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1990 Ls400 Brakes Won't Stop Car


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Hi guys, so my dad's '90 LS400 has had a brake issue that has just become worse and worse over the past year. Initially, the brake pedal would go down almost to the floor but the brakes still worked well, which we initially believed was a brake master cylinder or brake booster issue. There was also a small brake fluid leak which I did not find around a year ago. We replaced the master cylinder about 6 months ago, which did absolutely nothing, but the car was still able to stop so we temporarily abandoned the issue as we don't have much money to spend on things like this. About a week ago, the leak became far worse (fluid in the reservoir would be empty within a few days) but the only leak i could find was in traction control actuator unit (Part number 47990-50010) right under the intake.

The biggest issue, however, is that the brakes no longer stop the car.. The pedal goes right down to the floor, and even if the master cylinder reservoir is full, pressing the pedal all the way to the floor will slow the car down BARELY but is incapable of bringing the car to a stop if it is in Drive. I have to put it in neutral for the brakes to work enough to bring the car to a stop. I wanted to know if anyone else has experienced a similar issue, and if this extensive of a problem (including the leak) could be caused by a worn out brake booster or the traction control unit. Just to add, brakes have been bled at the time of installing the new master cylinder, but not since this issue became worse, so I won't rule out the possibility of air in the lines as a contributor to the issue, but I am quite sure that it is not the main cause of the issue. Any help or advice would be greatly appreciated, thanks.

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I would rule out air in the lines first. If the reservoir bottomed out then its very likely some air got in the lines. This would explain and spongy pedal and no braking force. Its easy enough to bleed the lines so I'd start there.

Once that is done I'd figure out where the fluid is leaking. If the reservoir drained out then a lot of fluid as spilled and it should be pretty messy where the leak is. The stuff doesn't evaporate so it should be easy to spot.

...."There was also a small brake fluid leak which I did not find around a year ago.".... If you didn't find it how do you know it exists? By the loss of fluid I assume. Just to be sure as pads wear the fluid level goes down in the reservoir. dropping fluid level over a long period of time can be normal as the pistons don;t retract as far..

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Yeah that makes sense.. now the little actuator under the air filter seems to me like it's the only thing leaking, but i've heard the whole assembly cost somewhere around $2000 which is ridiculous, and finding the O-rings for the actuator is difficult.. Does anyone know an easy/cheap way to pick either of those up? I am going to assume that the brake booster is contributing to the issue as well so replacing that goes without saying.. Not like it's a hard part to find.

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