Master Cylinder

[Dj Matt]

I recently took my 96 Lexus LS400 to a mechanic to have the brakes checked he said everything was fine but I had a leaky master cylinder and it needed to be replaced.So I checked it out myself and so no signs of any leakage and no drop of brake fluid.So Im asking is there a way to detect a leaky master cylinder and to replace it he quoted me a price around 600-700 dollars . :cries:

[SRK]

The master can leak externally, which means you'll see brake fluid running down the front of the booster unit. If it's dry, then there is no external leak.

That means it may be leaking internally, which most mechanics would describe as "bypassing", and that means fluid bypasses a primary seal and that side of the tandem piston assembly does not produce pressure. If that occurs, the brake pedal will drop further to the floor, and braking effort will decrease, which you'll feel as less powerful brakes. A brake failure light will come on as all modern cars must have a "pressure differential switch" which alerts the driver to an internal failure in the master cylinder.

Sounds like neither is the case with your car, and the only conclusion is that your "mechanic" is trying to sell you a part you don't need, that has a very big profit margin in it, and is easy to replace. He wins, you lose.

Drive the car, inspect it again in a day or so, and write back.

Lexus can supply a rebuild kit as well that is far less expensive than a whole new cylinder, if you do in fact have a problem. Your mechanic will tell you that rebuilding is not an option because it is a "safety item" and should not be messed with......If my LS ever has a master failure, I will rebuild it.

[Dj Matt]

The master can leak externally, which means you'll see brake fluid running down the front of the booster unit. If it's dry, then there is no external leak.

That means it may be leaking internally, which most mechanics would describe as "bypassing", and that means fluid bypasses a primary seal and that side of the tandem piston assembly does not produce pressure. If that occurs, the brake pedal will drop further to the floor, and braking effort will decrease, which you'll feel as less powerful brakes. A brake failure light will come on as all modern cars must have a "pressure differential switch" which alerts the driver to an internal failure in the master cylinder.

Sounds like neither is the case with your car, and the only conclusion is that your "mechanic" is trying to sell you a part you don't need, that has a very big profit margin in it, and is easy to replace. He wins, you lose.

Drive the car, inspect it again in a day or so, and write back.

Lexus can supply a rebuild kit as well that is far less expensive than a whole new cylinder, if you do in fact have a problem. Your mechanic will tell you that rebuilding is not an option because it is a "safety item" and should not be messed with......If my LS ever has a master failure, I will rebuild it.

Thank you so much for the valuable information and for taking your time to answer my problem .I will inspect again in a day or too and write back. You and members like you make this a great club and a valuable tool for information thank you again so much!!!

[blake918]

The master can leak externally, which means you'll see brake fluid running down the front of the booster unit. If it's dry, then there is no external leak.

That means it may be leaking internally, which most mechanics would describe as "bypassing", and that means fluid bypasses a primary seal and that side of the tandem piston assembly does not produce pressure. If that occurs, the brake pedal will drop further to the floor, and braking effort will decrease, which you'll feel as less powerful brakes. A brake failure light will come on as all modern cars must have a "pressure differential switch" which alerts the driver to an internal failure in the master cylinder.

Sounds like neither is the case with your car, and the only conclusion is that your "mechanic" is trying to sell you a part you don't need, that has a very big profit margin in it, and is easy to replace. He wins, you lose.

Drive the car, inspect it again in a day or so, and write back.

Lexus can supply a rebuild kit as well that is far less expensive than a whole new cylinder, if you do in fact have a problem. Your mechanic will tell you that rebuilding is not an option because it is a "safety item" and should not be messed with......If my LS ever has a master failure, I will rebuild it.

I agree almost 100% with you SRK. Having been through a long drawn out saga with my master cylinder which includes having one of the springs snap while I was drivng on public roads, I can tell you that their are no warning lights for this (before or after it broke.). The spongy brake pedal and fluid seepage are the only warning signs you are going to get. The cause of my trouble was that there was a hole bored in to the lining of the wall of my master cylinder that was chiseling away at my spring each time I hit the brake...

It seems that this is one of those parts that never really goes bad, so finding a rebuilt master cylinder is almost impossible. They charged me something like $60 for the rebuild kit, and the whole new cylinder is like $350, I believe. Since new springs were going to do me no good, I called TAP and got one from a junked car for $100. Worked great!

Matt, this is what you will see if your master cylinder is actually leaking (just that tiny little moist area below the cylinder):

http://us.lexusownersclub.com/forums/index...ost&id=4165

Also, $600-$700 is really high considering that Lexus charges less than $400 for a new cylinder, and labor time + bleeding should barely go past an hour.

[Dj Matt]

The master can leak externally, which means you'll see brake fluid running down the front of the booster unit. If it's dry, then there is no external leak.

That means it may be leaking internally, which most mechanics would describe as "bypassing", and that means fluid bypasses a primary seal and that side of the tandem piston assembly does not produce pressure. If that occurs, the brake pedal will drop further to the floor, and braking effort will decrease, which you'll feel as less powerful brakes. A brake failure light will come on as all modern cars must have a "pressure differential switch" which alerts the driver to an internal failure in the master cylinder.

Sounds like neither is the case with your car, and the only conclusion is that your "mechanic" is trying to sell you a part you don't need, that has a very big profit margin in it, and is easy to replace. He wins, you lose.

Drive the car, inspect it again in a day or so, and write back.

Lexus can supply a rebuild kit as well that is far less expensive than a whole new cylinder, if you do in fact have a problem. Your mechanic will tell you that rebuilding is not an option because it is a "safety item" and should not be messed with......If my LS ever has a master failure, I will rebuild it.

I agree almost 100% with you SRK. Having been through a long drawn out saga with my master cylinder which includes having one of the springs snap while I was drivng on public roads, I can tell you that their are no warning lights for this (before or after it broke.). The spongy brake pedal and fluid seepage are the only warning signs you are going to get. The cause of my trouble was that there was a hole bored in to the lining of the wall of my master cylinder that was chiseling away at my spring each time I hit the brake...

It seems that this is one of those parts that never really goes bad, so finding a rebuilt master cylinder is almost impossible. They charged me something like $60 for the rebuild kit, and the whole new cylinder is like $350, I believe. Since new springs were going to do me no good, I called TAP and got one from a junked car for $100. Worked great!

Matt, this is what you will see if your master cylinder is actually leaking (just that tiny little moist area below the cylinder):

http://us.lexusownersclub.com/forums/index...ost&id=4165

Also, $600-$700 is really high considering that Lexus charges less than $400 for a new cylinder, and labor time + bleeding should barely go past an hour.

Blake918 and SPK thanks for all your expertise in this area , i think a rebuilt is the best option but seeing no visable signs of leakage i will give a day or too or call the mechanic and ask him where the leak is accuring .But without great guys like you i would be stuck in a rut!!

[SKperformance]

Funny thing is the brake booster does go bad but many people have no idea that it is broken.

Did the rebuild kit come with only springs or what was included in it?

I know mine is slowly going as when i hit the brakes , if i release right away and press it again it will get harder and stop much better.

My friend also had to replace his for the same reason but his pedal would hit the floor.

[blake918]

It's been a while, but I think the rebuild kit came with the 2 springs and 2 piston stopper bolts. No rubber parts/snap ring/gaskets/etc. came with the kit from what I can remember.

[oldskewel]

It's been a while, but I think the rebuild kit came with the 2 springs and 2 piston stopper bolts. No rubber parts/snap ring/gaskets/etc. came with the kit from what I can remember.

I'm about to rebuild the MC in my '91 LS400 with ~170k miles. Not sure if this will fix the dragging problem I've got, but I've tried almost everything else, it seems. I just got the rebuild kit from parts.com. The box was opened, so I don't know exactly what was supposed to be in there. But the individual 3 bags are still sealed. Two spring/pistons with new rubber seals, and a bag with 2 screws, 2 washers, and a c-clip.

I'm expecting to do the rebuild and have no change, but we'll see.