I'd greatly appreciate your help with my 1995 F-150, 5.8L V-8.
On a recent trip, the brake pedal got lower and lower until it engaged the brakes only right at the floor. I thought it might be a master cylinder so I replaced that today but it's still bad. No signs of leakage of brake fluid anywhere. The vacuum hose to the booster is fine and the check valve on the booster is fine too. When I pull the check valve aside after running the engine then shutting it off, I can tell the booster has a vacuum built up. Pumping the brakes, even while running the engine faster has virtually no effect.
I'd be willing to guess something came apart in the rear brakes to lose the pedal that quick. Pull off the drums and see what's up with the rear brakes. Don't mash the brake pedal with the drums off though.
I inspected the rear brake assemblies on both sides and everything looks fine, same with the front disk brakes. When I have help tonight, I plan to bleed the lines to see if that helps. Any other ideas if that doesn't work?
I assume you have properly bled the brake system after M/C replacement to remove all the air. You need to chack the rear brakes for condition ie. broken/damaged parts or failed/frozen adjusters. You should also check all the flex lines to the front brakes and the rear axle. It is possible that one has failed and ballooning. You need someone to apply the brakes while observing for ballooning. Make sure the front wheel bearings are properly adjusted to prevent pad knock back. You might also want to examine the firewall around the booster to make sure it is not cracked. I believe that year had been corrected but, a few of the earlier model of similar design did fail requiring a repair kit to be installed.
I had a problem with my old f-250 . The acculmator for the abs was bad . Had very low pedal but no warning lites just brakes felt like they had air in system . Replace acculmator and my problem went away .
My brother and I bled the lines tonight and it's still bad. Can't pump up the brakes to any appropriate level. It just goes back to nearly the floor. We think the rebuilt MC may be bad but I'm interested in hearing more about the firewall problem. My brother noted that the MC does move up and down very slightly when you press hard on the pedal. Is this the firewall problem and was it a recall? It seems like a little motion might be normal but I'd appreciate your thoughts.
The rear and front brakes look very good, very little wear and nothing visibly broken. The parking brake works fine too.
We had not thought about line ballooning but will check for that.
Regarding the booster, can't we do the bleeding and tests with the motor off? My understanding was that the vacuum booster just made it easier to brake. In my Chrysler, I have full pedal with the motor off. Let me know if I'm off base on this.
Thanks to all who have written for your help. I'll be sure to post the resolution once I find it.
How many times did you bleed each wheel? It would take several times to get the air out from the master cyl.
Did you adjust the rear shoes as you put the drums back on? If the shoes aren't adjusted correctly, it can take half of the pedal travel just to get the shoes to contact the drums.
OK, I am not a mechanic and I haven't read all your posts, but it would seem to me the fact he can't bleed the brakes without the engine running to be a big deal. I don't know enough about how it works, but it seems the basic braking is not working without the extra push of the booster.
I had a master cylinder once that was leaking fluid past the internal seals so it could not build up pressure, but you have probably already mentioned this.
There was never a recall. Just a TSB and a service kit for those found with the firewall cracked. It was most common in manual trans vehicles. A visual inspection of the firewall will show it if it exist.
Make sure you manually adjust the rear brakes. This can be done using a thin probe to push the auto adjuster lever away from the star wheel while you adjust with a thin wide blade screw driver or brake spoon.
You can bleed either way. Keep in mind that the pedal will apparently be higher and firmer with the engine off after you deplete the vacuum by pumping. One quick check for booster operation is to deplete the booster vacuum by pumping the brake several times. While holding the pedal down at a normal stopping constant pressure, start the engine. The pedal should drop as soon as the engine starts and vacuum hits it. If it does not drop, you either have a vacuum problem or the booster is bad.
To properly bleed your brakes, have the vehicle relatively level so the air will go to the bleeder ports. Start by bleeding the master by loosening the lines one-at-a-time - rear port first - enough to leak pretty good as the pedal is pressed and held. Next, bleed the RABS valve located inside the left frame rail. From there bleed the brakes in the order of RR, LR, RF, & LF. You should bleed each and every port until the fluid expelled is clear and fresh with no sign of air bubbles. While you are bleeding a port, make sure you close the port before the fluid stops flowing and the pedal released. If you do, the air will be sucked right back in when the pedal is released. Do not open any port or line without first having moderate pressure on the brake pedal. Make sure the MC reservior never gets low and, make sure the pedal is always released slowly to avoid churning the fluid or sucking in air by an internal seal.
Thanks to the group for all of your great suggestions. I have checked all cylinders for leakage and they are fine. The fluid level in the MC was fine too which is a clue. It looks like the rebuilt MC I tried to install last week was defective. I returned it for a replacement but haven't had time to try it with the holiday activities. For some strange reason my wife wanted me to help in the kitchen for our family Thanksgiving dinner instead of working on the truck. Go figure...
I will get at it this coming week and will let you all know what I find out. It should have been a clue that the replacement MC failed the "bench bleed" procedure. I'll make sure this one holds pressure before installing it. So far I'm just out another quart of brake fluid and a fair amount of labor time. Now it's a "quest" to find out the final problem.
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