Lexs400

1993 LS400
problem: spongy pedal, not so effective brakes.
the brake problems all go away after I engage the ABS or traction 3 or 4 times manually. the pedal feel and the bite in the brakes remain for a day or so and the pedal goes back to spongy, extra pedal travel and loss of brake bite. I have to keep on activating ABS by driving in reverse and hard hitting the brakes to keep the brakes at their optimal.

parts changed so far:
brake booster
master cylinder
all the callipers greased
brakes bled several times, last week got the ABS system beld by the dealer

no change at all.
One of the private shops suggested that the ABS pump could be the cause of this problem. However the Lexus dealer said that the ABS doesn't come into action unless ABS is activated. The private mech. claims that with this system the braking system at all times has to travel through the ABS pump which in turn sends the brake fluid to the 4 wheels.
quesiton is, can the ABS pump be causing this ? If someone has a diagram of the system perhaps they could post this here. I would like to make sure this coudl be the cause before investing 1750 in the pump and 5 hours of labor.

Lexs400

should I have posted this in a different forums perhaps under ls400 to get some replies ?

csaxon

I'm assuming that someone other than Lexus installed all the parts you describe. The Lexus service department should have the ABS system checker depending on whether you have a Denso or Bosch Abs system..they installed both. I can't believe Lexus would release the car with unsafe brakes because of the legal/insurance liability if you get into an accident with bad brakes.

Your independent guy was correct, the brake system obviously goes through the ABS pump where it carries a preload of pressure to aid in panic stops/braking. It's obvious you have either an air leak or a fluid leak or both. If the dealer did all this work including the brake bleeding then you shouldn't have this problem and take it back to him or take him to court. If you did it yourself then respond and I'll take you through the diagnosis steps.

csaxon

I've discovered you've had this thread going in other forums since Oct of 2002? And you noticed this problem the day after you bought the car? And you didn't return the car? You obviously haven't been to a Lexus dealer since this would have been corrected before the sale and certainly one day after the sale! A lexus mechanic with the proper diagnostic equipment and parts can have the brake system working properly in one day! You've been playing with this for 18 months?

Lexs400

all the work and parts installed so far have been by the lexus dealer. which is the cause of my frustration ! u'd think they'll know what to do but they dont !

VVT-i

Let's them check all the rubber lines that connect to the calipers. Also, one of the line by the ABS pump( by the brake master cylinder, left hand side, close to the fire wall). I 've seen some of the line collasped and cause some wierd problem.

Lexs400

allright, here's an update.
for the past two days, for the first time ever the brakes worked flawlessly. the pedal was rock solid, and the was no siking effect at all. All that was done basically was the dealer had the bleading done all over again including the traction and the abs system. needless to say I had to pay them for an hour's labor again !
so the two days worked out and this morning the pedal was back to the old spongy feel. The question is, if the air has beeen taken out (if air infact is the problem in this case) and the brakes are working fine, is there a way for air to just enter into the lines by themselves ?
if there was a leak, then I'd expect the brake fluid to leak from that area, not air entering the lines.
And if the pedal goes from spongy to perfect and back again to spongy in two day's time, I would assume air in the system might not be the issue here since nothing has been changed since it came back from the dealer this time..
the rubber lines that connect to the calliper, are they the ones that carry the brake fluid ?

Maybe spongy effect is not really descrbing the scenerio really well. here's what hapens when the brakes aren't working right.
You press the pedal, you feel the brakes starting to work, at the same time there's not an abrupt but a gradual sinking of pedal. If at a stop, I slamm the brake pedal hard, i feel there's a point of resistance which feels as if its a metal curculating ball inside the fluid lines that's rolling forward as i push on the pedal harder.
when the brakes were working fine, the pedal would not go beyond the point where I would feel that rolling metal ball kind of effect. The pedal would be at a dead stop at that point. and that's how all the other LS400's are when i've test driven them.
From what I understand, the ABS pump works off of electrical components. Could the pump be causing this effect by any chance ?
how about bad callipers ? if i need to i'm willing to change the callipers as well but I want to make sure if something of this nature can be caused by callipers to begin with.

Lexs400

could a bad caliper be the cause of all this ?
even though the dealer told me they inspected them and also greased the pins, at this point i have my doubts.
my idea of a bad caliper is usually when it's stuck in the close position and one side of the brake pads wear off faster than the other side.
could there be a case where the caliper is not closing properly instead of not opening up properly ?
would that case the different pedal feels ?
just yesterday the pedal felt as if it was pushing back when i tried to brake, kind of like a very solid spring that i was trying to press on. the pedal wasn't sinking at all at that time. then this morning the spring effect has gone away and the pedal is back to the mushy feel but atlest i dont have to press hard to make the car stop.
please dont confuse the hard pedal with the bad booster effect. that one is rock solid if that had been the case.

Lexs400

Here's an article that I've found pertaining to the situation I'm experiencing.
http://www.babcox.com/editorial/bf/bf50434.htm
It refers to "lock lines" that I am not able to find at the local stores. Most of the lock lines I've found on the net are lock line kit's that hold the brake pressure allowing you to take the foot off the pedal. mostly for 4X4 use.
I, however, am looking at plugs that would fit/screw at the outlets of the M/C and also at the individual brake components to isolate the problem areas. they're called lock lines as well but are kind of different.
for those who don't know what I'm referring to there's a picture of those lock lines in this article.
http://www.babcox.com/editorial/bf/bf109954.htm

At this point, I want to know if there's anyone who has troubleshot the brake system taking the route described in the two articles. I've pretty much been to all the shops in the NJ area and everyone's given me a simple NO answer. That's a shame that the owners have to spend money on expensive brake parts because the shops just don't know how to troubleshoot the braking system properly.
The only shops that I can think of that are the shops who build the hotrods from ground up. Since they install all the components themselves I'm sure they would know what they're doing.
any comments will be appreciated.

At the same time I would like to know where the HCU and the pressure valve is located in the 93LS400 that the first article talks about.