Hey guys so I'm just about done with the brake conversion on my bump. Got a whole front axle out of 75 f150. I installed the brake booster as well and I am buttoning everything up before I bleed the brakes. Where the arm coming out of the brake booster and master cylinder goes into your firewall and meets the brakes pedal I noticed that the brake light switch that is attached to the pedal does not hit the flat spot of the cab where the switch would then be closed (brake lights off).

Now with that being said I noticed that the bracket that the switch hits has a oval slot in it so I loosens the bolt and slid it towards the switch and it didn't reach. I also noticed that the switch itself is adjustable on the threaded "shaft" it is on and it is still not reachable. Any ideas? Am I off on some things here or dother i need that bracket or switch off the 75?

 

The brake light switch is a N.C. (normally closed) device, held open.

The contacts of the switch are (should be) open as long as the brake pedal is in its static position (brake pedal not being applied). When the brake pedal is applied, the contacts of the brake switch close, the current path through the circuit is completed and it illuminates the brake lights.

Without photos, I don't know what booster/bracket arrangement you have but, it sounds like your brake pedal height, since the change, is a little lower than it was before and the pedal isn't coming back far enough to push the brake switch plunger in far enough to turn the brake lights off.

One alternative may be to make a bracket or modify (extend) the existing bracket that bolts to the under side of the dash, so that it can be slid outward, closer to the switch, to push the contact plunger in.

By your description, it sounds like you have the same brake switch setup as I do on my '69 F100. I have a '75 F350 dual diaphragm booster with the long, straight pushrod going into the back of the booster (no bellcrank style mounting brackets between the brake pedal and the booster).

 

If the switch operated before but doesn'actuate now, then the actuation rod and pedal position are a short and lower, respectively, than before the upgrade.

 

Not really sure how to upload pictures to here yet I'm still kinda new but yes the brake pedal current position is lower than it was before resulting in the switch not contacting with the bracket. According to the picture you took I have the same set up if need pictures I can take them but I'm not sure how to post them on here

 

How do I make the behalf position go from short and lower to back to original position? If that's possible otherwise I believe I'll have to make a new bracket to make contact with the switch

 

There were several different basic styles of brake boosters used in the Dentsides, as well as different input rod styles that connected between the brake pedal to the back of the booster.

Without an actual photo of what you have, it's going to be harder to suggest what you would need to do, to remedy the problem.

When you're making a post here, you'll see various selections and icons above the box where you type your reply. Above this text box, you'll see a square, yellow icon with a picture of mountains and a sun. If you click on that icon, it'll take you to "Upload Picture." From there, you have choices of posting pictures that are on your computer/laptop/IPhone.

 

 

Now, we're getting somewhere. That's the ~11" diameter single diaphragm high-mount booster that's attached to a bellcrank (cantilever) firewall bracket assembly.

The input rod on it (between the brake pedal and the bellcrank bracket assembly) is flat. There were two different length flat input rods on those boosters --one shorter than the other.

In order to get the pedal to make contact with the brake switch, you would either have to extend the tail end of flat input rod outward and drill a new 5/8" hole in the extension for the bolt/nylon bushing (where the flat input rod attaches to the brake pedal) or, cut out a new, longer input rod from a piece of 1/4" thick x 2" wide flat bar to install in its place.

The other alternative is to extend/modify the stop outward that's bolted to the underside of the dash.

This is what the flat input rod for that style booster looks like --sorta looks like a hockey stick.



If you were to modify the existing input rod by butt welding a piece of flat steel to the end of it, you would need to extend the end were the large hole is with a piece of 1/4" x 1" flat bar --you would just have to determine the length the extension would need to be. If you were going to fabricate a completely new, longer input rod from scratch, you would need a piece of flat bar 1/4" x 2" to cut the new flat input rod from.

--that MC. It looks like you installed the MC that came from the donor truck. This is not a good idea since you don't know how old the MC is or for how long the truck has been sitting in the wrecking yard. It would be VERY wise to get that MC off of there and install a new (not rebuilt) MC.

 

Okay thanks for the clarification I think know it will be easier to modify the bracket to make the switch make contact. Thanks guys I appreciate it once again. And yes that is the MC off the donor truck. I am using it for now for the mach up like I said. I took your advice in a earlier post I had and I went with a bendix MC just haven't installed it.

 

Ok. Good that you do have a new MC to put on. It gives me the boo boo jeebeez when I see someone install a donor truck MC on their truck. It's a recipe for a bad outcome.

When you take the old MC off the booster, to put the new MC on, look the booster over really good to make sure that the MC hasn't been leaking out the back end and over into the booster. Brake fluid will break down the rubber diaphragm inside the booster housing and will eventually cause the diaphragm to rupture --and that'll probably be at the most inopportune time.

In addition to not reusing wrecking yard MCs, it's really best to turn a wrecking yard brake booster in as a core for a newly rebuilt booster. This is what I did 4 years ago when I installed my power brake booster. 4 years later, I haven't had a bit of trouble out of my rebuilt booster and if I do, it does has a lifetime replacement warranty on it.

 

I had the same issue. The flat brake rod was 1" too short. Rather than extend the rod, I changed the brake pedal to a bump pedal. It changes where the brake switch mounts and now the brake switch works properly, and I got a wide brake pedal.

 

Well before I started welding anything I took the bracket off and made the slotted part of the bracket longer so it could slide back further. It seems to work so hopefully all is well otherwise back to the drawing board and either make it longer or I might have to snag that dentside brake pedal