Lexs400

Hello All,
I am trying to post this here in the maintenance section hoping to get an answer which I couldnt find in the LS forum.

The brakes on the 93LS seem to be 100% better than before after changing the Rotors, pads, front callipers, master cylinder, brake booster, and traction accumulator.
at this point the only two things that are left are the traction and the abs actuators.

Here is what happens, the brakes seem as if they have some oil based material on the rotors and therefore don't have that "grip" when i press on the brake pedal. This has been like this evenn before new rotors/pads/and callipers were put on.
I have done some research and foud out that if the brake fluid pressure is leaking internally amongst one of the components then not all the pressure from the booster/master cylinder transfers to the callipers.
My question is, how does one find out where this leak is.. ?
any suggestions would be appreciated.
thnx.

Lexs400

no one ? ?

VVT-i

You may have some air trpped inside of your brake system. Try to bleed it.

Also, check all the rubber lines that connected to the brake calipers and make sure the lines virtually looks o.k.

It's hard to do the online diaganostic to resolve the problem without test drive the car and feel of what you're feeling about your brake's problem. My suggestion may cost you more money and still doesn't fix the problem.

All we can do is read your post and seem like nobody ever experience this problem before and we don't want to give you some wide a$$ guess. I recommend take the car to the dealership( I know it will cost more) and get proper diaganostic. Good luck.

RA40

iTrader: (6)

Are you having to refill the brake fluid reservoir routinely? Have the lines been inspected for kinks?

If the car is not braking well, I agree with VVT-i...take it in. While you may solve it by replacing the ABS and traction modules, this is an expensive proposition if these do not work out to be the culprits.

Lexs400

thanks for the replies. believe it or not, i'm struggling with this problem for the past 3 years. and everytime the only place the car has went is to the dealer in NJ.
So far the bills for this diagnosis and repairs is 4500. But to date the dealer's incompetence has only resulted in changing parts and guess work. Their next recommendation is to replace the traction and abs actuators.
the rubber brake hoses have all been replaced two months ago, the system has been bled atleast 15 times now, I paid 100 dollars at 7 different places and have receipts therefore i know the other 8 times were at the dealer.

RA40

iTrader: (6)

When this initially began, what symptoms were you expereincing?
As each new replaced part was added, what occured?

For the most part, brake problems expressed here have been "routine" in nature. Warped rotors, stuck pistons, kinked line, master cyl...etc. To have gone through and done as much of the system as you have is unique. While mine is a different generation, Iam certainly curious as to what is occuring with yours.

Perhaps by posting some of the prblems some other members that may have encountered it can chime in.

I would certainly consider consulting another repair shop since this one has been this fruitless in nailing it down. That is A LOT of money invested.

Lexs400

I agree with you.
here is a copy/paste from my 2 year old post just to provide some history. Since then I had spend a lot of money at the dealer and at the end it turned out that the mechanics at the dealership were not aware of a simple adjustment of the pushrod of brake booster. I adjusted that myself and the spongy feel has gone away. now the only problem that remains is that the brakes done seem to "bite" on the rotors with the same force that they should. and that is what I am trying to troubleshoot. I have all the hayes manuals on ABS system for Nippon Denso and by now know the brake system from the brake pedal down to the pads/rotors. It's a shame the dealer couldn't do the same!

here's the earlier post.

It's a 93 LS400 with 60K miles. I've had it since it had 40K and I'm the second owner.
A few months ago it developed a wierd brake problem. The pedal travel increased by twice as much as it used to. It's intermittent meaning while driving the pedal would be perfectly fine but the next time you're thinking of applying brakes the pedal would've travelled down. During stop and go driving it's not a pleasant situation. More over at times when the pedal travel increases the pedal feels spongy as well. The pedal seems to have a mind of it's own where it fixes itself back to normal without any reason.

I've taken the car to the local lexus dealer and at this point they've done the following :
1. replaced master cylinder
2. replced brake booster
3. bled the system three times already, replaced the brake fluid with new.
4. replaced the front callipers, lubricated the rears.
5. resurfaced front rotors and installed new brake pads.
6. repalced traction accumulator
7. replaced front rubber hoses that attact to the callipers.
8. replaced the brake fluid by complete drain and refill.

Strange symptom as per the dealer but maybe can help the diagnosis. When I experience the "low bite" in the brakes, I engage the ABS pump by hitting the brakes hard while driving in reverse. Once the ABS pump activates, the brake bite from then on for atleast half a day is back to perfect how it should be. But once the car sits over night the next day the brakes are back to where there is absence of "bite" when engaging. Which tells me that there is something going on in the system but I need to figure out what it is.
If someone is close to NJ area I would be more than happy to pay them if they know how to fix this. I made this offer to a mercedes specialist in California after posting this problem in the mercedes forum, and the person apologized for not taking this offer as it would take the shop too many diagnostics hours...

RA40

iTrader: (6)

When the car is off, can you build and hold pressure when pumping on the brake pedal?
To me, after all you've done to it, my thought is a vacuum line.

Lexs400

yes, i can.
i believe this was part of the test for the brake booster to check whether or not it is working correctly. with the car off and with the pressure built, the pedal does drop when the engine is turned on. resulting an OK according to the charts.
when you mention a vacuum line leak, i'll be more than happy to change all lines in question if i can only find out which ones to change. more over if the pressure can be built and kept while the car is off, does that validate the vaccum line leak concern ?

Jet

Was that after the booster install? Did you adjusted in towards the booster or out towards the pedal?Did you check you rod length adjustment against specifications on your manual?

i know its kinda hard to distanguish the two but did you noticed that before adjusting the rod? Not trying to offend you in anyway, but the length of the push rod needs to be within the manufacture tolerance and its critical for proper brake booster operation/performance. which might have something to do with your spongy pedal and the "bite" feeling.

Jet

RA40

iTrader: (6)

In simplier times, yes. The system is tight as you are not experiencing a loss of pedal pressure. So as far as the brake and hydraulic lines, you are good. As per the book, these issues have been addressed by the dealer: Fluid leaking, air in brake system, piston worn, master cylinder and push rod out of adjustment.

After a while, some of the band clamps cut into the line as the rubber hardens so any loss of vacuum may not be obvious. As well, some lines do not have clamps but rely on a friction fit, with age these stretch, become hard and crack. It is a PITA to wiggle through the miles of rubber hoses to find a problem like this.

I would start with the vacuum line that goes into the brake booster and inspect it for kinks or loose fittings. Go in and check the snugness of each these lines leading to the braking hydraulic components. Most should be snug and or stuck to the hard lines they attach to. If any move eaisly when you twist of pull on it, replace it. As well, any line that is not reasonably flexible as they would have been when fresh, go ahead and replace it. These lines can be bought at most auto supply shops by the foot so it is not a big $$ expense.

Good luck

Lexs400

my question regarding the vacuum tubes:
the booster gets the vacuum pressure from the big hose attached to it.
the smaller vacuum tubes that are sitting on top of the engine are the ones assumed to go bad. what exactly is the function of these tubes and how are they related to the abs or braking system ? if there's a leak shouldnt some warning light turn on ?
thnx.

Lexs400

bump.
any input would be appreciated.

nthach

the 3/8-1/2" black hose from the back of the intake plenum to the brake booster is the booster vacuum. the smaller hoses are all emissions hookups.

Lexs400

if there is lack of engine pressure coming to the booster, would that turn up either the check engine or brake light on ?
moreover can someone kindly describe the procedure to find out if the brake booster is working OK or not. I've already done the search and didnt really find any concrete steps to follow for the troubleshooting/isolation of the booster.
thnx.