Welcome to 911UK
The only place for Porsche, 911uk is the definitive enthusiast and resource site for the Porsche 911.
Registration is fast, simple and absolutely free, so join up today for full access to the site and benefit from latest member offers.

Porsche Classifieds
Sell Your Porsche on 911uk
Create a Free Classified Advert
Search Ads
Classified Adverts FAQ
Trade Classified Information
Buyer & Seller Fraud Protection
Consumer Rights Act
Pre Purchase Inspection (PPI)
Porsche Car Sourcing
Porsche Cars Wanted
Official Porsche Centre Reviews
Model
Stock
Porsche 911
991 : 2011- 17
997 : 2004- 65
996 : 1997-2005 31
993 : 1993-1998 3
964 : 1989-1993 6
Carrera 3.2 : 1983-1989 2
Carrera SC : 1977-1983 2
930 Turbo : 1975-1989 0
Early 911 : 1964-1977 3
Porsche Other Models
Classic : 1950-1965 0
Boxster : 1997- 18
Cayman : 2005- 12
Cayenne : 2003- 3
Macan : 2014- 1
Panamera : 2009- 0
912-914-924-928-944-968 1
959 - CarreraGT - RaceCar 1
Car Parts For Sale & Wanted
Other Items For Sale & Wanted
Wheels Tyres For Sale & Wanted
Number Plates For Sale Wanted

Porsche Services
Porsche Body Shop Repair
Paint Protection & Wrapping
Porsche Classic Insurance
Porsche Classic Parts
Porsche Classic Restoration
Porsche Design Collection
Porsche Engine Gearbox Rebuild
Porsche Heritage & History
Porsche News
Porsche Picture Gallery
Win a New Porsche 911

Porsche Parts
Body Parts, Body Styling
Brakes, Clearance
Electrical, Exhausts
Engine Cooling, Engine Electrical
Engine Rebuild, Heating Cooling
Interior Incar, Lighting
Rubber Seals, Service Parts
Steering, Suspension
Transmission, Workshop Tools
Early 911, 911 - 930, 928 - 968
964 - 993, 996 - 997, Boxster
Cayman, Cayenne, Panamera

Porsche Model Range
911 [991] 2011-Current
Porsche 911 [991]
911 [997] 2004-Current
Porsche 911 [997]
911 [GT] GT1-GT2-GT3
Porsche 911 [GT]
911 [996] 1997-2005
Porsche 911 [996]
911 [993] 1993-1998
Porsche 911 [993]
911 [RS] RS-RSR
Porsche 911 [RS]
911 [964] 1989-1993
Porsche 911 [964]
911 3.2 1983-1989
Porsche 911 3.2 Carrera
911 SC 1977-1983
Porsche 911 SC
911 [Early] 1964-1977
Porsche 911 [Early]
Boxster & Cayman
Porsche Boxster & Cayman
Cayenne & Panamera
Porsche Cayenne & Panamera

911uk Site Partners

Post new topic   Reply to topic
Author Message
craig15
Newbie


Joined: 10 Sep 2018
Posts: 7



PostPosted: Mon Sep 10, 2018 12:29 pm    Post subject: Brake/clutch bleeding Reply with quote

Hi All

First post but i've been a long time reader on here and gained lots of useful information. I'm looking for some ideas to help me narrow down a problem I have after I replaced the clutch (and clutch slave cylinder) myself on my 2006 997.1 3.6 (so non-self adjusting clutch cover).

I replaced the clutch then came to bleeding the clutch. I tried pressure bleeding, vacuum bleeding, pressure back bleeding (pumping into the slave bleeder) and the traditional two man, pedal pumping method. Eventually using the pressure bleeding method and about 2-3 litres of fluid i got a decent clutch pedal.

However I have now noticed that I can be driving along then if I pump the brakes really hard 3 times (and they pump up slightly) then when i hit the clutch it doesn't return fully. I can also replicate this by hitting the brakes hard to activate the ABS, then when i go for the clutch it again doesn't fully return. But after using the clutch once it returns to normal operation.

So I bled all the brakes (and the clutch again). I didn't find any air or old looking fluid but it still behaves in the same manner.

With the car sitting idling I can slowly press the brake pedal and it will slowly fall slightly more to the floor. Is this normal?
But with the car idling then pumping the brakes I can't replicate the clutch pedal falling to the floor (the brake pedal doesn't pump up).

Now I am trying to decide if my brakes and clutch have always behaved in this manner and i just didn't notice it before or if there is still actually something else wrong.

Any tips or advice gratefully received!

Sorry for my first post being a book.....

Thanks
Craig
 
  
View user's profile Send private message
   
Rossi911
Suzuka


Joined: 06 Apr 2008
Posts: 1229
Location: England

2011 Porsche 991 Carrera

PostPosted: Mon Sep 10, 2018 5:52 pm    Post subject: Reply with quote

Possible master cylinder seal failure ??

Is there any change in the actual braking or might just be a pedal issue ??
_________________
911RS
 
  
View user's profile Send private message
   
HSC911
Long Beach


Joined: 23 Jul 2014
Posts: 6286
Location: Bedford


PostPosted: Mon Sep 10, 2018 8:33 pm    Post subject: Reply with quote

Welcome
 
  
View user's profile Send private message
   
craig15
Newbie


Joined: 10 Sep 2018
Posts: 7



PostPosted: Tue Sep 11, 2018 11:58 am    Post subject: Reply with quote

Hi All

Thanks for the welcome! Its good to be here. Smile

Rossi. Yes, master cylinder is on my mind. I just can't figure out how the hydraulic brake circuit can effect the clutch circuit so much. They share the resevoir but in my mind thats only the supply of fluid. I can't understand how the pressure in the closed brake circuit (after the brake pedal has closed off the path from the resevoir) can change the clutch fluid pressure?

Can anybody tell me if when they activate their ABS does the clutch pedal behave completely normal if it is depressed instantly after the brakes are hammered on?

And no, my braking performance is just as good as its always been for the last 3 years. I love the brakes, lots of modulation and power.

Thanks
Craig
 
  
View user's profile Send private message
   
deMort
Long Beach


Joined: 21 Mar 2015
Posts: 6155
Location: Brighton


PostPosted: Tue Sep 11, 2018 5:59 pm    Post subject: Reply with quote

Very strange .. logically if we say it wasnt there before hand then its something on the clutch system .. im thinking clutch master cyl if we go by logic.

The resevoir is shared but unless theres some sort of pressure build up which i cant see at all then it wont effect the clutch .

What will however is the brake pedal shaft .. same shaft locates clutch and brake pedals .. so perhaps some wear that is putting a small amount of pressure on the clutch pedal .. that along with a worn master cyl or booster spring is causing this issue.... is the clutch pedal soft or hard to depress ?

I dont suppose your any where near Brighton ? as its much easier for me to have a look than just guess on here !
_________________
.

My Daughter's Crowdfunding page Here

Mechanic

7pm - 9pm

Now At An Indy.
 
  
View user's profile Send private message
   
craig15
Newbie


Joined: 10 Sep 2018
Posts: 7



PostPosted: Tue Sep 11, 2018 8:20 pm    Post subject: Reply with quote

Hi deMort

Just the person I was hoping who would reply! (No offence to anybody else. 😄).

I agree and don’t understand how pressure from the brake could affect the clutch system. But saying that, after the ABS has been triggered then when I quickly depress the clutch it feels soft/light when pressing it down. It feels like it does when air is present in the clutch. But then pump the clutch again and it’s back to normal.

In normal operation the new clutch feels smooth and lighter than the old one. What I was expecting really.

I didn’t know the brake and clutch pedal share the same axle though. Thanks. I’ll try and look at that, see if there is any play in anything.

The other thing I wasn’t sure about was the need to bleed the ABS valve block properly? Could air in the valves make things behave weird?

As for your offer to look at the problem in person, that’s very generous and appreciated! I’m up in the wilds of Scotland however.

Thanks
Craig
 
  
View user's profile Send private message
   
deMort
Long Beach


Joined: 21 Mar 2015
Posts: 6155
Location: Brighton


PostPosted: Wed Sep 12, 2018 7:31 pm    Post subject: Reply with quote

Unless the resevoir totally drains out then you dont need to bleed the brakes .. in other words we clamp the slave cyl pipe.

You only need to use a tester to operate the brake abs when its been replaced .. on a normal bleed its not needed .

Ok so you have replaced the clutch , when released the cover plate pushes the release arm and therefor pushes the slave cyl .. this will force fluid to push on the clutch master cyl and there for push the pedal up .. booster spring will assist here.

If the clutch master cyl has worn the fluid will bypass the seals .. BUT i would think the clutch would be soft and stick on normal operation with this .. also why was it ok before or was it ?

Bleeding a brake system useing the pedal and its possible to damage the seals .. basically the brake master cyl never goes full travel so corrosion , rough edges etc and it can get damaged when it does go full length.

This is much more for older cars though .. been there done that and had to replace the master cyl.

Clutches go full travel all the time so i think not .

Im struggling to see that its air .. fair enough they are not easy to bleed but i think you have that sorted by now .

How you are testing it not .. i assume how you would normally drive the car ..

Soo do you actually have a problem .. does the car drive ok if you drive it normally ?

Got to admit ive not tryed what you are doing to see if theres a problem on a car .. i will now but not untill i get one in .

If you do have a problem then all i can think of is on the pedal assembly .. pict below .

btw .. a pm and ill answer .. i dont always get to read every post .. Embarassed
_________________
.

My Daughter's Crowdfunding page Here

Mechanic

7pm - 9pm

Now At An Indy.
 



702_00.gif
 Description:
 Filesize:  70.18 KB
 Viewed:  1913 Time(s)

702_00.gif


  
View user's profile Send private message
   
craig15
Newbie


Joined: 10 Sep 2018
Posts: 7



PostPosted: Sat Sep 15, 2018 2:06 pm    Post subject: Reply with quote

Hi deMort

Thanks for the detailed and logical reply. Really appreciate your input.

I went for a spirited 300 mile drive last weekend. I wasn't testing the clutch along the way but in the back of my mind I was thinking/hoping it was getting better. But.... I went for a drive today and tested the clutch again and it's still behaving weird.

I've refined my test technique. Driving along, 4th gear around 4k revs, then brake really hard just up to the point before the ABS triggers, keep braking hard until you should have changed gear to 3rd or 2nd (so the engine is struggling a bit, not a normal emergency stop but no ABS) keep the brake depressed hard then go for the clutch. As soon as you're depressing the clutch it feels different, there isn't as much resistance as there should be. The clutch pedal doesn't operate the clutch plate properly, I was grinding gears trying to get 3rd. then the clutch pedal stayed nearly (not quite) on the floor. Hook the pedal back up with my foot and then it works perfect if you depress the clutch again. No spongy action or soft pedal.

It feels like the reservoir is stopping fluid flow into the clutch master cylinder and when you depress the pedal you are pulling a vacuum somewhere rather than pushing fluid..... Like pulling a vacuum when you fill a syringe with brake fluid and you pull too hard. but I can't see how on earth the brake system can do that to the clutch system.

I'm stumped.

Think i'm going to order a clutch master cylinder and go from there. The brakes feel great so I'm not so keen on replacing the brake master cylinder (and the price of it.....).

Just for thread completeness, my car is a 56 plate with 45k miles.

Thanks
Craig
 
  
View user's profile Send private message
   
deMort
Long Beach


Joined: 21 Mar 2015
Posts: 6155
Location: Brighton


PostPosted: Sat Sep 15, 2018 4:05 pm    Post subject: Reply with quote

Ok so very hard brakeing ..

With the brake pedal pressed hard and driveing .. so repeat how you do it when you press the clutch and it feels wierd can you actually select a gear at that point ?

You said grinding so i assume not but this is kinda an important part of the diagnosis.


Ok if you can select a gear at this point then the clutch is actually working but sticking down .. all we are left with is the pedal shaft or the bushes worn causeing pressure on the clutch pedal.


If you cant select a gear .. it just bulks or grinds then the slave cyl is not being pressurized .. this would be a clutch master cyl or this strange vacumn bit .. not the best way to test this but slacken the brake resevoir cap so the chamber is not sealed then try .. cant get a vacumn this way.

I suggest some rags around it just in case .

Some cars have a tiny hole in the cap .. im not sure on the 997 though as ive never really studyed one.




This is not an easy one but im wondering if the fault has been there all along but the stiff cover plate put more pressure on the slave cyl .. now you have a new one its soft so not as much pressure .
_________________
.

My Daughter's Crowdfunding page Here

Mechanic

7pm - 9pm

Now At An Indy.
 
  
View user's profile Send private message
   
craig15
Newbie


Joined: 10 Sep 2018
Posts: 7



PostPosted: Mon Oct 01, 2018 12:17 pm    Post subject: Reply with quote

Hi deMort

A bit of an update on my clutch.

I tried driving the car with the brake resevoir cap loose (so no possible vacuum created) but it was just the same result. There is no vent hole in the cap as far as I can see.

I then replaced the clutch master cylinder. Before I tried the new cylinder I stripped the old one out of curiosity. It looked like new. I was hoping to see some broken plastic spacer or something floating about in the bore. So it was no real surpise to feel the clutch acting the same way as with the old master cylinder.
When the cylinder was off I had a look at the pedal itself. It's build like a tank. I couldn't feel any wear or slop in the pivots. The helper spring mechanism was in working order.

I then tried pressure bleeding the clutch again but I kept the pressure bleeder hooked up to the resevoir for 4 days and every now and then I pumped the clutch pedal. Just in the hope I was removing some small stubborn bubbles. No real surprise this didn't change anything.

To answer your question on how the pedal feels and can I select a gear. I think when I previsouly mentioned grinding gears that had been my own fault and a muddled gear change in the heat of the moment! Very Happy . After further testing I can select gears without grinding. I think there is always enough slave cylinder movement just at the bottom of the pedal stroke that the clutch is activated.
For the fault to show itself I need to brake hard and for a prolonged peroid of time. It is if it's the G-force of the braking that is causing something to move out of position. When I press the clutch pedal it is very light in its initial travel, as though the slave cylinder is not pressing on or in contact with the clutch lever until a lot of the stroke is extended.
I am now wondering if somehow the clutch lever arm at the pivot end (end attached to the gearbox) is loose?? And during hard braking the lever arm moves slightly away from the pivot stub?? If I can work up the motivation I'm thinking about dropping the box in the winter and replacing the lever arm and the pivot bush and anything else I can think of.

I would like to know if anybody else can replicate the fault, or if there is still something wrong with mine. I can't really imagine Porsche would manufacture a car with a clutch that behaves like this.

Thanks
Craig
 
  
View user's profile Send private message
   
wasz
Sepang


Joined: 28 Dec 2012
Posts: 2864


1999 Porsche 996 Carrera 2

PostPosted: Mon Oct 01, 2018 4:01 pm    Post subject: Reply with quote

I replaced my clutch slave and brake pipes all round on mine.

I used my gunsons pressure bleeder, but I wouldn't get a decent brake pedal or clutch action no matter how much fluid I pushed through.

The gunsons has a cap connected to a tyre and "pushes" fluid through from the master.

I took it to my local trusted garage, they hooked it up to their bleeder, which is a vacuum type, and "pulls" the fluid through from the nipples.

This worked a treat and the car is spot on. I must have let too much drain out / replaced long lines that somehow trapped air.
_________________
My special order MY99 Vesuvious Charcoal 996 | Clutch, Fly RMS IMS AOS Job |
Steering Rack Hard Lines | Air Con Compressor / System
 
  
View user's profile Send private message
   
deMort
Long Beach


Joined: 21 Mar 2015
Posts: 6155
Location: Brighton


PostPosted: Mon Oct 01, 2018 6:50 pm    Post subject: Reply with quote

I like your hypothesis .. what we are saying is the clutch release arm / release bearing is pushing against the slave cyl and foreing it back on very heavy brakeing ..

First application of the clutch after this and it has to travel further for the bearing to reach the cover plate .. hence only the bottom part of the pedal actually seems to do anything .

Ones thing is for sure ... this couldn,t happen in reverse !

Well .. a new bearing and it would certainly slide easier on the shaft , new slave cyl .. hmm .. it might be looser allowing this to happen.

Logically if you repeated this test but pushed the gear lever into neutral without useing the clutch pedal then once at a stop with your foot off the brake then you will still have a soft pedal for the first depress as it takes up the " slack " from slave to release arm ... then it will be normal again .

Is this normal for these cars .. that i cant say but it would be nice if someone could test theirs .. trouble is unless its all new and loose then it think the answer would be no .

Its not something i can test on a customers car im afraid so i cant help there .

I would double check the part numbers of what bits you have fitted .

release arm on the pivot .. its got a clip to locate it and also the wrong end for movement to make any diff. i feel .

as i said earlier .. i just cant see air being the cause .. you would have a soft pedal at other times and not how you are testing it to get the fault and whilst they are not the easiest to bleed they are not the hardest .
_________________
.

My Daughter's Crowdfunding page Here

Mechanic

7pm - 9pm

Now At An Indy.
 
  
View user's profile Send private message
   
craig15
Newbie


Joined: 10 Sep 2018
Posts: 7



PostPosted: Wed Dec 19, 2018 12:59 pm    Post subject: Reply with quote

Hi deMort

Just thought I would update this thread with an outcome.

I dropped the gearbox again and replaced the clutch lever arm, the guide tube and the lever arm pivot. When I removed the old parts I couldn't see anything suspect at all so i decided to order another new slave cylinder.

I bought this slave from my OPC. It was a Sachs unit, the same as the previous new slave I had fitted (not purchased from my OPC).

The old/new slave looked a bit crooked when I removed it. The rod wasn't sitting square to the body. So I removed the rubber boot and the circlip holding the rod in place was half off. Then I stripped the rod and the piston out completely to find the piston wasn't attached to the rod!

So I'm presuming under hard braking, the piston was (amazingly) moving along the bore of the cylinder towards the front of the car and pushing the fluid back into the resevoir. The piston is alloy and is very light weight which makes it even more surprising to me.

I'll hold my hands up and say, realistically, it must have been me that damaged the slave somehow when I was fitting it, although I don't how I managed to dislodge a circlip that is buried within the cylinder body behind a sturdy rubber boot.

Thanks deMort for taking the time and effort discussing it with me, much appreciated! Smile

Craig
 
  
View user's profile Send private message
   
infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8140
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Wed Dec 19, 2018 1:23 pm    Post subject: Reply with quote

What can happen by accident is when you fit a new slave cylinder and it is not yet attached to the release arm/gearbox, you may have got in the car and touched the clutch pedal, (or maybe even brake pedal, although it shouldn't) it only takes a little pressure to pop the piston out.
_________________
http://euroroadtripper.blogspot.co.uk/

 
  
View user's profile Send private message Visit poster's website
   
Display posts from previous:   
Post new topic   Reply to topic   All times are GMT - 12 Hours
Page 1 of 1

 
Jump to:  

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You can attach files in this forum
You can download files in this forum
You cannot post calendar events in this forum