1972 m35a2 brake light issues

[72m35a2]

as it says i have a 1972 m35a2 with brake light issues after doing a light check i noticed the brake lights were not coming on have tail lights. ordered a new brake switch and have brake lights but have to press brake pedal very hard to get them to come on.

i cleaned brake light sockets and checked for ohms from output of brake light switch to brake lights all good
any ideas?

 

[davidb56]

Its not a electrical issue if it works when you stomp on the brakes. Id pull the switch off and make sure there is plenty of pressure to operate it.

 

[72m35a2]

thank you sir for responding respectful i have had issues in the past that were not so nice. from this forum. i was afraid it was an airpac issue as in the below freezing temp i had zero brake boost at times. but not all the time. does anybody know the spec of psi i should have at the airpack switch? sucks because the city i live in wont let me keep it at my house/shop as they say its to scary so its 2 hrs away. runs fantastic just dont want anyone running in the back of me
thanks

 

[davidb56]

you should look into rebuilding, or replacing the air pack if its giving you problems. Id, be more worried about running in the back of someone else if you loose some braking force. Do you keep your tanks moisture drained?

 

[72m35a2]

yes i drain the air tanks every time. i only had the no boost issue in freezing temps i oiled the air pack with air compressor air tool oil and havent had a issue with hard pedal since but still need lots of force to work brake lights. im sure the airpack could use a rebuild. i replaced 3 of the brake cylinders due to leakage. i dont want to run into back of someone for sure. thanks

 

[Scrounger]

If the brakes work well there shouldn’t be a pressure issue. This sounds like a pressure switch issue.

Inside the switch is a diaphragm that flexes under pressure that closes the contacts inside. Over time the switch can get gummed up or the diaphragm can become brittle and either stop flexing or brake. When you install the new switch, it will help for the future to coat the contacts in the plug with dielectric grease.

 

[frank8003]

But which switch is in there. Have to start with that fact.
Is the switch on the air side or the hydraulic side?

 

[cattlerepairman]

Do you have the upgrade to the air operated switch or still the switch in the hydraulic line?

 

[72m35a2]

thanks i have it in the air system on air pack put a new one in and still have to push extra hard to get them to come on
but brakes work good. i got the switch from a good source not a cheap one off ebay. truck is a couple hrs away so hard to look at it. is there maybe a way to increase the pedal pressure a little?

if i use a gauge what is the minimum air pressure at the switch port to operate switch?

 

[frank8003]

The actual switch is maybe wearing out or it is too high of a pressure rating. Replace the switch.
I replaced mine and added an LED in the cab to light up when switch activates.
Now I can't find my own posts but it was around 02272017 sometime.
Never had another problem and it didn't cost much.


I found one of the posts about it but not particulars on the little switch itself.

https://www.steelsoldiers.com/showthread.php?165379-Brake-light-switch-upgrade-Deuce

https://www.steelsoldiers.com/showthread.php?130915-Air-stop-light-switch-issue/page4

 

[frank8003]

deleted as redundant

 

[72m35a2]

yes brake switch is new. does anyone have a bulb number (stock brake bulb) maybe that will help but would like to replace bulbs to led anyway
live right by superbrightleds,com

 

[72m35a2]

found with search turn/brake for rear is a 1683 bulb correct? turn signal if works same bulb works perfect

 

[72m35a2]

ok i found that the 1157 is same bulb as i cant find a cross for the brake light bulb superbrightleds have a dual function 1157 in 10-30 vdc will this work in stock military lamp?

 

[72m35a2]

a few pics

 

[cattlerepairman]

The air pressure operated switch should open at 3-5 psi, so "extra pedal pressure" should really not be needed. The deuce air system runs up to 120 psi.

 

[frank8003]

Sometimes it really doesn't matter if a new switch was just put in. Put a correct new known good switch that can be bench tested easy before changing out all kinds of other stuff.

It took a couple of whiles to find the switch I used, but here it is.
I paid about 16 bucks (20 bucks to the house) in 2017.


Stoplight Switch
Part no. BE13250
Item status Active
Product line Midland
Service Circuit Stoplight Switch
Notes
1. 12 volt or 24 volt - 1/4-18 NPTF Thread -Typical


TECHNICAL SPECS
Actuation Pressure 3-5 PSI
Circuit Position Normally Open at 0 Pressure
Design Single Pole, Two Terminal
Pole Size 1/4-18 NPT
Notes Silver Contacts, Snap Action Design to increase Switch Life,
Tested at one million cycles at 30 AMPS
OEM Number 3250
Haldex 3250


The extra terminals is for a dash mounted green LED that illuminates when the switch functions, I like it. All the lamps could be burnt out but I know my switch is functioning.

 

[m561gamagoat]

I recently spent awhile trying to figure out why I had no brake lights on my 72 Deuce. All other lights worked. I became suspicious of the turn signal switch as it felt like it was about to fall apart. I researched it and figured out obviously that the turn signal interacts with the brake lights to blink and these tend to loosen and self destruct. I replaced the switch with a new one from Mike's and Bingo brake lights! Just my .02. Hope it helps someone else.