Hey guys,

So I recently did a bunch of work to my '99 SC300 suspension and brakes. I installed LS400 calipers up front, rebuilt them as well before installing. Everything on the car is done, except the brake bleeding. I've spent several days and almost killed 6 bottles of DOT 4 brake fluid trying to bleed/flush the system. No matter what, there is still air in the system. The brake pedal feels useless, it goes pretty much right to the floor with little to no feel and when I took it for a test drive it barely wanted to stop.

I've tried the one person bleeder method, and it fakes me out (let me explain). Most of the air seems to be in the front calipers, which makes sense, since I drained those calipers of fluid to rebuild them. The problem is that when I'm bleeding the brakes, (mostly up front) it'll look like you've gotten all the air out of that line/caliper (only fluid in the line on the bleeder valve), but if you wait like 30 seconds a lot of tiny air bubbles start coming out on their own. Once this slows down, you can push more out by pumping the brakes, and this just seems to never end. So I bought a vacuum brake bleeder, which is helping tremendously in getting the air out, but there's just so much air coming out - it's literally non stop, even in the rears now. I don't see how there could be that much air in the system?

I don't see any leaks anywhere, all of my calipers and pistons seem to be working correctly (none are seized that I can tell), and my brakes felt fine before this upgrade. Not great but fine.

Can anyone chime in as to what the problem could be? Is my master cylinder failing? Do I need to bleed the abs system? Should I just get more brake fluid and keep going until it seems like all the air is out? I'm just not sure what to do at this point and I'm very frustrated that this is preventing me from driving the car again. I've been doing research on my own and haven't found any clear answers or anyone with a similar problem to mine so I figured I should just ask directly before wasting more time and money.

Thanks

 

There shouldn't be that much air in the system. I replaced all 4 brake calipers before and bled it out with less than 1 liter of fluid.

Are the bleeder valves all pointing up? I don't think it's possible to mount them upside down on our cars, but I have seen it done on other cars before.

Which order are you bleeding the calipers in? I usually go farthest to closest from the master cylinder, so passenger rear to driver rear to passenger front then driver front. Are you making sure that the master cylinder never goes below the "low" line?

Everything is a shot in the dark right now without seeing the car in person and feeling it first hand.

 

Yes, the bleeder valves are on top of the calipers. (As a related side note I think it may be possible to install the calipers upside down because when I was mocking the calipers up at first I got it to pretty much bolt on upside down, realized it looked wrong and that the bleeder was on the bottom and realized I was being dumb lol). Yes I did the same order you described. I used that order for the 1 person bleeder method, plus with the vacuum bleeder. The vacuum bleeder did make a difference in the pedal feel compared to the manual 1 person method, but I am very sure there is still air trapped somewhere. I also made sure to keep the master cylinder topped off while doing it, and never went below the low level.

I realize it is hard to know without seeing/feeling the car in person but I do appreciate the help. That is why I came to post about it here, I feel like I've done everything correctly and I did my research before attempting all this (since I'm new to this kind of thing). I'm also going to continue trying different things here and see if I get any results in the meantime.

 

Get somebody to help you and do a combination of vacuum and pedal pump bleeding. Would seem odd to be a problem with the master cylinder since it worked fine up to this work. We went thru this yesterday on the race car, had to get both methods going to get all the air out.

 

I actually did that for my final round of brake bleeding the other night, I had my brother help me. We used the vacuum bleeder and pumped the pedal until each corner had no air bubbles in the line. The brake pedal feel got a lot better, but it feels about the same as it did stock. I'm realizing now that there probably was a problem with the braking system since I bought the car and didn't know because I figured that's just how the stock brakes felt. I never did think it stopped well stock but I figured they were just crappy stock brakes.

Upon further inspection, I came across this leak between the master cylinder and the brake booster, I don't know how I didn't notice this before when I checked for leaks... but anyway I'm guessing this is the culprit? So, would this point to the master cylinder failing or the brake booster failing? Also, I'm assuming they're probably both stock honestly so they're close to 20 years old at this point. Should I just replace both?

 

I am guessing master cylinder after seeing that.

 

I just went through the same situation o my 99 SC400. Replaced both the Brake booster and master cylinder. Pedal is still a bit soft but the car stops much better even with Stop Tech SS brake lines.
I suggest you change the brake master cylinder at least, both if you can.

 

I currently building/restoring my 93 SC.

I would suggest rebuilding the brake cylinder internal seals and gaskets. Driftmotion sells the kit and so do the Lexus parts websites.

The brake master piston rebuild kit will save you from buying a new master and I would also suggest replacing the gasket behind the booster on the firewall.

Here are the part #'s : 0449330241 for the rebuild kit. Driftmotion also sells it and that's where I purchased mine.
And the gasket behind the brake booster 4478514020.

I did this along with StopTech lines, LS400's and TT rears and my pedal is confidence inspiring stiff. No dead travel after a good bleeding. If you can get someone to pump and hold the pedal for you. It makes the process much easier and quicker. The job in a bit time consuming and single leg tedious when done properly.

Of important note is that you it helps to bleed your master cylinder before you do the brake lines. There is a specific tool for it and you may be able to rent from an auto supply store. I borrowed mine from a mechanicand it made the job much easier and I'm pretty confident it's why the brake project went successfully the first time we tried.