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914World.com _ 914World Garage _ Brake Noise When Pushing Car Forward
Posted by: Miniwerks Sep 2 2023, 05:31 PM
New to this forum, picked up a very nice Nepal Orange 1976 with under 50k original miles. When I push it backwards in the garage it rolls without resistance, however when pushing it forward I hear the calipers rubbing on the rotors and feel resistance. May need to just drive it more but need to get it registered first. PO did not drive it as it was in his collection with many other Porsches. Other than driving it more, any other possible causes? Seems odd it rolls fine backwards. Looking at service history, PO did have the rear brakes done at 47,421 miles in 2018 and only another 2500 miles since then. Replaced rear calipers, pads and rotors, flushed and bled entire system and adjusted caliper pistons and parking brake.
Posted by: PatMc Sep 2 2023, 05:39 PM
New to this forum, picked up a very nice Nepal Orange 1976 with under 50k original miles. When I push it backwards in the garage it rolls without resistance, however when pushing it forward I hear the calipers rubbing on the rotors and feel resistance. May need to just drive it more but need to get it registered first. PO did not drive it as it was in his collection with many other Porsches. Other than driving it more, any other possible causes? Seems odd it rolls fine backwards. Looking at service history, PO did have the rear brakes done at 47,421 miles in 2018 and only another 2500 miles since then. Replaced rear calipers, pads and rotors, flushed and bled entire system and adjusted caliper pistons and parking brake.
The calipers don't know which way the car is rolling.
I would jack up the rear of the car and spin the wheels, then do the front. Get someone in the car to stand on the brake pedal and see if the wheels release nicely as soon as the pedal is released...if not, time for hoses and / or calipers.
Posted by: Miniwerks Sep 2 2023, 05:44 PM
New to this forum, picked up a very nice Nepal Orange 1976 with under 50k original miles. When I push it backwards in the garage it rolls without resistance, however when pushing it forward I hear the calipers rubbing on the rotors and feel resistance. May need to just drive it more but need to get it registered first. PO did not drive it as it was in his collection with many other Porsches. Other than driving it more, any other possible causes? Seems odd it rolls fine backwards. Looking at service history, PO did have the rear brakes done at 47,421 miles in 2018 and only another 2500 miles since then. Replaced rear calipers, pads and rotors, flushed and bled entire system and adjusted caliper pistons and parking brake.
The calipers don't know which way the car is rolling.
I would jack up the rear of the car and spin the wheels, then do the front. Get someone in the car to stand on the brake pedal and see if the wheels release nicely as soon as the pedal is released...if not, time for hoses and / or calipers.
Great idea, will give that a shot. Thank you.
Posted by: Cairo94507 Sep 2 2023, 06:17 PM
See, if you can, if the rubber lines that go to the calipers have ever been replaced. They get old and swell shut and restrict fluid and cause the brakes to drag. 
Posted by: Miniwerks Sep 4 2023, 11:33 AM
Got her up in the air and all brakes are dragging. I can rotate each wheel by hand but very noticeable scraping sound.
Posted by: fixer34 Sep 4 2023, 11:42 AM
ALL wheels or just rears?
If jusr rears, maybe adjusting screws on rear calipers are too tight?
If all, see above, plus...
Front caliper pistons binding?
Or as someone mentioned, rubber hoses swollen all the way around? Quick test for this, crack the bleeder screws and see if fluid squirts out (rag is handy here..) and then the drag goes away.
May also be maladjusted master cylinder pushrod, not letting the internal pistons back far enough.
Posted by: Cairo94507 Sep 4 2023, 11:44 AM
Are the rotor faces rusted? I still believe your issue could be swollen lines at the calipers.
Posted by: Spoke Sep 4 2023, 06:04 PM
Question about brake pressure: How does one test their brake system if it appears pressure is remaining in the system after the peddle is pressed? Is there a pressure gauge that can be put in place of a caliper to see if after the peddle is pressed the system pressure goes to zero?
Posted by: bkrantz Sep 4 2023, 07:53 PM
Also check for a bit of free play in brake pedal movement, adjusted with the push rod into the MC. If no free play, then the MC can hold a bit of pressure.
Posted by: PatMc Sep 4 2023, 08:33 PM
Question about brake pressure: How does one test their brake system if it appears pressure is remaining in the system after the peddle is pressed? Is there a pressure gauge that can be put in place of a caliper to see if after the peddle is pressed the system pressure goes to zero?
If you suspect residual pressure in the system...open a bleed screw and see if the wheel becomes easier to turn...if it does, you have a residual pressure problem. Now go over and try the other side (same end) and see if it also became easier to turn after having loosened the first bleeder....
if it did, then you have an issue with master cylinder holding pressure due to either the pedal not returning all the way, the pistons in the master not returning all the way, or possible contamination that caused the seals in the master to expand.
If the other wheel is still dragging, crack the bleeder...if it gets easier, you have constricted hoses.
If neither gets easier to turn when you open the bleeders, you have sticking calipers.
Posted by: Miniwerks Sep 6 2023, 09:35 AM
Also check for a bit of free play in brake pedal movement, adjusted with the push rod into the MC. If no free play, then the MC can hold a bit of pressure.
Thank you, will check that as well.
Posted by: Miniwerks Sep 6 2023, 09:36 AM
Question about brake pressure: How does one test their brake system if it appears pressure is remaining in the system after the peddle is pressed? Is there a pressure gauge that can be put in place of a caliper to see if after the peddle is pressed the system pressure goes to zero?
If you suspect residual pressure in the system...open a bleed screw and see if the wheel becomes easier to turn...if it does, you have a residual pressure problem. Now go over and try the other side (same end) and see if it also became easier to turn after having loosened the first bleeder....
if it did, then you have an issue with master cylinder holding pressure due to either the pedal not returning all the way, the pistons in the master not returning all the way, or possible contamination that caused the seals in the master to expand.
If the other wheel is still dragging, crack the bleeder...if it gets easier, you have constricted hoses.
If neither gets easier to turn when you open the bleeders, you have sticking calipers.
Excellent input, will add to the list of checks.
Posted by: Dave_Darling Sep 6 2023, 10:50 PM
It's typical for a car that sits, especially in a humid environment, to develop surface rust on the rotors. Usually a couple of good stops will clean it off. This can also happen in relatively dry environments, even.
--DD
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