JBH

The addition of an hydraulic brake booster in the C2 Turbo, makes it appear the task of bleeding the brakes is fairly difficult with a number of steps - in other words, I can't rely on my wife to step on the brake pedal as I open the bleed valve.

The manual describes a multistep approach requiring an automatic filler for the resevoir and automatic bleeder for the caliper.

Does anyone have any insights to offer on how to best accomplish this task:
(1)Am I making too much of this - after I have done it once, it's no big deal?
(2)Do I really need a pressurized feed and vacuum bleeder? If so, what is the best choice?
(3)Any tricks to make it simplier?

Thanks!

Adrian

You are taking the correct approach. You cannot vacuum bleed, nor pump the pedal bleed the hydraulic brake system of the Turbo, Turbolooks or the C4s. This system is a 180 bar system. C2s by the way have vacuum boosted brakes.
On the Turbo you can get away without using a Bosch Hammer but have one handy. You must pressure bleed the Turbo brakes.
I highly recommend you follow the procedures in the manual on how to do this. Believe me it is worth the extra time and expense. No brakes can be a real problem or a brake applying itself at speed can also get pretty scary.
Just for info. If the brake pedal goes really hard and you cannot apply them. This means you have no pressure but full fluid. If the brake pedal goes straight to the floor, this means you have no fluid or pressure. If you pump the brakes and the pressure comes up, this means you are low on fluid or have major air in the system. If you have lots of air in the system you will hear the hydraulic pump cavitating,
Ciao,
Adrian
911C4

Bill Gregory

An additional consideration - on higher mileage vehicles, you really shouldn't pump the brake pedal to move brake fluid through the system. What happens is during normal operation, the seals in the master cylinder move over a limited area. When you bleed the brakes by having someone push on the pedal, it pushes the seals into areas that don't normally see action, where rust and crud resides. In many cases, this causes tears in the seals, leading to a rebuild or new master cylinder. On a higher mileage vehicle, you can use either a pressure bleeder or, if so inclinded, a vacuum bleeder. And in the case of certain others, a Bosch hammer as well.

Julian Allen

I am curious about the bleeding.
First of all, I don't have a 964 Turbo, but have transplanted the hydraulic boost to my 951 racecar. I bleed the brakes, defined as the brake master cylinder, ABS, and calipers in the old fashioned pedal or vacuum bleed method, depending on availability of help. I flip my circuit breaker for the hydraulic boost pump (you can do the same thing by pulling the fuse), then use the pedal without the benefit of the boost. Works the same way in my Suburban with hydraulic boost provided by the power steering pump, only here you pump the pedal without the motor running.
When I need the hydraulic boost bled (I actually use a separate reservoir so I can use SRF for the brakes and Ate blue for the pump), I just use a hand or tire air pressure bleeder like the ones you see in Pano or Excellence.
It seems to work for me. I have a set of the instructions from the 964 Turbo brakes to "point the way" for the hydroboost bleeding.
Couldn't this work for the stock car?

DrJupeman

Adrian,

I'm going to bleed the brakes on my Turbo soon. My mechanic has said that he should do it because the Bosch Hammer is needed. When I searched the archives I ran across your comment above. Your book seems to suggest I don't need the Bosch tool. I believe my mechanic said I would need the Bosch tool to open up the ABS system(?).

Clarification? Help?

Thanks!
Charlie

Adrian

Dear Charlie,
You do not need a Bosch Hammer to bleed the brakes of a Turbo. There is no requirement to activate the ABS when bleeding the brakes. The only time this may be necessary and Porsche do not have a procedure for this either is, if the ABS hydraulic unit is replaced with an unit which has not been primed with brake fluid first.
Ciao,
Adrian
964C4

jeff91C2T

JBH...do you have the factory manual? It descibes in decent detail the steps. I do this about twice a year (and it's pretty easy).

I can fax the pages if you need them.

DrJupeman

Jeff, note that JBH's post was from 1991 (!) but I am about to do this. If you can fax me the pages, please PM me and I will send you a fax #.

JBH

There are mutiple steps for different sections of the brake system. I do have the factory manual - if I get motivated, I'll type out the details and post them to this forum.

LOL - not quite 1991. That post was from 2001 and I just picked up the car from the previous owner in NJ. I think Rennlist was just getting started in 2000-2001.

DrJupeman

Sorry, typo on 1991, I obviously meant 2001.

loot87

Jeff,
Did you ever get around to writing up the brake bleed procedure? I'm thinking of changing out my fluid in my 91.

Anyone,
Which factory manual has the procedure? Also, what's a good fluid for street-only use?
Thanks.
Chris

nathanUK '81 930 G50

The 911 turbo 91> factory workshop manual has it.

Youcef

I just replaced the standard fluid with ATE blue in my 3.6. I made a pressure bleeder from a garden type chemical spray where I fitted a pressure gauge. I used the process from Adrians book, brake work fine and was easy to do.

Adrian, Welcome back, great to see you here again.

wagonface

My brother is a home mechanic and offered to replace my brake hoses. He ended up also replacing the small copper/nickel ones between the hose and caliper.

He has just rung asking if there is a knack to bleeding them afterwards. he says he has bled them like he would any other car, but the pedal feels a bit 'spongey' still.

I am not there so I cant tell if this because he isnt used to the progressive porsche brakes, or if there is genuinely a problem.

Is there anything 964T specific that he needs to do? My car is a 964T, 3.3L.

He is supposed to be driving it back to me this afternoon, so a quick response would be fantastic.

Thanks for any help, Josh

Metal Guru

The accumulator has to be bled too.