Topic: Potential brake master cylinder or other brake-related problem

[chrisfranklin]

For about the last year, have been checking the fluids when getting gas and have had to consistently add brake fluid to the rear, and sometimes the front portion of the brake master cylinder fluid reservoir. 
 
Initially, I chalked this up to pad/shoe wear.  But later, given the number of times I've been forced to top-off the brake fluid, I started to figure that pad/shoe wear could not account for all the fluid I was having to add. 

I checked to see if the cover was seating correctly on the master cylinder and it appeared to be doing so.  Then I looked for leaks in the lines, then looked at the proportioning valve. 

Figured I'd see evidence of leakage -- small puddle -- on pavement directly below the master cylinder, if that was the issue. But never saw anything except for one time.  And in that case, recalled that I may have slightly overfilled the reservoir and inadvertently caused that puddle myself. 

As it stands, am suspecting the brake master cylinder.  Thinking it is the original, circa '93/'94.  Going to have to get a mirror and light or something so I can see the backside of it and examine it for leaks. 

Saw this master cylinder "repair kit" http://www.quadratec.com/products/52449_1206.htm.  What do you think about that?   

 

 

   

[VA_YJ]

Check your rear wheel cylinders for leakage.  Normally, when a master cylinder (mc) goes bad, the pedal will sink to the floor and your brakes won't work very well.  What I described is an internal failure of the mc - it typically does not leak.  The mc can leak on the firewall end, but that is not very common.

[VA_YJ]

One more thing:  The large reservoir on the mc is for front brakes, the small reservoir is for the rear brakes.  The two systems are split, so focus your leak search on the front or rear system, depending on which reservoir you are topping off frequently.

[chrisfranklin]

The mc can leak on the firewall end, but that is not very common.

That's the only thing I could think of.  Maybe the seals on the deteriorated over guessing 18-19 years.  Started using synthetic Dot4 brake fluid about 6 years ago. 

Read that the proportioning valve tends to rarely leak also. 

Will take a look at, like you said, front and rear system, VA_YJ thx

[sharpxmen]

wouldn't the mc leak inside the vac booster?

[chrisfranklin]

wouldn't the mc leak inside the vac booster?

Good point, Sharp.  Mental image of my mc and "plumbing" didn't have the booster in it...doh!

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My brakes need a look for other reasons, too.  Rear shoes could be worn down or guess ebrake needs adjustment -- emergency brake doesn't hold jeep.  Think the front rotors are slightly warped and need to be turned.  Don't know the wear on the EBC Yellowstuff pads that have been on the front for about 6 years.  Brake lines probably need to be bled badly, also...

[sharpxmen]

Good point, Sharp.  Mental image of my mc and "plumbing" didn't have the booster in it...doh!

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My brakes need a look for other reasons, too.  Rear shoes could be worn down or guess ebrake needs adjustment -- emergency brake doesn't hold jeep.  Think the front rotors are slightly warped and need to be turned.  Don't know the wear on the EBC Yellowstuff pads that have been on the front for about 6 years.  Brake lines probably need to be bled badly, also...

for $25/piece i got new front rotors from Amazon (free shipping with Prime membership), if you go to a shop to turn your rotors will cost you considerably more than $50

same goes for the calipers, $30 for the right side, $21 for driver side (reman ones, it is cheaper of course if you buy the rebuild kit and do it yourself but for the time spent they're quite reasonable imo)

not sure about the rear since i have discs and never actually did anything on the drums before (i replaced the shoes but that's about it).

[reddogg]

Could be bypassing and leaking out the rear of the mc. If it's not losing a lot of fluid it could be easy to miss. Leaking rear wheel cylinders could also be the cause which is also hard to spot if it's losing a small quantity of fluid. I just finished replacing both front calipers on my 95. They were locking up and not releasing. Napa had same price as Autozone.

[chrisfranklin]

Could be bypassing and leaking out the rear of the mc. If it's not losing a lot of fluid it could be easy to miss.

That's the thing: topping off the brake fluid at fill-ups, I think I've been adding maybe 1/4" to 3/4" worth in the front/rear reservoirs.  Actually, rear is the one getting down to 3/4."  

Don't know what that works out to in fluid ounces or fractions of.  Don't know if that qualifies as losing a lot of fluid, either.  

But I can tell somethings "off" with the brakes when the fluid is down like mine gets by the time I need to hit the gas station.  You hit the brakes and the low or slightly low fluid in the reservoirs has to, I guess, ascend to the top of the mc before there's any pressure in the lines.  So braking doesn't feel as "positive" as when the reservoirs are topped off.  

Had a bad highway stop a few weeks ago during rush hour -- one of these deals where was going 70mph on the 134W, slid right and merged with traffic going about 55-60mph that was heading towards the exit loop to I5 South, then saw that traffic on the loop was backed up to a standstill clear up to the dude in a car that was just, I don't know, maybe 150ft in front of me at 0mph.  So, was forced in to a 60mph to 0mph "panic" stop on uneven pavement and had to veer left at the last second to keep from tail-ending the guy.  This put me in the adjacent left lane slightly, so of course ended up cutting somebody off and got an earful of some '90s Corolla horn...

[chrisfranklin]

One more thing:  The large reservoir on the mc is for front brakes, the small reservoir is for the rear brakes.  The two systems are split, so focus your leak search on the front or rear system, depending on which reservoir you are topping off frequently.

Ah sh-t.  You know VA_YJ if its like that on the '94s?  On mine, the larger reservoir is the rear and smaller reservoir is the front.  Naturally (to me), I figured front reservoir, though smaller, was for front brakes, and rear reservoir, though larger, was for rear brakes...

[sharpxmen]

i think they all have the smaller res in the front of the larger res (in regards to the front/rear of the vehicle), the front brakes are fed from the rear 1/2 of the m/c (and that would be the larger reservoir) - reason is the front brakes use more fluid as the pads wear out (larger pistons). I never seen one the other way around (i'm not saying it doesn't exist and i don't know to be honest but at least all YJs/TJs are the same).

[chrisfranklin]

The

i think they all have the smaller res in the front of the larger res (in regards to the front/rear of the vehicle), the front brakes are fed from the rear 1/2 of the m/c (and that would be the larger reservoir) - reason is the front brakes use more fluid as the pads wear out (larger pistons). I never seen one the other way around (i'm not saying it doesn't exist and i don't know to be honest but at least all YJs/TJs are the same).

It's the larger reservoir -- guess for the front end -- that I'm topping off every time I get fuel.  That makes more sense and probably accounts for the poor braking performance my jeep exhibited a few weeks ago

[sharpxmen]

The
It's the larger reservoir -- guess for the front end -- that I'm topping off every time I get fuel.  That makes more sense and probably accounts for the poor braking performance my jeep exhibited a few weeks ago

take the vac line out of the booster, remove the grommet and stick a rubber vac line (flexible and thin so it goes down to the bottom easily), when you pull it out if there's brake fluid on the end you got your answer.

EDIT: check for drips at the front calipers as well and on the inside of the rims

[VA_YJ]

If you don't see any leaks on the front lines, hoses or calipers, then Sharp is right - it's probably pumping fluid out of the firewall end of the MC.  I'll bet you the booster is filling up.  I did have this happen once on my old F250.

[chrisfranklin]

Finally found out where the fluid was going...  

I was getting a 51 code (different matter).  Friend of mine was looking at the engine see if there was any vacuum leaks.  My emergency brake needs adjustment, so I have my foot on the brakes while the engine is running.  

Friend says to the effect:  Don't hear any vacuum leaks, but do you have a foot on the brakes?  I say yeah.  He says he's seeing brake fluid seep out of the brake master cylinder at the cap.  I kill the engine and get out and take a look and yeah, fluid is leaking out where the master cylinder cap meets the lower reservoir portion of the master cylinder.  

Opinion I got was spend a few bucks and change the rubber membrane under the cap and then make sure the bar that holds the cap in place on the master cylinder is applying enough pressure.  Once I get that sealed up so there's no leakage when I apply pedal pressure then I'll probably bleed the brakes also.

Guess you guys with TJs don't have to sweat this since you've got plastic reservoir and screw on cap.