Brakes / bleeding / faults and master cylinder replacement

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rayofleamington
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Brakes / bleeding / faults and master cylinder replacement

Postby rayofleamington » Tue Oct 18, 2005 12:53 pm

Ray, would you like to cut'n'paste your master cylinder post as a new thread in 'tips'?
oh ok then………………

To get a very good pedal you will need the shoes adjusted to remove all clearance. If that is already done and the pedal travel is still wrong then there are many other potential reasons:
1) air in the system due to bleeding
2) wrongly fitted wheel cylinder cup seal (I've seen one upside down! it worked but gave spongy brakes). This is only possible with the cup seal and an upside down piston lip seal shouldn't give a springy pedal.
3) air in the system due to a leaky cylinder
4) Flexi-hoses are way past their sell-by date.
5) air in the system due to a faulty master cylinder
6) Faulty m/c

Regarding #1 it is not easy to bleed a Minor. The rear bleed nipples do not bleed the cylinders, they only bleed the pipe and connector, therefore you need to 'prime' the rear cylinders by removing the brakes (or at least slacken the adjuster) allowing the piston to move when under pressure. This movement allows fluid into the cylinder and when the piston is pushed back, the air at the top of the cylinder will be pushed back into the pipe leaving fluid behind. This can need to be repeated a fair few times when fitting a new cylinder.
The rear connector banjo should be aimed upwards to allow the air to collect under the bleed nipple, which helps with bleeding out the last remaining air.

If you press the pedal slowly and bubbles come up then you have a leaking secondary seal - fix this ASAP. Corrosion in the bore making the secondary seal leak is the most common failure of the Moggy master cylinder (it is more likely to happen in cold weather as the seals shrink just a fraction but it can happen at any time). If left unchecked you are likely to get a nasty surprise and no brakes one day.

The open end of the master cylinder bore suffers from damp and condensation, and also can get water trapped in it as the washer behind the circlip does no allow water to get out (therefore don't be hasty when it comes to driving in a flood - if the chassis leg gets a lot of water in it, so will the m/c!). Water in the m/c will make the bore rust and when the secondary starts leaking you can't ignore it.

You have to remove the m/c to inspect the seals and bore. I'd suggest not to risk wasting money on a seal kit unless you have already inspected the m/c and the bore is ok and completely rust free. If the bore is rusty around the secondary seal (the one nearest the pedal), a seal kit won't fix it.
If the bore is fine, then fit a new seal kit anyway as you don't want to take it out again in a few years!.
I'd double check 1 to 5 before removing the m/c (unless you can see bubbles rising, then it is best to do the m/c first)

Removing the m/c is not too bad when you're used to it. Most of it is overcome by determination!

Here's the best way I've found:

A) Under the rear floor pan, remove the brake pipe from the flexi that goes to the rear axle.
B) Place a container under the end of this pipe and catch the fluid from the m/c. Often it will empty itself (so have the container nearby)but that does imply a fault! If it doesn't pour out by itself then pump the fluid out - this is better than splilling it everywhere.
C) Remove the brake pipe (to the front brakes) at the connector by the side of the chassis leg adjacent to the m/c.
D) Using a strong bar (I use a 2 foot long wrecking bar) and a thick piece of wood on the floorpan (about 20" long - or more if it fits) check that you have the strength to lever the torsion bar away from the floor by about an inch. It's not easy so if you can't do that see if you can lever it with a jack on the end of the bar. The bar needs to be positioned just to the side of a bolt (or in the middle of both but getting it moved enough for both bolts in one go requires more effort)
E) When you are happy that you can move the torsion bar enough, take the nuts off the m/c bolts
F) Using a screwdriver / thin diameter bar and small hammer, tap the bolt head up to the torsion bar. Then bend the torsion bar just enough to clear the head and push the bolt throught the chassis leg from the far side [DONT GRAB THE BOLT HEAD WITH YOUR FINGERS UNTIL IT IS WELL CLEAR OF THE TORSION BAR just in case something slips - fingers are too precious to take any risk]
G) Push the master cylinder backwards into the chassis leg until it is clear of the brake pedal pushrod.
H) Lift the front of the m/c up above the pushrod and slide the m/c forwards and up, out of the chassis leg
I) Disconnect the rear brake pipe from the back of the m/c T-piece now that it is nice and easy to get to (If you try and disconnect this one whilst the m/c is in situ it can take ages - people cut the floor away for access, but it's not needed doing it this way)

To get into the guts of the m/c remove the circlip with any old circlip pliers and then also the big washer (it is spring loaded so you may need to press the piston into the m/c using a '3rd hand' to make it easier)
The piston will normally remove itself with the spring force.

If you can get that far, I'm happy to give further tips on inspecting the seals. The cup seal and outlet seal should be changed if the m/c seems ok and these will come in the seal kit anyway

Re assembly is 90% a reverse of the previous instructions, however you need to take great care when reassembling the m/c seals. It is often best to remove the pushrod from the pedal (not highly recommended) to get the boot to fit the pushrod and m/c correctly however due to the pedal return spring this is a prize pain and not good for a novice!

The seal kit I got (from #### ##### - major supplier who's name has been removed) 2 weeks ago was pretty awful. The output seal was the wrong size and I wasted 2 hours getting it to the right size so it would assemble The boot didn't have a drain hole! (I cut my own hole) and the boot was a bad fit meaning the whole thing was a paint to reassemble, and not even worth trying to get it to fit the pushrod properly.

Oh yes...if the brake pipes are being re-used but refuse to screw back into the connectors, then that means the end of the flare nut has been flared (the nut shouldn't get deformed but it can happen usually from being overtightened). The bodge way to cure it is to file down the end of the flare nut (highly not recommended) and the correct way to fix it is to replace the pipe so that you have new flare nuts.

If the pipes are old anyway it is worth just to replace them - then you don't have to worry if the pipe is damaged when you unscrew the flare nut (often the pipe rusts into the nut so it turns round with the nut and wrecks itself).
New pipes are cheap, so it saves a lot of aggro.

Excellent description Ray. When re-assembling the m/c into the chassis it's best to put the bolts back in the other way round - so much easier
Easier - yes but not better! I've done this myself when I was a teenager (didn't know you could bend the torsion bar out of the way so I cut the heads off the old bolts and reversed the new ones)
After a few years I noticed the new bolts had worn a groove in the torsion bar! :o When looking at other cars with the bolts the wrong way round, it appears this dangerous fault is common and many show damaged torsion bars!
There is a reason that the slim head goes next to the torsion bar, not the more stickey - out end with the nut.
Last edited by rayofleamington on Wed Oct 15, 2008 8:56 pm, edited 2 times in total.
Ray. MMOC#47368. Forum moderator.

Jan 06: The Minor SII Africa adventure: http://www.minor-detour.com
Oct 06: back from Dresden with my Trabant 601 Kombi
Jan 07: back from a month thru North Africa (via Timbuktu) in a S3 Landy
June 07 - back from Zwickau Trabi Treffen
Aug 07 & Aug 08 - back from the Lands End to Orkney in 71 pickup
Sept 2010 - finally gave up breaking down in a SII Landy...
where to break down next?
2013... managed to seize my 1275 just by driving it round the block :(

jtd.75
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bleeding

Postby jtd.75 » Thu Nov 17, 2005 7:24 pm

Hi Ray you mentioned above about bleeding the brake systom as you most proberly know from my previous questions I am restoring or should I say rebuilding a 1960 948cc and its like doing a jigsaw whithout the picture, I fitted all new break pipes and wheel cylinders anlong with the b/shoes and renewed the m/c rubbers as the bore seemed ok I filled up the cylinder with fluid and tried to bleed the brakes but nothing comes out all that happens is the fluid comes over the top of the m/c, what am I doing wrong
Jimmy

rayofleamington
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Postby rayofleamington » Thu Nov 17, 2005 10:51 pm

It sounds like the m/c is airlocked.
Try opening up at the T-piece on the back of the m/c and pump until you get fluid through it.

If that's not working, then I hope the m/c and new seals went back together ok :-?

Good luck.

jtd.75
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bleed

Postby jtd.75 » Thu Nov 17, 2005 11:16 pm

Thanks Ray will give it ago tomorrow, pritty sure the seals went back the same way, what I usually do is take a vidio of things befor I strip anything down as I have a terrible memory.
Jimmy

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brakes

Postby jtd.75 » Fri Nov 18, 2005 11:03 pm

Hi Ray, did like you said tried the M/C for air-lock and nothing next step was to remove the m/c, took it out and operated the plunger that operates the piston and still nothing so I stripped it down and all the seals are the correct way and thats as far as I have got at the mo, any more suggestions. When I pressed the plunger fluid came out of the cap vent holes. And while I'm in the info theme, how can I fit a temperature sender to the 948cc engine as it has now plug below the thermostat housing, without having to drill and tap anything.
Jimmy

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Postby rayofleamington » Fri Jun 09, 2006 8:19 pm

bumped!

wibble_puppy
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Re: Brakes / bleeding / faults and master cylinder replaceme

Postby wibble_puppy » Thu Mar 29, 2007 3:03 pm

Thanks for all that excellent info Ray, truly you are a king among men 8)
rayofleamington wrote: If you can get that far, I'm happy to give further tips on inspecting the seals
Yes please!! :D

And do you know of any way to modify things so that when you drive through water the M/C doesn't start rusting? :-?

juliet xx

rayofleamington
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Postby rayofleamington » Wed May 07, 2008 7:02 pm

bumped again
Ray. MMOC#47368. Forum moderator.

Jan 06: The Minor SII Africa adventure: http://www.minor-detour.com
Oct 06: back from Dresden with my Trabant 601 Kombi
Jan 07: back from a month thru North Africa (via Timbuktu) in a S3 Landy
June 07 - back from Zwickau Trabi Treffen
Aug 07 & Aug 08 - back from the Lands End to Orkney in 71 pickup
Sept 2010 - finally gave up breaking down in a SII Landy...
where to break down next?
2013... managed to seize my 1275 just by driving it round the block :(

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Re: Brakes / bleeding / faults and master cylinder replaceme

Postby Packedup » Wed May 07, 2008 11:33 pm

rayofleamington wrote:
Excellent description Ray. When re-assembling the m/c into the chassis it's best to put the bolts back in the other way round - so much easier
Easier - yes but not better! I've done this myself when I was a teenager (didn't know you could bend the torsion bar out of the way so I cut the heads off the old bolts and reversed the new ones)
After a few years I noticed the new bolts had worn a groove in the torsion bar! :o When looking at other cars with the bolts the wrong way round, it appears this dangerous fault is common and many show damaged torsion bars!
There is a reason that the slim head goes next to the torsion bar, not the more stickey - out end with the nut.
And yet the infamous BoL I've got says to put the bolts in the other way round when sticking it all back together!

I figure BMC wouldn't have used the bolts they did, the way they did, if they didn't have to. So if (when..?) the master comes out, the bolts will go back the correct way round. It's not like I'm not getting good at this dropping the torsion bar malarky.
[url=http://www.rottingheaps.me.uk/index.php]Ooh, it's all gone purple. But otherwise all that changes is the date...[/url]
[url=http://www.rottingheaps.me.uk/index.php?ind=articoli&op=entry_view&iden=3]The lazy way to derustify[/url]

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Postby MGFmad » Tue Oct 21, 2008 10:41 pm

Thanks for the excellent advice above, I got the master cylinder out in about 10 minutes (I had previously removed the mounting bolts when the torsion bar was out of the way) so much easier than than dismantling half the car like the workshop manual says.
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Re: Brakes / bleeding / faults and master cylinder replacement

Postby oddbod » Mon Dec 03, 2012 8:22 pm

Cheers for these clear instructions Ray, I'll take the advice offered on another thread and follow your method instead of the bodge I was considering! :oops:


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