94 Ls400 Brake Problem

[Champak]

The brake light is staying on (and the pedal is way down) and the pads are good. I got new rear rotors, the front ones are good. If I bleed the brakes, the light goes away for about a day and then comes back...yes I bleed them in the proper order. I've bled these brakes so much to the point where the next time I bleed them I'm giving the car away.

I've been told it could be the master cylinder by the engine losing pressure, but someone else tells me if I don't see leakage then it isn't that. Then someone else told me that it may be losing pressure by the brakes themselves. Can anyone here point me in any particular direction and a test I can do myself? Thanks.

[SRK]

Your description makes me think the master cylinder is bypassing - and they do it internally without any external leakage. The more you bleed the system, depressing the pistons to the bottom of the bore, the worse it will get. Lexus sells rebuild kits for the cylinders, and if there is no corrosion or pitting of the bore, it can be rebuilt. Otherwise a new master will fix it. This assumes no leaks in the system elsewhere.

The engine has nothing to do with the bleeding operation.

Bench bleed the new or rebuilt cylinder and then bleed at the fittings on the master when installed, and you won't even have to bleed at the wheels. Very straightforward.

[yoichisoma]

Hey,

I agree. I've fixed lots of cars with fine bubbles in the fluid when bled. When I bleed the brakes I use a clear plastic hose from a hardware store and poke it through an old oil jug so I can see the quality of the fluid being bled. Fine bubbles in the fluid are likely from the Master cylinder. Just get rebuild kit and rebuild the inside. Good luck.

Yo

[oldskewel]

I'm working on some brake issues myself that are proving tough to figure out.

I rebuilt the calipers several months ago (one needed it, the others were for good measure). ~160k on my 1991 LS400.

How common is this need for a MC rebuild? At what mileage is it commonly needed?

Thanks, Ed

[SRK]

With regular fluid flushes a master can last for years. The old iron cylinders would pit and corrode, and then leak after bleeding because running the pistons to the bottom of the bore, where they haven't been for years, is what tears the lip off the seals. I prefer to pressure bleed and flush, rather than using the cylinder to do it. Aluminum cylinders tend to last longer, and there is a better chance that they can be rebuilt because they don't pit.

[Champak]

Any idea where I can get this rebuild kit. I called the Lexus dealers in my area and none of them carry it...some of them even said Lexus doesn't carry them, which I know isn't true. I searched the internet and can't find any. So where do I go?

[AzHotLS]

Carson Toyota: http://www.trademotion.com/partlocator/ind...playCatalogid=0

Brakes > Hydraulic system > Hydraulic system > Overhaul Kit

[Champak]

Thanks. Now,

1/ Does that come with instructions?

2/ Never did it before so is it "relatively" easy or do you recommend me taking it to a mechanic?

3/ One of the lexus shops that was trying to get me to buy a new one asked if I have traction control or not, but I don't see an option on that link. Does the traction feature matter?

[Champak]

Bump

[Champak]

I'm fixing it now and running into a few problems, so any directions will be appreciated.

[SRK]

You cannot afford a mistake in rebuilding the master cylinder. Get help from a local person who is well-experienced, or list the problems you are having.

[Champak]

Everything went fine, I just wasn't seeing something simple in it. But the light is still on, the brakes still go all the way down. What else can this be?

[steve2006]

Does the brake pedal "firm up" if you pump it a few times?

[Champak]

During bleeding....I haven't tried it at any other time.

[python]

u have left out all the details of how u went about doing this job...did u bench bleed the m/c? once u get it on after u bench bleed it u now have to bleed it at the lines where they connect to the side of the m/c, this is done differently then just bleeding, u have to have someone slowly push the pedal and u crack the lines as they push the pedal down, before they reach the bottom of the stroke tighten it up, do this until u get solid fluid...after this is done then u r ready to bleed the system starting from the driver's side rear, passenger side rear, passenger front then drivers front..if u have never done this before u need to get help from someone who has