Dougs951S

I just finished swapping 951 spindels/hubs/brakes front and rear onto my 86 N/A. Problem is, I broke the inner bleed screw on the driver side rear caliper off. It doesnt leak, but I think its affecting my ability to bleed my brakes. I've now tried to bleed the brakes over a dozen times with my power bleeder, including a few "hot bleeds" and I still have a longer pedal than I'd like. It's obvious the issue is in the caliper with the broken bleeder since my other three rotors are scrubbed bright and shiny, and the one rotor still has surface rust, making it obvious the caliper isnt engaging the pads fully. I can only assume the softness in the pedal is from air still stuck in the caliper. I am unwilling to attempt to remove the screw, and I'm also not interested in replacing the caliper since it will be a non issue soon (I have some even bigger front calipers to put on, and when I do my current fronts will be moved to the rear). Does it sound reasonable that after all that bleeding and running over 1 quart of fluid through the lines, that I still have air caught in the inner half of that one caliper? If so, how should I go about bleeding it? The car stops ok, just not as well as my 951 the calipers came from did, and the pedal isnt nearly as firm as it was on the 951. I can't lock the brakes, whereas the 951 locked up with ease. The only thing different about the two brake setups are that the 951 had the stock 33? bar bias valve, and my NA does not have a bias valve at all since the early NA's (maybe all of them?) did not come with one. Do I have to do something silly like turn the caliper upside down while I bleed it using the outer screw? Since the crossover pipe is on the bottom of the caliper, it seems reasonable to me that there could still be enough air trapped in the top of the inner half to allow enough compression to make my pedal "softish" and make the caliper not grab fully. Turning it upside down might allow that air through the crossover so it can exit from the outer half? Does any of this sound reasonable?

This brake swap has been a huge PITA and all I wanted was better braking, but with the pedal being half-***, they stop about as well as my NA brakes with completely worn down pads. (say what you want about NA brakes being enough for an NA, but having DD'ed a 951 for years, the thing I missed most was the firm, immediate brake response that every 951 driver knows is way superior to an NA)

Dougs951S

One more question, in our master cylinders, is it a diagnonal split or front/rear split? It makes even more sense, the issue im having, if its front rear split. that would imply that the brake rod directly actuates the front brakes, but relies on a uncompressible, air free chamber to properly actuate the rear calipers.

Tom M'Guinn

Why? That's got to be the quickest/easiest thing to do...?

Dougs951S

im afraid of destroying the bleeder valve seat and junking the whole caliper. the bleeder is really soft metal and im scared to drill it.

Tom M'Guinn

Have a picture of where/how it broke off?

Player0

Well if you screw up the seat you can always get a larger bleeder

I think if you unbolted the caliper and held the thing at the right angles, you could get all the air out from the outer bleed screw. You'd just need some clever rotation a few times.

Dougs951S

I'm about to attempt just that, my plan is to flip the caliper 180* and then bleed the inner half using the crossover port, then remount and bleed the outer one last time.

rlm328

Go get a replacement bleeder and be done with it. If you are unsure of your ability to remove it without damaging it, take it to a good mechanic and let him do it. You will be faced with doing this Rube Goldberg stuff every time you bleed your brakes if you don't. There are 2 bleeders on there for a reason, you probably have trapped air.

Dougs951S

im nearly positive i have no air now. the brakes lock up and the car stops well, but the pedal feel still isnt as good as my 951 and it takes some force on the pedal to lock up. still air in the caliper, or is that caused by the fact that im not running any proportioning valve?

Techno Duck

Pump the pedal with the car off and it should get fairly stiff, if it doesn't you still have air in the system.

Are you using new pads and rotors? You may not have bedded the pads in enough yet.

Also not having the proportioning valve will cause the rears to lock up easier.

Why not just do this right... ? Brakes are kind of a critical item.

Dougs951S

could my problem be in the master? I did not swap in the MC from the 951 because Im pretty sure its the same as the NA. the pedal feel is basically the same now as it was before the 951 caliper swap. i never thought much of it since none of my Na cars have ever had a super firm, short pedal like my 951. im wondering now if thats not normal and the NA master is bad.

Tom M'Guinn

Try stopping hard with your hands lightly on the steering wheel. If one front side is causing it, the wheel will pull to the other side. If it stops straight, even without bracing the steering wheel, then it's probably not an issue at one front corner. I'd still fix it though...

dizzyj

I'd pull the caliper and get the bleeder out. If you cannot bleed properly then the caliper is junked. Use heat, spray, reverse bits, whatever it takes. Or get a new caliper

Dougs951S

i figured out the problem. everything is bled well, its just that the reason my pedal is longer now is because the NA MC has a smaller bore than the 951 unit. like i said before, the car stops great, pedal is just a bit long but not squishy. I also was able to extract the bleeder using a torch and a left hand bit. thanks everyone.

David Floyd

Wish we had access to larger master cylinders, I installed 996tt calipers on the front of my 951, stops great.....but as you found out.... longer pedal travel than I would prefer.
Going to look at adapting the GT3 mc