Long brake pedal.

[vincereynard]

Initially brake pedal goes down a long way, a quick pump and it is firm.

Repeated application with engine off, (exhaust the servo), gives a firm pedal with no suspicion of air in system.

Clue 2 - after the descent of a long hill with a closed throttle the pedal was firm.

Conclusions?
I assume the servo has a non return valve in the vacuum connection?
Should there also be a non return in the actual pipe?

Any other suggestions chaps?

[nmauduit]

depending on the amount of slack to be picked up, brake pad retraction (from loose wheel bearings etc) can require a similar first pumping after some curves to restore pedal firmness.

[Hawksfield]

Vince

To check servo vacuum run the engine for one minute, switch off vacuum should be maintained for two minutes
Check by pressing brake pedal and listen for air intake.

See attached

https://drive.google.com/file/d/1MDtKVk ... sp=sharing

Remember that the +2 is not the easiest to bleed !

[Foxie]

Vince

<Snip>

Remember that the +2 is not the easiest to bleed !

Agreed.

I've a bleed nipple on the master cylinder, and I've fitted another on the nose of the servo, but have never been able to completely eliminate a bit of sponginess

Any special tips ?

[elanfan1]

Initially brake pedal goes down a long way, a quick pump and it is firm.

Repeated application with engine off, (exhaust the servo), gives a firm pedal with no suspicion of air in system.

Clue 2 - after the descent of a long hill with a closed throttle the pedal was firm.

Conclusions?
I assume the servo has a non return valve in the vacuum connection?
Should there also be a non return in the actual pipe?

Any other suggestions chaps?

Sorry, no. You could ask JonB.

[JonB]

You could ask me, but I think I'm none the wiser in this instance.

I did recently bleed my brakes but using the old fashioned approach - open bleed nipple, attach pipe (with the other end immersed in brake fluid in a catch bottle, to prevent it drawing air back into the system), fill reservoir then pump the brake pedal, releasing slowly. Variants of this approach would be to have an assistant tighten the bleed nipple on the pedal release stroke then loosen on the down stroke, or to use a bleed kit with a non return valve. I ran a fair amount of DOT4 through the system, starting at the rear brakes as they're furthest away from the master cylinder. As my car is a UK model, it doesn't have a twin braking system.

Anyway, I got it to the point where it is working and I do not need to "prime" it in use.

I don't think that helps Vince out much, though, other than to demonstrate it is possible to get an acceptable result. Re-reading his original post, I'm inclined to agree with the diagnosis of servo problems.

@Vince, have you had a chance to try Hawksfield's suggestion?

[vincereynard]

Thanks for the replies.

I have not had the chance to try Hawksfield's advise yet, but, having exhausted the vacuum previously, I did nip out this morning to try the pedal. It has not altered so I assume I can discount air in the system.

As to the pads being knocked off by loose wheel bearings. That was a good call and something I had considered. Also the possibility of the seals pulling the piston back excessively which can have the same effect.

The servo is a (virtually new) Lockheed but I imagine the basic workings are much the same. I believe that a servo can be checked by starting the engine with the brake pedal depressed. The pedal should drop? Correct?

I don't really know how a servo works so figuring out what would cause it to need the initial long pump
is a mystery.

I'll try that, plus Hawksfield's suggestions, when I have a chance.

I think (hope) the clue of the hard pedal at the bottom of the hill suggests it is a leak in the vaccum circuit somewhere.

Thanks
Vince

[JonB]

If the long pump problem is caused by a servo vacuum leak (at the bottom of a long hill) it would mean that you are losing vacuum during the time it took to drive from the top to the bottom of the hill - in other words, in a few minutes.

If you do not hear a hiss after trying John's test then you definitely have a servo problem. Non return valve or servo leak would be my guess - unlikely if the part is new, but the test will only take a few minutes. On my car I hear it hissing for several brake depression actions; than as the vacuum is exhausted the hiss goes away and the pedal action feels harder because the servo is no longer able to assist.

[vincereynard]

If the long pump problem is caused by a servo vacuum leak (at the bottom of a long hill) it would mean that you are losing vacuum during the time it took to drive from the top to the bottom of the hill - in other words, in a few minutes.

Other way round. After descending the hill with the throttle shut (max vacuum) the pedal was OK.

"Clue 2 - after the descent of a long hill with a closed throttle the pedal was firm. "

[JonB]

If the long pump problem is caused by a servo vacuum leak (at the bottom of a long hill) it would mean that you are losing vacuum during the time it took to drive from the top to the bottom of the hill - in other words, in a few minutes.

Other way round. After descending the hill with the throttle shut (max vacuum) the pedal was OK.

"Clue 2 - after the descent of a long hill with a closed throttle the pedal was firm. "

Sorry Vince, my bad. I thought the firm pedal might be caused by loss of vacuum (it does feel firmer when there is no vacuum, at least on mine).

[Bigbaldybloke]

Are we getting confused here between long pedal travel and a spongy pedal. Long pedal travel but eventually firm would mean that the pads are being knocked back or that the master cylinder is small diameter. The pedal becoming firm after an initial stroke tends to point to this.
A spongy pedal would indicate that there is air in the system and will always feel spongy as the air will always be there till you manage to bleed it out of the system, which can be difficult and time consuming, having to go round the four calipers maybe several times to get rid of the last few air bubbles. This does give a longer pedal travel as you have to compress the air in the system but the give away is that it feels as if there is a spring under the brake pedal.
The air side of the servo is a bit of a red herring as all the servo does is effectively multiply the force you are putting on the pedal by a preset factor depending on which servo you have fitted, as they come in various factors, up to about 3:1 I think. If there is a loss of vacuum you will have to press very hard on the pedal, but loss of vacuum does not in itself lead to long pedal travel or a spongy pedal. Failure of the servo internal seals can cause a spongy pedal and the need for a second pump on the pedal as the brake fluid passes the seals inside the servo and gradually fills it up inside with brake fluid. If you are loosing fluid with no external signs then it?s probably inside your servo. How do I know, I?ve had it happen! Happy bleeding brakes!

[vincereynard]

Vince

<Snip>

Remember that the +2 is not the easiest to bleed !

Agreed.

I've a bleed nipple on the master cylinder, and I've fitted another on the nose of the servo, but have never been able to completely eliminate a bit of sponginess

Any special tips ?

That's a good idea. What adapters did you use? Presumably male/ female with a drain take off?

I have had some success with a Gunson Ezeebleed with particularly awkward bleeders.
I think one could include an Elan as an awkward bleeder.
http://www.gunson.co.uk/product/G4062

Available for about ?15 from the usual outlets.

[vincereynard]

[quote="Bigbaldybloke"]Are we getting confused here between long pedal travel and a spongy pedal. Long pedal travel but eventually firm would mean that the pads are being knocked back or that the master cylinder is small diameter. The pedal becoming firm after an initial stroke tends to point to this.
A spongy pedal would indicate that there is air in the system and will always feel spongy as the air will always be there till you manage to bleed it out of the system, which can be difficult and time consuming, having to go round the four calipers maybe several times to get rid of the last few air bubbles. This does give a longer pedal travel as you have to compress the air in the system but the give away is that it feels as if there is a spring under the brake pedal.
/quote]

That's my latest suspicion! There is no evidence of air. I emptied the servo vac a few days back and the pedal is still firm - no sponginess. There is no evidence of fluid leak,. The level is still exactly at the cast internal ridge on the cylinder.
Possible the hill descent was a red herring. Maybe as it was straight the pads were not knocked back.

When I get a moment I'll check the front wheel bearings.

[Bigbaldybloke]

Best way is with the wheels off and a dial gauge on the disc, the total runout should be 0.004? or less according to the manual.

[Andy8421]

A word of warning, I had exactly this problem, first push was long then all good from there onward.

I used a dial gauge as suggested above on the discs and all were within tolerance. What I had not foreseen was the rotoflex couplings were loading up the rear wheel bearings when the car was jacked up, masking the fact that one rear wheel bearing was completely knackered. It was only when I supported the suspension at normal running height with a jack under the bottom of the upright that it became clear that one rear disc was all over the place.