tranft

I believe from searching these forums that my brake booster is out.

Symptom is the ABS, VSC and brake warning lights are on and there is a constant warning buzzer on. Also it is very hard to brake, kind of like when you shut off the engine and try to brake, there is no power assisted brake. Good thing I was driving and not my wife!

Anyways could someone confirm that it doesn't use a vacumn line from the engine. I'm thinking it generates it;s own vacumn via an electric motor built attached to the master cylinder.

Second I called the dealer and they want $1,938 just for the part alone! Any good tips on used parts or getting them somewhere cheaper? I'm in SoCalifornia.

Thanks alot!

cartechpr

It does use a vaccuum line from the engine....

mine is making a strange whistle.... and its giving me a headache

Tammy

The rubber boost diaphragm is vacuum driven by intake manifold vacuum supplied to vacuum booster assembly. This rubber ages, cracks and then leaks vacuum.

Vacuum is supplied to a ninety degree hose fitting attached to the face of the booster, behind the brake master cylinder. Follow this hose as it changes to a 9mm o.d. steel line along the firewall. Then it changes back to a rubber vacuum line as it attaches to the intake manifold. It should be a point to point vacuum line, meaning there are no branches in the tube. If the hose is disconnected at the manifold and vacuum is applied to the hose, the vacuum should hold steady. If not, the booster assembly replacement is necessary.

Take care when using used parts, they can become defective on the shelf or in the yard. I'm not sure if a booster for Lexus is available thru local auto parts distributors.

salimshah

Vaccum is still needed to provide the assist .. less effort is needed when you apply the brakes. For ABS action, the pump provides the energy needed to reapply the brakes after pressure is purged (automatically) to momentarily relase the brake. Without the pump, you will need to pump the brakes or the pedal would need to travel further down every time to re-genrate the pressure to squeeze the pads.

Salim

tranft

I got the part used from a salvage yard... $160. Beats $2000 plus labor anyday. It includes the master cylinder along with the brake booster motor attached. My old brake booster motor was out. I was going to have a mechanic do it but ended doing it myself for fun! Wasn't too bad at all, took about 2 hrs to do. Plus need to bleed brakes.

Anyways the replies seem to be off with what I have. I removed the whole master cylinder and there are no vacumn lines whatsoever that connect to the manifold. It looks like for my year 1999 the brake booster motor provides all the vacumn needed for power assist. I have a diagm of it if anyones interested. As far as the ABS not sure how that comes into play with my system, maybe downstream somewhere there is another valve.

Tommorow I'm taking it to my mechanic to have him do the final brake bleed and checkout.

Maybe those of you that actually have a vacumn line could reply back with your model year.,,

Cheers!

salimshah

The advice you get on forum is worth the money you pay for it.


Advice is always well meaning and the seeker must keep in mind that most respondants are NON-mechanics. Enen mechanics have to bumble their way to fix things.


How did you bleed the brakes? I thought you need OBD based controller to actuate valves, specially when pump motor is dry/(air)

Salim

tranft

How did I bleed the brakes?...not sure if I did it right, I just had my wife turn on the engine, pump the brake 3 times and stay on it. Then I released each bleeder valve on the front wheel one at a time until the stream coming out was solid with no air. Couldn't do the rears as I don't have a working jack. But the brakes do work now though...

Anyways I thought to be safe I would bring it to my local independent mechanic to do a complete bleed, but he called me later to say he couldn't do and it has to be done at a Lexus dealer.

Called Lexus dealer and they said they do what's called a brake flush...using some sort of vacumn tool that sits on master cylinder to provide constant pressure. They didn't say anything about any electronic OBD tool,,,,,I'll have to ask them about that tomorrow. Didn't realize this whole brake bleeding thing would be so complicated... thanks for everyones inputs!!

Tammy

Inquire as to the tool transfering the pump solenoids for bleeding.... Thanks

Lexbox

The first thing I noticed about the GS is that the brakes work perfectly when the car is off, unlike my ES. Sometimes when I move my car I throw it in neutral with the car off and coast down the driveway.

tranft

You're right, the GS300 uses an electric pump to generate the pwr assist, therefore the engine does not need to be on for the pwr assist to work...unlike other cars,

tranft

Well I called several dealers and none of them use the OBD tool to bleed the brakes, they use a device attached to the master cyl to generate pressure to bleed the brakes. I do the same but with another person pressing down on the brake pedal.
Anyways I did it myself and as stated on some previous posts. Engine on, pump pedal 3-4 times and stay on it. Another person bleeds the brakes.... right rear, left rear, right front, left front. Always keep the brake reservoir full. No problems at all.

93 LS4

That's crazy, Google Lexus recycled parts to see if you can find a good used unit....