Lexs400

Guys,
I need either the steps outlined or the pages from the manual for a 93LS400.
The spongy brake pedal points out to misadjusted pushrod between the master cylinder and the brake booster.
I would appreciate the diagram and the steps to take it apart and also the measurements so that I can properly adjust the pushrod.
thnx in advance.

VVT-i

Did you check all of the sliding pins and all calipers to make sure they're not blinding/sticking?

Lexs400

the front two callipers have been replaced by the dealer.
the rear two, i doubt if they even bothered to check.
I will check them while I'm at it.
thnx.

Lexs400

calipers are fine. checked them.
now it's down to the pushrod. I just want to find out if the pushrod is adjustable before i open up the whole m/c and booster assembly.
does anyone have an answer to this one ?
thnx.

RTIS250

iTrader: (9)

There is a SST (special service tool) required to perform the adjustment... basically, there is a very small clearance that needs to exist between the pushrod plunger and the master cylinder.. its hard to judge this without the tool. If it hasnt been done, i would suggest doing an extensive bleed of your brakes, replacing the fluid in the process. Starting at the RR, then LR, then RF, then LF wheel.... then bleed from the abs block. Using a vaccuum type bleeder would work best for this, such as a Vacula. Most dealers have one... a spongy brake pedal doesnt sound like a misadjusted master cylinder though, a low pedal would suggest a misadjusted pushrod. your symtoms sound like air in the brake system...

Lexs400

well, intially there was confusion whether to call it a spongy or a low pedal.
I've now realized that the pedal from the top starts off as spongy with very minimal resistance but 3/4th way toward the firewall it becomes firm. and it never drops beyond that point, neither is the pedal spongy from that point on. that's the point where the brakes work how they should.
so when i'm trying to brake while driving i've made it a habit to start pushing the pedal a little earlier so that i can travel the initial 3/4th travel to the point where the brakes actually start to become effective and that's the point where i push onward when i want to completely stop.
my conclusion is therefore more of a pedal drop than a spongy pedal at this point.
given that you have mentioned a SST, does that confirm that the LS does infact have an adjustable pushrod ? someone has told me that the pushrods are not adjustable which is the reason I wanted to cofirm it before opening it up.
thnx.

RTIS250

iTrader: (9)

while i have not personally done a pushrod adjustment on a 90 LS400, i have done it on later ES and GS models, it would make sense to me, that the LS would have an adjustment as well, but i suppose there is only one way to find out. You should have enough movement, to be able to unbolt the master, and slide it forward enough to look down in there, i would still also recommend bleeding the brakes, this could still be the cause of your situation. Spongy at the top, but once the air in the lines have been compressed, the pedal becomes firm but low. In fact, i would suggest doing a full system bleed before pulling the master off. Just my opinion though...

Lexs400

thanks for the update,
I visited the local lexus dealer where the m/c and the booster was installed yesterday. told them about the SST and to my surprise the tech there had no idea what i was talking about. better yet the techs werent even aware whether there was a push rod adjustment.
so I had them pull the manual and yes infact there is an SST made for the adjustment. The service advisor asked me to give him a day so that they can locate the tool ! i have lost all trust in the dealership !
I have the pages from the manuals on how to bleed the system and I did infact have the system bled last week and the month before. Unless there is still some air lingering in the system, which it could be, i could take a last shot at it and have a local mech. bleed it again.
the thing that's funny is that the pedal has a mind of it's own, when the free play is there it's low but firm, at other times the pedal is high but very spongy. and that's very erratic.
the dealership service dept. as always are of no help...

Lexs400

well since the dealer wants labor all over just to open up the master cylinder to check the spacing, which i can easily do myself i decided to open up the m/c.

the sst required for the measurement of the push rod adjustment as per the manuals is 09737-00010.

but the botls are positioned in such a tight spot that the regular tools just can't seem to fit into that small area and leaves no place to turn the wrench either.
could someone kindly recommend a tool which can be bought from sears etc. either manual or power, that can be used to take the three bolts of the m/c out to loosen it from the booster assembly.
a picture perhaps or a part number for craftsman tool etc.

thnx.

Lexs400

for reference, i found a pic on the web explaining what I'm trying to adjust.

RTIS250

iTrader: (9)

Ive been able to get it with normal handtools, extentions, and swivles... maybe ill take a look at one tomarrow more closely, as i dont clearly remember how to do, havent done it in a while...

Lexs400

I went to a local mech. today and he was able to get it out with this tools, extensions etc.
given that I don't have the SST we had to adjust the setting several times to figure out where the pushrod should be. the difference is literally day and night !
with the pushrod outwards (towards master cylinder) the pedal was rock hard ! but at the same time it was locking the wheels. the mechanic was busy so I couldnt ask him to keep opening up the m/c . so I had it adjusted almost back to the original setting for now.
I plan on going to Sears and getting those extensions and tools so that I can open it up myself and find the optimal adjustings for pushrod.
I will keep you posted.
and thanks very much for everyone's input in this thread to help the troubleshooting. it is much appreciated ! especially RTCamaroSS.

RTIS250

iTrader: (9)

No problem bro, im glad we got it sorted it out and you're happy with the car! Thats the most important thing!

Lexs400

ok so one problem is solved, the pedal is no longer "as mushy" as it used to be. took a lot of tweaking of the pushrod.
now to the second problem. The brake pedal requires more than normal foot force to stop the car. this in no way is similiar to a non-working booster. I did the booster check as per manual and it checks out ok.
In a way the situation is as if there is something blocking the brake lines so that when the pedal is pressed the amount of fluid doesnt reach the callipers with the same force hence yielding a less than optimal stopping distance.
however, whenever ABS is activated, by force, the brakes are perfect for about 5 or so minutes. the pedal height drops for about 2mm while the brakes are working perfectly fine, but after that the pedal height increases a bit and brakes go back to being ineffective.
any idea what's going on here?
I appreciate the responses for this situation.

Lexs400

After exhaustive testing here's what the conclusion is so far:

The pedal travel is normal, but all the pressure from the booster/master cylinder is not reaching the callipers.
How I tested this, well the front rotors are warped. But, because of the fact that the car's not getting the full braking power at the front wheels, the warped rotors are never felt at braking (pusling pedal).
However, once ABS engages, afterwards for about 30 or so minutes, it yields the brakes to perform normal. The distance of normal braking is reduced resulting in excellent stopping power. If the car is then turned off or after about 30 minutes the brakes go back to the usual where there is less braking power and increased braking distance.

Question: does the 93 LS have integrated ABS or non-integrated ?
I'm assuming non-integrated as the master cylinder and accumulator are seperate assemblies.

Question: Does the Nippondenso system (employed in the LS400) have a RWAL dump valve ?

Question: Other than the HCU, is there any other component that normal braking system uses from the ABS portion ?

I would appreciave a response from the master techs.
thnx.