Brake Pedal soft
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Freshman User
Joined: May 2014
Posts: 49
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From: Bensalem PA
Brake Pedal soft
Hey All,
I have my 1991 f350 7.3 dually, the brakes were just done by prof mech. My truck stops great , but the brake pedal goes almost to the floor, the truck stops on a dime now. but i dont know if this is normal. I have also replaced the vacuum pump in the last few weeks.
is that normal for this truck? or ?
thanks
Dave
I have my 1991 f350 7.3 dually, the brakes were just done by prof mech. My truck stops great , but the brake pedal goes almost to the floor, the truck stops on a dime now. but i dont know if this is normal. I have also replaced the vacuum pump in the last few weeks.
is that normal for this truck? or ?
thanks
Dave
Laughing Gas
Joined: May 2009
Posts: 854
Likes: 49
From: Maine
+1
Maybe speak to the guy who did the brakes? Did you ever have a correct pedal after the brake work was done?
You are not down on fluid, right? Without fluid loss, bad pedal with good stop sounds like a MC issue.
Roy
i ain't rite
Joined: Mar 2005
Posts: 65,507
Likes: 5,563
From: Marlboro Mental Hospital.
the master cylinder used was marginal when new and the pedal would slowly sink almost to the floor.. after years of complaints from my drivers, i switched all the trucks from the stock 1 1/16 or 1 1/8 master cylinders to the larger 1 5/16 master used on the F-Superduty.
and all the brake complaints disappeared.
and all the brake complaints disappeared.
Laughing Gas
Joined: May 2009
Posts: 854
Likes: 49
From: Maine
the master cylinder used was marginal when new and the pedal would slowly sink almost to the floor.. after years of complaints from my drivers, i switched all the trucks from the stock 1 1/16 or 1 1/8 master cylinders to the larger 1 5/16 master used on the F-Superduty.
and all the brake complaints disappeared.
and all the brake complaints disappeared.
i ain't rite
Joined: Mar 2005
Posts: 65,507
Likes: 5,563
From: Marlboro Mental Hospital.
no, you need to modify the lines and booster to make it fit. the mount flange to the booster is 1/16 inch larger, and the lines are larger so they use bigger fittings.
i modified the boosters to accept the masters, and used larger line nuts to adapt them.
the larger piston moves a lot more fluid, resulting in much better brake applications with less pedal travel.
i modified the boosters to accept the masters, and used larger line nuts to adapt them.
the larger piston moves a lot more fluid, resulting in much better brake applications with less pedal travel.
Laughing Gas
Joined: May 2009
Posts: 854
Likes: 49
From: Maine
What's involved in the "modify the booster"?
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Senior User
Joined: Jun 2010
Posts: 291
Likes: 0
From: Long Island, NY
I'd be interested to see how you did this as well, I have had a soft pedal for years and don't want to make the jump into hydroboost. My entire brake system is new, from booster to lines and and everything at the wheels and the pedal is still soft.
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i ain't rite
Joined: Mar 2005
Posts: 65,507
Likes: 5,563
From: Marlboro Mental Hospital.
the master cylinder was 1/16 inch larger than the booster on my 88 to 91 trucks. so i used a die grinder and expanded the flange in the booster to make the master fit in it. then oblonged the mounting holes in the master so it would bolt onto the booster, because the bolt holes on the F-superduty master is a little wider than the holes on the 250-350 master.
i ain't rite
Joined: Mar 2005
Posts: 65,507
Likes: 5,563
From: Marlboro Mental Hospital.
what got me started on it was the fact my 88 superduty had fantastic brakes, but the F-250's and 350's did not. the very first thing done was bypassing the RABS valve. that made a drastic improvement in the fact that the brakes were no dependable, not hit and miss. but there was still always pedal fade.
so one day when i had one of the 88 F-350's in for brake service i decided to tinker with it to see if i could improve the brakes without doing a hydroboost conversion on it.
this was back in 89 when the hydroboost systems was still new technology on pickups, and they were not yet available in junk yards.
if i had to do it again, i would just look for the hydroboost system and get rid of the engine mount vacuum pump too.
so one day when i had one of the 88 F-350's in for brake service i decided to tinker with it to see if i could improve the brakes without doing a hydroboost conversion on it.
this was back in 89 when the hydroboost systems was still new technology on pickups, and they were not yet available in junk yards.
if i had to do it again, i would just look for the hydroboost system and get rid of the engine mount vacuum pump too.
Senior User
Joined: Jun 2010
Posts: 291
Likes: 0
From: Long Island, NY
Junk yards around here ( long island ny) don't keep anything this old for more then a day or 2. No one here wants anything that's not a power stroke or cummins. I just don't drive the truck enough to justify the cost of hydroboost as all new. Thank you for the info. Anything is better then the brakes I have. Everything is adjusted properly and is new and I still have a crap pedal, so this is a much cheaper way to try for a better brake feel.