and got a tilton set-up and have been in love with it ever scence....its a pedal assembly with 3 master clyinders....front brakes, rear brakes (with a balance bar) and clutch....about the price of 2 new midget master cly.


you might try applehydrolics, they will re-sleve, and rebuild your master and it will be as good if not better then new. vary reasonable to.

Hit the deck, In comming!!! Just the mention of apple gets peoples blood into a frenzy


Prop


http://www.tiltonracing.com/content.php?page=listb

http://applehydraulics.com/brakes.htm
Prop

I just keep telling myself "this too shall pass". I'll have good brakes soon and enjoying the car again. I got it tuned halfway decent for once and it made a big difference. Figures, about the time I get it go faster I can't stop it AT ALL.
J Van Dyke

>>>>>>>>I'll have good brakes soon and enjoying the car again<<<<<<<<<<


UUUuummmm, Good Brakes???? I dont know how to tell you this, But, you may want to lower your standards a bit to just "Brakes"


As in the movie "Blazing Saddles" BRAKES!!!, We dont need no stinking brakes.


Prop...."Good Brakes" would make a great punchline to a midget joke....Prop
Prop

Yeah, I hear you. Even when working properly, even though I have the first Midget with up front disc brakes, they are marginal. I thought something was still wrong until my on-line buddies pretty much told me that's as good as it gets.
I do wonder though, since I'm planning on trying a 7/8" bore master, what effects that might have on my systems. A guy on another forum said,
Going from 3/4 to a 7/8 master gives a 1/3 increase in the amount of fluid pushed for a given pedal travel. So it will take 1/3 more pedal force for the same stopping power. Of course the pedal will only have to move 1/3 less distance.

What will do the clutch side? I currently have a nut behind the slave pushrod as it wasn't throwing out enough with it. Maybe I can just loose the nut and be good to go?
J Van Dyke

Prop,
I think you will find that the movie in question was "The Treasure of the Sierra Madre".

Perhaps you have butchered your brakes a bit much? I have no complaints about my Midget's brakes at all. Bearing in mind that they are not power assisted, I find that I can stop quite well at will. It will lock up all four any time I ask it; what more can I ask?
David "now to go faster..." Lieb
David Lieb

Here in Australia we tend to get master cylinders and wheel cylinders re-sleeved with stainless steel. It's relatively inexpensive and solves the rusting and pitting issues, new seals and away you go. I'm sure this is not unique to our side of the pond?
David
David JM

In europe it is not realy mutch done.
Does anny body know of a good dutch sleever?

My 3/4 is a bit worn to

i have a 7/8 lying around
(bought the wrong one) but i wil not fit it because heavyer brakes ar not realy wanted (girl drives the midget to)

the clutch is also a problem since it displaces more fluid than std it can push the slave to pieces!

Onno Könemann

I have a spare 3/4" sleeved cylinder that may help, and John Platt from the Midget and Sprite Club has recently advertised two of them , so there is no shortage out there....

Mark.
M T Boldry

Onno, ive found one in Ruurlo in Limburg.
Not had contact with him yet.
Arie de Best

Make that Baarlo...

You should have mail by now!
Arie de Best

Tore it down again. Brake side main cup seal has a hole exactly like the last one. This developed during the bleeding process! So, not good. I must conclude the bore has a bad spot in it beyond the reach of my finger.
J Van Dyke

There's pitting down in there. Needs a sleeve job although I think I'll try a 7/8" first.
J Van Dyke

JVD dont forget the transfer port down there, if it develops a pitted hole, some of it can protrude into the main bore and act like a razor blade on the seal

(to be honest, having to have a new sleeve drilled down and possibly leaving a cutting edge is one reason I never went for a re-sleeving. And yes I know the engineers SHOULD be up to cleaning off the fraise round the hole, but...)

I dont think the bent pushrod would have that much influence down the bore, why not rehone the bore, perhaps using parrafin (kerosene) as lubricant this time.

What lubricant did you use before and did you hone down past the transfer port?

I have very heavy clutch pedal which may be down to using a twin bore master that was available at the time and the wrong bore diameter

I'll be converting to a 1275 type pedal box after Le Mans

(everything is on hold 'til I come back, head off and skimmed. Redesigned rear twin trailing arm setup, the lot)
Bill sdgpm

The wall of the bore is actually breaking down it appears (really hard to see down in there). I'm also a bit worried about the 7/8" MC making the clutch too heavy. It was pretty stiff already with the 3/4. I have a guy pretty close to me who thinks he has a 7/8 I can have for $20 and he might have a rebuild kit too. So I can try it out for minimal investment. If nothing else I can use it until I get my 3/4 fixed up then I dump the 7/8 on ebay or something.



J Van Dyke

I used brake fluid as lubricant and honed the entire length of the bore. But, all was in vain as the bore is trashed. This explains why I kept feeling some grit in there even after extensive cleaning. I think the wall is crumbling apart.
J Van Dyke

What year do you need J van?

I got 2-3 in my spares boxs, I know one is a good rebuildable...well I dont think its crumbling anyway

its a 1971 mg midget...let me know if you want it, needs rebuilding probably a hone also...I could never get them to work longer then 6 months, but I think that was due to wrong brake fluid

Prop
Prop

Honing is great for engines but not for rubber cupped brake bores.

I decided to use the newly available 7/8 master cilinders and I am very pleased with it. No extreme hard pedal and we all have pedals (especially clutch) that only engage just before the end of travel, so any bigger displacement is better.

Bas
Bas Timmermans

Maybe this helps:

http://www.brakecylinder.com/spridgetbrakes.htm

Cheers,

Nick, '63Midget

D.G.J. Herwegh

Mine is a '63, so has 3/4" bore for both clutch and brake. Bas, great to hear you like the 7/8"bore as an alternative, I'll be bolting one on tomorrow as a friend has one handy, so thanks Prop but I think I'm covered. Now a pair of early wiper blades I could use...
J Van Dyke

I got the 7/8" but no pushrods for it. Anyone have a set they're willing to part with? My old 3/4" MC pushrods are 3.75" and I think I need the 4 3/16" or so.
Does that make sense? My pedal hits the stop before any pressure is made.
J Van Dyke

Yep forgot to mention you need different pushrods. I ordered new ones. IIRC 20 euro's a set.

Bas
Bas Timmermans

I thought I could max out the shorter 3 3/4" length rods and get in the ballpark of the longer 4 3/16" ones but, no. The pistons on a 7/8" have a deeper socket for pushrod to fit into. Bummer.
http://www.brakecylinder.com/spridgetbrakes.htm
J Van Dyke

3/4 master cylinders are available new again at Abingdon MG Parts, according to an ad in MG Enthusiast, confirmed by their website.

http://www.jagspares.co.uk/Abingdon/partdetail.asp?partno=GMC112

http://www.jagspares.co.uk/Abingdon/company.asp

Tore
Tore

I stopped by University Motors and they let me grub around in their stash. I came up with two that are longer. Interestingly John Twist was highly skeptical that there were indeed different length pushrods. Not sure he believed me even when I found what I wanted, had my old one in hand and there ya go.
Had to pay $11 for two grimy old pushrods but the patina on them will match nicely. So, hope to fit tonight and see where I'm at.
BTW, in anticipation of more "response" from the clutch slave when using the 7/8" bore MC, I went ahead and removed the nut that I put behind the slave pushrod last year.
Wish me luck.
J Van Dyke

7/8" installed, bled. First thing I did was try the clutch, I needed to put the nut back behind the slave pushrod.
Brakes feel great. Clutch is good.
certainly a little more effort needed but I like the feel of it better than the 3/4" If I get caught in a traffic jam for an hour I might be cursing the clutch.
I'd say a 7/8" is a suitable swap if you're willing to change your pedal feel.
I'm happy with it.
PS
Car is running amazing, and stopping too!
J Van Dyke

Having read that John Twist was a skeptic over the pushrod lengths perhaps we'd better send him a free copy of the Mascot in which the subject was explained

Dr John wasnt it? I'd better look it up

I have the later clutch and brake "block"

I like the brakes but I hate the clutch and will be changing it all around after Le Mans in June

A certain cylinder head / bore relationship will also be addressed, time to up the ante.

Bill sdgpm

You know sports cars always have a heavy clutch:-)
Bas Timmermans

This thread was discussed between 23/04/2009 and 29/04/2009

MG Midget and Sprite Technical index

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