Lexus Ls400 1997 VVTI
I've got a soft pedal when the engine is on and rock hard when off. I'm going through everything and thought I'd start by bleeding the abs. It's easy on this car, just a bleed valve on the abs module and a hand pump to the master cylinder reservoir pressurised to 14.2psi.
Problem is the old & new caps are letting air out. The new one is a substitute, but considered the current model product code in America and a suitable substitute in Japan. I measured the new one with a vernier caliper and it's 1.5mm less in diameter at the seal. The seal sits in the neck of the reservoir.
I made the old and new caps like the old gunsen easybleed brake bleeding system. So I drilled a hole in the cap, Jb welded a valve, and cut off the plastic diaphram that allows air to escape from inside the system.
I think I'm a bit stupid, because all I can think of is the old cap must have a worn rubber seal, and the new ones must not fit. The master cylinder is an OEM Aisin not an aftermarket.
I didn't cut the diaphram off the old one, just drilled a small hole, so I've plugged it with JB weld and the central hole as well, and put it back. Pretty sure it's the original.
Any thoughts appreciated, thanks.
I should mention the new caps does push into the resrvoir neck with the same resistance as the old one for what that's worth.
I've got a soft pedal when the engine is on and rock hard when off.
so have all my cars
Master Cylinder Cap Not Holding Pressure.
it's not supposed to
thought I'd start by bleeding the abs.
just bleed it the old fashioned way by pumping the pedal
Are you having problems stopping?
Well I haven't driven it yet, as I'm getting it ready for the inspection, but when I say soft pedal what I really mean is the pedal sinks down only when the engine is on. The car does stop (on the driveway) but the brakes are weak.
Thanks for the advice using the pedal, I was going by the repair manual that says use the pedal for bleeding the master cylinder and pressurize the reservoir for the abs, but I'll try that.
the pedal is supposed to get "softer" when the engine runs because it is being assisted by the booster. But if the brakes are weak then you have a failure somewhere. On an almost 30yo car it could be almost anywhere... a leaking master cylinder, wheel cylinder, bad rubber hose, popped brake line, etc.
Air should not just suddenly appear in the brake system.
Yep, I've got the rebuild kits forthe calipers & master cylinder if necessary. This cap thing just threw me as I thought they were airtight, so I'll make one up that is then check for leaks > abs > air > caliper seals > master cylinder > push rod > and finally my own blood pressure if still crap.