No Brake Pedal Travel

[Bronco DLight]

I realize brakes have been discussed, even recently. But I didn't find an issue exactly like mine. On my '74, I have front disc, rear drums. I recently replaced my original 302 with a '98 explorer motor. With both, i have probably less than an inch of pedal travel and it's very hard. It feels like manual brakes.

The discs, calipers, and drums have been checked out as fine. I don't know exactly what master/booster setup I have but it was fairly recently replaced by the PO when he installed the discs. I have included a pic.

Thanks. My wife won't drive it unless it stops better!

D

 

[MR-CYN]

Sounds pretty much like mine. Check vac pressure first...

 

[Apogee]

Assuming that all of the components are in good working order, a high hard pedal can be caused by an undersized booster (dual-7"?) and/or oversized master cylinder bore (1.125"?). It looks like you have both.

Additionally, as noted above, vacuum levels will have an impact on the amount of boost/gain that the booster does or does not provide, but most Explorer 5.0's are going to provide decent vacuum levels (16-20" Hg @ idle) unless you've put a rumpity camshaft in it.

 

[plumbdoctor]

David, one thing I didn't check was the check valve at the booster. Your motor has good vacuum....since the brakes were the same as before the swap , maybe the check valve? And or as the above poster said...under sized booster, etc.

I am interested in what you find out as I was thinking of the same set up for my wife's Bronco

 

[plumbdoctor]

Also, I have a stock MC here , if you want me to ship up to you to try it out?

 

[Bronco DLight]

leaking booster

Mechanic who seems pretty familiar with the setup confirmed vacuum as you said but said that there is actually a leak in the rear seem of the booster itself. Bad case weld? Seems a bit odd. It's a summit racing booster with less than 5000 miles on it. Oh, well. We'll see. Should be replaced this afternoon and we'll see what happens. I'll let you know. BTW - how long should it take for that ecm to realize that we don;t need as much fuel at 9000 ft? it's running a bit rich, but didn't seem to be at lower altitudes. I figured that it would be instantaneous.

Thanks for your help, btw. Hope the extra can get your wife's project finished. I was planning to replace the alternator anyway - I'd already ordered one. Don't worry about that. I planned to ask you to put on new alternator and starter before installing the new engine but plum forgot.

 

[Broncobowsher]

While you are at it measure the bore of the master cylinder. Even with a booster an oversized master will reduce travel and make for a stiff pedal. Stock is a 1" bore. Even with hydroboost I was doing my best stopping with a 15/16" master cylinder. Little less effort, little more travel. All flex lines were braided stainless as well.

 

[Bronco DLight]

Mystery Solved

Put in new booster and all is well. There was an internal vacuum leak in the booster. Strange, was a summit racing with less than two years and 5000 miles on it.

thx for the ideas, though.