Anyone changed a brake master cylinder

[harrylime]

As per my previous post, I'm investigating spongy brakes on my 99 LS 400 and the master cylinder may be suspect. Has anyone changed this part, and has anyone investigated alternative sources beyond main dealers? I found this at Rockautos, anyone know whether it is compatible please? https://www.rockauto.com/en/moreinfo.php?pk=1610436&cc=1356083&jsn=367

 

[Malc]

never known one to fail BUT in any event might there be someone inn the UK that can simply refurbish the existing ?

Malc

[harrylime]

That was my thought Malc, I rang lexus and there are no refurbishment kits, seals available. I'm not sure it is the master cylinder, the car's only done 70,000 miles. I ay try just bleeding the brakes first

[ambermarine]

Another way to eliminate the chance of air in the system is to change out the brake fluid if you go round each wheel and take out old fluid until new fluid comes through it will express any air in the system whilst renewing the fluid.

If the system as air in it when you are done the master cylinder could be one of the suspects but you may have a pipe leak or a pot in one of the calipers both of these faults will be evident with damp spots . 

[BigBoomer]

Hopefully bleeding will work but don't get your hopes up.
See this thread from 2011.

Someone else had exactly your problem and a new master cylinder fixed it.

[harrylime]

I have found two possibilities on the Rockauto website, one is Advics, claims to be original manufacturer, the other is Centrics. The Advics part comes complete with reservoir, it is listed as fitting my car, but the part number is one out, it is part number 4720150230,as opposed to 4720150240. I wonder could they be handed for LHD/RHD cars? They are a fraction of the price quoted by Lexus dealers, even including shipping and duty

[harrylime]

A little more information, opinions welcome. I tried it again today and before starting the engine the pedal is firm. On starting the engine the pedal goes down quite a way, when driving it comes back up a bit and brakes just fine. I must sort it out though, it's very disconcerting, I'll be getting the car  over my pit next week and taking a good look.

[ambermarine]

There are the symptoms of a vacuum leak in the scenario you paint it might be a good idea to get the servo checked and its connections to the manifold of the engine.

[steve2006]

That sounds right for correct servo operation, with the engine off and pumping the pedal it should rise to the top after a couple of presses. You should then feel the pedal drop slightly under your foot when the engine is started as the vacuum builds up. 

When was the last time the brake fluid was replaced?

Regarding the Rockauto part be aware this will probably be for the LHD version and will therefore not have the unions on the correct side for RHD.