Need help with low vacuum

[Webygail13]

I just bought a 1966 M20C Ranger. I noticed when I picked it up that upon starting, it had a low vac light and the gauge was reading 0. On my test flight the gauge would come up to 4hg at cruise. The light stayed on, the AI and DG acted a  little strange and PC system is inop. The vacuum pump had several hours on it so I went ahead and put a new pump on it to be safe, but same results. All of my filters were just changed as well. So I have a few questions. 
1 Would the PC system be completely inop pulling 4hg’s of vacuum?

2. My A and P suggested adjusting the regulator, but I’m not so sure since the readings are so different at idle and cruise. I suspect I have a leak somewhere, but not sure where to start testing. 
 

Anyone have any experience with this and could help me find a place to start tracking it down??

[Jsno]

I would check your vacuum hoses and the lines to your PC.

[Hank]

8 hours ago, Jsno said:

I would check your vacuum hoses and the lines to your PC.

And the fittings on the PC tubing.

[LANCECASPER]

9 hours ago, Webygail13 said:

I just bought a 1966 M20C Ranger. I noticed when I picked it up that upon starting, it had a low vac light and the gauge was reading 0. On my test flight the gauge would come up to 4hg at cruise. The light stayed on, the AI and DG acted a  little strange and PC system is inop. The vacuum pump had several hours on it so I went ahead and put a new pump on it to be safe, but same results. All of my filters were just changed as well. So I have a few questions. 
1 Would the PC system be completely inop pulling 4hg’s of vacuum?

2. My A and P suggested adjusting the regulator, but I’m not so sure since the readings are so different at idle and cruise. I suspect I have a leak somewhere, but not sure where to start testing. 
 

Anyone have any experience with this and could help me find a place to start tracking it down??

Sounds like a leak. If you're planning long term on resurrecting the PC system and having vacuum instruments it's probably a good idea just to plan on replacing all of the vacuum lines if they are 60 years old.

But if you're not planning on using the PC system, it might be a good time to think about what autopilot you will have in the future and just putting the labor of replacing vacuum lines toward replacing the AI and DG with electric options (G5? AV-30?). This would eliminate the need for the vacuum system.

Too late now, but many times avionics are not looked at closely enough in a pre-buy. That would have been the best time to have catch this, since the seller may have been responsible to get this figured out. 

[N201MKTurbo]

Your vacuum gauge and switch are probably connected to the AI. I would remove all other hoses from the vacuum manifold after the regulator and cap off all the other ports. Then see how it works. Then add the hoses one at a time and see how it works. You should be able to isolate it to the bad branch and troubleshoot it from there. 

The hoses are probably oid and stiff, so cutting them off and replacing them with new supple hoses makes it a lot easier.

[Webygail13]

Well, I did pay an A & P to do a prebuy, I confronted him after the fact on this issue but he said it was functioning fine during the prebuy, so who knows.  When you say vacuum manifold, are you talking about the pilot valve where all of the hose leave out for the PC system?  Are you saying to just disconnect them all at the valve and cap off all the connections, adding one line back at a time?  Taht would make sense.  I've got a hand pump that I could put on each line and add vacuum too, but I'm not sure if that work work.  My service manual says that I can put a guage on two of the ports on the pilot valve and turn the yoke full tilt that that should create and hold vacuum on that line if there is no leak.  Anyone ever tried that?  

[Gee Bee Aeroproducts]

Silicone vac hose from aircraft spruce 

We send Rapco hose in pre cut for there kit .

use lined clamps on silicone 

[Fly Boomer]

59 minutes ago, Gee Bee Aeroproducts said:

use lined clamps on silicone

Like these from McMaster-Carr?

 

[N201MKTurbo]

2 hours ago, Webygail13 said:

Well, I did pay an A & P to do a prebuy, I confronted him after the fact on this issue but he said it was functioning fine during the prebuy, so who knows.  When you say vacuum manifold, are you talking about the pilot valve where all of the hose leave out for the PC system?  Are you saying to just disconnect them all at the valve and cap off all the connections, adding one line back at a time?  Taht would make sense.  I've got a hand pump that I could put on each line and add vacuum too, but I'm not sure if that work work.  My service manual says that I can put a guage on two of the ports on the pilot valve and turn the yoke full tilt that that should create and hold vacuum on that line if there is no leak.  Anyone ever tried that?  

The manifold is part of or near the vacuum regulator. It isn’t part of the PC system, except it gets its vacuum from the manifold.

[N201MKTurbo]

49 minutes ago, Fly Boomer said:

Like these from McMaster-Carr?

 

I believe he is talking about adel clamps. I would just stick to the hoses specified in the parts manual. It is cheap and only lasts 50 years or so.

[Webygail13]

I've been reading about this stuff all morning.  I'm starting to think that this all being caused by a leak in my PC system.  Either a hose, T, or possible Servo.  For anyone who has ever had to track down one of these, where do I access the T's that go into the wings and tailcone?  I've read in the baggage compartment, but not sure if I need to remove interior, etc...  Anyone have a good starting point or tips on how to do this?  

[N201MKTurbo]

14 minutes ago, Webygail13 said:

I've been reading about this stuff all morning.  I'm starting to think that this all being caused by a leak in my PC system.  Either a hose, T, or possible Servo.  For anyone who has ever had to track down one of these, where do I access the T's that go into the wings and tailcone?  I've read in the baggage compartment, but not sure if I need to remove interior, etc...  Anyone have a good starting point or tips on how to do this?  

If you want to troubleshoot the PC system, start with the two plastic tubes that run along the left sidewall. Disconnect the rubber hoses from them and suck on the plastic tubes or use a handheld vacuum pump to see if they will hold vacuum. Label the rubber hoses so you don’t put them on backwards. The plane flys badly with them reversed.

[N201MKTurbo]

BTW, the PC system has restrictors in the vacuum lines that preclude a significant vacuum leak. You should troubleshoot vacuum leaks separately from any PC troubleshooting.

[Webygail13]

14 minutes ago, N201MKTurbo said:

BTW, the PC system has restrictors in the vacuum lines that preclude a significant vacuum leak. You should troubleshoot vacuum leaks separately from any PC troubleshooting.

So are you saying that I could have a leaking PC system, but should still be holding adequate vacuum at the suction gauge?

[LANCECASPER]

4 hours ago, Webygail13 said:

Well, I did pay an A & P to do a prebuy, I confronted him after the fact on this issue but he said it was functioning fine during the prebuy, so who knows. 

One thing I’ve learned over the years is that if I pay someone for their time to do a pre-buy I’m going to direct what they do, and I want to be there for it. A lot of A & Ps don’t fly so they aren’t up on avionics, so I’m the one that is checking all of that out while they are doing something else. But I agreed ahead of time on the time I want them to spend and I give them a list of what I want looked over, with the deal-breakers at the beginning so if we find something early we can stop and they’ll get paid for their time plus the minimum time we agreed on so they feel it was worth it and I do too. Corrosion being at the top of the list of potential deal breakers. I never blame them for something they didn’t find since I’m the one that made the list and I always ask them, “What else should we be looking for?” so that they can give me input, which has been helpful.

[N201MKTurbo]

1 hour ago, Webygail13 said:

So are you saying that I could have a leaking PC system, but should still be holding adequate vacuum at the suction gauge?

Yes.

[Fritz1]

as stated before, disconnect everything from the vac manifold, then run new vacuum tubing from the manifold to the DG and the AI and see what happens, next calibrate the vacuum gauge with a vacuum meter. There may be debris from old vacuum tubing stuck somewhere in the system, start from the core replace piece by piece, soon you will have a working system and feel good about having figured out what the problem was.

[Webygail13]

Understood.  So could it possible that I have an issue somewhere on the vacuum side and once that is fixed, the PC may be fine, as it was operable at the last annual.  I find it hard to believe though that with 4hg of vacuum the PC won't do anything and that with just .75hg more, it would be operable.  Is there any chance that it's as simple as the regulartor just needs to be adjusted?

[Fritz1]

it has been 25 years since I had a PC, regulator is easily adjustable, unlikely though that this fixes the problem. About 10 years ago we had a vac horizon in a 182RG that failed intermittently, kinda scary, installed electronic backup horizon immediately, overhauled vac horizon, failed again, horizon bench tested fine, problem did not go away until we replaced each and every piece vacuum tubing, replaced the pump and tested the regulator, never figured out what caused it, to this day believe it was a piece of debris in the old tubing that fell out when the system was taken apart, vacuum tubing has a liner inside, think Teflon, buy the good stuff and replace all the old tubing

[Gee Bee Aeroproducts]

8 hours ago, N201MKTurbo said:

I believe he is talking about adel clamps. I would just stick to the hoses specified in the parts manual. It is cheap and only lasts 50 years or so.

Breeze aerospace 

lined clamps 

94 series 

I stock all sizes 1/2 to 4"

we use on all of my ducts or silicone hoses 

You can do things based on cost or quality 

we ship our ducts or hoses with a flex 8mm screwdriver vs a flathead screw driver 

Today we shipped a complete duct set for a MSE model .

Were the only mfg in the industry that has all of the different sizes .

 

 

[Fly Boomer]

9 hours ago, N201MKTurbo said:

I believe he is talking about adel clamps. I would just stick to the hoses specified in the parts manual. It is cheap and only lasts 50 years or so.

This is the one Gee-Bee Aero uses:

And this is the one from McMaster-Carr:

 

[N201MKTurbo]

38 minutes ago, Fly Boomer said:

This is the one Gee-Bee Aero uses:

And this is the one from McMaster-Carr:

 

Those are beautiful clamps, but they are not lined.

[Gee Bee Aeroproducts]

There are std Groved clamps and double wall 94 Breeze series.

stainless steel with stainless steel nut

8mm

We buy bags of 500 in various sizes for ducts and hoses.

we sell hose and clamps to Rapco for there kits .

Cost is less than 1.50 in 3/4 I.d.

This is why we include at no charge.

We mfg molded silicone hoses for fine automobiles in various colors, but the matte black finish on a German auto is perfect.

 

seadoos

Motorcycles

Automotive

Vespas

If it's nla , we will mfg it 

 

cheers to those who want the Best 

 

 

 

 

 

[Webygail13]

I’ve combed through all of my lines and vacuum system. All of my hoses look fairly new. All filters were just changed, with the exception of the one coming off of the remote gyro. It’s 2 years old, but looks clean. It’s the CV1J4. The only leak I have found is in one of the servo boots in the tail. The aft servo boot appears to have ripped from around the center piece. Is that repairable with tape?  Would that be a reason I’m getting low vacuum or as stated earlier the PC have nothing to do with how much vacuum I’m getting?  At this point, the only thing I haven’t tried is adjusting the regulator. Is that worth a shot?  Mine is installed upside down where the adjustment is on the top. So I would have to remove it to adjust it. 

[N201MKTurbo]

50 minutes ago, Webygail13 said:

I’ve combed through all of my lines and vacuum system. All of my hoses look fairly new. All filters were just changed, with the exception of the one coming off of the remote gyro. It’s 2 years old, but looks clean. It’s the CV1J4. The only leak I have found is in one of the servo boots in the tail. The aft servo boot appears to have ripped from around the center piece. Is that repairable with tape?  Would that be a reason I’m getting low vacuum or as stated earlier the PC have nothing to do with how much vacuum I’m getting?  At this point, the only thing I haven’t tried is adjusting the regulator. Is that worth a shot?  Mine is installed upside down where the adjustment is on the top. So I would have to remove it to adjust it. 

Can’t you get to it if you remove the left panel in front of the windshield?