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Author Topic: Brake servo  (Read 3699 times)
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droptop
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« on: April 01, 2014, 01:59:34 PM »

i have an ongoing problem with the brakes on my car.
they eat rear pads but the car just doesn,t stop as it should.
All front brake seals were replaced, the m/c rebuilt and the system bled (several times)
The brakes are a vast improvement over what I had to start with, but I've a feeling the servo isn't working. The m/c was assembled "wet" and I have no reason to suspect the seals have flipped but I can't rule it out.

The pedal just feels "disconnected" from what's going on and requires a harder push than I'd be willing to accept.
Having had the car parked for the winter really brought it home to me when I drove it last month.
Now, I know I can't compare the braking efficiency of modern vehicles to my Beta, but I remember my Fiat 132 as having some of the best brakes ever.
When I pump the brake pedal with the engine switched off, the pedal travel shortens and the pedal becomes "hard"
However, when I start the car with my foot still on the pedal, there is no feeling of the pedal going down as it should.
I have no vacuum leaks and have a couple of spare servos but before I gut the engine bay to replace the servo, is there A) a way to check my existing servo in the car and B), is there a way to test the servos in my stash of spares?
Now that i think of it, can the non-return valve in the servo vac hose be defective/
I don't have a spare to try but I'm sure they're fairly generic so I can steal one off one of the other cars in my herd
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droptop
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« Reply #1 on: April 01, 2014, 07:28:35 PM »

Update:
I'm back to suspecting the master cylinder.
i pulled the front brakes off this evening and the pads have literally no wear after four years and 6000 miles.
The discs are as new and highly polished!
I deglazed them with fine emery paper and fitted a set of Greenstuff pads and if tomorrow goes as planned, I'm going to pull the master cylinder and strip and rebuild it.
I presume I can do it with the reservoir attached as I know the plastic pipes can break off in the rubbers when you try to remove the reservoir and althouhh I have at least two spare m/s's, i don't have a spare reservoir
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Thotos
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Theo Kyriacou


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« Reply #2 on: April 01, 2014, 10:49:40 PM »

can the non-return valve in the servo vac hose be defective/

I'd say 'yes' as it was defective in my Trevi. I took it off and cleaned it with plenty of WD40 and it was fine after that. The problem I had was brakes that needed a hard push on the pedal (as you describe) but only when the car was cold. Brakes would be fine after everything warmed up and presumably the non-return valve 'loosened up' and was working properly.

When bleeding the brakes, was it an easy job or did the pedal still need a hard push to get the air out? On my Gamma I've had problems with the flexible pipes to the calipers which seem to collapse internally resisting the flow of fluid to the caliper.   
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droptop
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« Reply #3 on: April 02, 2014, 07:34:31 AM »

I felt inspired after fitting the new pads so I removed the calipers yet again and taking one side at a time with the pads in between the piston and the clamp side of the calipers, I pressed the brake pedal pushing the pads together without the disc in between to create a lot of piston travel. I released the bleed nipple for the auxiliary pistons only and wound the caliper pistons back forcing the fluid back into the master cylinder against the front brake seals.

It worked! Thinking about it, I don't know why as if the seals were already flipped, that wasn't going to restore them to their correctl position.
Maybe the pistons just needed freeing in the calipers? However it happened, I got a result so I'm happy for now anyway.
The pedal travel is a little longer than before when I reassembled all, but I know I need to bleed them today.
The brakes now feel like they are acting as they should without me feeling I'm pushing my foot against the wall and not the brake pedal.
Replacing the badly worn back pads should reduce travel further so hopefully I have the time to tackle them today.

I'm not suggesting this will work for everyone but as I had decided the cylinder was coming off today anyway, I had nothing to lose.

Regarding the servo, I removed the vac line from the manifold and sucked it. The vacuum held and I was unable to blow through it so I think the one way valve is OK but following Thoto's advice, I'm going to remove it and spray it with WD40.
« Last Edit: April 02, 2014, 07:44:36 AM by droptop » Logged

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lukasdeopalenica
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« Reply #4 on: April 02, 2014, 08:06:36 AM »

Great. In the past I also encountered problems after brake system rebuild. In my case the MC did not create the pressure, or at least too low. I was also a bit in desperation, but before I dismantled again the MC I found the source of the problem. The guilty one was the alloy banjo output at the MC that was slightly cracked and leaked only under pressure. A small element but big consequences.
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droptop
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« Reply #5 on: April 02, 2014, 09:16:47 AM »

Great. In the past I also encountered problems after brake system rebuild. In my case the MC did not create the pressure, or at least too low. I was also a bit in desperation, but before I dismantled again the MC I found the source of the problem. The guilty one was the alloy banjo output at the MC that was slightly cracked and leaked only under pressure. A small element but big consequences.

I was only reading of your fight with the brakes in this thread before i made mypost in case anyone else had the same problem.
It's the little details that cause all the hardship.
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