Author Topic: 1968 Cadillac RWD vacuum leak  (Read 545 times)

Offline Scot Minesinger

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1968 Cadillac RWD vacuum leak
« on: July 02, 2017, 11:47:53 PM »
Working on a 1968 Cadillac, and after about ten minutes the power locks don't work due to no vacuum.  The NS is bad and that is being replaced, but even with vacuum to it plugged, same thing.  This same thing happened on a 1967 Cadillac.  Yet on a 69 Olds with vacuum trunk release, it work for weeks after the car was shut off.

I know many usual places under the hood to look for vacuum leaks, so looking for perhaps a common place to look where this may be a characteristic on the 67/68 Cadillacs, where interior vacuum operated locks and trunk release suffer a common leak area.  Suspect an interior issue, are the lock mechanisms in doors vulnerable to leaks? 
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Offline Glen

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Re: 1968 Cadillac RWD vacuum leak
« Reply #1 on: July 03, 2017, 01:41:19 AM »
First place I would check is the vacuum reservoir.  The check valve can go bad and leak.  The   way to check that is with a hand vacuum pump on the outlet.  See if you can build and hold a vacuum just in the tank alone.             
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Offline Jeff Rose CLC #28373

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Re: 1968 Cadillac RWD vacuum leak
« Reply #2 on: July 03, 2017, 06:35:19 AM »
If you don't narrow it down to a specific circuit you will pull your hair out. I would suggest starting with the engine and work out. Should be only 4 or 5 points to start with. Pull every vac line including the choke brake, booster and vac advance. Put vac to each line (work from engine out). One of the lines will leak down . There is your tree and you can check that vac circuit outward until you find the culprate.
Jeff
Jeff
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1970 Coupe DeVille
1955 Series 62

Offline cadman56

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Re: 1968 Cadillac RWD vacuum leak
« Reply #3 on: July 03, 2017, 08:09:46 AM »
If memory serves me correctly, the door and trunk locks were isolated to one large reservoir on the firewall on my 67 Eldorado.  The heat/air systems were separate.  I think Glen is right.  If that tank holds vacuum go from it into the car.
Tje door vac pods only work when activated by by the door controls, they do not hold vacuum.  The NS switch is not in that circuit either, at least on my 67 Eldorado anyway.
Good luck.
1956 Cadillac Coupe deVille (sold)
1956 Cadillac Convertible (sold)
1956 Cadillac Eldorado Seville
1967 Cadillac Eldorado (sold)
1968 Cadillac Convertible
1991 Cadillac Fleetwood Brougham dElegance
Larry Blanchard CLC #5820

Offline DeVille68

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Re: 1968 Cadillac RWD vacuum leak
« Reply #4 on: July 03, 2017, 11:57:22 AM »
Hi

On my 68 there was originally one vacuum canister. This one is mounted on the firewall inside the engine. It is solely for the A/C transducer.

If one has vacuum door locks then there is a very large canister mounted vertically inside the driver side fender.
If one has only the trunk release there is a similar vacuum canister as for the A/C transducer mounted inside the driver side fender. If one has both systems there is only the large canister for the vacuum door lock.

In essence: If you loose vacuum on the trunk release the only possible sources are the switch inside the glove box, the vacuum hose to the canister, and (as mentioned above) the check valve of the vacuum canister.
If you also have vacuum door lock, then of course those could also add a vacuum leak in the switches. The vacuum actuators should only receive vacuum when the switch is pressed.

All other system are not connected directly to the canister and hence have no influence.


I had to rebuild my vacuum canister, you can read about it in my restoration blog: http://forums.cadillaclasalleclub.org/index.php?topic=130360.msg349177#msg349177
My system keeps vacuum for about one week. (after rebuilding the check valve)
« Last Edit: July 03, 2017, 12:00:31 PM by DeVille68 »
1968 Cadillac DeVille Convertible (silver pine green)

Offline V63

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Re: 1968 Cadillac RWD vacuum leak
« Reply #5 on: July 03, 2017, 05:00:42 PM »
A common failure is the door hinge hose (s) that fold when opening and closing get age cracks and leak vacuum.

Also there is a large plastic T with a round valve casting in it on the firewall. With age this plastic degrades and becomes porous.  I removed it and painted it heavily to seal.

The round die cast fitting at the end of the 'coffee can' resevour is another leak source. I used RTV around it.
« Last Edit: July 04, 2017, 09:11:50 AM by V63 »

Offline cadillactim

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Re: 1968 Cadillac RWD vacuum leak
« Reply #6 on: July 03, 2017, 11:24:03 PM »
Scot

Don't forget about the distribution block behind the glove box. Vacuum can leak off there also.

Tim
Tim Groves

Offline Scot Minesinger

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Re: 1968 Cadillac RWD vacuum leak
« Reply #7 on: July 04, 2017, 07:37:24 AM »
Happy 4th of July!  Just what I was looking for - thanks guys!
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Offline Highwayman68

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Re: 1968 Cadillac RWD vacuum leak
« Reply #8 on: September 11, 2017, 05:13:01 PM »
My door locks have been loosing vacuum lately so I did some troubleshooting today and found the issue is in the remote valve under the dash on the passenger side. I started at the canister in the engine compartment and followed and checked every connection along the way. Vacuum immediately starts to drain away when the remote valve is in the system. See diagram on page 6-20 of the Fisher Body Service Manual.

Does anyone know of a replacement available for this? They are assembled using rivets so once it is disassembled I don't see it going back together again.

Offline Glen

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Re: 1968 Cadillac RWD vacuum leak
« Reply #9 on: September 12, 2017, 01:17:19 AM »
Years ago, I took one apart.  I think reassembled it using long screws.  They were #6 or maybe #4 screws.  I donít remember what I did to the inside. 
« Last Edit: September 13, 2017, 02:41:37 AM by Glen »
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Offline Scot Minesinger

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Re: 1968 Cadillac RWD vacuum leak
« Reply #10 on: September 12, 2017, 07:08:52 AM »
The leak tested out to be the remote valve serving power locks under dash behind glove box.  Tried greasing up exterior but it is an internal leak.  I have a rebuilt one on order.  In researching the rebuild process specific "O" rings are required, and this could have been a time consuming project to rebuild it (getting the right parts - not the process of rebuilding it), so ordered one already rebuilt, should be here in a week.  Will keep you posted on progress/success.  The same remote valve was used from 1965 thru 1968.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Offline Highwayman68

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Re: 1968 Cadillac RWD vacuum leak
« Reply #11 on: September 12, 2017, 07:59:14 AM »
Thanks Scott, I look forward to hearing about your success.

Offline Highwayman68

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Re: 1968 Cadillac RWD vacuum leak
« Reply #12 on: February 07, 2018, 09:56:35 PM »
Hi Scot, did you get the rebuilt unit ? Did it install and function correctly?

Offline Scot Minesinger

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Re: 1968 Cadillac RWD vacuum leak
« Reply #13 on: February 09, 2018, 08:28:03 AM »
I never found the leak even after replacing the power lock block by glove box. 

This was a job I was doing for a friend, and it is all in the time finding it and he did not want to suffer any longer.  I can't blame him, as who wants to pay for ten hours (or more) to find a problem like this (power locks stop working after 15 minutes from engine shut off, but they work when car is running).  This is one of those jobs you have to do for the love of the car, cannot be hired out (to me) very easily without major pain.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Offline Highwayman68

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Re: 1968 Cadillac RWD vacuum leak
« Reply #14 on: February 09, 2018, 08:53:32 AM »
Yes this is something that requires personal time because it's your car and you want everything working right. Things like this will always cost more than it's worth when paying someone else to do it.

Where did you find the new remote valve serving power locks under dash behind glove box? I would like to buy one.

Offline Scot Minesinger

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Re: 1968 Cadillac RWD vacuum leak
« Reply #15 on: February 09, 2018, 07:29:19 PM »
This is not my car, it is a friends and was trying to fix it.  It is going to take a lot of time to run down the leak, and he is unwilling at this stage to do it.  Things change though - you never know.  The valve behind glove box was soured from a vendor that has disappointed a few friends of mine and so pm me if you really want it.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

 

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