15 or more seconds from pulling master to power

Leo O'Farrell

Leo O'Farrell

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Leo O'Farrell
Hi,

My 1959 Cessna 172 has the old school master switch. Since the weather has turned cold, it can take up to 15 or more seconds after pulling the master for the beacon to start turning, power to the fuel gages, stall warning, etc.

Whats going on and what might I have to do to fix this.

Engine is now 100 SMOH and the battery is fairly new. Have owned this plane for 12 years, but this is a first.

Thanks.

Leo
 
What do you mean by "pulling the master"?

What is the temps outside?

My first guess is the master solenoid getting weak. :confused:
 
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If you pull the switch and immediately have power on everything else, like the generator light, there is nothing wrong. Fuel gauges are NOT
instantaneous.

If it takes 15 seconds to get ANY power, then the master solenoid at the battery box is sticking.



My car's parking "lockout" soleniod is doing the same thing. Takes a bit of warming before it will move so I can shift out of park...:mad2:
 
It's no power to anything, so is the sticking master solenoid serviceable or just has to be replaced? I'm thinking replaced.
 
Leo O'Farrell said:
It's no power to anything, so is the sticking master solenoid serviceable or just has to be replaced? I'm thinking replaced.
Click to expand...

Pull it out, take it to NAPA, they will match it up. :eek: Seriously, someone here has the PN for a NAPA equivalent. Just take the NAPA stickers off. :lol:

Also, I found this on another site..... Don't know if it is accurate. .....You can upgrade to a newer 111-138D (same as they use in the newer birds) from Cessna for $51.90. Replace the defective part, its cheap. If you buy the old part it is over $500.
 
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Leo O'Farrell said:
It's no power to anything, so is the sticking master solenoid serviceable or just has to be replaced? I'm thinking replaced.
Click to expand...

Some of them are serviceable, some are sealed. It will be obvious if you have one that is serviceable.
 
Fifty Seven bucks at Aircraft Spruce for certified aircraft

07-01875.jpg
 
Another possibility to look at, if the new contactor doesn't fix it: Those old master switches had a bit of lubricant in them. After all these years it gets hard and kludgy, and resistance can occur. If there's resistance it will cause a bit of heat, which softens the goo, which them moves out of the way and allows enough contact that the contactor finally closes.

Dan
 
Dan Thomas said:
Another possibility to look at, if the new contactor doesn't fix it: Those old master switches had a bit of lubricant in them. After all these years it gets hard and kludgy, and resistance can occur. If there's resistance it will cause a bit of heat, which softens the goo, which them moves out of the way and allows enough contact that the contactor finally closes.

Dan
Click to expand...

Would you suggest a cleaning of the switch is in order? Going to consider this as another area to check.

Thanks.

Leo
 
Leo O'Farrell said:
Would you suggest a cleaning of the switch is in order? Going to consider this as another area to check.

Thanks.

Leo
Click to expand...

Bypass the old master. If it still doesn't work right you know what it is.
 
Leo O'Farrell said:
Would you suggest a cleaning of the switch is in order? Going to consider this as another area to check.

Thanks.

Leo
Click to expand...

Sure, if you can get to the contacts in the switch, that is the first step. Always start at the cheapest, easiest place.
 
bnt83 said:
Bypass the old master. If it still doesn't work right you know what it is.
Click to expand...

He could start by just grounding the terminal on that contactor that leads to the master switch. The master just grounds the cold side of the solenoid's coil.

Dan
 
Henning said:
Some of them are serviceable, some are sealed. It will be obvious if you have one that is serviceable.
Click to expand...


We pulled it today, it's serviceable, so we opened it up, cleaned and filed the contacts down, reassembled and it works great.

One thing we are not sure about is, should it have oil inside? There was some in there, but we didn't replace it, wasn't sure if it was from the oil from the engine over 50 plus years or if it should be added.

Cutler-Hammer solenoid.
 

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Replace the contactor . Some of the contactors had a coating on the points and when you file them you cut through it. It will then burn and pit rapidly resulting in a loss of power or a contactor that will not cut off, as in points weld together. Heck I am cheap and admit it but $50 bucks for what I would consider a critical item ???. No question which way I would go, replace it.
 
Leo O'Farrell said:
We pulled it today, it's serviceable, so we opened it up, cleaned and filed the contacts down, reassembled and it works great.

One thing we are not sure about is, should it have oil inside? There was some in there, but we didn't replace it, wasn't sure if it was from the oil from the engine over 50 plus years or if it should be added.

Cutler-Hammer solenoid.
Click to expand...

Open it back up, POLISH the contacts. If they are filed or sanded, the rough surface arcing will cause them to stick eventually. They typically operate dry, but light lubricant film is ok.
 
flyingron said:
You better watch that. While it claims "aircraft grade" it's not PMA'd and you need to check that it is a legal replacement for your particular aircraft.
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Yeah, like no pipers have the $75 facet fuel pump from spruce vs the $500 facet fuel pump from piper installed :rofl: let's not forget the gates alternator belts vs he gates alternator belts.
 
Vaflier said:
Replace the contactor . Some of the contactors had a coating on the points and when you file them you cut through it. It will then burn and pit rapidly resulting in a loss of power or a contactor that will not cut off, as in points weld together. Heck I am cheap and admit it but $50 bucks for what I would consider a critical item ???. No question which way I would go, replace it.
Click to expand...


The usual aircraft contactor has copper points. Filing or sanding them doesn't hurt them much. There might a few that have silver-plated contacts; those are the ones easily damaged.

Dan
 
Dan Thomas said:
The usual aircraft contactor has copper points. Filing or sanding them doesn't hurt them much. There might a few that have silver-plated contacts; those are the ones easily damaged.

Dan
Click to expand...

Polishing works much better on copper contactors, filed and sanded ones usually don't last much longer before they stick.
 
flyingron said:
You better watch that. While it claims "aircraft grade" it's not PMA'd and you need to check that it is a legal replacement for your particular aircraft.
Click to expand...

agreed - we just went through this (not same issue but replacement) and the one with the paperwork is more like $100. Kinda sick really - same f'ing part. Hell, in our plane (64 Cherokee 235) the part we replaced actually said Lincoln or Mercury on it, can't remember which. I mean it's a solenoid...it's on or off...

You need to look for another solenoid - the master - and it's probably going to be on or near your battery box. The one that is pictured here, on our plane anyway, was for the starter. Ours is a push button and this solenoid sent power to the starter once that button was pushed. The master is much bigger and feeds your electrical bus (and feeds this solenoid as well for the starter).

Anyway, don't recommend just buying crap and hoping it fixes it - especially when you're not 100% sure what you're trying to replace.
 
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Just because it says X doesn't mean it's not legal to install. We had a Alternator on a Cessna U206 that said Ford I believe. It was on a 135 certificate, and yes the right part. I've seen Chrysler Alternators on planes. R44 helicopters have Fram Air filters. The real point is to make sure that it is the right P/N and authorized. Which, as previously mentioned, can be tricky.
 
You don't know how tempting this scenario was when I found out what a landing gear hydraulic actuator cylinder was going to cost. I figured any decent hydraulic shop could make it for $300.00, it's just a simple cylinder. BUT NO, I get a PMA'd on for 20X's that amount!!:mad2::mad2:

Geico266 said:
Pull it out, take it to NAPA, they will match it up. :eek: Seriously, someone here has the PN for a NAPA equivalent. Just take the NAPA stickers off. :lol:

Also, I found this on another site..... Don't know if it is accurate. .....You can upgrade to a newer 111-138D (same as they use in the newer birds) from Cessna for $51.90. Replace the defective part, its cheap. If you buy the old part it is over $500.
Click to expand...
 
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