Good evening to all, my daughter was gifted a 1990 LS400 which is in overall great condition. After driving it home, the brakes were very soft and then stopped working until pumped repeatedly every time. The fluid looked AWFUL, we drained it all and cleaned the reservoir, bled all four wheels apparently the wrong order for this car and accidentally ran the reservoir empty. Per my Googling, I need to bleed the ABS and then re-bleed in RR, LR, FR, FL order. Several sources say there's a bleed screw like the caliper ones on top of the ABS module, but there just isn't (see photos). Does anyone know how to bleed a 1990 ABS module?

Best Regards,
Andrew

 

You sure the master cylinder is good? There is no special procedure to bleeding the system do as normal although it could take awhile since the system had no fluid in it. Bleeding order doesn't matter contrary to conventional wisdom. Source: I've done it in different sequences with the same positive result.

 

The master cylinder very well may be bad, just wanted to ensure all air was out of the lines first. Are you aware of a bleeder screw at the ABS unit?

 

I'm aware of bleeder screws on some ABS units, does your car have traction control? This shows a bleeder screw if equipped.

https://www.japan-parts.eu/lexus/us/...n=47990#47547G

 

This looks like the non-Trac ABS module, 44510-50010
https://www.lexuspartsnow.com/oem-le...ol_module.html

Note the ones with Trac are noted W(TRC) in the description

I believe the only way to bleed these is to activate the ABS. I could not find a way to do it without an old OBD-I Toyota scan tool (which I don't have), so I waited until I activated the ABS a couple of times and then re-bled the system.

 

I was doing some further research on why this bleeder screw is only on cars with the TRAC ABS module

The bleeder screw is specific for the TRAC system, which has a corresponding brake line coated in red.

This is because that line and that bleeder screw remain under high pressure at all times.

The bleeder screw will only bleed the TRAC system, not the whole ABS module. Do not open this screw without taking proper precautions, or fluid will come out everywhere.

Source:

 

i second the master cyl to be likely bad, if pumping produces more brake pressure.

 

I am not aware of any ABS bleeding procedure. Regular bleeding, sure, but not ABS.
I've changed my brakes (1990 LS400), including the calipers, twice, and bled my brakes a few times, and have even flushed the lines and the entire system only a few days ago, but I never bled the ABS module. Yet, the ABS works just fine. Not that I run into much snow in N. California, but some finely polished manhole covers triggered the ABS a few times in rain and the car responded marvelously.
Considering the terrible state of your brake fluid and almost certain presence of air in the system, your master cylinder seals are almost certainly shot. That means you either need to rebuild the master cylinder or replace it. OEM is not available any more, save for used ones. Same is true of your caliper pistons - they have rubber seals and it is safe to say they should be replaced too, meaning, you want to rebuild those calipers. You may also have a leak somewhere, so inspect for that too.
BTW, Lexus proper order for bleeding is Left rear, and then the rest - RR, RF, LF which is different from other cars: RR LR RF LF. But as someone said, it will most likely be fine if you do RR, LR, RF, LF. I don't know if there is a separate line for each rear wheel, but if there is, then the wheel order for rear wheels matters even less.