risaac928

Okay Forum here is the deal....I picked up a used Mastercylinder from a Rennlister about a year ago and has work fine until now.

I went in and bleed the brakes but I still have little to no brake pressure.

I noticed when I tighted the Brake Bleeder Valve as tight as I could I was still getting air. I am using a Mightyvac pump to vacuum the brake fluid out.

After putting some teflon tape around the Brake Bleeder Valve that stop the air bubbles, however I still have litte to no brake pressure.

This video is before I put teflon tape around the Brake Bleeder Valve. After I wrapped the teflon tape no more bubbles or air. But still no brake pressure.

http://www.youtube.com/watch?v=dgai6zDUF9o

http://www.youtube.com/watch?v=vcUAiHgTnZw

risaac928

So no one has ideas. So where do I start?

Replaceing the Brake Bleeder Valve?
Calipers?
New Master Cylinder?
All the above?

jpitman2

Tried pressurizing the reservoir (with mityvac?) to drive fluid out? Worked for me when I flushed the fluid recently.
jp 83 Euro S AT 53k

dr bob

If the calipers or hoses are leaking, you'll find puddles of fluid. So start looking at the master cylinder. Pressure-bleed the system first, just to make sure it's full.

Installation details play a part in how a master cylinder works. Most important is that the piston is allowed to withdraw enough for fluid to fill the chambers. The pedal pushrod to the booster is a place to start looking to make sure there is some play. Then the pushrod from the booster to the master.

You can crack the lines at the master sylinder to see if the MC is actually pumping, once you are sure the chambers are filling. If the pumping is weak, it's time to look for another master cylinder.

risaac928

Thank you Dr. Bob it was pain the *** to get the MC out and back in. Can I use the Mightyvac to Pressure-bleed the system?

When I buy a MC do I need to bleed that thing frist? (Dumb question, YES). What is the best way to Bleed the MC, given how tight that area that it sits in is really tight...

rixter

remember that $1500 you were going to use on another shark?

dr bob

Last MC I did had instructions and fittings to "bench bleed" prior to fitment on the car. It eliminates any little pockets of air. If the rest of the system is intact, it's possible to not need an on-the-car bleeding. I haven't needed to change any 928 MC's so don't have any specific guidance for you. I did collect all the "bench bleed" pieces, which include plastic nipples that scrw in where the external steel lines connect. Little hoses are connected there to the plastic nipples, and run right back into the reservoir. You can buy short steel lines cheap at the parts store, cut them in half so each connects to a port on the MC, and get the same results. With the MC clamped level in the bench vise,fluid in the reservoir, pump gently with a screwdriver, full stroke, to push all the air out. Then bolt it into the car, pull the bench-bleed lines, and connect the car's lines. When I have lines disconnected from a MC, I cap the steel lines with rubber vacuum-port caps. Keeps the fluid in and dirt out.

risaac928

Ok, Dr. Bob looks like I am going to have to pull that MC and bleed it...suxs

Do I need to pull the MC to bleed? Cant I fix some sort of cap the the top the plastic reservoir and vacuum it from there?

If I do need to pull it...there are 5 lines if I am not mistaken for the MC 2 on each side and one up front.

I guess I will plug each line up with one of those plastic nipple screws. Then pump the MC...

Is it possible to have the reservoir and MC intact and installed on to the Brake Booster. IDK thats a tight fit, I remember I had to install the MC first then pop on the plastic reservoir.

pjg

Has Dr Bob mentioned you can get some short steel brake lines from the auto parts store and connect as seen in the picture to bleed the MC.
If you have the old MC bring it with you to ensure you get the right size brake lines.
No need to remove MC, make sure the steel lines stay submerged in the brake fluid reservoir.

risaac928

Thanks, pjg - That helps alot....

Now the MC has 5 lines....2 on the left and 2 on the right and 1 up front.

Once I got the set up as show in the picture, I will just pump the break peddle until no more bubbles? Right....

I will do this for each side of the MC and the front...right.....?

risaac928

Okay, forum take a look at this video....

I have no to little brake pressure. I have to pump the brakes to get any stopping power.

Is there a way to take off those brake lines without have to remove the reservoir or taking the MC out...

The last time I pulled the MC out it was a pain....I had to take reservoir out just to get the back bolt out that one brake line on the inside of car.

Do you think I need a new MC?

dr bob

The idea of the bench bleed is that you can get the MC attitude so that the bubbles get pushed out the ports. You haven't been able to do that with the MC in the car, no reason that that will change, right? On the car, you can do just as well with standard pump-the-pedal bleeding.

Start off with pressure bleeding the system with a real pressure bleeder. The MitiVac won't do it. The cute little Motiv works just fine.

More to think about: A system with a little air in it can be at least partially pumped up with rapid repeated pumping of the pedal in the car. If you can't find any braking with that, you need a master cylinder.

risaac928

Okay forum I think I found the problem....and I quote....

"Installing
1. Renew the O-ring between the master brake
cylinder and the brake booster, or else a
loss of vacuum may occur."

When I took the MC out the first time there was no O RING.....WTF.....thats why I hear air coming from behind the MC.

How did I uncover this....PET CD...of course...

dr bob

That will solve a too-hard-pedal problem, not the soft- or no-pedal problem you mentioned originally. Vacuum leak just means less booster effect, plus the engine will likely idle poorly. Put the o-ring in by all means, but this isn't likely your problem.

risaac928

Bought a new MC and sure enough now the 928 stops. No more pumping brakes to stop.