17mm vs 19mm Brake Master Cylinder, again! Options

[davep]

That is way too much free play. I think spec is 1-2 mm; just enough that it is not touching.

[87m491]

A quick adjustment of the push rod to ~1mm spec and as I suspected, all that did was bring the pedal "hitting a wall" a few mms closer to the driver! For all intents and purposes it seems as if the MC is frozen which I guess is possible given the length of time of non use but it was also full of fluid as the brakes were fully bled after install.

And if trully the case, amazing I had what little braking I did have.

Next item will be removal of MC and bench inspect/test.

That is way too much free play. I think spec is 1-2 mm; just enough that it is not touching.

[87m491]

Finally got into the hydraulics to see if the MC was frozen up. Seems as pliable as the day I installed it. I removed and inspected, then bench bled and reinstalled. Several times actually as getting the pedal cluster and push rod fit is a bit of a PITA with only one person. Quick try and the brake pedal total travel was still only about an inch and like pressing into a brick wall!

I decided time to check to see if the front pistons are seized from sitting. Took quite a bit to get the front wheels off as I had the wheels powder coated years back then installed and sat. Turns out he powder coater had not taped off the hub bores so they easily went on with a torque wrench, not so easy off.

So the front calipers came with brand new pads which I had installed as a unit. So there was no way to tell if the pistons were moving. I pulled the pads and inserted some used ones I had that were about 1/2 worn. I installed those on both fronts and pressure bled all calipers and all ports. With a number of pedal pushes the pistons sat the pads right snug to the rotors.

The MC works and the front calipers are fine. Took the car for a ride and while pedal travel is now "normal", braking is still underwhelming, car will not lock up but pedal pumping indicates there is still some air in there and the rears are dragging noticeably need to be readjusted for proper clearance.

The original problem seems solved, though not sure why, now seems down to a better more thorough bleed and rear adjustments.

A quick adjustment of the push rod to ~1mm spec and as I suspected, all that did was bring the pedal "hitting a wall" a few mms closer to the driver! For all intents and purposes it seems as if the MC is frozen which I guess is possible given the length of time of non use but it was also full of fluid as the brakes were fully bled after install.

And if trully the case, amazing I had what little braking I did have.

Next item will be removal of MC and bench inspect/test.

That is way too much free play. I think spec is 1-2 mm; just enough that it is not touching.

[VaccaRabite]

Bleed more. Use a power bleeder to pressurize the system. Start with the caliper furthest from the reservoir and use a longish tube going from the caliper bleeder valve to our catch can. The idea is that you want to be able to watch for bubbles in the tube.

Make SURE (like 100% positive sure) that your bleeder valves are on TOP of the caliper. Calipers can be put on the wrong side, which puts the bleeder low, and will ensure you never are able to get all the air out.

Tap the proportioning valve with a mallet to help free up the air trapped in it.

When a 914 is set up right it STOPS. Using a 19mm cylinder does not impair that. Like many here, I'm also using the 19mm and porterfields and my car STOPS.

Zach

[87m491]

Looking forward to it. As mentioned did use a power/pressure bleeder. All my calipers are 2 bleeder types, top and bottom. Have not check the prop valve yet. But we are running which is good.
(IMG:http://www.914world.com/bbs2/uploads_offsite/i.imgur.com-14731-1692026776.1.jpg)

Bleed more. Use a power bleeder to pressurize the system. Start with the caliper furthest from the reservoir and use a longish tube going from the caliper bleeder valve to our catch can. The idea is that you want to be able to watch for bubbles in the tube.

Make SURE (like 100% positive sure) that your bleeder valves are on TOP of the caliper. Calipers can be put on the wrong side, which puts the bleeder low, and will ensure you never are able to get all the air out.

Tap the proportioning valve with a mallet to help free up the air trapped in it.

When a 914 is set up right it STOPS. Using a 19mm cylinder does not impair that. Like many here, I'm also using the 19mm and porterfields and my car STOPS.

Zach

[87m491]

I finally got back to these over the 3 day weekend. This time I went old school 2 person style vs power bleeder last time. After 3 clean pumps and bleeds on the rears, the 4th pump, on each side oddly enough, produced a mini geyser of air bubbles! (so much so that the low fluid/low pressure warning light from the MC switch was set off!) i continued the bleed to the fronts which seemed fine.

Long story short, the pedal is right there. 1mm engagement and maybe 1.5 inches. total pedal play the brakes engage right off. Effort is high but fine for me just no linearity all all in pedal effort and stopping urgency. As of now there is no possibility of locking them up, at any pedal pressure or at any speed down to walking speed.

I'll drive it a bit and see if, as PMB says any seals need to wear in etc. but that's where it is at.

Bleed more. Use a power bleeder to pressurize the system. Start with the caliper furthest from the reservoir and use a longish tube going from the caliper bleeder valve to our catch can. The idea is that you want to be able to watch for bubbles in the tube.

Make SURE (like 100% positive sure) that your bleeder valves are on TOP of the caliper. Calipers can be put on the wrong side, which puts the bleeder low, and will ensure you never are able to get all the air out.

Tap the proportioning valve with a mallet to help free up the air trapped in it.

When a 914 is set up right it STOPS. Using a 19mm cylinder does not impair that. Like many here, I'm also using the 19mm and porterfields and my car STOPS.

Zach

[VaccaRabite]

There is weirdness going on for sure.

Is the venting set correct on the rear brakes?

Is there maybe oil or grease contaminating your pads or rotors? Maybe hit everything with a can of brakeclean to make sure nothing is contaminated?

Are your flex lines old? They can collapse in age. Look fine from the outside but are swollen nearly closed on the inside.

Something is wrong. If you have your system fully bled - and it sound like you do - you should be able to lock up your brakes at will.

Zach

[mepstein]

There is weirdness going on for sure.

Is the venting set correct on the rear brakes?

Is there maybe oil or grease contaminating your pads or rotors? Maybe hit everything with a can of brakeclean to make sure nothing is contaminated?

Are your flex lines old? They can collapse in age. Look fine from the outside but are swollen nearly closed on the inside.

Something is wrong. If you have your system fully bled - and it sound like you do - you should be able to lock up your brakes at will.

Zach

(IMG:style_emoticons/default/agree.gif) I’ve had plenty of stock 914’s with stock braking systems that never left me wanting for brakes. The good thing is, it’s a simple system with very few parts. Once you track down the issue, you will be happy with the performance. Don’t give up and definitely replace rubber hoses if you don’t know the last time they were done. Then cut the old ones open and inspect.

[87m491]

I just wanted to give a final update for those who contributed to the thread as like many, I hate unfinished "fixes". I'm likely done futzing and will be driving so maybe a winter project.

Venting on rears likely imperfect as I have not touched them, but pads are engaging thee rears as well as noted on the rotors. All new or rebuilt bits on the front, calipers, pads, rotors and hoses and no lock up. Engagement yes, no lock up.

All flex lines are SS replacements.

Will likely send out press regulator over winter for a rebuild and revisit again in the spring.

Thx All

There is weirdness going on for sure.

Is the venting set correct on the rear brakes?

Is there maybe oil or grease contaminating your pads or rotors? Maybe hit everything with a can of brakeclean to make sure nothing is contaminated?

Are your flex lines old? They can collapse in age. Look fine from the outside but are swollen nearly closed on the inside.

Something is wrong. If you have your system fully bled - and it sound like you do - you should be able to lock up your brakes at will.

Zach

[Shivers]

I just noticed your home state. Rotors and a lot of pads will rust and it takes a while to wear through that rust. I live in CA and after a few years of storage the brakes will be crusty for a bit. Not sure if you had it stored in a climate controlled area or not. Pedal travel and feel sounds familiar.

[bkrantz]

Some speculation:

If you have a firm/hard pedal that does not pump up at all, you probably have the system properly bled.

If the pads are newish, you may still need to bed them. And there is a chance you glazed the pads by being too gentle to start. Ask me how I know. A zero cost process is to lightly sand the pads, reinstall, and then bed them again. And bed them HOT and HARD. You should smell brakes.

Finally, like I mentioned above, make sure the MC is not moving with hard pedal pressure. I had to make a brace for mine.

Like others have said, even with a 19mm MC, 914 brakes work. It took me a year (with a winter season off) to go from weak brakes to good brakes.