Brake pedal goes soft, can be pumped back up, diagnosis? (1 Viewer)

IanB

SILVER Star
Joined
Jan 23, 2010
Messages
4,379
Location
Winnipeg, MB
This started yesterday, go for the brakes and the pedal has resistance, then the bottom just drops out and the pedal needs pumped to get brake power back. Once pumped up the pedal is firm and holds pressure, but once in a while the pedal just goes soft and needs pumped. Is this a failing master cylinder? Brake booster? Check valve?

The brakes were flushed with fresh fluid and bled at the end of August, and had a very firm pedal up until yesterday when this started. Any help is appreciated!
 
Joined
Feb 19, 2013
Messages
390
Likely its a master cyl, autozone sells a great aftermarket that includes a bench bleed kit for about half of dealer if I remember correctly.
 
Joined
Jan 6, 2013
Messages
1,793
Location
Golden, CO
I would guess master cylinder. Bad booster would give you a hard pedal but still have braking power if you push really hard.
 

IanB

SILVER Star
Joined
Jan 23, 2010
Messages
4,379
Location
Winnipeg, MB
That was my suspicion as well, looks like it's a RHD specific part, might have some luck tracking down a used one fairly quickly, but a new one is going to be a few weeks or better, doh!

Is there a way to test it's a bad MC for sure before I start throwing parts at it?
 
Joined
Jan 6, 2013
Messages
1,793
Location
Golden, CO
If you can get it to do it while parked with the hood open you might hear noise in the master cylinder or see turbulence in the fluid in the reservoir.
 
Joined
Jul 22, 2014
Messages
514
Location
Goodyear, AZ
If its too much of a pain in the ass to find another RHD one, you can rebuild the master cylinder pretty easily. I rebuilt the one on my RX7 with an overhaul kit from Mazda.
 
Joined
Jul 22, 2012
Messages
2,009
Location
Ann Arbor, MI
Pumping soft things is a job for @NLXTACY ...

Nobody else caught that in the title? Really?

What is the part number for the RHD master cylinder?
You might be able to just use a LHD and make your own lines from the master.
Rebuilding the seals yourself isn't a terrible job. that shouldn't matter RHD or LHD.
 

NLXTACY

Wits' End
Supporting Vendor
Joined
Dec 7, 2007
Messages
26,771
Location
West Hills, CA
Pumping soft things is a job for @NLXTACY

It was one time! All you had to do was say my name and look up at me with those approving eyes. But no, you insisted on wearing that hideous blue eyeshadow and it reminded me too much of Mimi from the Drew Carey show. Come on man, at least try.
 

SmokingRocks

I bought a Cruiser to keep miles off my Cruiser
Joined
Oct 6, 2014
Messages
3,374
Location
Colorado
master cylinder all day. Easy diagnosis. Just rebuild or replace with aftermarket cylinder.
 

IanB

SILVER Star
Joined
Jan 23, 2010
Messages
4,379
Location
Winnipeg, MB
Ordered a new MC from Milner's Offroad in the UK, tried to go through Akella but haven't heard anything back from him, which is odd. Hoping it's here for next weekend...winter has struck and I'm really missing the truck.
 
Joined
Jun 19, 2010
Messages
2,173
Location
Coquitlam, BC
Humm, he is around as he posted on Instagram this morning.

Hopefully that fixes things! I had a soft pedal at one point but it kinda fixed itself after I changed my seized rear callipers....
 

IanB

SILVER Star
Joined
Jan 23, 2010
Messages
4,379
Location
Winnipeg, MB
Well the MC I ordered from the UK was not the right one (my fault), so I got new OEM one last night and installed it, bled the brakes, and my issues are solved! Truck had been down for nearly a month, I really missed it.
 
Joined
Sep 28, 2014
Messages
627
Location
Atlanta
Mine did this and it turned out I had a hard brake line that had rusted through and was leaking very slowly under hard braking.
 

Users who are viewing this thread

Top Bottom