So, where's the fluid gone.....?

[Galwaylotus]

Thanks a lot for the replies.
Sounds like time to order some pads.

I suspect that the knowledge that the braking will be consistent will outweigh any feelings that the braking isn't strong enough.
When I went for a slow drive around with no servo I at least felt sure that the brakes would work as expected, whereas before it was bit of a lottery as to what was going to happen.
Is "SJ Sportscars" the place to go ? OK to use their on-line ordering, or give them a ring ?

Thanks a lot guys,
Cheers,
Ralph.

If it's EBC Greenstuff pads you want, try the EBC website. I ordered mine through one of their authorised dealers. Just chose the cheapest and pads were delivered promptly.

[robertverhey]

Sorry I know I sound like a broken record, but simply plugging the vacuum line does not equate to "by-passing the servo", or allow for "servo/non servo" comparison. If the servo has an internal hydraulic issue, it'll still gonna be affecting your pedal feel, even without vacuum. Only that short u-shaped piece of tube with a female 3/8 unf at each end will allow you to fully isolate this problem, in my humble view

[rgh0]

Hi Robert
With the vacuum disconnected the vacuum piston fully retracts and an open passage exists from the brakes to the master cylinder - the equivalent of your straight pipe.
cheers
Rohan

[Galwaylotus]

When my servo locked the brakes I could only release them by disconnecting the vacuum line to the servo. I plugged it and haven't used a servo since! Took the opportunity to remove the servo from the car, fit a tandem master cylinder, remote reservoir, Aeroquip brake lines at all four corners and EBC Greenstuff pads on the front. I wouldn't want to go back to the old setup.

[robertverhey]

Hi Rohan my understanding is that even with no vacuum the control piston inside the booster is still moving under the pressure of the brake pedal and transmitting the pressure to the outlet (and on to the wheels) , albeit without vacuum assistance. To me it looks like that piston doesn't get bypassed, vacuum or no vacuum. So if, for whatever reason, there's a problem with the smooth movement of that piston, it will persist, even without vacuum

That's why I'd be taking the booster right out of the equation. But happy to be corrected on this if I've misinterpreted the schematic.

[rgh0]

There is a hole in the piston that is sealed when the vacuum piston is pushing and which is opened up when vacuum is removed or when your foot is off the pedal. This is what is required to allow fluid to flow back to the master reservoir. The failure of this to open up due to the vacuum piston sticking is what causes the brakes to lock on. With the vacuum removed this hole stays open the whole time and sticking of any of the pistons has no affect which is why the problems all go away and you get a solid pedal that you can modulate.

cheers
Rohan

[Galwaylotus]

Hi Rohan my understanding is that even with no vacuum the control piston inside the booster is still moving under the pressure of the brake pedal and transmitting the pressure to the outlet (and on to the wheels) , albeit without vacuum assistance. To me it looks like that piston doesn't get bypassed, vacuum or no vacuum. So if, for whatever reason, there's a problem with the smooth movement of that piston, it will persist, even without vacuum

That's why I'd be taking the booster right out of the equation. But happy to be corrected on this if I've misinterpreted the schematic.

Please see my submission above. All I did was to disconnect and plug the vacuum line and I then had normal, unassisted brakes.

[YellowS4DHC]

Ralph,
Count me as yet another "convert" to a straight, non-servo system.

My PO eliminated the servo (retaining the original MC), and cautioned me against re-installing it. I really questioned his recommendation after my first hard stop from high speed. I practically pushed the pedal out of the car and it scared the hell out of me.

Having said that, I was new to the car and not used to a non-boosted system. At the recommendation of several on this forum, I installed EBC pads up front and now am quite satisfied. It is, for me, the best compromise between simplicity, reliability, pedal pressure, and pedal travel.

Yes, extra pedal pressure is still required to stop the car over and above a servo equipped system, but I do like the hard pedal and very short pedal travel - both make heel/toe much easier.

regards
Rick

[reb53]

Thanks for the link Rohan.
As you say, there're a lot of spring/seal tensions that need to be right before you have any hope of it working as it should.
How I got it so good when I rebuilt it myself 20 years ago I don't know but I suspect beginners luck.

Robert, the brake feel at the moment with the servo plugged is the same as it's been in the past when coasting down a hill with the engine off, ( no steering lock......).

I know virtually all braking effort is on the fronts but do I only need softer pads on them, or would doing the back lighten it further ?

Really appreciate all the replies to date.
Cheers,
Ralph.

[rgh0]

HI Ralph
I suspect 20 years ago the rebuild kit components were all correct to the original design so they worked properly and it was not so much beginners luck as a beginner with the right bits

I suspect today the components supplied are not precisely to the original specifications and a combination of weaker or stronger springs and seals with more or less than the intended drag gives the varying results like you have experienced. Potentially if you drive it for a while unboosted like I did with mine and then reconnect the booster vacuum again you may find it works better as the seals wear in a little with time

cheers
Rohan

[robertverhey]

Excellent article here http://www.hitchhiker.org/fiat/referenc ... Manual.pdf

But I gotta say, still struggling to see how that control piston (as pictured on bottom of page 7) gets by-passed when there's no vacuum......

Not trying to be argumentative, just want to understand! Have rebuilt at least a dozen of these and thought I was just beginning to understand how they work!

[reb53]

Thanks Robert, that is a good article.

At the moment the plan is to go servo-less and get out on the road as Summer has arrived and we have some excellent, sparsely populated roads.
I don't really want to spend a lot of time analysing and experimenting when I should be driving.
The car normally gets put away in the Winter so that sounds like a good time to investigate further.

Like you Rohan I'll leave it plumbed in at the moment so I can re-connect the pipe at any time and see if anything has changed, but even if it does I don't think I'll ever trust it again unless I find a definitive answer.

Ralph.

[rgh0]

Excellent article here http://www.hitchhiker.org/fiat/referenc ... Manual.pdf

But I gotta say, still struggling to see how that control piston (as pictured on bottom of page 7) gets by-passed when there's no vacuum......

Not trying to be argumentative, just want to understand! Have rebuilt at least a dozen of these and thought I was just beginning to understand how they work!

Hi Robert
It is the primary output piston that has a hole in the middle and is bypassed not the control piston when there is no vacuum and the piston rod from the vacuum cylinder is fully withdrawn. See the cutaway drawing figure 1 page 2 of the article you listed above

cheers
Rohan

[robertverhey]

Okay, penny's dropped at last, thanks

[reb53]

Oh joy ! I now have brakes again.

When I priced out pads, and postage, I thought that as I may not like the un-servoed experience the money would be better spent going towards a new Lockheed servo.

Which it was.
Servo installed and no more heart in the mouth experiences.

Thanks for all the replies and suggestions.

Cheers
Ralph.