I’ve got a couple of ‘66 big cars. Each car has vacuum heater/AC controls, vacuum trunk lock release, and vacuum power door locks. I’ve got spare parts for most of these accessories. The cast metal parts are pretty solid, but I don’t know about the 56 year old rubber diaphragms inside. Let alone getting any rubber parts remade…

My hardtop maintains vacuum for 24 hours or more. I think that’s amazing given the age of the rubber lines, switch diaphragms & actuating diaphragms. They’re all approaching 57 years old!. The convertible vacuum accessories don’t work much beyond 15 minutes after the engine shuts off. So I’m tracing out the leak(s).

Same design, different performance is my dilemma. Since both cars use the same heater/ac controller design, isn’t it a little weird that one holds vacuum and the other doesn’t?

The leaks could be anywhere so I’m beginning unit testing of all the vacuum components in the convertible. I will replace what I can with fresh vacuum hoses and any tested-good actuators that I can scrounge from under the house.

What I don’t know is whether the heater/ac controller leaks by design. There is a felt seal in the unit which cannot be vacuum sealed. Yet the hardtop one doesn’t lose vacuum…Anybody have any ideas / knowledge / experience?

I’ll be unit testing components to isolate the leak(s) over next few days.

Hopefully I’ll find the big hole. I’m toying with replacing _all_ the lines to the switches and actuators just as a preventative measure, but that’s a lot of snaking & pulling. When maybe it’s just a bad diaphragm letting the atmosphere in…

Looking forward to your thoughts. My thanks in advance for any you can offer.

Cheers
Chris

 

I would expect a slight leak on any of the diaphragms. I’d suggest testing each one, hopefully you find one that behaves differently. Get a hand held vacuum pump with a gauge. Then you monitor how much vacuum it takes to cycle and the rate the vacuum falls off

 

I tested all the heater actuating diaphragms in the car and 56 years later, they’re still good.

It seems that the control unit is designed to leak. Or at least only be operable when the engine is running.

The guts of the vacuum switch mechanism is 2 cast metal discs which have grooves to permit vacuum to be directed. They’re held in place and together with a slotted spring clip to press them tightly (ideally vacuum tight, but not quite so well 56 years later. The discs rotate to different points on a circle when I push the keys of the controller.

I was expecting to find a gasket between the two, but of my 4 or 5 spares, there isn’t one with any kind of gasket. The lack of gaskets does allow the discs to rotate smoothly as metal on metal.

If it’s designed to leak down, I think I’ll put a check valve on the heater vacuum supply line so vacuum can come in, but not atmospheric pressure to the other vacuum systems.

Suggestions most welcome.

 

Maybe some sort of grease on the disc faces to help retain vacuum?

 

I’ve got some heavy grease, but it seems like it would get sucked to, and possibly block, tiny vacuum passages. I was also giving some thought to polshing the mating surfaces with a #0000 steel wool, so they’re at least really clean.

When I disassembled a spare heater disc set yesterday, there was a bunch of dirt in the passages. It looks like the design allows for nothing but well-machined surfaces between the discs. I’d love to get a super thin 1/64” teflon gasket in there, but if it separates the discs to seal at the edge, it would also create a vacuum leak in the center where the vacuum suction is directed. It’s doable, but I don’t know where the center would have to be perforated to allow the unit to work properly directing vacuum flow.

It looks like one or more of my un-messed-with units may have some kind of gasket, screw or circular seal which could help sealing, but I haven’t yet had time to look more closely.

Chris

 

Vacuum Grease:

 

My vacuum switch for my 62 Starfire is of the same design. The switch wasn't providing any vacuum to the diaphragms so I disassembled the switch and like you I was surprised to see the metal to metal seal. I cleaned it all up and put it back together and still no vacuum. After some thought and study I took it back apart and added a couple drops of 3 in 1 oil and after reassembly the switch worked as advertised providing vacuum to the diaphragms. So, I deduced after that the felt pad under the spring was there to put a drop of oil on occasionally to help lubricate and provide a seal for the two halves of the switch.

 

Interesting question. I don't know the answer from a factory design standpoint but it would seem logical that leakdown would be desirable after shutoff. If all vacuum was designed to hold permanently this would put constant unnecessary strain on all rubber parts and negatively affect their service life. Vacuum is available immediately on startup and there is no real reason to maintain it upon shutdown.

 

Don,
You make an excellent reliability point. Hadn't considered the wear & tear if the system held "perfect" vacuum when the car is shutdown.

I'll avoid over-restoring, but have noticed that since I've been tightening up on my vacuum accessories, the repsonse from the systems is noticeably snappier.

Will remove & mechanically repair the heater/vent vacuum system in next few days. I'll report back.

Cheers
cf

 

I had 2 '68 Caprices with the Confortron system and the vacuum switches had a small amount of "grease" in them, and, the systems had a bleed line which was a short piece of ruber tubing with a very small orfice in a plug at the end. It was mentioned in the CSM. And it did have a check valve on the vacuum supply line but its purpose was to hold vacuum in the system during WOT or near WOT conditions.

 

I'm just shocked y'all were able to disassemble the disc vacuum controllers successfully. I tried once and completely destroyed the clip.

If anything I would just lightly lap the disc mating surfaces on a flat surface. Yeah, the design simply cannot be a perfect seal, but it's reliable, simple, cheap, and "good enough". A system designed purely as a vacuum switch would be much more complicated. So it'll always leak a bit, but that bit is insignificant compared to the vacuum source of a stock engine.

Plus I always found that to be a funny Power Indicator. About two seconds after flooring it all the air would stop blowing out the dash and come out the floor!

 

Unfortunately Oldsmobile used vacuum for just about every control and accessory, especially on a factory AC car. With my 63 Starfire I gradually replaced about half of the hoses, etc. but found out my main problem was a defective power brake booster. Check everything!

 

I took v8al's advice and got some high vacuum grease. On the bench, it seals up the Olds vacuum control valve. This is not car-tested yet. I wanted to make sure it worked on the bench before pulling the car unit for the 2nd time in a week.

Here's a typical mid-60's Olds heater/A/c control unit. The visible keys in the dash rotate 2 discs & may engage an electrical switch to engage the fan. But a felt washer and spring steel spring hold the 2 vacuum-sealing discs together. When the felt washer wears down, the rotating discs start to leak vacuum. The high-vacuum grease seems to solve this problem, but there are other ancillary improvements, which I've used that I wanted to let you guys know about before confirming that the grease works...

Typical mid-60's Olds heater/a/c control unit. These principles probably hold true for the other GM makes too:

A key push rotates the vacuum valve and may engage the electrical fan. If the vacuum valve leaks, the system works less well. It can also cause vacuum power door locks and trunk release to not work when the engine is off.

Here's a top view of the heater control so you can see the parts you may know & what's behind the dash:

The parts of the mid-60's big Olds heater control unit. Push a key & stuff happens. If your vacuum system is working...

The guts of the vacuum part of the system are this rotating valve which is sealed by a combination of tension from a felt washer on the opposite side and a spring steel tension spring pushing 2 discs together to seal & direct vacuum. Eventually the felt wears down & the spring steel gets loose. Causing a vacuum leak.

#2 is the vacuum supply port in my '66 big cars. In this position, the rotating valve shoud hold vacuum from your hand-held vacuum pump.

This is the special grease that seems to help hold vacuum better. I tried traditional grease and it wasn't sticky enough. This stuff is. It's more the consistency of vaseline than grease, but I'm impressed that it can seal machined parts with 56 years of use on them:

This grease can help seal leaking vacuum components. Clean the visisble vacuum passages & ports and apply a thin coat - just enough to seal. Don't goober it all up...

The system vacuum seal is maintained by pressure against the disc from 3 parts: a felt seal on the opposite side of the mechanism, a spring steel clip and a slightly special washer which allow the valve to rotate as directed by the keys.

This felt seal wears down over 55+ year, but can be replaced with a nylon washer to restore tension on the vacuum valve.

Here's a shot of the replacement nylon washer:

Restore vacuum disc tension with a nylon washer or 2. Loose enough to allow valve rotation. Tight enough (with the high vacuum grease) to seal the vacuum signal.

On the outside (drivers side) of the valve there's another felt seal which I view as a giant leak source. In my bench test, I just replaced the felt with a round piece of closed cell foam rubber.

It's crude, but here's a view that may help:

Original felt seal replaced with closed cell foam. Felt was permeable (aka designed to leak), closed cell foam is not. I don't know if this will work.

What I can report conclusively is that the high vacuum grease helps seal these ancient devices. My bench test heater control had no leak for 10 or 15 minutes _on_the_bench. I suspect it will work well in the car, but don't know yet.

Along the way I greased up and reassembled a vacuum trunk release with the high vacuum grease and it restored the seal just fine. The trunk release actuators have a large surface area so I'm even more impressed that I was able to get that working again.

Overall, I'm impressed enough that I'll pull my dash-installed units over the next few weeks an attempt to restore them to much better vacuum sealing with the grease. Many thanks again to v8al for the suggestion. Great to learn about good stuff.

Final note on the electrical side: while you have the control unit out, you can remove the master electrical switch & polish up the long-used electrical contacts with a dremel to improve voltage to the fan. If you want to get ___really___ picky, take the high/med/low swith apart and clean it up too. Just look out for all those spring loaded parts. They love to fly all over the garage. And it can be tricky figuring how it all goes back together again...

Well into the weeds/cornflakes/molecules here, hope this is of interest and helps some of you.

Cheers
Chris