Hi guys, mind if I pick your brains?

Situation: brakes felt a bit spongy, figured I'd change the fluid, do a good bleed to fix.

Friend picked up fluid for me, brought home dot3. Ok, I thought full flush should not matter. Built a hose / receptacle, BTW 3/16 inch ID is too small, flushed both rear brakes. Got to front realized i needed new pads. Drove to pick them up, scary low pedal.

Replaced front pads, rear pads good. Bled front until clear fluid. Test drive.

Not happy. Pedal must be pumped, sinks to floor, couldn't stop hard enough to set off ABS.

Thought of stories about using the tube not working because bleeder valve sucks in air with pedal going up. So started bleed again today with assistant. Bled proper order, pump brake, push, open valve, close valve before pedal goes too far, repeat a bunch of times each wheel.

New test drive: much much better, though pedal is low, despite trying i couldn't lock up wheels even with effort. Pedal seems to gradually sink, but nothing like last night. Once or twice pedal got hard.

Vacuum leak? Tried to find it this morning, nothing found with propane, soapy water. Though car hits small flat spot now on acceleration, plus can't lock up brakes.

Master cylinder? Pedal fades, but huge improvement after today's bleed. Hypothetically if air was in master cylinder could I have purged some of it today during bleed? If it needs bench bleed, would pedal sink? (Fingers crossed - don't want my next post to be how the f*** do you get to the bottom nut on the master cylinder;-)

Gotta ask: dot 3 vs 4 does not change pedal feel right?

Thanks for looking. Love to hear where you'd go next.

John

 

Hi John,

Since your brakes felt spongy before you changed the fluid, you can't rule out a problem with the master cylinder and/or one or more brake hoses.

The X100 is supposed to be bled in a different order than the traditional one (caliper farthest from master cylinder then working to the one closest). Instead, the X100 order is front left, front right, rear left, rear right. The procedure for pumping the pedal is also different. Here are the instructions from the 1998 Workshop Manual:







It's unfortunate that you can't get the ABS module to kick in, because sometimes that can help if air is trapped in the module. I can't remember if IDS/SDD has a routine for running the pump during brake bleeding to pump air through the modulator so it can then be bled from the caliper nipples, but you might research that possibility. If your brakes are working well enough to engage ABS, you might try doing so repeatedly, then bleeding all for corners again in the above order. Sometimes that will do the trick.

Cheers,

Don

 

This all sounds a lot like my recent brake problems, all of which turned out to be related to the ABS unit. If there is air in there, obviously, you will have air / spongy problems, but in my case, I believe there was a particle (perhaps a piece of seal) causing the problem. If the flow through the ports and channels are not correct (or if the valving / solenoid operation is bad) the symptoms can be identical. In my case, fearing that I would have to find another ABS block, I first disconnected the lines and blasted air through the channels backwards and forwards (during which I noted a sliver of rubber appear) and then bled the passages back and forth, and also back to the reservoir, before doing another bleed through the brake cylinders. It's a tedious and messy operation, but it completely cured my pedal problems, and a year and a half of fighting what I thought MUST be air problems suddenly went away.
I am sure it has nothing to do with the problem at hand but, given that the book says to use DOT 4 plus, why would you use DOT 3?

 

dot 3 vs 4 is irrelevant to feel. dot 3 technically has a longer lifespan than 4 at the cost of hi temp performance but this is pretty irrelevant on a street driven car.