Long story short, I've replaced brakes etc which don't work! Did everything and finally found out that some of my vacuum lines were disconnected do to cracked ends etc and I've noticed that one vacuum line is missing.

Could any of you owners of 1963 Cdillac with an AC Unit please take and post some photos of the vacuum lines coming out of the firewall and where they're connected to??
Would be great if you could take the air filter out of the carb for the better view!


Views: 779

Reply to This

Replies to This Discussion

It's got a lot to do with location of crack on intake manifold. 95% of the cracks I have seen are at the exhaust port and do not think that would affect vacuum in any significant way. Since engine vacuum is created by the rotation and suctioned of the pistons pulling downward as they draw in the air fuel mix, a significant crack across any of the air fuel intake ports probably would affect vacuum. A razor thin hairline crack, however, probably would not significantly affect vacuum.
Feels like the master cylinder that pressurizes the brake system is not doing its job
Did you change the MC or add a valve to balance the disc brake pressure ?
Does your brake peddle go to the floor ?
If it does change you MC
The vacuum lines that you are trying to find where they go have nothing to do with the brakes
The only vacuum line for the brakes goes from the intake to the break booster behind the MC
( second time i noted that )

Too funny...I've got the brand new MC and Booster, same problem! Manufacturer had replaced me the MC which was bench bled...still the same!
Since I have two 63CDV then I think I'm going to run a long vacuum hose from my good/working 63Coupe's intake manifold to that 'not working' booster!
If brakes will work then it's a poor vacuum on the car, if the brakes still won't work then it must be bad booster... At least this idea of checking the vacuum came to My head ;)

In the beginning you used the words "disc brakes". Have you converted your car to disc brakes? If so are you certain the system is workable with our cars?

Mack, I am going to insert a few pictures that may help.

First some basics. Off the intake manifold connector you should have a fitting with 2 nipples (maybe 3 if you have vacuum power door locks & trunk). One of the vacuum lines goes to the throttle check valve at the firewall to control throttle deceleration, and the other goes into the main forward lamp harness wiring block to feed the Neutral Safety Switch and the AC/Heat System. Throughout the pictures below I have highlighted these 2 vacuum lines in yellow.

Second, at the round engine cranking harness connector, you should have one blue striped hose on AC equipped cars that feeds the Fast Idle (Speed-Up) Vacuum Power Unit. I have highlighted it in blue.

3 obvious alterations to your car, is a 2nd line at the round engine cranking  grommet; the missing cabin feed line to the main wiring block;, and an altered back of intake fitting that I am not sure where it goes after the short hose then a worm gear clamp. For the 2nd line and to see what is on the back of the  main wiring harness block and what happened to the main vacuum feed line, you will have to get under the dash and see where it goes. Anything beyond that on my part is pure guesswork.

Here are some pictures that may help:

This is a stock setup showing the intake fitting going too the throttle check valve and the cabin vacuum feed at the forward lamp harness connector (yellow), and the fast idle vacuum unit (blue).

Here is another view noting that the Idle Speed-Up Feed is cut and disconnected:

Here is the same picture with the color highlights (yellow for intake to cabin feed at forward lamp harness connector and Throttle Check Valve; and blue to Idle Speed-Up)

Here is a picture showing the relationship of the actual pictures to the shop manual illustrations which does not provide details of the intake fitting connections:

Here is one more final picture showing the same feeds, and again the Idle Speed-Up line has been disconnected, but you can clearly see the blue stripe which is correct for this line.

So I have just measured the vacuum of the hose connecting booster with the intake manifold on my other 63CdV and compared it to the one with not working brakes - same exact pressure!!!

I guess the next and LAST try will be unplugging te lines from te MC, plugging each outlet to see if MC works good. If pedal stays hard then I'll bleed each line at the time to locate the problem.

I will keep you guys posted!

These illustrations were copied to our Vacuum Schematics and Pictures Help Page. They are not the definitive pictures I would  like to have on file but hopefully will help someone.

The intake cannot be leaking air for any reason or it will not draw the fuel thru the carb as it SB doing
All air leaks must be removed from the intake for the vacuum the intake creates to work as it should to operate the things the vacuum does in the cars cabin ( heat and AC)

An air leak into the intake ( vacuum leak ) prevents the intake from building the vaccum That it Is designed to do to work the systems in the cabin of the car
The intake manifold is the source of --all vacuum --required to work all vacuum related things in your car ( brakes - for the brake booster - AC and heat )

A crack in the manifold or any air leak must be repaired if you have one
That would include any hose leaks in the cars cabin that have not been sealed if leaking
That is why i suggested --plugging the hose from the back of the intake --that goes into the cabin to work the systems in the cabin

Trying to explane the same thing a few ways

In the service manual for your car there is a proceedure to check if your brake booster is working
Do that test to check it

Looks to me that there is no hose on the fitting with the doulble yellow hose that Jason posted in your fist picture of you car
That fitting if not plugged is allowing a major amount of air into the intake --possibly preventing the intake from producing enough vaccum to work the brake booster as it SB doing

I am back to the MC being the problem

Don't you need a proporstioning valve to run --front disc brakes --on our cars to balance the MC pressure properly ?




  • Add Photos
  • View All


Exhaust Manifold Gaskets......Again

Started by Ian Osborne in 1963/64 Cadillac Specific Discussion. Last reply by Ian Osborne 10 hours ago. 21 Replies

I know I'm not the only one who has dealt with constantly failing exhaust manifold gaskets but I have the heads off for a valve job and I'm trying to fix the issue once and for all. Well, maybe for a…Continue

Current 1963/64 Cadillac Listings on eBay

Started by Jason Edge in For Sale. Last reply by Jason Edge 20 hours ago. 0 Replies

To see all 1963/64 Cadillacs Listed on eBay in the USA…Continue

Tags: ebay

Caddy Daddy

Started by Dan McNarry in General Discussion. Last reply by Dan McNarry yesterday. 10 Replies

I'm looking to buy a new fuel sending unit for my car and was wondering if anyone has had recent dealings with Caddy Daddy and if so, yeah or nay?Continue

help adding fluid to top motor for '64.

Started by john kilbourne in 1963/64 Cadillac Specific Discussion. Last reply by Charles Fares yesterday. 3 Replies

Is there a Youtube about this? From what I can learn for other lesser cars, such as they may be, the drill is: remove rear seat bottom and back, remove the plug from the top motor reservoir, use a…Continue

Blog Posts

63 Caddy Horn

Posted by Robert Alan Shannon on May 27, 2020 at 9:25am 9 Comments

 Just noticed a 1963  Caddy trumpet horn on Ebay. No part # given but some of his other items are 1963 specific, just throwin this out there, I have no connection to this listing .

Wiring connection help.

Posted by Jimmy Davis on May 24, 2020 at 9:15pm 2 Comments

Can someone help me figure where these connections go? I have a 64 60 special if it matters.…


Wood grain finally done.

Posted by Jimmy Davis on May 20, 2020 at 4:57pm 3 Comments

After years of wanting to, I finally redid my wood dash paneling on my 64 60s. Not too hard to do either.…


390 engine replacement needed

Posted by Jason on May 18, 2020 at 7:54pm 1 Comment

I’m looking for a 1963 Cadillac 390 engine that runs. 



  • Add Videos
  • View All

© 2020   Created by Jason Edge.   Powered by

Badges  |  Report an Issue  |  Terms of Service