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914World.com _ 914World Garage _ Front caliper dragging?
Posted by: Wanna9146 May 13 2008, 09:28 PM
I just rebuilt my front calipers, including new pads. Have yet to re-fill/bleed.
On one side, the hub/rotor spins freely with only slight rubbing of the pads. Feels "normal" as compared to other cars I've worked on.
On the opposite side, the hub/rotor does not spin freely. It spins only with some effort.
Both rotors measure the same thickness (a little under 10mm).
Will this issue fix itself once I re-fill & bleed or is something wrong?
Posted by: davep May 13 2008, 10:25 PM
push the pistons in
Posted by: Wanna9146 May 13 2008, 10:27 PM
push the pistons in
I did to get the pads in and they slowly expand to their current position. Again, there is no fluid in the system yet.
Posted by: SGB May 13 2008, 10:30 PM
Will this issue fix itself once I re-fill & bleed
I think so.
Posted by: Eric_Shea May 13 2008, 10:57 PM
Sounds like your knock-back mechanism is hanging on that piston. It may free up when lubricated with the fluid.
Posted by: Wanna9146 May 13 2008, 11:43 PM
Sounds like your knock-back mechanism is hanging on that piston. It may free up when lubricated with the fluid.
I knew you were going to chime in...you're going to make me take everything apart again, right?
You say it "may" free up, but I would rather disassemble now while it's still clean. Is there a way to free-up the knock-back mechanism once I have everything apart?
Posted by: Eric_Shea May 14 2008, 01:59 PM
Should be a 20 minute fix if that's what you want to do.
Clamp the other piston. Blow this piston out. Inspect the knock-back shaft. Make sure it isn't bent as this can happen when using compressed air to get the pistons out.
Clean and inspect the mechanism in the piston. You probably won't be able to get the assembly out because of the odd-ball clip so just spray and clean with brake cleaner and compressed air. You may want to let the piston sit with brake cleaner filling the cavity. This will helpd disolve some shellaced brake fluid.
You should put some caliper grease on the shaft and reassemble.
Posted by: Wanna9146 May 14 2008, 07:29 PM
Should be a 20 minute fix if that's what you want to do.
Clamp the other piston. Blow this piston out. Inspect the knock-back shaft. Make sure it isn't bent as this can happen when using compressed air to get the pistons out.
Clean and inspect the mechanism in the piston. You probably won't be able to get the assembly out because of the odd-ball clip so just spray and clean with brake cleaner and compressed air. You may want to let the piston sit with brake cleaner filling the cavity. This will helpd disolve some shellaced brake fluid.
You should put some caliper grease on the shaft and reassemble.
Already cleaned it out well before re-assembly.
Assuming the shaft is bent, how to remove? I believe I read in an earlier post that the pin(s) were not necessary. As I mentioned previously, this is a temporary braking system (until I get my 911 stuff installed).
Posted by: davep May 14 2008, 09:08 PM
Or you could try clamping the piston as far back as possible and wait for the knock-back mechanism to slip back on the pin as far as it is able. All the years I have rebuilt calipers I never had this problem. It may well be a bent pin, but is more likely a sticky mechanism. While you can run without the pin, I don't think it is the best long-term solution. Many race car calipers omitted the pin, and many new designs use an inverted piston, so no pin is possible there. Anyway, both the pin+mechanism and the main seal act together to withdraw the piston. That is helped by any runout (wobble) in the rotor.
Posted by: Eric_Shea May 14 2008, 09:37 PM
The pin and knock-back mechanism knock the piston back "toward" the rotor to give a higher pedal feel. That's what the PDF from ATE translated to.
The knock-back mechanism seems to be hanging high on the pin.
I like Dave's idea of clamping it down to see if it stays. When you clamp a piston with a knock-back mechanism down all the way, it "should" spring back about 1/16th of an inch when you remove the clamp. I always look for this when pressing pistons in. Slight spring back means it's working properly. If it's springing back more than that you have a problem.
Vise Grips
Posted by: Wanna9146 May 14 2008, 10:45 PM
I'll give it a go.
As I mentioned, this set of calipers isn't permanent. I will be swapping everything over to 911 brakes in the near future. I just need brakes right now to move the car around and take it to the shop.
Posted by: Wanna9146 May 16 2008, 08:36 AM
push the pistons in
Well...that was it. I removed the caliper and squeezed in the pistons a little further with a c-clamp. They stayed in position and all is well.
Thanks again everyone!
Posted by: !Wet Spot! May 16 2008, 10:08 AM
You checked the front wheel bearing?
Posted by: Wanna9146 May 16 2008, 03:06 PM
You checked the front wheel bearing?
Yes, bearings/run-out is fine.
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