Gary Lewis Posted February 3 Share Posted February 3 I don't know if the one I keep showing from uhaultruckpartsonline has the port. I know it's still listed but I don't think U-haul wants drivers being lazy Kurt has a later master, but apparently not one with the switch. In this thread Larry/ratdude747 says that the Raybestos MC39634 comes with the residual pressure valve and a "reservoir level sensor". Is that possibly the port where the pressure switch would go instead? I wouldn't think they put pressure to a level sensor, but then I wouldn't think that they'd have two different master cylinders. And, by the way Kurt, I don't know whether you have an F150, 250, or what as you didn't say in your signature. But the master certainly changes between them. Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 3 Share Posted February 3 I did the MC upgrade over 10 years ago. I installed an ‘87 version w/ the plastic reservoir so, I’m reluctant to change out my MC at this point Just to have a switch that seems redundant, because I think the stop lamp switch on the brake pedal serves the purpose of shutting off the servo. The ‘85 EVTM shows indicates that the stock stop lamp switch get 12v/ 15a at all times via fuse 1 and describes the function as “closed with brake depressed” In stock form, in 1985, there were only two things that could get the servo to shut down. 1 - touch the brake pedal 2 - touch OFF on the horn pad Am I missing something? In stock form the vacuum dump also shut down the servo, so there were three things. But since the later system doesn't use vacuum you'd only have two ways to kill it - the brake light system and the Off switch. And if the fuse blows on the brake lights then you won't have that. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted February 3 Share Posted February 3 Larry/ratdude747 says that the Raybestos MC39634 comes with the residual pressure valve and a "reservoir level sensor". Is that possibly the port where the pressure switch would go instead? I wouldn't think they put pressure to a level sensor, but then I wouldn't think that they'd have two different master cylinders. The '87/ master has a float switch and three pin connector on the side that trips the brake light, like the / '86 would if the combination valve shuttle gets off center. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted February 3 Share Posted February 3 I did the MC upgrade over 10 years ago. I installed an ‘87 version w/ the plastic reservoir so, I’m reluctant to change out my MC at this point Just to have a switch that seems redundant, because I think the stop lamp switch on the brake pedal serves the purpose of shutting off the servo. The ‘85 EVTM shows indicates that the stock stop lamp switch get 12v/ 15a at all times via fuse 1 and describes the function as “closed with brake depressed” In stock form, in 1985, there were only two things that could get the servo to shut down. 1 - touch the brake pedal 2 - touch OFF on the horn pad Am I missing something? One alternative I can think of is to make up a brake line with a banjo. 💡 In motorsports/motorcycles we have banjo bolts with switches. I'm sure there's a NC one instead of the NO that would act as a brake light. https://a.co/d/aeJ0keE this one is NO but you get the idea. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted February 3 Share Posted February 3 One alternative I can think of is to make up a brake line with a banjo. 💡 In motorsports/motorcycles we have banjo bolts with switches. I'm sure there's a NC one instead of the NO that would act as a brake light. https://a.co/d/aeJ0keE this one is NO but you get the idea. What's the thread pitch on the splitter block/combo valve? My truck doesn't have one Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 3 Share Posted February 3 What's the thread pitch on the splitter block/combo valve? My truck doesn't have one I don't know, but will look to see if I have one that isn't installed... (Haven't made it to the shop yet.) Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted February 3 Share Posted February 3 I don't know, but will look to see if I have one that isn't installed... (Haven't made it to the shop yet.) I was just trying to come up with a safe and simple solution for Kurt. I'm sure you (or he) can find the same switch I can. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted February 3 Share Posted February 3 I don't know, but will look to see if I have one that isn't installed... (Haven't made it to the shop yet.) The call-outs are on the section drawing IIRC..... Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 3 Share Posted February 3 The call-outs are on the section drawing IIRC..... I don't have a spare, and the illustration I found in the Brake section of the FSM, below, doesn't have thread sizes. And I know this is for the F350, but the illustration for the lighter trucks has even less info. Do you remember where you saw them? Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted February 3 Share Posted February 3 I don't have a spare, and the illustration I found in the Brake section of the FSM, below, doesn't have thread sizes. And I know this is for the F350, but the illustration for the lighter trucks has even less info. Do you remember where you saw them? My 'special' mind has a filing system of its own..... It could have been ANY of the section drawings. Maybe it's the one on Keith's forum? Maybe it's the drawing of one of the aftermarket ones I tried to show that member who wanted to gut his???? I am NOT good at knowing exactly where I come up with the minutiae I have in my head. Just yesterday I was driving to my brothers and we saw a purple fence. I turned to him and said it was OSHA Safety Plum. He was incredulous.... (until I looked it up on my phone and showed him!) Then he said "You are a (explitive) retard." Yeah, I'm THAT GUY! Link to comment Share on other sites More sharing options...
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