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914World.com _ 914World Garage _ Excessive pedal travel on rebuilt S callipers
Posted by: phillstek Apr 8 2013, 04:54 PM
Just finished rebuilding the front callipers with new pistons and seals. Bled them 3 times including power bleeding but the pedal just won't come up. It feels like half the available pedal travel is in free motion before the brakes engage.
Car stops without pulling or locking up and the pedal pressure holds when stomping on them but I would prefer to have the pedal engage pretty much as soon as I hit them.
Any suggestions on possible cause and what I need to do to fix it?
Thanks
Posted by: mepstein Apr 8 2013, 05:19 PM
Have you bled the MC?
Posted by: '73-914kid Apr 8 2013, 05:21 PM
Is it a nice firm pedal once they do engage? And is it a freshly rebuilt pedal cluster?
There is an adjustment at the brake pedal to extend the arm into the MC a little farther. If you have a really solid pedal, that is where I would look.
Posted by: 904svo Apr 8 2013, 05:21 PM
Does the brake pedal return all the way? The brake light switch may be stopping it now.
Posted by: phillstek Apr 8 2013, 06:16 PM
Thanks for the replies.
Have you bled the MC? Yes.
Is it a nice firm pedal once they do engage? And is it a freshly rebuilt pedal cluster? Yes and yes.
Does the brake pedal return all the way? Yes
I rebuilt the rear callipers about 2 years ago and replaced the brake lines, re-bushed the pedal cluster and installed a new b/f reservoir as well. I don't know why but I left the fronts callipers alone. Brakes were great for the first 250 miles of driving with proper pedal feel etc. The pedal went bad when taking the car for an extended road test and required pumping to get pressure and the right front was wanting to lock up when applying the brakes hard.
Determined that both fronts were leaking and discovered some incorrect pistons had been installed earlier by someone unknown. Got some correct replacement pistons from PMB, put those in along with new seals, pads and rotors.
The car pulls up really well without pulling left or right it's just that micro second of doubt when hitting the brakes and thinking "are they there"
I'll do a full inspection on the weekend and see if I can work it out.
Posted by: THE STIG Apr 8 2013, 06:21 PM
I just ran into the exact problem, went from a Brembo 4 piston to 911S calipers on my Vintage Race Car. No rebuild on the S caliper, but exact same problem. Pedal with the Brembos was rock hard and immiediate. Switched to the S calipers, had to adjust brake plunger inward to get the same pressure point for heel/toe purpose, and now have to bleed the brakes after every 30 minutes session. They get bad. Have brake cooling as well, so I know its not OVER heating. I know the previous owner installed stainless steel pistons, and car was for AX use only. Rarley had to bleed them with the Brembos. Maybe after a test, qualify and race, they would need to be bled. They do stop the car, stops straight, but why the pedal feels different is a mystery. Its possible that the known flex in the caliper body is the cause of this, but you can feel it sitting in the car, stopped with no pressure applied. Pedal travel increased because of a caliper makes no sense. I also experienced great difficulty with bleeding the 911S caliper. Fluid runs air free while bleeding, but they just never feel good. Most folks say that is just they way thay are. What I do know for sure, is that I could run anything else on my car, I would.
THE STIG
Posted by: laflaur Apr 8 2013, 06:37 PM
Did you check the venting clearances on the rears yet?
Posted by: THE STIG Apr 8 2013, 06:58 PM
Did you check the venting clearances on the rears yet?
I think you missed it...only change made to the car was the front calipers, put them on and the pedal travel increased. Not a little, allot. Rear brakes untouched, already set.
Posted by: laflaur Apr 8 2013, 07:06 PM
He is bleeding brakes right?
he emptied the system of fluid?
He should be bleeding the entire system,no?
Posted by: bulitt Apr 8 2013, 07:21 PM
17mm or 19mm MC?
Posted by: phillstek Apr 8 2013, 07:24 PM
He is bleeding brakes right?
he emptied the system of fluid?
He should be bleeding the entire system,no?
Yes, entire system has been bled 3 times,
I haven't had a chance to take it for a decent drive after the rebuild. I've only driven it around the block a couple of times. I'm going to take it out for thorough road test later in the week.
Thanks again for the replies.
Posted by: Eric_Shea Apr 8 2013, 07:35 PM
Yup:
1. Take out the knockback mechanisms.
2. Check the pad clearance on the S-Calipers. New seals will pull the pistons back aggressively. To verify, check the clearance of the pad and rotor.
3. Bed the pads. Multiple times. This will be good for the pads, rotors and the seals. It will help break in the seals.
Once the seals begin to break in your pedal will come back up.
Posted by: sixnotfour Apr 8 2013, 09:00 PM
Posted by: phillstek Apr 8 2013, 11:09 PM
Yup:
1. Take out the knockback mechanisms.
2. Check the pad clearance on the S-Calipers. New seals will pull the pistons back aggressively. To verify, check the clearance of the pad and rotor.
3. Bed the pads. Multiple times. This will be good for the pads, rotors and the seals. It will help break in the seals.
Once the seals begin to break in your pedal will come back up.
Thanks Eric,
I'll do that, though I didn't use the knockbacks that you sent me.
Posted by: brant Apr 9 2013, 08:25 AM
eric beat me to it...
knock back mechanisms
I vintage race on S calipers and mine are removed.
sometimes the initial pedal is still long
but once you hit it, no more "flex" feeling
I honestly believe that all of the hype over "flexing" is really the spring effect of the knock back mechanism and mis attributed all of these years.
Posted by: rhodyguy Apr 9 2013, 08:50 AM
guys...easy stuff first. haynes, p110, fi. 8.4. "Adjusting the piston rod free play".
Posted by: Cap'n Krusty Apr 9 2013, 09:36 AM
Put a few hundred miles on it. BTDT, a LOT of times.
The Cap'n
Posted by: Eric_Shea Apr 9 2013, 03:00 PM
Posted by: THE STIG Apr 9 2013, 09:38 PM
eric beat me to it...
knock back mechanisms
I vintage race on S calipers and mine are removed.
sometimes the initial pedal is still long
but once you hit it, no more "flex" feeling
I honestly believe that all of the hype over "flexing" is really the spring effect of the knock back mechanism and mis attributed all of these years.
Opened them up tonight, found these knock back mechs in place, and a rolled piston seal. That'll do it. Ordering kits from FPS tomorrow.
Who are you running with? Just did my first HMSA Club Event at Laguna. I had a blast.
THE STIG
Posted by: brant Apr 9 2013, 10:24 PM
eric beat me to it...
knock back mechanisms
I vintage race on S calipers and mine are removed.
sometimes the initial pedal is still long
but once you hit it, no more "flex" feeling
I honestly believe that all of the hype over "flexing" is really the spring effect of the knock back mechanism and mis attributed all of these years.
Opened them up tonight, found these knock back mechs in place, and a rolled piston seal. That'll do it. Ordering kits from FPS tomorrow.
Who are you running with? Just did my first HMSA Club Event at Laguna. I had a blast.
THE STIG
RMVR, CVAR, and HMSA
I hope to be at the June legends event at laguna
send me a pic of your car?
what are the specs and details of your car?
it would be great to meet... any chance your going to the June Legends event?
brant
Posted by: THE STIG Apr 9 2013, 10:33 PM
Hoping to make the Legends Event! Its my plan. I may try to attend Coranado Festival of Speed. Considering Portland...Wanted to be a Laguna today, but the one day deal kinda was a show stopper, being in the middle of the week. I have a SONAUTO replica. One thing I learned at this last event...how FUCKING fast Cobras are...
THE STIG
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Posted by: brant Apr 9 2013, 10:44 PM
Coronado is absolutely awesome
I've been the last 2 years and just had a blast
here is my picture thread from http://www.914world.com/bbs2/index.php?showtopic=195372&hl=coronado
Posted by: THE STIG Apr 9 2013, 10:57 PM
I'll check it out. Are there any good boards for Vintage Racing? Or where Vintage Racers hang on the web? Seems like a really good Alfa following with VARA SoCal. They ran with HMSA when I was there. A GTA was hit by a 2002. It was bad. Hope it never happens to me...but it can. I made some friends in the Alpha community while I was there. Guy I went to SCCA Comp School with has the Barber Shop GTA. I even got passed by Jon Norman. There are some photos of the HMSA event on Sports Car Digest. One shot of me in the top of 8 @ Laguna.
THE STIG
Posted by: brant Apr 9 2013, 11:02 PM
I'll check it out. Are there any good boards for Vintage Racing? Or where Vintage Racers hang on the web? Seems like a really good Alfa following with VARA SoCal. They ran with HMSA when I was there. A GTA was hit by a 2002. It was bad. Hope it never happens to me...but it can. I made some friends in the Alpha community while I was there. Guy I went to SCCA Comp School with has the Barber Shop GTA. I even got passed by Jon Norman. There are some photos of the HMSA event on Sports Car Digest. One shot of me in the top of 8 @ Laguna.
THE STIG
I haven't found them... but if you do please pass along the info
I've been hit 3 times now.. not a fun thing at all
the worst was by a stupid miata that took out my front fender, front suspension, door, and rear fender all at once.
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Posted by: THE STIG Apr 9 2013, 11:14 PM
Miata in Vintage? Strange. Disposable car. Great for SCCA, not Vintage. When I was in SCCA school Guy told me if you can't leave the track without what you showed up with you shouldn't be there. I agree, but it would tear me up to lose the car. Its why I like HMSA so much. More of a high speed car show. Sounds like your guys are a bit more aggressive. Also, no modern equipment allowed in HMSA. Car is supposed to be built with a specific date in mind. I like that as well. I do it for the fun of it. Exspensive fun, however.
THE STIG
Posted by: brant Apr 9 2013, 11:23 PM
The miata was with a different sanctioning body than I had never run before.
It is a club called "nostalgia". That was in 2007 and I have never returned to one of their events since.
they were allowing a couple of cars in to fill out their grid
the @#$%% miata driver also owned an alfa vintage car
he was friends with the steward and they let him bring the miata instead of his alfa...
I asked him why he didn't lift when he went off the track and hooked it back on to t-bone me. I dodge into the gravel on the opposite side of the track before he got me but I couldn't get out of the way far enough in time.
not a fun weekend at all
The other 2 accidents were both by the same 356 driven by the same driver in seperate years... I chalk that one up to completely incompetent driver.. he next rolled the car at a California event. I've seen him back, and just avoid him at this point.
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