A Question About Disc Brakes
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BLB27
Topic author - Posts: 892
- Joined: Thu Jul 23, 2020 9:28 pm
- First Name: Bruce
- Last Name: Brakke
- * REQUIRED* Type and Year of Model Ts owned: 1927 coupe
- Location: Ames, Iowa
A Question About Disc Brakes
Disc brakes have been installed on my 1927 coupe. The pads are tight against the rotor. I can't get a .003 feeler gage between the pad and the rotor. What clearance should there be? What would cause the tight fit?
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pete eastwood
- Posts: 198
- Joined: Sun Jan 13, 2019 6:17 pm
- First Name: Pete
- Last Name: Eastwood
- Location: Southern Califiornia
Re: A Question About Disc Brakes
I build a lot of hot rods, I see problems often occurring with inexperience with "mix & match" brake systems.
the problem may be with the master cylinder.
if the master cylinder has an internal residual valve, (most drum brake m/c have those)
it could be preventing enough fluid from returning to the m/c to release the brakes.
also, check to make sure when the pedal is released, that there is a little free play between the push rod & the master cylinder piston.
the master cylinder piston must return all the way when the pedal is released.
a return spring on the pedal is a good idea.
the problem may be with the master cylinder.
if the master cylinder has an internal residual valve, (most drum brake m/c have those)
it could be preventing enough fluid from returning to the m/c to release the brakes.
also, check to make sure when the pedal is released, that there is a little free play between the push rod & the master cylinder piston.
the master cylinder piston must return all the way when the pedal is released.
a return spring on the pedal is a good idea.
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Craig Leach
- Posts: 1906
- Joined: Tue Jan 08, 2019 12:22 am
- First Name: craig
- Last Name: leach
- * REQUIRED* Type and Year of Model Ts owned: 1919 Firetruck/1922 Speedster
- Location: Laveen Az
Re: A Question About Disc Brakes
Hi Bruce,
What disc brakes do you have? If they are sure-stop brakes I would ask them. Most all disc brakes have no return spring mechanism & rely on a
little rotor run out to give some clearance so if you have not turned the wheel a few turns they will be real close. Are the wheels hard to turn
when the wheel is jacked up? Try jacking both wheels up running the car in gear (block the front wheels ) and shutting it off with out using the
brake with the lever straight up check for a relative free spin ( when the come to a stop ). If they are still hard to turn gently (slowly) open a
bleeder if the fliud squirts a strong stream then there could be a residual valve in the master cylinder or a line. Disc brekes usualy don't need a
residual valve. Drum brakes do if the master cylinder is mounted below the wheel cylinders.
Craig.
What disc brakes do you have? If they are sure-stop brakes I would ask them. Most all disc brakes have no return spring mechanism & rely on a
little rotor run out to give some clearance so if you have not turned the wheel a few turns they will be real close. Are the wheels hard to turn
when the wheel is jacked up? Try jacking both wheels up running the car in gear (block the front wheels ) and shutting it off with out using the
brake with the lever straight up check for a relative free spin ( when the come to a stop ). If they are still hard to turn gently (slowly) open a
bleeder if the fliud squirts a strong stream then there could be a residual valve in the master cylinder or a line. Disc brekes usualy don't need a
residual valve. Drum brakes do if the master cylinder is mounted below the wheel cylinders.
Craig.
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John.Zibell
- Posts: 361
- Joined: Mon Jan 07, 2019 9:09 am
- First Name: John
- Last Name: Zibell
- * REQUIRED* Type and Year of Model Ts owned: 1926 Tudor
- Location: Huntsville, AL
Re: A Question About Disc Brakes
Disk brakes have basically no clearance between the pad and the rotor. The rubber seals on the pistons will retract the pads just enough so the wheel will spin freely with little to no drag. It is like this with cars and motorcycles as well. If the pads remain tight to the disk, the master is not releasing pressure and has issues. Be sure the reservoir is not completely full so the fluid can go somewhere when the brake pedal is released. Also make sure there is adequate free play at the brake pedal or the master can't relieve pressure on the system.
1926 Tudor