Brake Pedal becoming hard to press and brakes failing!

[Lummox]

Right chaps I think I've sussed it! Current long standing problem Transit 350 T90 brakes ok then stiff then rock hard pedal and no brakes.
Fitted new Vacuum pump, new master cylinder, new servo.
Tried to get a new brake pressure proportional jobbie but mine doesn't have one!
Then after 2 more garages had a go at it, basically just bleeding it its still really bad.
If I'm belting along and brake its fine, if I'm ticking over the pedals rock hard.
I had a young lad put it on the rolling road to check them again and he sussed it straight away!
He said your vacuum pump has a leak, did you fit the gasket/o ring when you installed the new one?
I said I don't know, he said at tick over the pump system is not producing enough pressure to activate the servo, when you rev it it worked so there's a leak somewhere!
I remember when I bought the new vacuum pump it had a metal type gasket with an in built black painted looking gasket but I also saw that there should be an O ring? I didn't have this it didn't come with the kit.
So I now have to dismantle the pump and servo and master cylinder and look for any leaks!
Watch this space!

[Lummox]

Apparently its the vacuum pump not producing enough pressure at low revs to operate the servo.

Theres a leak in the system which means that at low revs it cant top up the servo and produce braking. What happens is a rock hard pedal and no braking until you rev it and they work again!

Ive fitted new vacuum pump but not sure wether it needs an O ring? It came with a metal gasket with what looked like like 2 painted built in gaslet O rings integral to the metal gasket.
https://www.ebay.co.uk/p/1509768577

[metalworker0]

this kit here ..shows it with two o-rings a green one and a black one

https://www.ebay.co.uk/itm/253587562859

all the best.mark

[knobby1]

No that wasnt me under another name on that over thread but very similar problems!

I posted this...

Blimey this is exactly my problem, Brake normal on first push, stiff on second rock hard on third, no brakes!
I have renewed master cylinder, vacuum pump, brake servo. Still the same. Just failed MOT on the brakes, 46%.
He said its uneven pressure being delivered to the slave cylinders. Pass front and back locking up when driver side not?
Mine is a 2006 Mk6 T350 90 RWD LWB and it dosent have a load sensing proportional valve just a junction box splitter type arrangement. Does that mean its ABS?
It does also have corroded brake pipes covered in grease?
Dunno what else to replace!

Apparently there is a brake pump thats not the brake vacuum pump?

What actually decides what pressure goes where as mine is locking up yjr fromt and back on the passenger side only?

If it doesn't have a load sensing valve on the rear axle, it will have ABS. If the vacuum pump and servo is new and you still have no boost assist, the vacuum line from the vacuum pump to the servo might be damaged, blocked, leaking etc...

We've had some brake master cyls which were less than cooperative if not genuine.

Has an ABS brake bleed been carried out using Forscan or IDS..??

Lord Knobrot

[Lummox]

Posted this ...

I've had exactly the same problem hard brake pedal no real brakes. Replaced Vacuum pump, master cylinder, Servo unit been bleed upteen times brake pedal still rock hard especially at low revs.
Herein lies the problem apparently. Somehow during the renewing of all the brake parts leak has managed to creep in. When the van is ticking over theres not enough pressure to activate the servo so hard pedal and and no assisted braking. Rev the engine and brakes work again!
I noticed that my new pump came with a metal gasket that had 2 what looked like painted on black O rings? I wondered if it needed anymore seals but apparently not but then I saw an exploded diagram of the pump (how can I post the pic on here?) which shows an O ring 2A (see diagram) which fits between the gasket and the block.
So now Ive found a Transit expert whos gonna attempt to source the leak and get my full braking back!
Ill keep you updated.

[Staffdog420]

Hi, did you ever get to the source of the problem as i have exactly the same issue after my vaccuum pump went, first press is fine but second is rock hard and no brakes but wait ten seconds and they are back for 1 press then hard again. Any suggestions please?
Cheers.

[Staffdog420]

Hello mate did that o ring solve the issue with the brake pedal? Cheers

[knobby1]

Hello mate did that o ring solve the issue with the brake pedal? Cheers

He hasn't been back since Feb so we'll probably never know.

Lord Knobrot