Brakes only work at the bottom

Joined
Jan 23, 2014
Messages
539
Location
Australia
Hi guys, I recently rebuilt all 4 calipers + swapped in a second hand BMC. After bench bleeding the BMC and bleeding the brakes multiple times the brakes only worked at the bottom of the travel so I went and bought a brand new BMC thinking I had a faulty BMC (since it was used). I did a bench bleed + bled the brakes at the calipers (helper method) and the issue still persists. The brakes do nothing for the first half of the travel and only work when the pedal is near the floor. What could this be? And what should my next step be in testing/fixing this issue? Brake setup is from a Mitsubishi FTO in a Mitsubishi Mirage 2001.
 
Joined
Nov 20, 2006
Messages
28,156
Location
MA, Mittelfranken.de
Does this have power brakes? Did you swap the booster? From all you previous post on this I suspect a pedal to booster or booster to MC rod mismatch. Did you swap the booster and are the front calipers the same as on the car you liberated the rear calipers from?
 
Joined
Mar 20, 2006
Messages
2,287
Location
Canada
Originally Posted By: Spetz
the brakes only worked at the bottom of the travel
The master-cylinder pushrod needs to be adjusted. It's too short right now.
 
Joined
Dec 7, 2008
Messages
4,057
Location
Virginia
Since this is a brake swap between different models, wrong master cylinder piston diameter for the calipers being used?
 
Joined
Jul 9, 2017
Messages
116
Location
GA
Had a similar problem on my 51 after swapping from drum to disc. Turned out there was a small leak in the brand new master cylinder.
 

Spetz

Thread starter
Joined
Jan 23, 2014
Messages
539
Location
Australia
Yes it does have power brakes and yes the BMC and booster came in as one unit from the same car so I am not sure if there could be a rod mismatch? I’ve also tried pressing the brake pedal by hand before filling the BMC with brake fluid and could feel the resistance of the BMC so it seems like there isn’t any free play? Why would the pads not be seating against the rotor? The pistons etc all move easily and smoothly as the calipers have been rebuilt with genuine parts. The 2nd hand BMC and booster I installed was a 15/16” that came in a car with the same brakes as I have now. The new BMC I bought is a 1” (a size which also came in cars with the same brakes as mine). The only thing that may not be adjusted properly is the brake pedal free play but I would not expect this to cause such a big issue? At most a few mm or so of free play?
 
Joined
Nov 20, 2006
Messages
28,156
Location
MA, Mittelfranken.de
Did you take the brake pedal rod from the donor car also, That's where I would start looking, it may have used a longer rod depending on how the other cars pedal assembly was mounted
 
Top