RotorJoe

I have a 93 FD and the brake pedal feels a little mushy. It takes one pump before the pressure is threr and then it holds it. Although the next time I have to stop I need a slight pump to build up pressure. Also in revers coming to a stop is sounds and feels like the ABS tries to kick in. I notice the same thing on harder stops. It only feels like the ABS kicks in at the last 5mph, and I don't think it should have (I didn't think I was breaking hard enough to kick the ABS in).

So, I know that pressure loss is usually contributed to the master cylinder, but this is the first car that I have owned that has an abs system with problems. My previous car had no issues with the abs.

Do you guys think this is a problem with the abs pumps or the master cylinder?

PS: I have checked all my brake lines, no leaks and I just replaced the front brake pads.

rzograbian

well since no one is helping out:

have you tired to bleed the air out of your brake system? if you dont know how to do that, mechanic shops can do that but its really easy (requires 2 people though)

DigDug

You have air in the system. Sounds like a lot. Bleed the brakes thoroughly.

If you haven't in the past year or two, you may want to completely cycle out the old fluid for good measure. I'm guessing that hasn't been done recently...

rxtasy3

iTrader: (2)

I bleed mine by myself. 20oz coke bottle 1/4 full brake fluid and piece of vac hose.

RotorJoe

Yes I did bleed the system. I had to open the lines to force the pistions in the calipers to return. I did not have the specialized mazda tool. After that I blead the system. I then felt the same mushyness as before and though I still might have air. I then only went to the two rear brakes and tried again. I pretty sure air is not the case. Could be though, I will bleed and flush the whole system when I replace the master cylinder.

I tend to think it is the master cylinder but I don't know if the ABS pumps can make it feel like that too when they start to go out. I can buy a used master cylinder for 30 bucks shipped so I will try that first. I hear the ABS pumps are more expensive.

Thanks for the replies. I was just going to let this thread fall into a deep dark hole. Maybe it sounded like I was asking a stupid question. I just don't want to buy the pumps if its the master cylinder and vis versa. Although the master cylinder is at a price that is an acceptable if it is not it.

DigDug

When you let some air get in the system (like when a mistake is made when bleeding), it can take several times of bleeding the system to get it all out. Make sure you are doing it in the correct order, and do not allow any air in! That is to say, make sure you are closing the valve BEFORE your buddy lifts any pressure off the brake pedal. Then he can release it.

You may have to go around all four corners as many as four or five times (maybe even more) before you get some of the harder-to-reach air out of the system. Also, drive the car between each bleeding session, and attempt to actuate ABS each time. When the ABS actuator cycles, it opens a normally-closed section of the circuit to the main system - this part is closed when you are sitting there bleeding the brakes with the car turned off, so if there is air there, it will not come out until the actuator is cycled.

DigDug

Seriously, it does not sound like the master cylinder is faulty. I really think you just have air in the system. No offense, but I think you probably let some air in while bleeding it, or even more likely, while retracting the pistons. It is quite easy to do...

Also, why bother opening the system just to push the pistons back in? Every time I change pads (which is fairly often), I push them back in using a self-designed tool that is basically a C-clamp (with a little plate to catch both the pistons simultaneously), and I never have to open the system.

RotorJoe

Thank You, This was what I was looking for. I will try bleading the entire system again at each corner. I will make sure we pump the pedal four to five times in each corner while I close the nut prior to the pedal hitting the floor each time. Then I will drive it around and blead the entire system again the same way. I also use a tube connected to the nipple and the open end into a cup of brake fluid, so if it sucks in hopefully it gets fluid, not air.

This is a more indepth process then just bleading non abs brake systems. Thanks for the help. I will let you know how this goes.

DigDug

Yeah, it's a tedious process, but when you get it down, you can get a very solid pedal every time. The brake pedal on my FD has virtually no travel whatsoever, even when pounding on the brakes lap after lap for extended periods of time on track. It just takes some practice, and preferrably one buddy that will learn to communicate with you, then each time it will get easier and easier.

I usually do between 6 and 10 repetitions on each corner, and of course in the prescribed order: RR, RL, FL, FR. Also make sure that you keep the fluid level at or above the MAX line the ENTIRE time - this is one of the most common mistakes that people make when bleeding, and it is certainly the way to get the most air into the system. After bleeding all four corners, drive it and try to actuate ABS. Then repeat. Each time, you should feel some improvement in the solidity of the pedal. If you don't, you are not doing it right...

DigDug

I should probably share the procedure I use for bleeding. Assuming your buddy is in the car already, it's like this:

1) Get to corner, get ready to open bleed screw.

2) Have buddy pump brake pedal 5-8 times. On the last pump, he must hold the pedal down with reasonable pressure and not allow it to travel back at all. When the pedal is depressed and he is holding it, he should say "open!".

3) Hearing "open", you open the bleed screw just enough to get some flow through the tube. As soon as you have it open, repeat "open" so that you buddy knows to expect the pedal to gradually drop, which it will begin to do as soon as you open the bleed screw.

4) Your buddy is important here - he should call out "close!" before the pedal hits the floor. Plus, he should not back off the pedal any during this time - rather he should keep consistent pressure on the pedal as long as the bleed screw is open. This prevents drawback of air into the system.

5) Hearing "close", you close the bleed screw immediately, and repeat "close" when you have the screw tightened, so your buddy knows when he can release the pedal. Your buddy will notice that the pedal stops gradually dropping towards the floor when you call out "close" (when you close the bleed screw). He can then release the pedal.

6) Repeat from step 1. Do this 5-8 times on this corner.

Then, once you have repeated enough times on that corner, move to the next. Be sure to follow the correct order: RR, RL, FL, FR. Once you have done this for all four corners, drive the car and actuate ABS. Then, if it still feels mushy, repeat this entire process. Keep doing that until it feels solid!

RotorJoe

Cool, Thanks. I have the general idea down, it's just this way is way more indepth. I have pulled air out of my brakes in the first gen by just going to the corner furhtest away from the master cylinder. I never had to go to the other corners.

Thanks
Again

RotorJoe

Maybe I will buy that special mazda tool so I don't have to crack the brake lines next time I change my pads.

DigDug

Oh, I left out an important detail! When the fluid is flowing through the tube, you are looking for bubbles of air in the fluid. These can be quite small, especially if you have gotten your fluid up to its boiling point. You will see the largest bubbles in the first repetition, then they will gradually get smaller with subsequent repetitions. If you hit a pocket of air, you may see larger bubbles come through suddenly. My rule of thumb is, if I see any bubbles at all (even tiny ones), I am going to do at least two more repetitions. Thus, the first time you get no bubbles in the fluid, do it one more time. If you still get no bubbles this second time, do a "final" tightening of the bleed screw and move to the next corner. This is a bit more specific than "5-8" times. It could take less, it could take more...

rxtasy3

iTrader: (2)

Noone has mentioned this but always start at the wheel farthess from the master cylinder, RR, LR, RF, LF.

RotorJoe

[Be sure to follow the correct order: RR, RL, FL, FR.

But Thanks

It's too rainy today to do any work, I will try tomorrow.