wice.lt

So if I find that one Channel of my MC is "spongier" does that mean I should be looking for a new or used MC and if used does anyone have one for sale. Also how involved is MC swap?

austin944

It worked fine for me with all of the outlets blocked using the pipe plugs, the engine running, the car stopped, and me pressing very hard down on the brake pedal. With the teflon tape there were no leaks at the MC and no sign of looseness in any of the plugs after I removed them. The brake pedal was unbelievably hard with all the outlets blocked.

You may be right about the fitting, but I did it several times with the plugs I had and nothing came loose.

(You would have to block all of the outlets to test the master cylinder, wice.lt. Actually, I would consider this test method to be the last resort, it is kinda messy and potentially dangerous if tinman is right).

wice.lt

<austin944>
But what will this test tell me??? If it's still spongy then it's bad and if not then problem is somewhere else? Am I understanding it right. Thanks in advance.

austin944

If you block off one outlet and the pedal becomes harder as a result, then you know the problem lies in that circuit that was blocked off. Then you can manually inspect that circuit for any problem. Otherwise if the pedal is still spongy, then you need to block off more outlets until the brake pedal firms up.

With all the outlets blocked, if the pedal is still spongy then the problem is most likely the master cylinder.

Here are some easy things you can check before doing this "last resort" diagnosis that I described:

1) Are there any leaks? Start the car, and keep the brake pedal depressed hard.
2) Have you tried bedding in the pads?
3) Were you getting any air sucked in around the caliper bleed screws during the bleed process? They are notorious for doing that.
4) Is the fluid aerated? Are there a lot of tiny air bubbles in the fluid?
5) I forget, but can you separate the caliper halves on the 944? I believe this is a big no-no because it can cause the caliper to leak.
6) Did you happen to allow any air to get into the master cylinder?

wice.lt

<austin944>
As far as I can tell there are no leaks, because everything looks clean and I have tried pushing the pedal hard.
I did try to be very easy on my brakes (still am) and don't go to a complete stop after that.
I think the answer to #3 and #6 is no, because last time I bled them I used the power bleeding method with my Motive.
Fluid should not be aerated because it sat on the shelf fore few weeks after shipping and I didn't shake it, so I think not aerated would be it.
#5 944 NA has only one half since it's one piston and I had to rebuild it so it was all disassembled.
I think I will have to just replace the MC unless someone will come up with another idea. I mean my brakes are OK they just don't feel very strong, so I can still enjoy my car

RedlineMan

Hey Wice;

Austin is giving some good advice here. Let me chime in with something other than ranting!

I see you had the calipers apart. Did you bench bleed everything? Brake components that are clean and dry internally can cause problems. You have a situation where there is a high degree of surface tension, meaning when the surface is dry (like new or very clean), air bubbles will "stick" to that surface, and it can be incredibly hard to dislodge them. Take a brick and dunk it in a bucket of water. Look at all the air bubbles that stick in the crevices. Same with brakes, because not all the internal surfaces are machined smooth! ALWAYS, ALWAYS, ALWAYS wipe things down with fluid before assembly, and then bench bleed everything first.

Check to make sure all of your lines are still fastened to the chassis. Some of these old buckets have had a lot of the line holders broken off or unhooked, and this can lead to increased mush in the peddle.

Did you ever try bleeding with the tail as high in the air as it could go? It is not common, but sometimes air can get into the nose of the MC and it is virtually IMPOSSIBLE to get out otherwise. When you tip the car up, the air comes back into the cylinder and will be forced out a line. I would never bleed the MC as you did, as I think you are just asking for trouble. Raise the tail and bleed through the bleed screws and you will be fine.

All that stuff is occasional stuff. HERE'S THE BIGGIE, and where I'm putting my money.

You replaced pads AND rotors. This is a recipe for lousy brake performance for SURE. New rotors are not polished smooth like used ones. They need to be burnished with a proper bedding process. New pads also need a proper bedding process, and this is very specific. New pads are full of all kinds of resins and oils from production that need to be heated up and burned off. The last part of this is developing an even transfer layer of pad material onto the rotor face. This is actually what does most of your stopping for you, and it is very near impossible to do properly with rotors that have not been burnished.

Doing either rotors or pads requires proper break in procedures. Doing both at once is NOT recommended. Until those rotors are burnished, and the pads bedded, your brakes will SUCK.

I suggest two things. First, put some old pads in and burnish your rotors. Then, once the rotors are ready, put the new pads in and bed them on the burnished rotors. Second, go to http://www.stoptech.com/technical/ and read the excellent articles on how brakes work. You'll be very surprised at how much you didn't know, and be an expert when you are finished!

Oddjob

I used the identical little brass plugs that austin is talking about, chasing the same problem in my 944S a few years ago. Had a spongy pedal and after rebuilding the calipers I was convinced it was a bad master cylinder. So swapped it out and still had the problem. Then thought it was something with the vacuum assist or this or that, whatever, caused me quite a headache. Ended up putting the pipe plugs in and got a firm pedal, so that told me that master cylinders were fine and the vacuum assist was working properly. Came down to air in the lines. And it just kept getting worse and worse the more parts I pulled and replaced, just introduced more air into the system. Finally after mutiple bleeds I finally got the brakes to work like they should. So you might want to start with a quart of fluid and just start flushing the system before you start replacing more parts. Also, try to find another car in your area to drive for comparison.

EDIT: John also made an excellent point above in reference to pad and rotor glazing. Make sure you also dont have that problem before buying additional and expensive parts.

joonas

I also did rebuild on all my 944S calipers and after job was done brakes felt like really spongy. I was very sad. So i just drove with those spongy brakes for a while and they started to get better. I think that fresh seals want time to seat correctly before you get hard pedal response. My advice, drive it for a week and lets go on from there.

TheRealLefty

Wow you guys have covered some ground since I last logged in (and covered the ground with some pretty thick stuff while you're at it.) Agreed that everyone here is pretty much saying the same thing. Allow me to summarize some basic points that make sense to me:

1) Porsche 944 NA brakes are good units and anyone driving an NA with nearly original power whose brakes do not function well in light track, autox or street situations likely has some other issue with their braking system than the design of the calipers. They are well matched to the performance envelope of the NA engine. As power increased through additions to the model line, Porsche increased the sophistication of the brakes accordingly, which is not a condemnation of the original spec brakes.

2) The biggest advantage of upgraded brakes, be they beefier factory applications on faster, heavier 944 variants or modern aftermarket kits, is their resistance to fade and ability to handle heat under competition/hard driving conditions. To that extent, any car that is going to be driven hard under track conditions can benefit from thoughtfully upgraded brakes.

3) The real limiting factor to ultimate braking power is rubber vs asphalt and anyone who cuts the wheel hard while jamming on the brakes won't get much stopping power out of the one overworked corner of the car they're throwing all the weight toward no matter how much they spend on their brakes. For most of us, other factors, like improved driver skills, brake bias adjustment (33/5 valve rocks), optimized front/rear ride heights and anti-dive chassis tuning will do more to reduce stopping distances than upgraded rotors and calipers.

4) The point has been also well made that a 944 NA racer is looking to use his/her brakes as little as possible and make maximum use of momentum. 944's can go fast by not diving as deep, getting a smooth line in the middle of turns and inducing a little bit of "loose out" attitude by applying throttle in mid turn. We need to be on the go button as much as possible Successful 951 and 951S racers learn a different approach to going fast, waiting longer, using their brakes harder and diving more deeply into turns to make the most of the their end-of-straight-stretch boost. 951 models seem to respond better if they can pirouette the nose at the end of the braking zone and get it pointed toward the exit line before they reapply power since many LSD equipped Turbos tend to track out at a tangent if power is applied while turning. Vastly different animals in terms of the most advantageous way to use brakes and throttle. I've seen many 951 rockets square off turns that 944's consider sweepers and make two turns out of one with their brakes in order to avoid mid turn "rear end hook up" that pushes them wide on exit.

A fast 951 racer will generally be much harder on brakes than a 944 guy. Both drivers are doing the "right thing" to get the fastest lap time from their car and both are enjoying adequate braking performance to accomplish their goals.

wice.lt

Thanks for all of your input I really appreciate being a part of great rennlist community. Let's keep it up.
Seems that I really just have to start driving it for a while (I have other cars for daily drivers) and then see what happens. I will make sure I will bed the brakes and then maybe bleed them once again.