Disk brake problems....HELP!!!

Post by **53buick** » Fri Jul 11, 2008 9:33 am

Hi All,
I have almost finished my wifes morris traveller and the one main thing she has requested is decent brakes.
So, I know some of the club will say that the brakes are fine as they are but we have been down that route and my wife was not happy so here is what I have done and my problem...

Brand new Lockheed master cylinder fitted with the small valve removed.
Rear banjo sealed to remove the rear brake feed.
Remote fluid filler fitted.
New brake pipes from master to a servo fitted on the engine bay floor.
From the servo to a 5way union on the drivers engine bay floor.
New pipes to the rear from the union.
New brake switch fitted.
New pipes to the fronts which in turn feed into new goodrich brake hoses.
These feed into brand new marina calipers/disk with new pads.
The servo vaccuum is taken from a pipe fitted to the stock intake (modified).
New rear drums fitted and fully adjusted.

So, alot of money spent here and.....The brakes lock up as soon as you start the engine and touch the pedal.
The only way to get the brakes off is to release the pressure in the fluid lines.

The pedal is returning fine and no pressure is upon the master cylinder piston.

I have been buying new bits for this brake conversion for 6 week replacing a new bit each time, even tried a different servo with no improvement.
I am seriously considering trying it without the servo today.

My wife has been very ill recently and I think getting her morris on the road after 7 years of waiting would make quite a difference....

Any help much appreciated.
Spence

Post by **jonathon** » Fri Jul 11, 2008 9:46 am

Email sent

Post by **d_harris** » Fri Jul 11, 2008 12:18 pm

Interesting colour! I like the rear windows - are they one piece?

The only thing that springs to mind for me is that the servo is plumbed wrong. But Go with what Jonathon has said. Hes forgotten more about this stuff than I will ever learn!

Post by **53buick** » Fri Jul 11, 2008 12:32 pm

Hi Dan,
The colour is "Milka Bar" purple as that is what my wife spotted and said " I want my car that colour".
The bad bit is, I wanted the black bit done in metalflake to give it a custom look without doing any heavy modifications and then.....I got carried away (or should have been) and did the whole car in metalflake...
So it should look interesting in sunlight although it hasnt seen much of that yet!
The back windows are not fitted in that picture although it does look like they are, I have tinted all the rear and the glass has now been fitted.
IF I get the brakes done this weekend then I will drive her out the garage and take more pictures, she does look nice.

I have a friend coming around this evening to help me fit the new rear doors as they were just positioned for the photo...

Anyway, the servo is plumbed in correctly but I have not fitted a non return valve in the vaccuum line, never have in the past but maybe that ios my problem?
What purpose is this valve?

Post by **Rob_Jennings** » Fri Jul 11, 2008 1:49 pm

the non return valve maintains the partial vacuum at low engine speed without it the pressure would keep varying giving brakes that vary. It really should be in place but its not vital to make them work and would not create the fault you describe.

The fault sounds like residual pressure on the non servo side? or a fault in the servo. but your description of all new parts sounds ok, are you sure you reassembled the master correctly after removing the cup valve at the end?

Post by **53buick** » Fri Jul 11, 2008 2:31 pm

yep, assembled it pefectly as I have done a couple now but never seen this problem ever.
I will be bypassing the servo later today or tomorrow and trying it then as the servo, although new, was bought second hand and could be faulty but this is the second second hand servo i have tried.
But, sods law may be in full swing here...

Any other suggestions welcome before I pull ot all the hair I have left ( which isnt much)

Post by **Wal** » Fri Jul 11, 2008 2:47 pm

53buick,
I did have a similar problem on my Triumph Spitfire, which doesn't have a servo. Basically I found that the piston in the master cylinder was not returning properly and it was maintaining a residual pressure in the brakes which when you pressed the pedal got worse each time and after a couple of presses would lock up the brakes. Which you could only relieve by releasing one of the bleed nipples. I know you have said that the pedal returns fine and no pressure on the master cylinder piston, but I thought that too and it was only trial and error that showed me what the problem actually was. The movement was only really limited but it still managed to lock the wheels up.

Anyway I hope you find the problem.

Regards,
Wal

Post by **simmitc** » Fri Jul 11, 2008 4:20 pm

I've found only two things that cause this: (a) the "top hat" rubber in the master cylinder left in place and (b) brake pedal yoke incorrectly adjusted leaving slight pressure on master cylinder.

I know that you've discounted both these, but the pedal can return correctly whilst still leaving pressure in the master cylinder. Good luck.

Post by **bmcecosse** » Fri Jul 11, 2008 4:42 pm

You say they lock up - as soon as you start the engine and touch the pedal. So is it the engine starting or the pedal touching that does the damage ? Take the vacuum hose off and plug it - does it still lock up the brakes when you touch the pedal ? If so - it's not the servo (unlikely anyway since you have tried two) and it will be the master cylinder either faulty - or not adjusted correctly with some free play, or the top hat has not been removed. Did you remove it - or did someone else 'say' it was removed ?

Post by **PSL184** » Fri Jul 11, 2008 5:14 pm

Can I show my ignorance here and ask what the "top hat" is pls. I changed my M/C earlier this year and didnt remove "top hat or anything else for that matter?

Post by **bmcecosse** » Fri Jul 11, 2008 5:17 pm

Only requires removal if using front disc brakes. Must be there for drums.

Post by **PSL184** » Fri Jul 11, 2008 5:18 pm

Ahhh, all clear now - Thanks

Post by **53buick** » Fri Jul 11, 2008 6:03 pm

Hi,
It is a brand new master cylinder and I removed the top hat seal personally.
I have held the brake pedal and I have a small amount of travel before it touches the master cylinder.

I can start the engine and drive the car fine but as soon as i touch the brakes it locks on.

I will try without the vacuum connected later.
Cheers
Spence

Post by **MoggyTech** » Fri Jul 11, 2008 7:10 pm

In master cylinder there is a dished copper washer that lives behind the main seal. If put back in the wrong way round the system will get pressurised first touch of the brakes.

Post by **bmcecosse** » Fri Jul 11, 2008 7:15 pm

Oh dear - all this trouble with disks and servos . Tchhh There is a much easier way to stop the car!

Post by **MoggyTech** » Fri Jul 11, 2008 7:21 pm

bmcecosse wrote:Oh dear - all this trouble with disks and servos . Tchhh There is a much easier way to stop the car!

Don't you dare

Post by **bmcecosse** » Fri Jul 11, 2008 7:39 pm

Saying nothing more - don't worry.

Post by **Matt** » Fri Jul 11, 2008 8:13 pm

But BMC... the problem doesn't appear to be anything to do with the discs at all ;)

Post by **jaekl** » Fri Jul 11, 2008 8:31 pm

MoggyTech can you explain to me the importance of the orientation of the dished copper washer? All the books mention to note and maintain the orientation of the washer but in either direction it will maintain a residue force on the piston and spring. The difference between the outer tips of the washer verus a full diameter pressure point seems rather insignificant.

Post by **MoggyTech** » Fri Jul 11, 2008 9:45 pm

jaekl wrote:MoggyTech can you explain to me the importance of the orientation of the dished copper washer? All the books mention to note and maintain the orientation of the washer but in either direction it will maintain a residue force on the piston and spring. The difference between the outer tips of the washer verus a full diameter pressure point seems rather insignificant.

Fitted incorrectly it blocks the main seal flange breather holes, which allow fluid to flow back.