C4: Brake bleed / hydraulic system bleed procedure
#46
Rennlist Member
#47
Instructor
Next up is the clutch slave cylinder bleed. The first question is where the hell is it? Its on top of the transmission and accessed from the left rear wheel well.
Thankfully previous rennlisters pointed me in the right direction and I tried to provide better photo documentation below.
(1) Clutch slave cylinder bleed
1) The procedure for this is the same as bleeding the calipers. You pinch off the reservoir overflow line (unless you did the TSB and went to the vented cap, see Laker's post below) and hook up the motive bleeder and pressurize the system to 15 to 20psi.
2)Remove the rubber cap on the bleeder screw, hook up the bleeder bottle and tube, and using a 7mm flare nut wrench (or box end of a 7mm combination wrench which I regrettably had to use) and crack open the bleeder valve. I did about 250ml. Close bleeder valve, put on rubber cap and your done.
Wow, thank goodness I did this one, as first shot of liquid came out black. The rest of my car's fluids look clean but its obvious that either previous techs skipped this step or clutch slave cylinder fluid dirties faster.
Thankfully previous rennlisters pointed me in the right direction and I tried to provide better photo documentation below.
(1) Clutch slave cylinder bleed
1) The procedure for this is the same as bleeding the calipers. You pinch off the reservoir overflow line (unless you did the TSB and went to the vented cap, see Laker's post below) and hook up the motive bleeder and pressurize the system to 15 to 20psi.
2)Remove the rubber cap on the bleeder screw, hook up the bleeder bottle and tube, and using a 7mm flare nut wrench (or box end of a 7mm combination wrench which I regrettably had to use) and crack open the bleeder valve. I did about 250ml. Close bleeder valve, put on rubber cap and your done.
Wow, thank goodness I did this one, as first shot of liquid came out black. The rest of my car's fluids look clean but its obvious that either previous techs skipped this step or clutch slave cylinder fluid dirties faster.
Is that the same? (does look a bit different?)
#48
Rennlist Member
That isn't the slave. That looks like the traverse lock. Slave is high on the transmission.
#51
Race Car
damn my new to me C4 is proving hard at every turn ...
just went thru 5 quarts on the bleed per the advice above:
- pedals good, lots of schmoo and bubbles then all went clear
- turn on the car and .... pedals soft (clutch to the floor, brake way too soft.)
Did this twice hence the 5L ... pooped and stumped.
I followed Ricardo/Adrians Book exactly save for the poor mans (no hammers in service near me) approach Darrell mentioned above to the two gbox mounted units (ie other than the clutch slave).
I did not get much schmoo or bubbles from the two locks but I bled them one at a time .. maybe that's the problem?
Also when draining the fully charged accumulator there seems to be an internal cutoff valve as the main pressure comes out fast but after a few seconds it sort clicks closed rather than running down slowly as pressure dissipates. Either way there were no bubbles there either after a couple bleeds and I bled at least 250ml per nipple or 10 sec of clear bubbless liquid per nipple.
Could be master or slave but pedals were fine before I started the refurb .. so beside draining pretty completely (caliper refurb etc...) nothings changed ITR.
As always thanks for throwing out any ideas .. ordering the handheld device tonight but the fact that the pedals go hard then soften on the ignition (ie pump activation) means I must be doing something slightly wrong from a bleed order perspective ... must the accum and abs be done first then the calipers then the clutch then the locks .. that's been my process.
just went thru 5 quarts on the bleed per the advice above:
- pedals good, lots of schmoo and bubbles then all went clear
- turn on the car and .... pedals soft (clutch to the floor, brake way too soft.)
Did this twice hence the 5L ... pooped and stumped.
I followed Ricardo/Adrians Book exactly save for the poor mans (no hammers in service near me) approach Darrell mentioned above to the two gbox mounted units (ie other than the clutch slave).
I did not get much schmoo or bubbles from the two locks but I bled them one at a time .. maybe that's the problem?
Also when draining the fully charged accumulator there seems to be an internal cutoff valve as the main pressure comes out fast but after a few seconds it sort clicks closed rather than running down slowly as pressure dissipates. Either way there were no bubbles there either after a couple bleeds and I bled at least 250ml per nipple or 10 sec of clear bubbless liquid per nipple.
Could be master or slave but pedals were fine before I started the refurb .. so beside draining pretty completely (caliper refurb etc...) nothings changed ITR.
As always thanks for throwing out any ideas .. ordering the handheld device tonight but the fact that the pedals go hard then soften on the ignition (ie pump activation) means I must be doing something slightly wrong from a bleed order perspective ... must the accum and abs be done first then the calipers then the clutch then the locks .. that's been my process.
#52
I've always employed a home made, one man pressure bleeder. I modified a reservoir cap by adding a tire valve. I use a clip on air chuck, and two air regulators (one at the compressor and one near the car) to make sure I don't over pressurize the system. I set the air pressure at about 10psi, fill up the reservoir all the way and then bleed in the recommended sequence; taking car not to let the reservoir get too low.
Basically you are using air pressure on top of the brake fluid to push new fluid through the system.
I use a box end wrench that I put on the bleeder before the hose, so you go even one step beyond a flare wrench.
Like the garden sprayer pressure bleeder, you never have to pump the pedal, and it's worked on every Porsche I've owned, 914, 964, and Boxster, although the 964 and Boxster were both Tip. I don't see why this wouldn't work fine with the clutch too.
Basically you are using air pressure on top of the brake fluid to push new fluid through the system.
I use a box end wrench that I put on the bleeder before the hose, so you go even one step beyond a flare wrench.
Like the garden sprayer pressure bleeder, you never have to pump the pedal, and it's worked on every Porsche I've owned, 914, 964, and Boxster, although the 964 and Boxster were both Tip. I don't see why this wouldn't work fine with the clutch too.
Last edited by A914MAN; 11-22-2017 at 12:01 PM.
#53
Race Car
^^ yes thanks A924 ... as discussed at length above the 964 C4 requires a pressure bleeder (motive or like yours) and the 'traditional' method of foot pumping is specifically noted to not work with the complex 964 C4 setup (off the 959, very different from the simplified version in the later 993).
#54
Rennlist Member
Just revisited this thread. I haven't been on the 964 forum in ages, although I still have the 92 C4. I just went through the full procedure a couple months ago prior to tracking my C4 for the first time in 9 years.
A couple thoughts and suggestions:
Do the accumulator and PDAS block purges (per Adrian and shop manual) first. These purges use a LOT of fluid and its a good way to to fully flush out the large volume of old fluid in the reservoir. Otherwise, you have to go through a LOT of fluid on the caliper bleeds to get to all clean/fresh fluid. But, be absolutely sure you do not let the reservoir get too low while purging the high pressure system - it is easy to do because you can go through a Lot of fluid. Don't ask me how I know. If you do, you will have to go through a Lot more fluid to get the high pressure circuit full. If there is air in the high pressure circuit, the pump will be Very noisy (probably is damaging it) until you get it clear. Plan to use a full liter of fluid, minimum, on the accumulator and block.
Also, I recall that with the hydraulic boosted system, you should NOT pump the pedal while the Motiv is attached to the reservoir or you can damage the master cylinder. One of the experts out there will know for sure.
Good luck.
BTW - the C4 was a HOOT back out on the track, not as fast as the other cars, but who cares.
A couple thoughts and suggestions:
Do the accumulator and PDAS block purges (per Adrian and shop manual) first. These purges use a LOT of fluid and its a good way to to fully flush out the large volume of old fluid in the reservoir. Otherwise, you have to go through a LOT of fluid on the caliper bleeds to get to all clean/fresh fluid. But, be absolutely sure you do not let the reservoir get too low while purging the high pressure system - it is easy to do because you can go through a Lot of fluid. Don't ask me how I know. If you do, you will have to go through a Lot more fluid to get the high pressure circuit full. If there is air in the high pressure circuit, the pump will be Very noisy (probably is damaging it) until you get it clear. Plan to use a full liter of fluid, minimum, on the accumulator and block.
Also, I recall that with the hydraulic boosted system, you should NOT pump the pedal while the Motiv is attached to the reservoir or you can damage the master cylinder. One of the experts out there will know for sure.
Good luck.
BTW - the C4 was a HOOT back out on the track, not as fast as the other cars, but who cares.
#55
HiWind,
The clutch fluid pickup in reservoir is much higher than you'd guess by a quick look at it. I tried a dry bleed at first and got air in system, peddle went to floor. Reverted to wet bleed and all is well. Bleed the bomb. I noticed no effect from a shutoff valve, but I made sure the bleeder pressure stayed at 20 psi. Make sure you do double bleed. First one you depressurize bomb with 20, or so, peddle pumps, unplug pump, and bleed. Second one, plug in pump, let it pressurize, unplug pump, then bleed. Make sure to hold onto hose as initial squirt will be forceful. This worked for me.
Good luck,
Dan
The clutch fluid pickup in reservoir is much higher than you'd guess by a quick look at it. I tried a dry bleed at first and got air in system, peddle went to floor. Reverted to wet bleed and all is well. Bleed the bomb. I noticed no effect from a shutoff valve, but I made sure the bleeder pressure stayed at 20 psi. Make sure you do double bleed. First one you depressurize bomb with 20, or so, peddle pumps, unplug pump, and bleed. Second one, plug in pump, let it pressurize, unplug pump, then bleed. Make sure to hold onto hose as initial squirt will be forceful. This worked for me.
Good luck,
Dan
#56
Race Car
thanks Dan .. will try the wet bleed (noticed one or 2 of the chambers in the reservoir can be very narrow and caught me out a couple times) and redo the accumulator as you suggest
#57
Rennlist Member
The shop manual specifies the bleed quantities:
- 250 cc at each wheel, bleeding both nipples (thus, 125cc each nipple.)
- 50-100cc at the clutch slave cylinder.
- 250-300cc at the Lateral PDAS lock (side of differential)
- 200 cc at the Axial (longitudinal) PDAS lock (front of transaxle)
- The shop manual recommends doing 2 full purges (pressure relief) from the accumulator and the solenoid valve bleeders. This will use a LOT of fluid, close to a full liter. But it is worth it
- 250 cc at each wheel, bleeding both nipples (thus, 125cc each nipple.)
- 50-100cc at the clutch slave cylinder.
- 250-300cc at the Lateral PDAS lock (side of differential)
- 200 cc at the Axial (longitudinal) PDAS lock (front of transaxle)
- The shop manual recommends doing 2 full purges (pressure relief) from the accumulator and the solenoid valve bleeders. This will use a LOT of fluid, close to a full liter. But it is worth it
#58
The numbers are correct as far as whats written in manual, however, I would think if you bleed one nipple at a wheel, the second will take much less as the line is already bled. So the split would not be 50/50 as suggested. I dont know how much the first nipple will take though. Also, the right rear should require more fluid than the left front. The 250 cc probably includes chamber in reservoir, which may be the largest part of the total.
I have never measured how much it takes but bled until color change. Someone who still has ATE blue could make definitive measurements.
I have never measured how much it takes but bled until color change. Someone who still has ATE blue could make definitive measurements.
#60
Rennlist Member
I used 1.6 litres to bleed the calipers, clutch, accumulator and dual solenoid. Unfortunately I couldn’t finish the job as the PDT999 would not connect to the PDAS. I know the PTD999is working as it connected to the Motronics on this car and the PDAS on my other C4. I think I will have to use the switch method.
Btw the nasty fluid is from the clutch slave.
Btw the nasty fluid is from the clutch slave.