Is it possible for a caliper to release too far?, 911 rear brake conversion |
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Is it possible for a caliper to release too far?, 911 rear brake conversion |
tomeric914 |
May 3 2009, 05:32 PM
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#1
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One Lap of America in a 914! Group: Members Posts: 1,263 Joined: 25-May 08 From: Syracuse, NY Member No.: 9,101 Region Association: North East States |
ok, so I converted my 914 rear brakes to vented disc with 911 M calipers and internal drum parking brakes. Brakes work great but the pedal travel is longer than it should be. Went to rebleed everything and found that one of the rear calipers had a pad to disc clearance of .010" which probably explains the travel. Also verified that the pistons were working and not hanging up.
I've got a rebuilt proportioning valve from PMB that is working correctly. Running an ATE 19mm MC (bought a new one thinking it had the 17mm). No bubbles in the system using ATE SuperBlue brake fluid. I've never seen a caliper piston release that far just on one side. Anyone have any ideas? This is frustrating! |
jaxdream |
May 3 2009, 06:43 PM
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#2
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Senior Member Group: Members Posts: 974 Joined: 8-July 08 From: North Central Tennessee Member No.: 9,270 Region Association: South East States |
Do you have the 5mm spacer between the caliper and the mounting bracket on the trailing arm ?? Are you sure they are M's ?? 84 on up 911's used a rear caliper the same size except the middle spacers were 4mm wider for 24mm wide rotor versus the earlier 20mm wide rotor the M's used. Some one else probably knows what else to check. Good luck. (IMG:style_emoticons/default/confused24.gif)
Jaxdream |
Wes V |
May 3 2009, 07:10 PM
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#3
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Member Group: Members Posts: 482 Joined: 11-October 07 From: Los angeles Member No.: 8,211 |
Is it returning that far, right after bleeding, or after a drive.
As I understand it, the 911 rear M's had an "anti-knock back" mechanism within the piston that was to prevent this, if there was excessive wobble of the rotor (due to the fact that you can't snug up the one piece rear bearing). This would only effect you if the run-out (or wobble) of the rear rotor is excessive. Wes |
tomeric914 |
May 3 2009, 08:45 PM
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#4
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One Lap of America in a 914! Group: Members Posts: 1,263 Joined: 25-May 08 From: Syracuse, NY Member No.: 9,101 Region Association: North East States |
Is it returning that far, right after bleeding, or after a drive. As I understand it, the 911 rear M's had an "anti-knock back" mechanism within the piston that was to prevent this, if there was excessive wobble of the rotor (due to the fact that you can't snug up the one piece rear bearing). This would only effect you if the run-out (or wobble) of the rear rotor is excessive. It returns that far just sitting in the driveway pushing on the pedal multiple times and releasing. The wobble is ruled out. Most of the early calipers have the "anti-knockbacks" in them. Knockback or not, they shouldn't be releasing this far. I had an extra .050" shim on the calipers that I took out but that didn't solve anything. I'm down to: A. Tearing apart the calipers, honing the bores, polishing the pistons, putting it all back together AGAIN or buying a pair of rebuilt calipers. B. Something weird going on with the proportioning valve where it is pulling back too much fluid. I doubt this though because it can only pull back as much fluid as I push through it. C. Something weird going on with the master cylinder. D. All of the above |
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