Question about brakes
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Senior User
Joined: Jul 2003
Posts: 101
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From: Colorado
Question about brakes
I've got a 1991 F250 XLT Lariate 4x4 7.3L Diesel E4OD with 291,000 miles on her. I've got an issue with the brakes that needs to be fixed NOW 
The brakes seem to work normal when the rpms are over 1500 (i.e. over 35 mph or so) but the brake light comes on and the brake pedal gets rock hard but doesn't stop that well below this speed/rpm. It is dangerous to drive. I rebuilt the front calipers last winter and replaced the master cylinder last week. Like a fool a forgot to bench bleed the master cylinder so I had to bleed both ends of the brake line, but I feel like I did pretty good job getting all the air out.
However, the fact is that the brakes still don't work. So either I still have air in the lines or it's the vacuum booster right? Any thoughts or suggestions are appreciated!
Thanks,
Bart
The brakes seem to work normal when the rpms are over 1500 (i.e. over 35 mph or so) but the brake light comes on and the brake pedal gets rock hard but doesn't stop that well below this speed/rpm. It is dangerous to drive. I rebuilt the front calipers last winter and replaced the master cylinder last week. Like a fool a forgot to bench bleed the master cylinder so I had to bleed both ends of the brake line, but I feel like I did pretty good job getting all the air out.However, the fact is that the brakes still don't work. So either I still have air in the lines or it's the vacuum booster right? Any thoughts or suggestions are appreciated!
Thanks,
Bart
Elder User
Joined: Feb 2004
Posts: 855
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From: Ocean Park WA
The regular F250 does have a vacume booster brake system. The diesels had a vacume pump to provide for the heater controls, trans and the brake booster. It is mounted directly below the alternator with a single short belt driven of the alternator. Sounds like the vacume pump is going south for the winter. Also the fitting that the vacume hose goes to on the booster is a check valve and I've had them cause problems especially on the diesels. Check the belt and the pump. The pump mounts using metric heade bolts so you need a 10mm amd a 13mm (1/2 " might work).
Thread Starter
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Senior User
Joined: Jul 2003
Posts: 101
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From: Colorado
Thanks Eric C. I'll check out the vacuum pump and the hoses now! Also, Ever since I had my E4OD rebuilt the rpms drop off to zero when I'm idling, but then bounce back to normal as soon as I get going. Could this also be atributed to the vacuum pump?
Thanks again,
Bart
Thanks again,
Bart
Elder User
Joined: Feb 2004
Posts: 855
Likes: 0
From: Ocean Park WA
That sounds like the speed sensor for the Tachometer. it should be on the upper side of the front cover right abve the injection pump on the pre Power Strokes. Disconnect it electrically and pull it and clean it then reinstall, I dont remember the exact gap but most engines I've ever worked on call to turn it in till it touches the tooth on the gear (Use a light and check the position) then turn it back 1/2 to 1 turn. Be advised on the vacume pump also to check the alternator belt tension and if you replace the vacume pump I usually replaced both belts as it can save you heartaches. Also be extra careful not to put to much tension on the vacume pump belt as this will cause early pump and alternator failure, light downward prssure is sufficent.
