[Rutger Gert-jan]

Hi,



As you might know I experienced a light vibration while pulling away at traffic lights (see my previous post). Today I received all the parts (cylinders, motor mounts, clutch ass. kit etc etc). I wanted to start working on the master clutch cylinder, when I took away the panel that covers the master cylinder i was shocked....I too have crack in my firewall...... <img src="/forum/images/smilies/968/mad.gif" class="smilie" alt="" /> I already found the post which was posted by a fellow member. So I know what to do, but now I need to remove the brake booster as well. I disconnected all the lines and hoses but still it will not come out of the car, it is loose but that`s it. So do I need to remove the inlet manifold or am i missing something? The 968 shop manual says little about removing this item or should I look in the 944 shop manual?



Any help is appreciated!



Rutger

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[Eric_K]

I'm pretty sure the intake manifold has to come off to get the booster out.

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[PorscheDude]

If you remove the intake, be sure to replace the gasket. I think it was somewhere around $12.

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[jjvflihy]

Hey Rutger,



Just in case you did not get my email . Remove the drivers seat and the 4 nuts holding the booster once loose pry it out, its tight but it will come out without removing the manifold. good luck

John

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[Rutger Gert-jan]

Today I got yhe booster out, I did remove the intake manifold from the engine, otherwise it was just not possible to remove the booster. So the only thing left is welding a nice piece of metal to the firewall and I can start putting things back together.

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[Roboman]

Recently I lent my 968 to a friend ( I know, really bad move!) as they needed another car and I was too busy to help.


When they got back the said the brakes were very stiff to apply and were pretty ineffective, which turned out to be true when I tried them.


My first thought was maybe they drove with the handbrake partially engaged and the brakes had overheated, so I just left the car overnight to cool down and tried again the next day.... unfortunately they were still the same.


So now I suspect the brake booster and that lending the car to a friend was just a coincidence (or else my car is trying to tell me something).


I can hear that hiss as the brake pedal moves down a touch when the engine is running, so I was surprised when the brakes didn't work properly.


Anyone got any other thoughts? .........Apart from DON'T LEND OUT YOUR CAR!!!!

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[Waylander]

Just to let you know, you cant get the booster off with out removing the inlet manifold


When you do this, take it off with the fuel rail still bolted to it, any attempt to remove the rail and injectors could dislodge a injector seal and pintle cap, if that happens the only place they can go is in one of the cylinders, been there done that


Brake boosters are extremely expensive from OPC, there is a french breakers that has quite a lot of 968 parts


https://www.pieces-occasion-classic.com/...modele=968

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[Roboman]

Thanks Waylander, I've not yet started to investigate, but if that's how it turns out then I'll check out that link.  Hope you had a good weekend.

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[Waylander]

A very hot one, doing a auto jumble with my brother

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[Roboman]

Need more space in your garage??  Room for more projects

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[Roboman]

So, managed to get the car back in my garage after  all the wedding debris was cleared out.

 

I inspected the hoses and couldn't see any rips or holes, however I did notice that the idle revs rose when I put my foot on the brake pedal.  So I suspect I have a leak, hopefully not a torn diaphragm in the booster.

 

I shall put the symptoms into google and see what results. 

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[Waylander]

If I get a chance I will compare your results with my car

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[Roboman]

Thanks Waylander, that would be useful. People have been talking about a "check valve", I need to locate that.

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[Waylander]

Its in the big vac hose,

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[Roboman]

My thanks to John for this post from April 2010 ....

 

http://www.968forums.com/topic/9290-vacu...entry91175

 

The way I see the system working is (airing my thoughts and happy to be corrected/ receive additional advice)

 

1. Inlet manifold creates vacuum which draws air OUT of the booster chamber.... the diaphragm of the booster is much greater than that afforded by the piston from the brake pedal, and hence amplifies the pressure on the brake pedal.

 

2. The check valve (90 degree plastic thingy) which plugs into the booster maintains the booster vacuum as a constant, even though the engine revs change, and also for some time after the engine is stopped....so the brakes should be effective for a brief time after the engine stops???

 

Failure options:

A: no vac build up so brake boost ineffective....inlet drawing air from surroundings instead of the booster chamber.

  - vac tube from inlet to check valve leaking

  - leaking around joints: manifold to vac tube / vac tube to check valve / check valve into booster

  - check valve stuck closed (would that collapse the vac tube when the engine is running???)

 

B: brake boost works but variation in effectiveness....inlet drawing air from booster but not being held constant.

  - check valve stuck open

  - leaking around joint check valve into booster

 

C: Some vac build up but boost ineffective....booster chamber being evacuated but no amplification of pedal action

  - Torn booster diagram (ugh!!).

 

Okay, off to the garage ..... please let it be A or B .....

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[Roboman]

So I found problems, but THE problem, I don't yet know ......

 

Firstly the check valve looks pretty stuffed, it has discolouring about the seal as though it is drawing in air, and when I removed it and the vac tube, the bottom joint of the vac tube could spin around so was a loose fit. I prised the check valve from the booster and blew/sucked on the CV to see if it was working.  It appeared to be blocked. So I removed the CV from the vac hose and blew/sucked again ... now it worked, so not sure if I had loosened something up or what.

 

   

 

Then on further inspection I spotted this "sucker" .....

 

   

 

The elbow to the fuel reg (is that what it is??) is cracked.

 

So, nothing definitive.  I've ordered the parts and await arrival, but I won't be surprised if the problem still exists.  However, the parts need changing in any case, so it's not a waste of time or money.

 

PS These "one time only" hose clips are a PITA to get off when the engine is in situe!!

 

 

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[Roboman]

Ahead of the vacuum parts arriving, hopefully today, I'm checking out replacement boosters.  I've noticed mine has evidence of a previous leak, ie a vertical line of discolouration (presumably paint stripped off by the brake fluid) downwards from the booster/cylinder junction.  It is dry, and I don't remember any previous seepage, so I think there was a leak in the past which was fixed, but may well have contributed to my present problem.

 

Anyway, ATE make an OEM booster but only if one has an ATE master cylinder ..... I've looked at my master cylinder but see no manufacturer's stamp on it.  I've also looked at online publicity photos of ATE cylinders.  But given the prevalent use of stock photos, I'm unsure if these photos represent the real thing.  So ......

 

HOW DO I KNOW IF MINE IS AN ATE master brake cylinder??  Any help/photos/knowledge of markings/numbers would be useful.  Thanks

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[Waylander]

There is only one part listed in pet for the 968 all years, no alternative or replacements


That would suggest they are all the same spec regardless of manufacture


There is only one booster listed as well

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[Roboman]

Thanks Waylander, I agree that suggests the boosters/ master cylinders are made to the same blueprint. Cheers

 

Edit .... and of course ATE may well be promoting their own master cylinder at the same time!  If it comes to replacing the booster I'll let you know.

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[Waylander]

So I looked up the prices and numbers for parts for you

 

now i have PET working again, windows updates hate em

 

booster 944 355 023 11 £699.18

master cylinder 951 355 011 04 £481.37

one way valve 191 611 933 F £33.24

 

thats a lot of money for a servo.....

 

if you do need a servo.

https://www.pieces-occasion-classic.com/...tegorie=-1

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