Brake pressure problems after full system re-build

iwish

Active Member
HI All,

I am currently doing a full restoration on a 3500s, some of you will have seen my progress in the members projects area, which is overdue an update.

I have stripped and fully overhauled the master cylinder, servo, brake calipers and fitted new pipes. I wanted to test the system for leaks before i take the body off its rotisserie and drop it back on to the wheels.

I have filled the system with 5.1 fluid and bled the system (the traditional way)

The problem i have is there is no pressure on the brake pedal which moves freely in both directions.

The master cylinder and servo looked in fairly good condition so i purely cleaned everything and replaced the seals and lightly smeared the bores and seals with red grease to stop any rusting whilst the system was empty.

Currently there is no engine so the servo is not connected to anything and i have no signs of any leaks.

Before i rip everything apart any ideas on what might be wrong will be a great help?

Thanks
Dave
 
Was the brake pedal moving freely in both directions when you bled the brakes? Just wondering how you completed the bleeding if it was.

If not, when did it start doing this?

It has been known for the master cylinder piston to stick in the end of the piston, as you move it further in when bleeding, than you do when braking. Try whacking the end of the master cyclinder with the handle of a screwdriver, and see if it frees itself - you'll hear it if it does.

Richard
 
With no servo working the pedal should be solid when pressed. When you say you bled the brakes the traditional way, I presume you pumped fluid through using the brake pedal. You could clamp off the flexible hoses to see if there is any difference and eliminate the wheel cylinders. Is the free play on the master cylinder push rod correctly set, but it does sound like a possible problem with the master cylinder as you say it freely moves. Even with a little air, one should feel some pressure on the pedal as the fluid is moved. Unfortunately the red grease is hydroscopic so one cannot guarantee it will totally resist rusting.
 
Was the brake pedal moving freely in both directions when you bled the brakes? Just wondering how you completed the bleeding if it was.

If not, when did it start doing this?

It has been known for the master cylinder piston to stick in the end of the piston, as you move it further in when bleeding, than you do when braking. Try whacking the end of the master cylinder with the handle of a screwdriver, and see if it frees itself - you'll hear it if it does.

Thanks Richard, in reply to your comments:
With a little help from my son to operate the pedal we bled the brakes normally with the pedal operation pushing the fluid around the system and got plenty of bubbles as you would expect. We did the rear calipers first, then the near side and finished with the off side. I did not check the brake pedal as I then repeated the bleeding operation to make sure we got all the air out. It was only when this had been done we noticed there was no pressure when pushing the brake pedal down.

'Im certainly going to try hitting the master cylinder as suggested and will let you know if it works?

Dave
 
With no servo working the pedal should be solid when pressed. When you say you bled the brakes the traditional way, I presume you pumped fluid through using the brake pedal. You could clamp off the flexible hoses to see if there is any difference and eliminate the wheel cylinders. Is the free play on the master cylinder push rod correctly set, but it does sound like a possible problem with the master cylinder as you say it freely moves. Even with a little air, one should feel some pressure on the pedal as the fluid is moved. Unfortunately the red grease is hydroscopic so one cannot guarantee it will totally resist rusting.

Currently, with no pressure from the pedal i do not know if any of the calipers are working. I am beginning to wonder if the new seal kit was the right size?

Your comment regarding the red rubber grease really does worry me, as my garage is a bolt together concrete construction with a corrugated asbestos roof. I suffer from extreme temperatures, condensation and damp, which is compounded by the fact the garage is only 20 paces from the waters edge in Portsmouth harbour so as you can imagine it is also a very salty environment. D
 
Hi Dave.
A bit of a silly question but were the seals on brake master cylinder fitted correct way round? If not could be your problem.
Was the cylinder bore in perfect condition? not many are now, normally better to fit new ( not new old stock )
or better still get cylinder bore stainless steel lined by Mark Grey.
Took apart a old cylinder for correct seal location, only part missing is the wavey washer between small seal at end and white plastic Bush.
Clive 20161018_191120.jpg 20161018_191011.jpg
 
Is the pedal ratio definitely correct? As in does the pushrod allow the full stroke of the master cylinder piston before bottoming out on the floor? If the system is full of fluid with no leaks there should be some kind of pressure. When your son was working the pedal was there not any pressure building throughout the bleeding process? If there was none the flow of fluid from each nipple would have been more like a trickle rather than a fountain if you like? Clearly you could never achieve a good pedal under those circumstances and the master seems to be the obvious culprit one way or another, either internally or incorrect pushrod length. Did you accidentally allow it to run dry whilst bleeding at any point?
Jim
 
HI Guys,
Thanks for your comments and suggestions.
My first course of action was as suggested by Richard to give it a good bash (a lot of bashes in fact) it always used to work on the TV back in the days, but sadly had joy with this.
My next thoughts were the same as you all, there had to be a problem with the master cylinder. Could i have put the new seals in the wrong way round as Clive suggested, iv'e been beating my self up with the same question all week?
So i set about removing the master cylinder, i started with releasing the push rod from the brake pedal, as the pedal rose upwards, naturally i gave the pedal another push! I can only assume that with an extra bit of travel it must of loosened the cylinder and hey presto it works!
I don't know what caused it to stick, lack of grease on the rubbers or too much maybe?
Thinking back as Jim commented, the fluid flow from the bleed nipples had no real pressure, so i proceeded to re-bleed the system and the fluid now squirts out.
Everything seems to work as it should, i had a few leaks on the new pipe joints, which is down to the fact i'm wary of over tightening things.
With Thanks
Dave
 
I wonder if the pushrods was incorrectly adjusted and wasn't allowing the piston to return all the way back? It would certainly cause those symptoms.
 
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