Left Rear Caliper getting air in
02-26-2019, 02:35 PM
#1
Advanced
Thread Starter
Left Rear Caliper getting air in
Hi,
I am having a consistent issue with the left rear caliper on my 70 Vette with manual brakes. This started last summer when the brake pedal started fading and I thought it was the master cylinder. I changed it out but the problem didn't go away. I thought I wasn't bleeding it properly so after a long time bleeding the entire car I finally capped of both ports on the cylinder and the pedal wouldn't move. That told me it wasn't the master cylinder. I then clamped off the flexible lines at all 4 wheels and isolated the issue to the left rear. I got a remanufactured caliper, bled it and the pedal was rock hard. After driving the vehicle for a few times and one hard braking event the peday was fading and finally had no pressure. It turned out again to be that caliper so I got another remanufactured caliper, bled it, and it did the same thing. Rock hard for few rides until a hard, not real hard, braking event and again the pedal started fading. Actually I forced the hard braking event to see if the problem was still there. I am not sure what to do. I plan to replace the caliper line and the flexible line but I don't really expect that to be the issue. Should I buy a bran new caliper? Is there something I'm missing. Please help as the new driving season is coming soon and this problem is frustrating me.
I am having a consistent issue with the left rear caliper on my 70 Vette with manual brakes. This started last summer when the brake pedal started fading and I thought it was the master cylinder. I changed it out but the problem didn't go away. I thought I wasn't bleeding it properly so after a long time bleeding the entire car I finally capped of both ports on the cylinder and the pedal wouldn't move. That told me it wasn't the master cylinder. I then clamped off the flexible lines at all 4 wheels and isolated the issue to the left rear. I got a remanufactured caliper, bled it and the pedal was rock hard. After driving the vehicle for a few times and one hard braking event the peday was fading and finally had no pressure. It turned out again to be that caliper so I got another remanufactured caliper, bled it, and it did the same thing. Rock hard for few rides until a hard, not real hard, braking event and again the pedal started fading. Actually I forced the hard braking event to see if the problem was still there. I am not sure what to do. I plan to replace the caliper line and the flexible line but I don't really expect that to be the issue. Should I buy a bran new caliper? Is there something I'm missing. Please help as the new driving season is coming soon and this problem is frustrating me.
02-26-2019, 03:18 PM
#2
Le Mans Master
Rotor
I would use a dial indicator on the rotor and measure the run out. Factory settings say over .008 is excessive and will "pump" air back into the brake system. Most rebuild vendors try to keep run out at between .001 and .003. I have corrected run out by adding shim stock to the backside of the rotor until the run out was acceptable. You could also have a bearing going south as well. You can Google the topic on You Tube and you will see what I am referring to. Lastly, if your rotors have been cut to deeply, they can also warp causing your problem. Good luck. Jerry
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bill69 (03-11-2019)
02-26-2019, 04:08 PM
#3
Drifting
Hi,
I am having a consistent issue with the left rear caliper on my 70 Vette with manual brakes. This started last summer when the brake pedal started fading and I thought it was the master cylinder. I changed it out but the problem didn't go away. I thought I wasn't bleeding it properly so after a long time bleeding the entire car I finally capped of both ports on the cylinder and the pedal wouldn't move. That told me it wasn't the master cylinder. I then clamped off the flexible lines at all 4 wheels and isolated the issue to the left rear. I got a remanufactured caliper, bled it and the pedal was rock hard. After driving the vehicle for a few times and one hard braking event the peday was fading and finally had no pressure. It turned out again to be that caliper so I got another remanufactured caliper, bled it, and it did the same thing. Rock hard for few rides until a hard, not real hard, braking event and again the pedal started fading. Actually I forced the hard braking event to see if the problem was still there. I am not sure what to do. I plan to replace the caliper line and the flexible line but I don't really expect that to be the issue. Should I buy a bran new caliper? Is there something I'm missing. Please help as the new driving season is coming soon and this problem is frustrating me.
I am having a consistent issue with the left rear caliper on my 70 Vette with manual brakes. This started last summer when the brake pedal started fading and I thought it was the master cylinder. I changed it out but the problem didn't go away. I thought I wasn't bleeding it properly so after a long time bleeding the entire car I finally capped of both ports on the cylinder and the pedal wouldn't move. That told me it wasn't the master cylinder. I then clamped off the flexible lines at all 4 wheels and isolated the issue to the left rear. I got a remanufactured caliper, bled it and the pedal was rock hard. After driving the vehicle for a few times and one hard braking event the peday was fading and finally had no pressure. It turned out again to be that caliper so I got another remanufactured caliper, bled it, and it did the same thing. Rock hard for few rides until a hard, not real hard, braking event and again the pedal started fading. Actually I forced the hard braking event to see if the problem was still there. I am not sure what to do. I plan to replace the caliper line and the flexible line but I don't really expect that to be the issue. Should I buy a bran new caliper? Is there something I'm missing. Please help as the new driving season is coming soon and this problem is frustrating me.
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bill69 (03-11-2019)
02-26-2019, 05:56 PM
#4
Melting Slicks
I would use a dial indicator on the rotor and measure the run out. Factory settings say over .008 is excessive and will "pump" air back into the brake system. Most rebuild vendors try to keep run out at between .001 and .003. I have corrected run out by adding shim stock to the backside of the rotor until the run out was acceptable. You could also have a bearing going south as well. You can Google the topic on You Tube and you will see what I am referring to. Lastly, if your rotors have been cut to deeply, they can also warp causing your problem. Good luck. Jerry
This is usually caused by excessive runout in the rotor.
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bill69 (03-11-2019)
02-26-2019, 08:32 PM
#5
Le Mans Master
Member Since: Nov 2003
Location: Maryland
Posts: 5,661
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St. Jude Donor '05, '09, '15
A little spendy but premade shims are available.
https://www.napaonline.com/en/search...h_form-allprod
Tom
https://www.napaonline.com/en/search...h_form-allprod
Tom
03-11-2019, 10:18 AM
#6
Advanced
Thread Starter
The rotor was out by 10 mils so I am replacing them both and I have o-ringed the calipers Once the snow melts and I can drive it, next few weeks, I will let you know if it fixed the issue. Thanks.
Last edited by bill69; 03-11-2019 at 10:19 AM.