Spongy brakes

[harrylime]

I have a 99 LS 400. Today I noticed that on start up the brake pedal went down a hell of a long way with hardly any resistance. On driving the car the brakes work fine but am I right in thinking it's likely that the brakes need bleeding? Is this straightforward on a series 4 400? Does anyone have the procedure for this? I will probably do this over my inspection pit with someone operating the brake pedal. I have done this before although not for many years and never on a Lexus. The brake fluid level is fine and two years ago I asked my Inie to change the brake fluid, although I'm not sure this was done. Even simple advice  like what diameter tubing I need would be useful

[GS300h2014]

Possibly you've got a faulty brake master cylinder.

[Tinonline]

Hi

I’d check fluid level which I’m sure you’ve done.

Look for any leaks around reservoir, master cylinder and brake lines, calipers. See how worn the pads are.

Best tool is a self bleeder. It’s a standard size. From memory I recall the wheel that is furthest away in terms of position is not actually so in terms of brake circuitry. 

I don’t think it will be the fluid itself...you might have a tired, failing brake master. Not the end of the world...as always with a Lexus once fixed, whatever it is it’ll be good for years.
 

 

[BigBoomer]

If you have your foot on the brake pedal when you start the engine, and the pedal then goes down after you started it with the same pressure applied, then it is 100% the master cylinder that is the cause. My 98 Legend had exactly that fault at 140k miles and the new master cylinder and a good bleed sorted it. By the time I discovered that it was the master cylinder I had already replaced all 4 calipers and had the ABS module tested at a total cost of well over £1000.

[harrylime]

On 11/23/2020 at 9:49 AM, BigBoomer said:

If you have your foot on the brake pedal when you start the engine, and the pedal then goes down after you started it with the same pressure applied, then it is 100% the master cylinder that is the cause. My 98 Legend had exactly that fault at 140k miles and the new master cylinder and a good bleed sorted it. By the time I discovered that it was the master cylinder I had already replaced all 4 calipers and had the ABS module tested at a total cost of well over £1000.

thanks George, I will check exactly what happens when I start the engine

[harrylime]

A little more information to work with, 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 work 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.

[The-Acre]

4 hours ago, harrylime said:

A little more information to work with, 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 work 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.

It's normal for the brake pedal to start hard and go down when you start up, that's when the servo which assists braking kicks in.

[Spacewagon52]

I have had the same on my LS 400, the brakes have been checked and they are fine. Pedal travel does seem spongy compared to other cars. As long as your fluid levels are ok, I doubt there is anything wrong but still worth checking for peace of mind.