C4: Brake bleed / hydraulic system bleed procedure
09-06-2022, 02:01 PM
#76
Hi guys,
I really want to thank all of you this terrific thread!
Last Friday with the super useful help of one my beetle-head friends, I replaced the hydraulic pressure switch and flush the whole system (all the 13 bleeds)
I needed 2L of ATE Dot 4 brake fluid and my these are my learnings to it:
Just after we finished I purchased the pneumatic one like the video shown here.
I do really believe that this whole process is not performed in most of the C4 out there because people (and shops) are afraid of.. dirty work!
I really want to thank all of you this terrific thread!
Last Friday with the super useful help of one my beetle-head friends, I replaced the hydraulic pressure switch and flush the whole system (all the 13 bleeds)
I needed 2L of ATE Dot 4 brake fluid and my these are my learnings to it:
- Clean prior and be gentle with the brakes nipples. those are the hardest to open and is easy to damage them if you are not feeling the right movement to torque ratio. I'll need to replace one of them.
- Clutch bleed had really dark fluid in it. it's difficult to reach but not imposible. It seems that no one had did before in my car.
- PDAS locks are tricky and a bit scary when the presurice process starts. I used a KTS300 with a copied cart and it got freeze a couple times, but in the end worked and finalize and depressurize the circuit.
Just after we finished I purchased the pneumatic one like the video shown here.
I do really believe that this whole process is not performed in most of the C4 out there because people (and shops) are afraid of.. dirty work!
09-07-2022, 09:57 AM
#78
Rennlist Member
If you buy the smaller motive and only use it for pushing fluid through the system it isn't so bad. The larger bottle takes many more pumps but I always use mine dry. The C2's are a bigger PITA as they have a smaller reservoir and the clutch works off a tube that sits high in the reservoir. If you are bleeding the clutch you better drain a small amount at time otherwise it is easy to draw air into the line. The C4's do use a huge amount of fluid. I had to use several liters to flush the old ATE Blue out and even then it took some driving and an additional flush to remove it all.
I hope you mean 15 psi and not 15 bar?
I hope you mean 15 psi and not 15 bar?
09-07-2022, 11:59 AM
#79
Sure 15 PSI and not bar!
03-08-2024, 06:36 AM
#80
Another thread to document some work on my car. Credit has to go to dfinnigan and garrett376. I followed garrett's procedure exactly to start for the brake caliper bleeds. I will post how to do each of these as I complete them.
Here is the summary, partly from dfinnigan, of the thirteen total bleeds required on a C4:
(8) Brakes - 4 brakes x 2 nipples each = 8 bleeds
(1) Clutch - 1 slave cylinder left rear wheel area
--- section below is if you have a C4 ------ can stop here if you have C2
(1) Accumulator - 1 in front trunk; bleed via onboard hydraulic pump
(1) Dual solenoid valve block - 1 in front trunk
(2) AWD/PDAS - 1 transverse lock and 1 longitudinal lock; bleed via Hammer or equivalent (PDT999)
-----------------------------------
(13) total bleeds
Flare nut wrenches needed for bleeder valves: 7mm, 9mm, 11mm
Do yourself a favor and treat your 964 Carrera 4 super car properly. Don't destroy your bleeder valves by using regular wrenches that could slip and damage the nuts. I didn't have a 7mm flare nut wrench but its on my list now. Don't know what a flare nut wrench is? Look at the attached photo. It will securely grip the bleeder valve nut and allow you crack it open if its on super tight with little risk of bleeder valve nut damage
I started with the brake caliper bleeds because I changed out all 4 flexible brake lines on the car. The way to do this is with a positive pressure Motive brake bleeder. Essentially you pressure the reservoir with 15 to 20psi of pressure. You MUST pinch off the reservoir overflow to do this. I used some vice grips.
I followed garrett376's procedure.
(8) Caliper bleeds
1)pinch off brake reservoir overflow line with vice grips or equivalent
2)I am doing this dry like garrett376, which means I put no fluid inside the motive bleeder. My car had ATE blue at the last bleed so I am using ATE gold now. I opened the reservoir and overfilled with ATE gold beyond the max line then hooked up the motive bleeder and pumped to 15 psi. Make sure the pressure holds. I had to tighten the motive cap on the reservoir the first time with some channel lock pliers to get decent hold of the pressure.
UPDATE with comment from Darrell below: Its a great idea to use a turkey baster to suction as much fluid out of the reservoir as possible so to not have to flush that out via the system.
3)Start with the caliper furthest from the reservoir which on a USA car is the right rear. There are two bleed points per caliper on a C4.
4)I used a 11mm flare nut wrench on my bleeder screws but others have used the closed end of an 11mm combination wrench. I prepared a water bottle to catch the bleeding fluid.
5)You basically crack open the bleeder valve, after removing the little rubber caps of course, and the positive pressure in the system will force the fluid out. You don't open the bleeder unless you have positive pressure in the system. All this happens slow enough so you can check the PSI gage on the motive bleeder and make sure pressure is being maintained or pump it up some more if it drops a bit. You also keep an eye on the reservoir fluid level to make sure it doesn't drop below min. If you use different color fluid every other bleed you can use the color change in the fluid to make sure the system is totally flushed. Close the bleeder valve after the bleed is complete. Please note ATE blue will stain your reservoir tank. A previous owner had already done this on my car so I am using this two color approach. Garage queen purists may not want to do this to their cars.
Repeat this procedure working your way closer to the reservoir. On a USA car this is right rear, then left rear, then right front, then left front. Since I did this without any fluid in the motive bleeder you have to occasionally refill the reservoir with fluid and re-pump up the bleeder. I used a bit more than a liter of brake fluid to do this.
Here is the summary, partly from dfinnigan, of the thirteen total bleeds required on a C4:
(8) Brakes - 4 brakes x 2 nipples each = 8 bleeds
(1) Clutch - 1 slave cylinder left rear wheel area
--- section below is if you have a C4 ------ can stop here if you have C2
(1) Accumulator - 1 in front trunk; bleed via onboard hydraulic pump
(1) Dual solenoid valve block - 1 in front trunk
(2) AWD/PDAS - 1 transverse lock and 1 longitudinal lock; bleed via Hammer or equivalent (PDT999)
-----------------------------------
(13) total bleeds
Flare nut wrenches needed for bleeder valves: 7mm, 9mm, 11mm
Do yourself a favor and treat your 964 Carrera 4 super car properly. Don't destroy your bleeder valves by using regular wrenches that could slip and damage the nuts. I didn't have a 7mm flare nut wrench but its on my list now. Don't know what a flare nut wrench is? Look at the attached photo. It will securely grip the bleeder valve nut and allow you crack it open if its on super tight with little risk of bleeder valve nut damage
I started with the brake caliper bleeds because I changed out all 4 flexible brake lines on the car. The way to do this is with a positive pressure Motive brake bleeder. Essentially you pressure the reservoir with 15 to 20psi of pressure. You MUST pinch off the reservoir overflow to do this. I used some vice grips.
I followed garrett376's procedure.
(8) Caliper bleeds
1)pinch off brake reservoir overflow line with vice grips or equivalent
2)I am doing this dry like garrett376, which means I put no fluid inside the motive bleeder. My car had ATE blue at the last bleed so I am using ATE gold now. I opened the reservoir and overfilled with ATE gold beyond the max line then hooked up the motive bleeder and pumped to 15 psi. Make sure the pressure holds. I had to tighten the motive cap on the reservoir the first time with some channel lock pliers to get decent hold of the pressure.
UPDATE with comment from Darrell below: Its a great idea to use a turkey baster to suction as much fluid out of the reservoir as possible so to not have to flush that out via the system.
3)Start with the caliper furthest from the reservoir which on a USA car is the right rear. There are two bleed points per caliper on a C4.
4)I used a 11mm flare nut wrench on my bleeder screws but others have used the closed end of an 11mm combination wrench. I prepared a water bottle to catch the bleeding fluid.
5)You basically crack open the bleeder valve, after removing the little rubber caps of course, and the positive pressure in the system will force the fluid out. You don't open the bleeder unless you have positive pressure in the system. All this happens slow enough so you can check the PSI gage on the motive bleeder and make sure pressure is being maintained or pump it up some more if it drops a bit. You also keep an eye on the reservoir fluid level to make sure it doesn't drop below min. If you use different color fluid every other bleed you can use the color change in the fluid to make sure the system is totally flushed. Close the bleeder valve after the bleed is complete. Please note ATE blue will stain your reservoir tank. A previous owner had already done this on my car so I am using this two color approach. Garage queen purists may not want to do this to their cars.
Repeat this procedure working your way closer to the reservoir. On a USA car this is right rear, then left rear, then right front, then left front. Since I did this without any fluid in the motive bleeder you have to occasionally refill the reservoir with fluid and re-pump up the bleeder. I used a bit more than a liter of brake fluid to do this.
I am wondering about the steps needed to replace all my calipers. My plan at the moment is following but I am unsure as its the first time:
- Replace all 4 calipers
- Pinch off brake fluid tank overfill hose to assure vaccum
- Unbolt caliper
- Unbolt caliper line
- Quickly rebolt new line
- Rebolt caliper to bracket
- Repeat for each corner
- Bleed all calipers following the tutorial in this topic
- Done.
- I am wondering if pinching off brake lines before removing the caliper could help somehow with fluid loss?
- I have no powerbleeder so I will need to check the reservoir often enough to not get below the MIN I guess? Top up as the fluid flows into the new empty calipers or is that something not happening due to pressure?
- How important is it to have the same fluid "property wise" (it's going to be mixed) as I won't flush the whole C4 circuit (only brakes)?
- How much liquid is needed in total if I replace all 4 calipers?
03-08-2024, 08:02 AM
#81
Instructor
If you're quick enough, you'll lose no more than a couple of drips switching calipers, but obviously you need to 'fill' the new ones. Bank on 250mL per corner.
Mixing old and new fluids isn't a problem, but if you're in that deep it feels daft not just doing the whole lot. Especially as you may well end up having to buy a second 1L tin of DOT4 towards the end. The clutch in particular benefits massively from fresh fluid. Mixing DOT 3 and 4 is fine, adding DOT5.1 is not.
I don't know where you are, but buying or making a pressure bleeder shouldn't be much more than 30€/£/$. Mine's a 5L garden sprayer bought from the local garden centre for 12€, with a butchered old brake fluid reservoir cap on the end of the lance. I cannot imagine trying to bleed brakes and clutches with two people now.
Mixing old and new fluids isn't a problem, but if you're in that deep it feels daft not just doing the whole lot. Especially as you may well end up having to buy a second 1L tin of DOT4 towards the end. The clutch in particular benefits massively from fresh fluid. Mixing DOT 3 and 4 is fine, adding DOT5.1 is not.
I don't know where you are, but buying or making a pressure bleeder shouldn't be much more than 30€/£/$. Mine's a 5L garden sprayer bought from the local garden centre for 12€, with a butchered old brake fluid reservoir cap on the end of the lance. I cannot imagine trying to bleed brakes and clutches with two people now.
03-08-2024, 08:04 AM
#82
Instructor
Oh, and pinching lines? You should have braided hoses by now. Never pinch those.
03-09-2024, 12:38 AM
#83
Race Car
If you have a c4, it's really worth the cost to buy a pressure bleeder and bleed the system with the bleeder full so it pumps in fluid as you bleed.
Bleeding the hydraulic master with the foot pump method is likely going to create a problem. So i recommend finding a pressure bleeder.
If you release the pressure from the system prior to removing. The calipers, you won't loose a ton of fluid. I did brake lines on a c4 a few weeks ago and then a quick bleed after and all was well.
Bleeding the hydraulic master with the foot pump method is likely going to create a problem. So i recommend finding a pressure bleeder.
If you release the pressure from the system prior to removing. The calipers, you won't loose a ton of fluid. I did brake lines on a c4 a few weeks ago and then a quick bleed after and all was well.
03-11-2024, 05:05 AM
#84
Noted. Thank you all for your answers. Ordered a pressure bleeder.
Before bleeding, first step will be replacing the calipers, would you already pressurize the bleeder with fluid before this step so the fluid can top up the level automatically in the fluid reservoir?
Before bleeding, first step will be replacing the calipers, would you already pressurize the bleeder with fluid before this step so the fluid can top up the level automatically in the fluid reservoir?
03-11-2024, 11:11 AM
#85
Race Car
Noooooooooo
With everything intact, pump the brakes until the pedal is dead hard. You will know. Dead hard is when there is zero pressure.
Then replace the calipers. Very little fluid will drain.
Then once the calipers are plumbed in, and you are ready...fill the pressure bleeder- pump it to approx 21-23 psi, open the rear-most bleeder and start running fluid through the system. Bleed as normal.
Then pressurize the system pump the brakes a few times to get the pads seated. And feel the pedal. If it's squishy - you may need to do a little as a repeat..but you should be ok.
With everything intact, pump the brakes until the pedal is dead hard. You will know. Dead hard is when there is zero pressure.
Then replace the calipers. Very little fluid will drain.
Then once the calipers are plumbed in, and you are ready...fill the pressure bleeder- pump it to approx 21-23 psi, open the rear-most bleeder and start running fluid through the system. Bleed as normal.
Then pressurize the system pump the brakes a few times to get the pads seated. And feel the pedal. If it's squishy - you may need to do a little as a repeat..but you should be ok.
03-12-2024, 06:25 AM
#86
Okay, so you're mounting the new calipers with the valve closed so they don't fill with fluid and drain the tank, then only when you start the bleeding process you let the calipers fill up with fluid?
I just don't want to get the level too low and having to bleed everything.
I just don't want to get the level too low and having to bleed everything.
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n1ne11 (03-14-2024)
04-15-2024, 11:17 AM
#88
Hello
Any advice or trick to remove the lower bolt on the rear C4 calipers? Pretty sure you need to access through the hole in the trailing arm but there might be some helpful other advice idk about.
Also, do you loctite when rebolting and how much Nm?
Thanks!
Any advice or trick to remove the lower bolt on the rear C4 calipers? Pretty sure you need to access through the hole in the trailing arm but there might be some helpful other advice idk about.
Also, do you loctite when rebolting and how much Nm?
Thanks!
04-15-2024, 04:42 PM
#89
Instructor
Get a pick in there and make sure that all the gunk is out of the hex before you even think about sticking a long allen key in there!
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n1ne11 (04-16-2024)
04-15-2024, 08:32 PM
#90
Race Car
Originally Posted by n1ne11
Hello
Any advice or trick to remove the lower bolt on the rear C4 calipers? Pretty sure you need to access through the hole in the trailing arm but there might be some helpful other advice idk about.
Also, do you loctite when rebolting and how much Nm?
Thanks!
Any advice or trick to remove the lower bolt on the rear C4 calipers? Pretty sure you need to access through the hole in the trailing arm but there might be some helpful other advice idk about.
Also, do you loctite when rebolting and how much Nm?
Thanks!
Make sure whatever you buy is very high quality if your calipers have never been taken off. If they have been off and on to your knowledge, and no over torqued- basically any good long Allen will do.
Problem is - if they haven't been off you might find you have a very stuck bolt. So when you first attempt- tap the Allen socket with a plastic hammer to be sure it's properly seated- use a half inch drive breaker bar 18-24", and give it a good crack.
Then just unscrew and done.
Going back on - i don't have the exact torque spec in my head but it's something like 63ft lb.
It's in the shop manual and the Bentley manual.
...and all of this is shown somewhere in the suspension madness thread, including the tools.
I find myself using my shortest 1/2 drive torque wrench when installing - gets tight up top.
For the top bolt, i use a 1/2 drive Blackhawk 10mm impact socket. Also in the suspension madness thread...
Good luck. It's very easy- but just keep in mind that if they are stuck it takes a lot of force and the better quality socket is less likely to round the heads.
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n1ne11 (04-16-2024)