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Brake lights only on at half pedal

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Old 10-21-2012, 01:46 PM
tberr tberr is offline
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Brake lights only on at half pedal

I checked through the threads and found some old posts about my problem but thought I'd see if anything new has been found.

Truck - 1993 F250, 5speed manual, 5.8L, 2wd, 150K miles.

The brake lights only come on at about half pedal (with good pressure applied). Brakes seem fine as far as when brakes are engaged relating to pedal depression and stop the truck quickly with no fuss.

The older post recommended a few things: pedal switch replacement, power booster replacement, and adding a jury rigged spring on the shaft at pedal to increase pressure on switch (not exactly sure about this one).

I replaced the switch as this was easy and cheap but no difference. Is the booster weak do you think? The booster looks newer than the truck (I bought truck a few months ago - it's done this the whole time). Would the rear brakes out of adjustment cause this - I need to check them but have not yet. Master cylinder? Air in lines?

Any new thoughts on the matter?
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Old 10-21-2012, 01:50 PM
jumbofordman jumbofordman is offline
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When you replaced the pedal switch did you press it all the way in? If so, it's in too far. It should have threads so you can adjust the point at which the brake lights come on.
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Old 10-21-2012, 05:36 PM
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Quote:
Originally Posted by jumbofordman View Post
When you replaced the pedal switch did you press it all the way in? If so, it's in too far. It should have threads so you can adjust the point at which the brake lights come on.

The OP's truck should use this style brake light switch:


There is no adjustment.
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Old 10-21-2012, 05:41 PM
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Quote:
Originally Posted by tberr View Post
I checked through the threads and found some old posts about my problem but thought I'd see if anything new has been found.

Truck - 1993 F250, 5speed manual, 5.8L, 2wd, 150K miles.

The brake lights only come on at about half pedal (with good pressure applied). Brakes seem fine as far as when brakes are engaged relating to pedal depression and stop the truck quickly with no fuss.

The older post recommended a few things: pedal switch replacement, power booster replacement, and adding a jury rigged spring on the shaft at pedal to increase pressure on switch (not exactly sure about this one).

I replaced the switch as this was easy and cheap but no difference. Is the booster weak do you think? The booster looks newer than the truck (I bought truck a few months ago - it's done this the whole time). Would the rear brakes out of adjustment cause this - I need to check them but have not yet. Master cylinder? Air in lines?

Any new thoughts on the matter?
The text in bold could be your cause. You may need to adjust the brake actuator rod. The previous owner may not have checked the clearance and adjusted accordingly.

Some info from another forum: http://www.fullsizebronco.com/forum/...d.php?t=178635
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Old 10-22-2012, 10:43 PM
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My truck is the exact same way. Might give the rod adjustment a try. Booster is stock and never replaced.
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Old 10-23-2012, 10:25 PM
tberr tberr is offline
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Quote:
Originally Posted by rla2005 View Post
The text in bold could be your cause. You may need to adjust the brake actuator rod. The previous owner may not have checked the clearance and adjusted accordingly.

Some info from another forum: Brake Booster Pushrod Adjustment - FSB Forums
I'll give it a look this weekend. Thanks.
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Old 10-23-2012, 10:27 PM
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Quote:
Originally Posted by jumbofordman View Post
When you replaced the pedal switch did you press it all the way in? If so, it's in too far. It should have threads so you can adjust the point at which the brake lights come on.
Appreciate the reply. I'll have a look asap.
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Old 10-23-2012, 10:27 PM
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Quote:
Originally Posted by rla2005 View Post
The OP's truck should use this style brake light switch:


There is no adjustment.
Thanks. I appreciate your response.
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Old 10-24-2012, 08:54 AM
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You are welcome
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Old 10-28-2012, 11:38 AM
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pedal adujustment rod

I tried the adjustment but no difference. I did notice that on second examination the booster was not as new as I thought. I believe it is original. I saw this granual looking stuff on and around the rod and opening for the rod. It was sort of jellied. Not a lot of it. Also when I clamped priers onto rod to hold it I could hear a little air escaping if the rod moved sideways any (maybe normal?).

I checked the rear brakes while at it and they did need adjusting. Did not help with pedal/light issue but my parking brake is way better now.

Anyway I think the booster may need replacing? Any other ideas?

Thx in advance.
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Old 10-28-2012, 12:28 PM
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My truck has the same problem... There was another guy on here a while back who also had the problem. He did something with a spring on the brake booster rod or something and it fixed the problem... I am not exactly sure what he did and he never reported back on the 'how to' even though a few others asked about it.

http://www.ford-trucks.com/forums/11...ke-lights.html
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Old 10-28-2012, 03:15 PM
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My old 1992 F350 had a very similar problem with the brake light coming on late. Steve83 pointed out an issue he dubbed "over-active brake booster". To summarize the brake booster is TOO sensitive. It is supplying too much assist.

The brake light switch is more or less a pressure differential device that will not activate until you over come the spring preload on the switch. If the booster is supplying too much brake assist the switch will not activate until well into the brake pedal travel.

I ended up replacing the booster and the master cylinder because of other issues, but both contributed to the problem. After the R&R the brake light operation returned to normal. I have driven many Ford trucks, and other vehicles, but had never ran across this problem until I purchased the '92 a few years ago.
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