caverman

Anyone know of a DIY video or post on replacing the master cylinder on a 2004 LS430?

I'm having my brakes slightly bleed down when I sit at a stop. Reminds of when I have manually bleed brakes and you pump/hold then the caliper valve is opened. My brakes are going down that far but they are going down about 1/4" or so. It's enough to make the car start to slightly move forward at a stop.

I'm thinking the master cylinder is going bad and pressure is getting by the stopper. I've found some MC online for around $80-$100 but wanted to see if there was anything out of the ordinary about doing the replacement.

BTW: I've been searching online and can't find anything.

Tom57

If you are getting that kind of brake travel at a stop, you need to get on it.

caverman

I've only had the car for about 4 months and I'm pretty sure this is a new issue. I do slightly pump the brake and hold a little harder and that seems to work until I need to leave from my stopped position. However, I don't think it should be doing this and I'm betting it's only going to get worse over time. It's annoying me so I'm going to try to fix it. I'm just hoping it's nothing really major. I can do all the basic repairs myself and if there is nothing tricking about the master cylinder than I should be able to handle it. That's why I was looking for a DIY to see the steps and make sure I don't get in over my head.

BTW: didn't mention in the first post but it's a 2004 with 115k on it.

Tom57

Have you first tried a complete brake fluid flush? It's quite possible that you have air in the brake line. (Master cylinders are not typical at 115K miles.) Squishy brake pedal feel is often a sign that brake fluid needs to be changed and brakes bled. Start with bleeding the brake farthest from the master cylinder (right rear), and work your way closer (left rear), then right front, then finally left front.

caverman

I haven't tried anything just yet. I'm due for an oil change and tire rotation and will probably do that this weekend. I'm going to look at the brake pads when I do.

I'm still thinking it might be a master cylinder that is letting pressure by the rubber. I took a look last night at the MC and it doesn't look like it would be that hard to change. It also looks like I can pick one up for $100 or less. So, depending on the look of the brake pads I might just replace all four rotors and pads as well as a new MC which of course means brake fluid bleeding.

Kind of a shotgun affect but for about $300 and me doing the work I think I will fix the issue and be set for a while (at least as far as brakes are concerned).

toddmorr

yeah you could do all that work but your symptoms really just sound like air in your lines, especially if you pump while sitting and it gets firm again. I had exactly that issue in an Infiniti because I hadn't bled it properly to begin with.

caverman

I agree it sounds like some kind of air. However, there is no reason why there would have been any air introduced to the system. The guy I bought it from is a personal friend of mine and had everything done at the Lexus dealer. He doesn't even have any tools to work on a car.

Talking if over with someone they suggested that it's possible that the plunger inside the master cylinder might not be making a good seal for whatever reason (might even be trash in the system from a deteriorating brake hose). They believe it's something causing the pressure to bleed off from the MC since nothing has been done to the brake system in quite some time.

I ended up changing the oil and rotating tires yesterday. While I was at it I looked at the brake pads and they were definitely gone. The front pads were worn down to right at the sensor. So close I'm surprised the sensor wasn't telling me they needed to be changed.

I ended up doing a new set of brake pads on both the front and rears. I haven't had much time to drive it since then to see if I'm getting the same kind of bleed off feel or not. I'll find that tomorrow when I have to sit in stop-n-go traffic. If the bleed off is still there then I will probably be changing the master cylinder and possibly the brake hoses as well. That will also force a new brake fluid flush.

I will say that with the new pads it feels like the brake pedal has a much higher grab now. I don't have push down on the pedal as far to get it to start grabbing.

caverman

I'm still looking for a DIY video or thread just to see what it will entail. By the looks of it I don't think there will be anything out of the ordinary.

rkw77080

Hope this will help...

Tom57

Air can be "introduced to the system" from high brake fluid temperatures. While DOT 3 has a high boiling point, over time, and with heavy use of the brakes, there can be fluid boil that releases air into the brake lines. If the brake fluid has never been flushed, it is time now since you changed the brake pads.

Tom57

You're not finding a thread or video on LS430 master cylinder replacement because it's just not a common failure component. I have 258K+ miles on my '01. Never had to replace the master cylinder.

Tom57

OP, did you end up replacing the master cylinder? Did it solve your squishy brake pedal?

rkw, do you have instructions on bleeding the master cylinder? (page 32-4)

rkw77080

Here you go, Tom...