14 replies to this topic

[mattaebersold]

 

 

I made this short youtube video, but the short story is: 

 

- installed brand new servo/master cylinder

- worked great for about 3 months

- now every time I apply brakes while driving, I have to pump the pedal a couple times to build up pressure

- so that means vacuum pressure is escaping? 

- I've bled the brakes multiple times, they're good

- I'm suspecting the vacuum line that goes to the servo, the one with the 1 way valve in the middle

- but there's no indication that it's bad. It's a harder plastic, but there's no obvious cracks, etc

 

 

Other thoughts

- I have a smoke test machine, but I don't know where to introduce the smoke

- would a servo fail that quickly? 

[sonscar]

Random thoughts,testing the servo is done by pumping the pedal until there is no vacuum and holding it down.Then start the motor and it should go down further.Pumping the pedal uses up the vacuum so should make it worse not better.If the servo has failed the brakes should still work but need a harder press,not much harder as the servo is only about 1.6 times assistance.It was not clear where you were pulling the vacuum from,on my car that is the water heated inlet pipe.Is the engine producing vacuum?Good hunting,Steve..

[andyapanel]

Use a piece of tubing to listen for leaks; I had a grommet fail on my servo once
I am surprised you have not experienced an effect on engine speed
What is the line plugged into in the manifold?
Good luck

[Spider]

As well as the great suggestions the other guys have made, try disconnecting the Vacuum Line from the Manifold and plug up the Manifold side on it. See how the brakes behave after doing that, they should work as they did prior to fitting the Servo. If they do, without having to pump the pedal, then I'd say your Servo is karput. The cheap ones generally can't be overhauled.

If you find you still need to pump the pedal, then I'd say your Master Cylinder is the likely culprit here.

[coopertaz]

if you have to pump to get brake pressure up sounds more like brake master than servo as servo boosts pressure and vacuum is depleted not increased as pedal is pumped then rebuilt by inlet vacuum. you can test for vaccum by removing 90 degree elbow  from servo and check for suction with engine running. keep thumb on end and turn off engine, if it maintains suction then non return/ one way valve is ok if not then this is u/s. refit elbow to servo and repeat on master cylinder hole (with master cyliner removed), while master is out pull back cover on operating rod, these have a habit of leaking here on mine it even went into servo, cue red arrows when hard cornering!

Edited by coopertaz, 15 July 2022 - 07:57 AM.

[mattaebersold]

Thank you for the replies, and yes, definitely have to pump the brakes to get pressure, then it's lost pretty quickly, then I have to pump to get pressure again. I did replace the master cylinder recently as well. I will take a look at that. 

[panky]

Am I looking at this this wrong or was the vac line connected to the manifold water jacket?

[Maccmike8]

As panky says it looks like the vacuum hose is connected to the water pipe on the manifold. 

It needs a connection so it accesses the inside of the manifold for the negative pressure created by the engine sucking in air. Even with that connected incorrectly, it wouldnt need pumping you just wouldnt have servod brakes.

That sounds like an hydraulic fault.

[cal844]

So, the servo vacuum pipe has been cut. Looks like the inlet manifold is the wrong manifold, it needs the servo vacuum take off.

[panky]

Maybe it's been internally drilled into the water jacket.

[mattaebersold]

Was able to drive it around the driveway today to get a little bit more specific on when/how the issue crops up: 

- new servo

- new master 

- new pads

- braided lines

 

The brakes were working fine with the new parts for a few months. Then, all of a sudden, I’m losing ALL vacuum pressure (I think). Let me break down how to recreate this issue. 

 

 

1. Start car and idle, brake pressure feels nice and solid

2. Do any amount of driving, ALL pressure drops almost instantly and pedal goes to the floor with no pressure at all

3. Once I get the car to stop, and idle for like 10 seconds, the brake pedal is firm again

4. If I’m driving and loose pressure, pumping the pedal a few times will build the pressure back up temporarily so I _can_ stop, but then if I drive for a few more seconds, I will lose pressure again. It’s strange that pumping up the brakes will restore pressure

 

Side note: 

- when there is pressure in the brakes (like after pumping them, or idling for a bit, constant pedal pressing does hold pressure, like the pedal is _not_ slowly sinking to the floor

 

 

Possible thoughts: 

- vacuum pressure is escaping somehow when the car’s under a load or in motion? 

- doesn’t seem like the servo is bad because idling keeps pressure in it and pumping the brakes does increase pressure?

- doesn’t seem like the master cylinder because of the fact that if there is good pedal pressure, it doesn’t slowly sink to the floor

- could it be the hard plastic line that goes from the servo to the intake manifold? 

- could it be that one-way valve on the aforementioned hard plastic line?

- Vacuum pressure being lost elsewhere? Or draining the pressure in the servo? Like that grommet on the servo itself? I replaced that also when doing the servo, so that’s new

[mattaebersold]

Also I'm seeing these replies about a water jacket and the wrong intake manifold? Can someone help me out by explaining this? Maybe with some photos?

[sonscar]

The servo has NO effect on pedal travel,that is NO effect,it just helps push it down using atmospheric pressure/vacuum assistance.If your pedal goes to the floor it is not the servo.It is fluid leaking out or past a seal.Steve..

[GraemeC]

Two things, all previously said:

- Your problem is in the hydraulic system of the brakes, most likely the master cylinder.

- As it was installed that servo was never working. As said, the port the servo vacuum line was connected to is just a simple tube that goes from one side of the manifold to the other and it is usually connected to the heater circuit to warm the manifold. It has no connection to the actual inlet tract where the vacuum is generated.  .

 

You need a manifold similar to this that has the vacuum take-off port on the top (this also has the heater pipe running through from side to side):

http://www.minispare...|Back to search

 

You will then also need a banjo fitting, washers and bolt to connect the vacuum line (which may now be too short) - sourcing a full secondhand set up may be the easiest fix.

Edited by GraemeC, 22 July 2022 - 07:06 AM.

[mattaebersold]

Hey all, Just wanted to circle back here and talk about what I found that ended up being the problem. I did some tests in the driveway like I mentioned, and I noticed that every time the car moved, I would loose 'pressure', but when stopped, and pumping the brakes, it would restore pressure. 

 

I spoke to Jack at Seven Enterprises and showed him this forum, and he had an interesting thought that it might be suspension related, rather than servo/master related. Like there was possible wobble in the hubs, and the pads weren't clamping like they should...

 

Turns out the left side front cotter pin was sheared-off by the castle nut, and it was working it's way loose! Which makes sense to me that if the hub is wobbling when the car moves, the pads aren't grabbing until you stop, and pump the brakes a couple of times. 

 

I re-torqued the castle nut, added a new cotter pin, and test drove yesterday, and it's all corrected. So yea, red herring with the brake system!

 

Thank you for the ideas and input!

Matt