Does this sound like a bad brake booster now?

2001 Ford Taurus - 6cyl - OHV. Just replaced the master cylinder because it was leaking. When I took it for it’s initial test drive after I got everything buttoned up, the brakes just didn’t feel right. Wouldn’t described them as “soft”, but I would say that I couldn’t come to a real quick stop if I had to. Went back and re-bled all the lines starting at the right rear and finishing at the left front. Took it for another test drive and brakes still aren’t right. Checked the vacumn hoses going to the booster and they were fine. No hissing or whining noise coming from the booster either. Best way to describe the way they feel now is, if I slam on the brakes, instead of “screaching” the brakes, it feels like the ABS is kicking in. I’m not even sure this car has ABS or not?? Is there a way to diagnose if it’s definitely the brake booster ?? Also, the rubber seal on the booster behind the master cylinder was intact and I’m doubting any brake fluid got in there (but who knows?).

IF you just did a new master cylinder DID you follow the instructions on PROPERLY pumping up and bleeding the master cyl while it is still OFF the car? Most have instructions in the box to do so…otherwise you will never be able to get the new cyl bled properly while it is on the vehicle…this is why they tell you to do it off the car… Then after you bled the master off the car…you then need to bleed the brakes at all four corners of the car…starting with the wheel furthest from the master…the rear passenger…then rear driver…front pass…front driver…

I have been (of late) simply cracking the bleed screw open and attaching a short piece of rubber hose to the nipple of the bleeder to each wheel…one by one… Crack the bleeder open and give it bout 10-15 min to run out…all the while topping off the master cyl reservoir. Do this to each wheel and you can bleed all 4 with no assistant. Did you follow all of these procedures Sir?

I read your post again and notice you said that it feels like the ABS is kicking in…thats a mighty strange thing to say…I mean when ABS kicks in the pedal pushes against your foot and you hear the ABS pump and your stopping is severely limited…this isn’t what I would expect… I’d expect a semi-soft pedal…soft up top biting the brakes near the bottom, but all round weak… Each of these symptoms would be what I expect from an improperly bled master from the get go.

Remember the repair manuals are free online at Autozone dot com… silly not to utilize them for specifics.


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I bench-bled the master cylinder off the car (right out of the box per the instructions), and then made sure that brake fluid was dripping out of the two brake line fittings after I bolted it to the booster, but before I connected the brake lines themselves to it. I have a shop manual for my 05 Taurus which I did indeed use. To my knowledge, there is no difference in the 01 Taurus concerning master cylinder replacement. As for bleeding the brakes, as I stated, I started at the rear passenger bleeder and worked my way around as per procedure. The reason I specifically mentioned the feel of ABS, is because I’m thinking this isn’t related to air in the line (although I certainly would have no issue bleeding them again). I’m still leaning towards the brake booster but I really don’t want to replace it without properly diagnosing it first.

Let me preface this by saying I don’t know anything… but to confirm its not an ABS issue, you could remove the ABS fuses from the fuse box (I have no idea if there are ramifications to doing that), then test drive it. If there are no ABS fuses present, that could indicate you don’t have ABS anyway. Also I think there should be speed sensors going to each wheel and an ABS pump under-ish the master cylinder. You could also plug your VIN into a VIN breakdown site and it should spit out the specs.

I’d like something a lot more descriptive than “it feels like the ABS is kicking in”. Skip that. Go with actual feel & sound (if any).

If the brake booster was bad the pedal would feel incredibly stiff and like it took all you could to apply the brakes with any force. You can also sit with the car off, pump up the brake pedal until it gets very stiff. Then, while holding your foot on the brake, start the car. When the car starts you should feel the pedal sink. If that’s what happens, its good reason to look elsewhere.

Leave open the possibility that you new MC was bad out of the box.

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Pumped up the brakes with the car off and started it and the pedal did indeed sink. The best description I can give is that the pedal is somewhat stiff as opposed to spongy. Also, it’s almost like the brakes seem to be fine for the “first half” of depressing the pedal (will easily slow the car down). But almost seems to bottom out the second half of depressing the pedal. During the test drive, I pulled into a parking lot down the street and slammed on the pedal. The car came to a complete stop but certainly didn’t come close to that head jerking, screaching that you’d expect.

Another test would be, with the engine running apply the brakes. The paddle should sink the normal amount. With your foot still on the brake shut off the engine. If within 30 seconds you feel the brake peddle try to rise with your foot on the brake then the brake booster is bad.

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I think you might have a mating problem. Since you have a factory service manual, did you follow the instructions for adjusting the pushrod in the booster before installing the master cylinder? Sometimes those instructions are located in the replacing the booster section.

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I didn’t see any specifics concerning the installation in the service manual but at this point, I think it’s probably better if I just remove the MC and then re-bleed and re-install. I will add that the brakes definitely do not “pump up”.

“I will add that the brakes definitely do not “pump up”.”

This sounds like the pushrod is not adjusted properly. While you have the MC out, measure the distance from the mounting surface to the tip of the pushrod. Then measure the distance from the mounting surface on the MC to the plunger in the master cylinder. The measurements should be the same. There is often a special tool for this job.

If you still have the old MC, you could compare the plunger depths of the old vs the new one.

You will have to find the procedure for adjusting the pushrod in your service manual.

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In most cases, every 1mm of gap translates into about a half inch of extra pedal travel.

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Just re-read the shop manual on this a few times. There is no mention whatsoever of adjustment of the pushrod for removal/installation of the master cylinder. It goes into detail on bench-bleeding or on-vehicle bleeding of the MC. But no where does it mention any adjustments whatsoever to the pushrod. Even read the section on the brake booster and again, no mention of adjustment of the pushrod.

Went back and started fresh with re-bleeding the master cylinder. Pumped through a lot of brake fluid without any air bubbles. Still can’t pump up brakes. The last thing I’ll do again is bleed the brake system (again). Assuming that doesn’t work, I’m going with Cigroller’s suggestion that the master cylinder could be bad out of the box. As an FYI: with the old MC I could pump up the brakes normally (the pedal would just eventually sink down since it was leaking). Now, almost the opposite. Can’t pump them up, but they hold. The problem is, I couldn’t stop “instantly” if I tried to now.

Is this “new” master actually new? Or rebuilt? It is possible that you got yourself a lemon Master…I had this happen to me once or twice across MANY masters in my day… Doesn’t happen often but it is not impossible. Reading your post I can tell you are doing the procedure correctly.

Now does your Taurus manual say anything specific pertaining to bleeding the brakes with ABS?

I don’t think there is a special procedure but just checking with you…

Not that this is your issue but an interesting story nonetheless…I was pulling my hair out one time trying to bleed the brakes after a master cyl replace on a Toyota Rav4… I bled and bled and bled…to no avail…spongy pedal… I was contemplating suicide near the end of this… suspecting the master and or my abilities. Thats when I looked up online what my issue was and stumbled across this info on a Toyotie site…as soon as I read it I KNEW this was my issue…read below…

Know what it was? There was a load sensing device on the rear axle…you had to have the vehicle down on the ground in order to get a proper pump up of the brake system…it wouldn’t bleed and give you a nice strong pedal no matter what I did while the truck was in the air with all 4 wheels off the ground… I had the truck up on my lift at the time and NEVER thought about anything like this… Apparently on trucks and SUV’s since there is the possibility of overloading the vehicle due to their cargo/people carrying ability…they use this device to tell the brakes how to operate…brake bias…when load of vehicle changes…May be possible that the Tortoise has a similar device thats messing with you? Or the ABS needs a special bleed procedure? Other than those things…you could have a bad master cyl. Just some food for thought.


The manual doesn’t state anything different for bleeding ABS (which I’m pretty sure this one doesn’t have anyways). As for the MC, it is a new one and not rebuilt. All good info above - thanks! Will report back when I finally figure this one out and/or replace the “new” master cylinder.

You should know whether you have ABS or not…I mean there is a huge conglomeration of brake lines and an electric motor at the ABS unit…its rather large and not easily missed… If you dont think it has ABS you are probably right as i would think you would have already seen the ABS unit during your Master cyl adventures…


Download this. It has more info than you probably need, but it gives you two methods of checking the adjustment of the pushrod.

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Thanks Keith. I’m going to follow this procedure before I run out and get another MC. There was no mention of any pushrod adjustment in the shop manual that’s why I didn’t think it needed any adjustment. Thanks again.

Just by chance, does this have rear drum brakes? And if so, did you remove the drums at any point - e.g. to inspect? If you did, then the shoes need to be adjusted before using the brakes. If rear shoes are out of adjustment you will get a soft pedal that will hold. Unlike calipers, it will take forever for the auto adjusters on the rear to get them adjusted to the proper engagement point, and the pedal will stay soft all the way. You manually adjust the auto-adjusters to just short of where the shoes drag.

Just a thought.

Cigroller - yes, it has drums and yes, I actually adjusted them just short of drag when I was bleeding them initially. I’ve adjusted rear drums before in an 05 Taurus in the family so I’m familar with these. I just can’t get these brakes to “pump up” for the life if me since I’ve replaced the master cylinder.