brake servo broken ? how to solve / fix

deQuincey

deQuincey

Quousque tandem...?
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Hi, here again seeking for some help

I am experiencing a strange behaviour on the brakes:

1- the pressure that i have to apply on the brake pedal, seems higher than usual
2- when i brake, the engine revs seem to go up

my assumption is that the brake servo membrane is leaking or broken,

I have checked in walloth&nesch and in bmw, and the part is not available anymore, so then i checked ATE in germany, and a very kind guy answer me that unfortunately there is no more production of that part, and gave me no solution

so the question is:

- any tips, advices for a solution ?
- is there any repair kit for this part ?
- can it be opened to check / fix ?

my brake servo model is the thin one (my car is dated 1971), look at the picture attached

120820073307.jpg


thanks and regards
 
DQ,

You should take the booster/master cylinder assembly out of the car and with a vacuum pump, hand operated or electric, try to create vacuum in the booster and see if it holds and if it loses it. It sounds like your diaphragm is bad. It could also be (hopefully) the O-ring where the cylinder mates on the booster.

Even if you were to find the diaphragm, opening the booster is not trivial. I have done it for the smaller booster on my 1800 and had to have a jig welded up to do it. If you look st the booster you will see the two halves come apart after rotating them against one another about an inch or so. The challenge is it has to be done under a lot of pressure in a hydraulic press so that the two halves can be rotated and even then it requires a tremendous amount of force to open them.

For the one in my Si, I sent it to White Post Restorations www.whitepost.com, which someone here posted about. They insist on doing the booster and cylinder since cylinder leaking is typically the cause of failure. I'm sure there is some outfit in Germany/Europe doing this work.
 
Booster

I suggest that the vacuum lines, check valve operation, etc. be examined closely first for leaks, unsecure, etc.

If the booster is the cause, there would be a noise or hissing when the brakes are applied. A length of hose, stethescope, etc.

You can hook up a vacuum source such as a mightyvack, hand held pump, and see it the booster holds.
 
Here in the States, there are local companies that rebuild ATE boosters. I had the booster for one of my Alfa Romeos done by a company in an industrial section of Los Angeles - this was ten or so years ago, and at that time, the cost was about $125 US.
 
can this other servo booster be used in the e9 ?

hi,

after some searching I was only able to find a very rusty servo booster from a wrecked e9; I can not tell if it is working ok, it seems so, but my bigger worries are that introducing my finger inside I can find rust in the inner wall, so I am worried about the future breaking of the rubber membrane (all this to say that this is probably not a definitive solution), so new searching has been done

this is the second hand servo booster from a old 1972 e9 CS:

171020073629.jpg


so I am making a geometric comparison with a much more easy to find servo booster from an E30 car:

171020073631.jpg


you can see that I am comparing the total length of both servos (provided they have exactly the same fixing points), in the first picture you can see how I painted a blue mark for noting the length of the original e9 servo (the rusty one), and in this second picture you can see how the E30 one reproduces the same dimension:

171020073630.jpg


this is good, because one of the key issues for me is to maintain unaltered the position of the master cylinder, and subsequently (and this is important) the position of the brake steel hoses that depart from that master cyl.,

so, as the meassured length is the same, this first comparison has been succesful

the second issue is the diameter of the servo boosters, and here it comes a difference:

original e9: is 12,5cm radius (25cm diameter)

171020073634.jpg


newer E30: is 13,5cm radius (27cm diameter)

171020073636.jpg


so geometrically there is only a 1cm ( 0.39 " ) difference in radius, that I will have to check in the vincinity of the servo assembly for interferences (I am only worried about the position of the power steering box), but the thing seems do-able

and now it comes the question:

being this the same type of simple effect servo booster in both cases, and considering that the overall dimensions are similar, DO YOU THINK THAT THIS E30 SERVO BOOSTER CAN BE USED IN THE E9 ?

the specific question is that i have made a geometric comparison, but, do you feel that other parameters as: pressure, response, volume,...can worry me and can prohibit the swap ?

regards

remark: see the simple efect servo booster principle:
esquemaseccionservoT51.jpg
 
STLE9 said:
I have one for sale in excellent condition if you decide you need a replacemen.
Click to expand...

thank you

depending on:
-it was from a 3.0CS ? the part number is: T51/920 ATE 3.6150 0700.4 ?
-excellent condition is working condition ?
-where are you located and
-the price
I would consider it
regards
 
I did one of the thin ones today and was so lucky
to have only the o- ring be bad. Pull the master and verify the o-ring is thick enough to seal the hole correctly
 
sfdon said:
I did one of the thin ones today and was so lucky
to have only the o- ring be bad. Pull the master and verify the o-ring is thick enough to seal the hole correctly
Click to expand...

thanks sfdon,
aquestion, when you did so, i mean when you checked the master o- ring and pulled out the master, did you need to dismount the steel brake hoses ? or there is enough play with the hoses engaged to change the o- ring ?
regards
 
Lo siento- the steel lines have to come off - at least 3 or 4 of them and the others need to be loose.
 
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