Master cylinder can it be repaired

Delp · October 7, 2020

Has anyone ever had the master cylinder repaired on there GS. As the ABS kicking in low speeds. I know could get one from scrapyard, but don't want to get one that's one Its way out. Trying to out weigh getting current one repaired or scrapyard.

steve2006 · October 7, 2020

It’s been a while since I last looked but at the time no one repaired the brake actuator units from the GS300.

The fact that they don’t use a conventional vacuum servo system and numbers on the road probably means that repair is not possible due to spares issues or not viable due to low volumes.

I know a couple of owners who scrapped the car due to this problem.

Before assuming it is the actuator have you had the fault codes read as it may just be either crud or rust build up on the ABS sensor/ reluctor ring or a broken ring ( very common and replacements are available).

Delp · October 8, 2020

14 hours ago, steve2006 said:

It’s been a while since I last looked but at the time no one repaired the brake actuator units from the GS300.

The fact that they don’t use a conventional vacuum servo system and numbers on the road probably means that repair is not possible due to spares issues or not viable due to low volumes.

I know a couple of owners who scrapped the car due to this problem.

Before assuming it is the actuator have you had the fault codes read as it may just be either crud or rust build up on the ABS sensor/ reluctor ring or a broken ring ( very common and replacements are available).

Hi Steve

Ran tech stream for codes. Nothing showing up. Abs wheel sensors are showing readings. I've cleaned the rear abs sensors which did have magnetic filings on them, I've not dobe the fronts. Is it worth cleaning the front sensors even though no fault causes are showing. Also do you know the part no for unit as I'm asking specialist companies to see if it can be repaired.

ColinBarber · October 8, 2020

The pre-facelift GS series II suffer from master cylinder issues, primarily the vacuum pump and you end up with a VSC warning and buzzer going off the whole time. The face-lift models (which you have) don't seem to suffer this so I wouldn't be too concerned about getting a used unit from a scrapyard - obviously you could be very unlucky and have a problem with the replacement but I think you should be ok. Having said that it doesn't really sound like a master cylinder issue, rather that something is triggering the ABS to operate and the master cylinder is operating correctly.

rock on · October 9, 2020

I've got a spare one from a 2000 gs300 sport currently on the bay of E

I'm not sure if I can advertise parts on here not being a gold member so please delete if I'm breaking forum rules.

Sent from my Pixel 3 using Tapatalk

Delp · October 9, 2020

On 10/8/2020 at 6:34 PM, ColinBarber said:

The pre-facelift GS series II suffer from master cylinder issues, primarily the vacuum pump and you end up with a VSC warning and buzzer going off the whole time. The face-lift models (which you have) don't seem to suffer this so I wouldn't be too concerned about getting a used unit from a scrapyard - obviously you could be very unlucky and have a problem with the replacement but I think you should be ok. Having said that it doesn't really sound like a master cylinder issue, rather that something is triggering the ABS to operate and the master cylinder is operating correctly.

This is my hunch also. How can this be diagnosed then. Any advice be welcome. It also pulling to the left when braking that's when abs kicks in sometime. Is it worth measuring the resistance of the abs sensors..

ColinBarber · October 9, 2020

Reading the resistance of the sensor isn't an accurate way to test them unfortunately. When you say low speeds, what speed are we talking about - under 5 mph, under 3 mph? If it is that low then any dirt can affect the signal these sensors produce which is weak at low speeds, so you need to make sure they are all clean and the ring isn't at all damaged (no cracks).

steve2006 · October 9, 2020

From past experience the symptoms of a contaminated sensor or damaged reluctor ring causes the ABS to kick in just before the car comes to a stop when you get a pulsation of the brake pedal under your foot and a crunching sound. It also doesn’t tend to flag up a fault code.

I would continue to check the front sensors also...a bit of metallic grit could be causing all your problems.

runsgrateasanut · November 19, 2021

This thread interests me. Having driven on two six hundred mile journeys, only once did I worry about breaking when I came up behind a stopped vehicle and for a moment I thought I had to apply the Brake pedal harder than usual. This said, I had been experiencing the Car make a vibrating sound upon left turn of the steering wheel outside my house when just pointing the car in a different direction at say 3mph.

I'd had VSC lights stay on a while back pre MOT and a CEL which was cleared after replacement of a down bank Lambda sensor and not long after the VSC light issue seemed to clear itself.

I will have to check the front wheel sensors for any build up of crud. Not sure if this 2000 Car is a Post- facelift model? How can I tell? Car reg 01/01/2000 but manufacture date earlier.

Also, I suspect the Hubs are different for later model GS's. Is there a Reluctor (exciter?) ring on the Hub that I should check for damage? Have seen photo's of sensor described as looking like Hedgehog with filings. Where do they come from as the sensor surely doesn't make contact.?

Any images of the hub might help. Thanks

ps I've not had any warning continuous noises from inside or under the bonnet so hopefully a complete Brake fail or needing a new Actuator is not on the cards. Fingers crossed.

steve2006 · November 20, 2021

Bear in mind that if the brakes have not been applied for some time they will be cold, the discs possibly be contaminated by oil and diesel off the road so greater initial brake pressure may be required.

If you have no fault codes or other brake faults I would leave things as they are, personally I wouldn’t consider crud cleaning of reluctor rings and sensors as essential maintainance.

Mihanicos · November 21, 2021

From my limited knowledge about Lexus brakes, which operate along similar principles in most models and considering your case, I would consider the following:

The speed sensors detect the rotational speed of the wheels and this data is entered to the skid control ecu.

The skid control ecu in turn controls the ABS, Traction control and Vsc.

ABS main relay is controlled by the skid ecu. It supplies power to each solenoid and to the skid control ecu.

ABS motor relay is controlled by the skid ecu and supplies power to the pump motor.

The brake pedal stroke sensor detects the brake stroke volume and this data is fed to the skid control ecu.

Check all relevant connectors for good clean contacts, cables and harnesses for damage.

Clean the speed sensors and remove any dirt and rust from their seats. Make sure they are squarely and fully home seated.

Chris.

Malc · November 21, 2021

Blimey ... more modern cars than mine seem sooooo complex in braking as well as most other avenues of operation :unsure:

Got my car back from it's annual service and MOT and the first thing that impressed me was the seemingly ( maybe psychologically ) more efficient braking ............ just seemed a little more " spot on "

I know he checked all discs and pads etc and proclaimed all to be well and good for another year AND he does always check out, on the annual service, the callipers for efficiency of operation ... and to date I'm not aware of any replacement of callipers or components at all, ever ....... in 26 years

Malc

maybe this is some sort of record achieved by diligent servicing ?

there's nowt mentioned on any of the Lexus Main Dealer servicing bills before I had the car 10.5 years ago

runsgrateasanut · November 21, 2021

1 hour ago, Malc said:

I know he checked all discs and pads etc and proclaimed all to be well and good for another year AND he does always check out, on the annual service, the callipers for efficiency of operation ... and to date I'm not aware of any replacement of callipers or components at all, ever ....... in 26 years

Malc

That's amazing Malc. What sort of mileage do you do? Is the Car garaged? I seem to always need to replace Calipers on toyota and lexus cars that I've bought. Just been unlucky perhaps?

Malc · November 22, 2021

Stuart hi .. she's now covered 235k miles and before this covid stuff etc when I seem to have only managed 4k, I was previously regularly doing 10/12/15k miles a year for the 10.5 years I've owned her. Covered lots of Europe on holidays in that time too . I bought her from a member on here with about 123k miles on the clock

She had full Lexus service history prior and well documented Since then my indy has looked after her ..... never been garaged in my ownership, rarely washed ( maybe that's the key :whistling: ) and lived all it's life by or on the coast ............ ,always had an annual service with the MOT and always done, where possible, preventative maintenance ......... BUT she's had one or two age / mileage related issues from time to time ... UCAs, an alternator about 30k miles ago and other bits and bobs that weren't too demanding tbh

With the callipers, I think it's actually having them checked every year by someone who does actually check them, knows what they're doing ( whatever that might be ) ... and service them properly . I think it's a simple enough job :unsure: ..... just needs doing !

Not sure it's a scheduled part of any Lexus Service Schedule though and that's why they are rarely looked over at a " normal " garage doing your servicing maybe

Malc