help!!! brake pedal dropping

[tezzer]

hi all, hope someone can help, bled brakes and now the pedal drops if you hold pressure on it, i can't see any leaks and i have pulled master cylinder forward and it looks dry, the load sensing valve seems damp and could be the culprit, where the best place to buy these parts? thanks tezzer

 

[Thermostat]

You may have damaged the seals in the master cyl when bleeding.

Have you checked the rear wheel cyl's

Also if the load valve is damp why ? (this might be something different)
Never known one of these to fail when bleeding though.

Hope some of this helps

 

[iandouglas]

brake pedal dropping

hi tezzer.
is the pedal dropping while engine is running.
if so this is a problem with these trucks, its caused by loss of vacume
shark1e went into this problem .
the vacume pump is on the back of alternator have look see if pipe is loose or split.
do a search as it was well documented.
rgds.iandouglas

 

[elty001]

brake bleeding

have you tried bleeding the brakes again.i fitted 2 new rear cylinders and had to bleed them a couple of times before it felt o.k.

 

[zippy656]

i seam to remember some one saying the bolts that hold the pedal to the bulk head can come lose, could it be that simple?

 

[tezzer]

thanks for all your replies i will look into it tomorrow, i;ve bled the brakes twice and pedal would be ok but when you hold pressure it go's nearly to the floor, brakes were fine before i replaced corroded pipes, anyway i got a few ideas now to try thanks to you all, tezzer

 

[tezzer]

hi iandouglas, yes pedal drops when engine is running if i turn engine off and pump pedal it holds pressure, as soon as i start engine pedal drops, i checked alternator and there is no pipe etc on back, followed servo pipe to o/s of engine to vacuum pump? i think, tezz

 

[Thermostat]

Yes now that you have found that it drops only when engine is running then its deffo servo related.

 

[tezzer]

hi brian, thanks for your reply, i read in the seaches that you can clean something on the back of alternator, but my alternator does'nt have a pump on it, so would i be looking for a leak of some sort? thanks terry

 

[Terranosaurus]

What engine have you got? You don't say on your signature.

Only diesels will have a vacume pump, petrols just use manifold vacume.

 

[tezzer]

hi hummingbird, sorry it's a 2.7 tdi, i thought vacuum pump was on the alternator.

 

[Toolbox]

The vacuum pump on the tdi is below the injection pump bolted to the timing case where it takes its drive from the timing gears, if you look from under the front you will see it.

 

[tezzer]

hello toolbox, (jeremy) thanks for your reply, i thought the pump was on the alternator, i read some where you could remove blades and clean them then turn them round. i got that wrong did'nt i.

 

[Toolbox]

It is on the back of the alternator on the earlier td engine, there is no reason why you still cant remove the pump all be it a little more difficult than the earlier version and change the vanes around, also worth checking, is the check valve in the fitting screwed in to the pump where the large pipe connects, to make sure its seating ok.

 

[tezzer]

thanks for that jeremy i'll have a look tomorrow and let you know how i get on.







thanks
tezzer

 

[tezzer]

hi all, checked vacuum pump today and it did'nt seem to be working to well, so removed pump, bit awkward but only took 25 mins to get off, stripped and cleaned pump and turned vanes round put back together and filled with oil and even turning by hand i noticed the difference, refitted to truck and that is working 10 times better, but pedal still dropped to floor, so we changed the master cylinder, brakes are getting better, we are going to give brakes a good bleed tomorrow and hope that sorts it out, if not im going out and buying a disco...tezzer

 

[andrewk]

Re: brake pedal dropping

is the pedal dropping while engine is running.
if so this is a problem with these trucks, its caused by loss of vacume

This is a problem I thought I had on my Patrol. With the engine off, the brake pedal behaves exactly as you would expect - i.e. its very hard to press. With the engine running and the vehicle stationary in neutral, if you apply continuous heavy pressure to the brake pedal it will go nearly to the floor. The brakes work as expected during normal driving around.

I was concerned about the behaviour and queried it with Nissan Oldham when the car was in for service. They had a technical note about it, as it's been raised several times before. It is normal behaviour. It isn't caused by lack of vacuum but by the high level of vacuum assistance which causes the brake hoses to expand slightly. The pedal depression can be reduced by fitting braided hoses. It doesn't happen during normal driving as the car brakes heavily well before any excess brake pedal depression occurs.


Cheers
Andrew

 

[tezzer]

hi all, been in garage today bled brakes again and the pedal seemed better
then while having a good look underneath for any leaks i saw a bleed nipple on top of load sensing valve, it was abit awkward to get a spanner on so out with the air chisle and cut a inspection hole above valve, bled valve and brakes again, and what do you know a perfect pedal at last, made up plate and screwed over hole job done. anyway thanks to all you guys for your tips and advice