Best way to seal vacuum hose connections

[Mark E.]

My '70 has small vacuum leaks at several hose connections. What's the best way to repair these?

The leaks stop if I hold the hose tightly against its fitting. I applied silicon grease to the male part of the fitting as a sealant- it leaked less but still leaked. I'm reluctant to apply weatherstrip adhesive or gasket sealer because I want to disconnect them in the future without damage. And some of the connections are not compatible with a clamp or cutting a bit off of the end of the hose (for example the H/L and wiper door override switches).

Suggestions?

Can the hose be disconnected without damage if weatherstrip adhesive is used?

[Keith W.]

If excess hose is available as in “slack” I have a trimmed one of mine for a tight fit.

[Patrick H.]

I don't trim because many don't have extra length, and it's just against how I work.

However, using shrink tubing on the fitting to make it a bit larger works quite well. It seems to seal well, and the larger diameter is now "tight" to the inner wall of the hose. One can even pass a PV with this trick. IN addition, the shrink tubing is easily removable.

You may have made any repair difficult by applying the silicone grease.

[Mark E.]

I don't trim because many don't have extra length, and it's just against how I work.

However, using shrink tubing on the fitting to make it a bit larger works quite well. It seems to seal well, and the larger diameter is now "tight" to the inner wall of the hose. One can even pass a PV with this trick. IN addition, the shrink tubing is easily removable.

You may have made any repair difficult by applying the silicone grease.

Thanks Patrick for this creative solution. I'll give it a try and report back.

I'm confident the grease can be removed successfully.

[Patrick H.]

Thanks Patrick for this creative solution. I'll give it a try and report back.

I'm confident the grease can be removed successfully.

It has worked great for me and others with whom I've shared it.

[Duke W.]

Most vacuum hoses don't have clamps because if the hose is properly sized for the nipple it will essentially self-seal. Old vacuum hoses "creep" (stretch) and harden with time and heat cycles, especially where they mate with nipples resulting in leaks.

The best solution is new hoses. Measure the nipples and buy hose the same ID or even slightly smaller. One-eight inch ID is a common vacuum hose size. If your car is not going through judging tubing from any parts store should be fine as long and you size it correctly.

If you're going through judging you should look for hose with the proper configuration (stripes, ribs...) as called out by the applicable JG and check the GM restoration specialty outfits to see if they have something that matches.

Duke

[Mark E.]

Duke,

Thanks for the suggestion. I'm going to try shrink tubing and sealing the connections first. Replacing vacuum lines under the dash for the HVAC and headlight/wiper door systems is a project to avoid if possible. Stay tuned.

[Patrick H.]

Replacing vacuum lines under the dash for the HVAC and headlight/wiper door systems is a project to avoid if possible. Stay tuned.

I'm not saying never, but I have not found the interior hoses to be a source of leaks.
Look at engine compartment connections, relays, canisters, and the silver valve.
There are ways to check each of these, as some can leak internally and cause issues.

[Mark E.]

I'm not saying never, but I have not found the interior hoses to be a source of leaks.
Look at engine compartment connections, relays, canisters, and the silver valve.
There are ways to check each of these, as some can leak internally and cause issues.

The hose connection to the headlight manual override switch leaked. The leak would stop if I pressed the double hose fitting down.

I didn't want to use shrink tubing and heat on the plastic switch so I used a small cable tie to hold it in place.

Also had a loose hose connection at the wiper vacuum control solenoid behind the tach. That just needed to be pressed on better. The smoke maker found that one and stunk up the interior of the car in the process.

Now leak free: HVAC system, wiper and headlamp control system (small hoses), wiper actuator system (large hoses). I say leak free but that excludes the broken wiper arm vacuum valve in the cowl. I'm searching for a good one as you read this.

I still have small leak(s) somewhere between the tank and both headlamp actuators (large hoses).

BTW your shrink tubing method works brilliantly. That advice alone is worth my 30+ years of membership. Thank you again Patrick.

[Patrick H.]

I say leak free but that excludes the broken wiper arm vacuum valve in the cowl. I'm searching for a good one as you read this.

I still have small leak(s) somewhere between the tank and both headlamp actuators (large hoses).

BTW your shrink tubing method works brilliantly. That advice alone is worth my 30+ years of membership. Thank you again Patrick.

Check with Gary Bosselman or Bob Demmel for a rebuilt valve. Or, Dave J (that's his username) on the CF sells new ones that actually work.

The tanks can develop tiny rust holes, or holes in the seams.

[Mark E.]

Gary Bosselman is not accepting PMs. Does anyone know how contact him?

[Patrick H.]

Gary Bosselman is not accepting PMs. Does anyone know how contact him?

See your PMs

[Mark E.]

Check with Gary Bosselman or Bob Demmel for a rebuilt valve. Or, Dave J (that's his username) on the CF sells new ones that actually work.

Following up about sourcing a wiper door vacuum interlock valve-

I ordered two from different vendors and each looks identical and tests bad in the same way: The red port does not hold vacuum with the plunger extended (causing a vacuum leak when the wipers are on); and the black port does not purge vacuum from the white port with the plunger depressed (preventing the control vacuum from purging when the wipers park).

Because they look the same and fail in identical ways, I suspect many vendors source these from the same supplier. Either this supplier is making them to the wrong specs or has terrible quality control. Based on my sample of two that failed in the exact same way, I suspect the former. This is probably exacerbated by a Doc Rebuild YouTube video showing an invalid way to test these (these valves pass this invalid test but don't work).

Following Patrick's lead, I found this thread on CF confirming these repro switches are a problem:
https://www.corvetteforum.com/forums...ty-switch.html

In the above thread "DaveJ" says Corvette Central and Zip sell a different repro switch which is handmade by him and works. Here's CC's product page:
https://www.corvettecentral.com/c3-6...hut-off-453098

I ordered one and will report back when received.

[Patrick H.]

In the above thread "DaveJ" says Corvette Central and Zip sell a different repro switch which is handmade by him and works. Here's CC's product page:
https://www.corvettecentral.com/c3-6...hut-off-453098

I ordered one and will report back when received.

He (Dave J) sells direct too.
They work.
Note that his have a black end on the plunger, not the typical white, so it's easy to pick them out. The ones on CC's website appear correct. Use the original rubber boot from your unit on Dave's repro.

The bad repros have some internal defects from the manufacturing process. It's almost impossible to get one to work.

[Mark E.]

The DaveJ interlock valve arrived yesterday from Zip (CC's website had problems). This valve failed too. Tests performed:

With plunger depressed (wipers off):
- R port passes vacuum to the W port (PASS). This energizes relay to close wiper door.
- R port holds vacuum with W port plugged (PASS). This tests for leaks in the valve.

With plunger extended (wipers on):
- R port holds vacuum (PASS). This prevents a vacuum leak to the engine.
- W port should purge to B port, releasing vacuum to the relay's control line to open wiper door (FAIL- B port leaks to housing and W port does not pass air).

I'll reach out to Zip to see if they're willing to test another valve. If I had DaveJ's contact info, I'd like to reach out to him as well.