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Wade Joseph

Soft Brake pedal

15 posts in this topic

Ok, I have a 98 F150 and I have replaced every component in my brakes both front and rear with the exception of the actual lines, and the antilock unit. I have bled them numerous times and the pedal is still soft. Anyone got any ideas?

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Some newer vehicles with ABS have very specific bleeding procedures different from what we may have done in the past.

The traditional longest to shortest method may not be the right bleeding sequence, and also some ABS valves have to be purged by activating the ABS system. Shops ususally do that with the electronic service tools.

Dunno if all that applies to your truck, but it did to my Buick.

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Is the pedal soft or low?

Are the rear brakes adjusted up good?

Does this have 4 wheel abs, or just rear abs?

Did the hydralic system ever go dry? ( brake fluid)

If the pads and shoes are new, did you give them time to brake in?

If everything looks ok, then you may need to bring it into a shop and have them do a service bleed on the abs pump.

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Can you give us a time line. Basically from the beginning what happened and what you tried in order to resolve the issue.

Rarely do we have to "bleed the ABS" after replacing hydraulic components.

My bet is that you replaced the master cylinder with a remanufactured unit. If this is the case you have two choices. Keep replacing with remans until your pedal returns or try a new master cylinder. It is not uncommon to have to try several reman units to get one that actually works. I have also had the same thing happen with new units but typically the second one will work fine.

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Yeah, I did get a bad reman master cylinder one time.

Pedal was not soft, it just went completely to the floor on an intermittent/random basis. Talk about a scary feeling!!!

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Well, lets see. First I replaced the front brake pads. I used a C clamp to compress the calipers and get the new pads in place. I then bled the front brakes. Pedal was soft. But not that bad yet. Truck still seemed to take longer to stop. I pulled the back drums and the shoes were pretty thin, so I replaced the rear shoes complete with a new spring kit. Brakes were worse. I could not bleed rear brakes as the bleeder screws were frozen. Then between 25-30 mph I got a bad vibration and strong smell of hot brakes. I then replaced the master cylinder. Same result, still soft and takes a long time to stop. I pulled the back brakes apart again and found the emergency brake cables stuck. Got them pushed back and released. I replaced the rear brake cylinders and the rear drums. Still have soft pedal. I have bled nearly 2 qts of fluid from the system. Never once have I gotton a large air bubble. Today I bought a power bleeder kit. If I don't get good results after flushing and refilling and power bleeding, I think I am gonna have to take it in to a garage.

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What brand of brake pads and did you turn the front rotors?

I'm sorry but I have to ask (I've seen some things in over the years that boggle the mind grin.gif ). When you are bleeding the brakes you have somebody pushing down on the pedal while you crack the bleeder screws, correct.

The brand of brake pad is especially important. I have on more than one occasion run into cheep pads that will not stop a vehicle. Replacing the pads with higher quality/major brand has solved this problem in nearly every situation.

On the other end if you replaced them with the "ceramic" pads and your vehicle was not O.E.equipped with them than can also cause braking issues. Not all ceramic pads are created equal and some pads with very little ceramic material are marketed as ceramic. getting back to the point, If they are true ceramics they require more braking force to get the same affect as there non ceramic counterpart.

As far as turning the rotors. If the rotors are concave or dished in the center it can give a sinky pedal feel. It doesn't happen that often but occasional you'll run into it. Making sure the rotors are not only true to avoid pulsation but flat in order to fully transfer braking force is important.

When you pumped up the pedal after installing the new pads did you push the pedal all the way to the floor. Debris will accumulate in the bore of the master cylinder in the places that rarely get used. If you push the pedal to the floor it will allow the seals on the piston to travel through the debris and potentially damage them. Short pumps are always the best option.

I assume that everything was fine before you replaced the pads so I think that the last scenario is the most plausable

if that is true. As far as still having a soft pedal you didn't mention if you used a reman master or a new master. If it was e reman than I would probably either try another or spring the extra cash for a new one. I guess I would also be curious if you bench bled the master before you put it in.

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On my full size bronko my brake peddle is soft but it is due to a leak in the vacuum booster.

brakes still work, just takes a little longer to stop now.

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No, did not turn rotors, they were in good shape, reman master cyl. have good vacume from booster. Used OEM style aftermarket pads from reputable auto parts store. Maybe it is the master cyl. I purchased a power bleeder and am gonna try to flush system and the master cyl. Yes, I bench bled the master cyl, but am gonna re-bleed it without brakelines attatched with some short pieces of brakeline I purchased recircing the brake fluid back into itself once I empty the fluid thats in it now.

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Oh, I forgot to mention, I have also bypassed the rear abs unit by running the line to the back brakes straight from the master cyl.

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Bench bleeding requires lines to be returned to the reservoir while you are bleeding? I'm not really sure how you did it the first time.

When you bench bleed it pay particular attention to the fluid being returned. I have noticed a similarity between always having little bubbles come out of one or the other fittings and a bad master cylinder. This doesn't always happen but you can bench bleed the snot out of them with no change.

Keep us posted on what you find Wade!

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Well, finally some good news. I had everything disconnected today, I allowed all the fluid to gravity drain. I bled the rear abs unit, rigged some old tubing from the outlets of the master cylinder back into the resevoir and pumped the pedal thill I had good flow recircing. Hooked the brake lines back up, refilled with fresh synthetic fluid, allowed it to gravity bleed till I had good flow at every wheel. Tightened everything up, bled each wheel in sequence, and wallla! I have a good pedal again. I am off for a test drive. It stops well in the driveway.

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Quote:

synthetic fluid


I know ford doesnt recommend synthetic fluid in any of their vehicles, I dont know what aftermarket shops think of it, but I wouldnt use it!

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I have been using amsoil or mobile 1 in every ford I have ever owned. This particular truck has 171, 000 miles on mobil 1. Might as well go with the brake fluid as well.

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"Synthetic Fluid" ?????

DOT5 brake fluid is synthetic and very few vehicles use it!

DOT3 and DOT4 are interchangable and compatabile with each other. DOT5 cannot be used with either 3 or 4. You MUST completely flush before installing, and there are still frequently problems - the mix of 5 with 3 or 4 causes rubber failures in all brake components - master cyclinder, ABS unit, calipers and wheel cylinders. Don't change to it unless you know what you are doing.

AMSOIL doesn't have a brake fluid available at all, and I don't know of a Mobil1 brake fluid.

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