master cylinder question

quick question, and i do apologize if im beating a dead horse here. Ive just installed ss brake lines hoping to replace that spongy feeling in my pedal, and for the most part they made a difference. I bled the system and noticed i still need to do a bit of a double pump to firm the brakes up. No leaks in the system that i can see. New calipers up front, done several thousand miles prior to ss brake lines, with pads and rotors. The brake fluid has been flushed when i did the calipers, and also when i installed the lines. I bled the system alone, correctly. Truck has 165k. Prerunner dc v6. Also, if i put my foot on the pedal, it SLOWLY sinks (while the truck is on). Im assuming my mc is the problem, but could it be something else? Power booster? And to clarify i even bled the, for lack.of a better term, proportioning valve thing in the rear. I should note that when I did the calipers I bled the system with a friend and cannot say for certain that he didn't keep the pedal from going all the way down. Any and all help is appreciated!

 

Master cylinder would be my best guess, as well.

 

It sounds like you're uncertain about getting air in the lines. Maybe consider just taking it into a shop to have the fluids flushed out again and eliminate all possible air bubbles trapped in the system.

 

Just got done doing the lines and master cylinder on mine as well. I had a hell of a time bleeding the system after I changed the MS. I ended up vacuum bleeding each corner to get all the air out. I figure I went thru a qt of brake fluid to get it done.

I had the soft pedal, slowly go to the floor thing going on after I changed the MS. I would make sure that the lines are good and bled before dumping $117 into a new MS.

 

The braking system is sealed....

So, if your truck is in park....and you step on the brakes hard and the pedal slowly sinks (even with engine off)- You've probably got a leak somewhere. Could be small and minor ...but any leak is bad and allows air into the lines.

I would first check your SS brakeline install. Did you use NEW crush washers?
(copper washers that sit between the block & caliper)

You should get a buddy to stand outside the vehicle to 'listen' as you press your foot on the brake pedal (as it sinks) with engine off. Your buddy might be able to hear a faint hissing.

 

Whenever I have a brake pedal that stops the vehicle but continues to go slowly to the floor I replace the master cylinder to fix the problem (fluid leaking past the cylinder).

 

yep, if you have no leaks and you are sure the lines have been bled of air, if the pedal sinks on you the seals in the master cylinder are letting fluid bypass them internally or sometimes out the back of the master cylinder rod into the truck or brake booster so replace your master cylinder quickly before you lose brakes altogether.

if you redid your brake lines already then if it were me I would take this time to convert to a 2 reservoir master cylinder so that the front and rear brakes work separately from the same imput so if you lose one side (front or back) you still have the other to stop with. its a much safer setup that way.

like this:http://www.auto-repair-help.com/automotive_maintenance/master_cylinder.php

just find a Toyota car or suv with the double chamber master cylinder (im thinking 4runner or highlander maybe) and hook up your lines for a great safety upgrade at the same time you need a master cylinder anyway

I would like to do this brake upgrade myself so if you find out for sure which of the Toyotas have the 2 chamber master cylinders let me know

 

Sorry i was out of town. Thanks for all the advice and replies. I think ill bleed the system again before i replace the mc. Though im almost certain that it's air free. Yes i used new crush washers with the ss lines. And i should have mentioned the brakes are nice and firm when the truck is off. I will look into the dual resevoir idea, that sounds like cheap insurance to me. Im suprised toyota didn't do that in the r&d department. Thanks again.

 

So, im gonna revive my old thread... I plan to do the tundra swap after more or less just discovering it. Ive read a shit ton of info, and for the most part get it all. Question is, i plan to change my master, is there a tundra, t100 brake master cylinder that bolts right on? Im almost positive Its the culprit, and i dont mind. Plus, what size bore do the 2004 tacoma 4 door prerunner trd mc's have! Im not apposed to a bolt on wildwood either, which would have just a wee bit bigger bore. Any and all help is appreciated...

 

I don't recommend a non-standard MC until you talk to someone who has actually done that particular swap.

Years ago, when I had a 22R rig, I did a swap to a larger bore MC because of recommendations by total strangers on the internet, who suggested it, without any actual experience. It was a disaster. My brakes instantly went from good to horrible, because of the larger bore. That initial test spin was scary. I immediately went down to NAPA in my wifes vehicle and bought another MC that was meant for my rig. My brakes were restored.

If you know anything about hydraulics, you know that a larger bore can push more volume, but at less pressure.

 

Oh believe me,im not gonna do that till I get enough info. If i do it at all. I just figured since the tundra calipers hold a bit more, maybe it wouldn't hurt to upgrade the mc in that aspect.. Thats why im asking on this thread

 

OP did you ever do the swap?