Pressure Bleeding, ABS and the 35 psi Requirement.

[George7941]

I have a pressure bleeder (KD branded, exact same as the ubiquitous Branick pressure bleeder) and its instructions call for 35 psi pressure at the m/c when bleeding ABS systems. I do use the scan tool for ABS bleeding.
Why the requirement for this high pressure when ABS is involved?
As an aside I do not follow any sequence when opening the bleeders. I do the front axle first and then the rear axle. I chose which side to bleed first purely on convenience. Should I be following the recommended sequence?

 

[George7941]

To add, I am not bleeding air out, I am flushing old brake fluid out. I do this every three years on all the vehicles I maintain.

 

[LotI]

I would check to see if the car manufacturer has a recommended pressure for bleeding. I've always aired on the side of caution and only used 15psi(1 bar) vs. the 2.0 bar recommendations. I'm in no hurry since I'm not getting paid flat-rate for working on my own cars.

I would always follow the recommended sequence, and have when I had the information.

 

[George7941]

I have the GM FSM for my truck and it goes into great detail on manual bleeding,with an assistant operating the brake pedal. A bit surprising, considering the FSM is targeted at professionals and not so much at DIYs. It only casually mentions pressure bleeding, with no details.

The sequence for my truck is RR, LR, RF, LF. I was wondering if the sequence mattered during flushing fluid, as opposed to bleeding air.

I tried 15 psi and get vigorous flow at that lower pressure.

 

[mk378]

35 psi sounds like a lot for a plastic tank that wasn't necessarily designed to hold pressure.

 

[KGMtech]

Originally Posted by mk378
35 psi sounds like a lot for a plastic tank that wasn't necessarily designed to hold pressure.

I agree, it might pop a seal and spray BF all over !

 

[MasterSolenoid]

I have ABS brakes on my 2002 Ford Ranger.
I believe the ABS solenoid is always 'open' on mine because I presserize the Reservoir and can bleed all 4 wheel cylinders.

At first I tried 20 PSI, but the Reservoir started dripping fluid (leaking from 2 grommets underneath)
I then went with 10 PSI and can do all four wheels without spilling a drop.
Even with only 10 PSI, I get good flow.

 

[maxdustington]

I wouldn't go over 10 PSI especially on an old MC. I actually smoked a MC using a DIY pressure bleeder without a gauge,

 

[nthach]

AFAIK, those Brannick bleeders are a tank separated by a diaphragm. The tank is pressurized. My guess to why Brannick calls for 35psi is because of that and the length of small-bore hose that's supplied to hook up the pressure tank to the car. I'd start with a lower pressure first and see if you can get flow.

while it might not matter for flushing, I like to stick to the OEM-prescribed bleeding order. The master cylinder is on a diagonal or front/rear split to provide some braking if there's a leak after the MC. While modern ABS systems do have each wheel on a separate hydraulic circuit, that was before 4-channel ABS and traction control/stability control was a thing. The earliest ABS systems controlled the front wheels separately and the rear wheels were on the same circuit.

 

[George7941]

Originally Posted by nthach
AFAIK, those Brannick bleeders are a tank separated by a diaphragm. The tank is pressurized. My guess to why Brannick calls for 35psi is because of that and the length of small-bore hose that's supplied to hook up the pressure tank to the car.

That is not it. The instructions call for 15 psi for non ABS systems.

My best guess is that some ABS systems are more restrictive to flow and hence the higher pressure needed to get adequate flow. As I posted earlier, that is not the case with my truck, there is adequate flow with just 15 psi.

 

[E365]

I've always done 10 psi on every car and it works just fine.

 

[Cdn17Sport6MT]

I am guessing that using 27" Hg vacuum, and using teflon tape solely on the threaded-portion of the bleedscrews - works pretty well, too? That would be equivalent to using about 14 psi positive pressure... Not as messy... and reservoir grommets will not leak, bleedscrew threads will not leak.