In Park, when pressing the brake pedal the idle goes up...

[RC92234]

...by a few hundred rpms. Is that normal (never heard of it), or not such as a vacuum leak? It's a '73 California Q code w automatic, a/c, ps and brakes. I've never found the correct vacuum diagram, so my vacuum routing is hooked up as best I could figure, but there are no uncapped ports and all the tubing is new. Foot off the brake and returns to the regular idle. May happen when in gear, but much harder to detect.

 

[Bentworker]

Sounds like a bad brake booster diaphragm.

Booster Dewey could fix it for you

 

[RC92234]

Sounds like a bad brake booster diaphragm.

Booster Dewey could fix it for you

That's what I fear if it's not a vacuum issue

 

[Doug's 73 Mach1]

The standard 73 Q code was equipped with a 4300D carb that included an electric solenoid that held the throttle open a bit while the ignition was on. Idle speed would be set with the solenoid energized. When the ignition is off the solenoid retracts and lets the throttle close more fully helping to avoid "dieseling" when the engine shuts down. If there is something wrong with wiring, energizing the solenoid when the brake peddle is pushed (turning on the brake lights and the solenoid if it was connected to the brake light circuit), that would cause an RPM increase. In that case your normal idle would have been set with the solenoid de-energized. I know this is probably not a likely scenario but it would cause what you have described.

 

[70cobrascj]

Sounds like a bad brake booster diaphragm.

Booster Dewey could fix it for you

650 for a restored 71-73 booster

 

[Steve McMahan]

I had great luck with a So Cal local co, KARPS, located in Chino. They rebuilt my 73 stock unit and have an excellent reputation. Here is a link to their site:

http://www.karpspb.com/power-brakes

 

[giantpune]

My initial guess is a vacuum leak at the brake booster. You can verify this by disconnecting the large vacuum hose that connects the brake booster at the carb or intake manifold. Put a cap on the line and see if the problem persists.

It would also not be a bad idea to post a picture of how you've routed your vacuum lines.

 

[Hemikiller]

650 for a restored 71-73 booster

Minus your core credit - whatever that is...

Harmon has a rebuild and return service for $325

https://www.parts123.com/parts123/y...~S6UA0O9Z3J1042265265z/~Z5Z5Z5~Z5Z5Z50001029z

 

[Bentworker]

650 for a restored 71-73 booster

Wild- that is about twice what I paid a few years ago.

It’s too bad David isn’t active on the board anymore. I think he bought all the stuff to crimp and rebuild bendix boosters.

I know that Booster Dewey isn’t actually Booster Dewey anymore, he sold the shop.

 

[351c1971]

Leeds

Wild- that is about twice what I paid a few years ago.

It’s too bad David isn’t active on the board anymore. I think he bought all the stuff to crimp and rebuild bendix boosters.

I know that Booster Dewey isn’t actually Booster Dewey anymore, he sold the shop.

I believe Leeds makes a new unit that is bolt in.

 

[70cobrascj]

Leeds

I believe Leeds makes a new unit that is bolt in.

I bought a Leeds one and it works and fits perfectly. Not show car correct but a good replacement

 

[351c1971]

I bought a Leeds one and it works and fits perfectly. Not show car correct but a good replacement

 

[351c1971]

70cobrascj,
Your response is in line with I have heard from others.

 

[351c1971]

Could a leaking check valve cause the same problem?

 

[70cobrascj]

Could a leaking check valve cause the same problem?

I think that is possible but like others have mentioned disconnect that hose and plug it off and see if it corrects it.

 

[RC92234]

My initial guess is a vacuum leak at the brake booster. You can verify this by disconnecting the large vacuum hose that connects the brake booster at the carb or intake manifold. Put a cap on the line and see if the problem persists.

It would also not be a bad idea to post a picture of how you've routed your vacuum lines.

When I got it, there were unused (but not capped) vacuum hoses, uncapped ports, open manifold vacuum, etc. Sold first in Long Beach, CA, so this is definitely originally a California car, and with a California configuration at one point. Also seems CA-only vacuum diagram are just not available.

'73 351 4V (non-CA) should be diagram 3-16A, but that would have omitted quite a bit, whereas 3-14A 2V (non-CA) was the closest to what existed *on* the car: I have both the 3-port PVS and the 2-port temp control valve, but what I don't have from 3-14A is the #5 open solenoid valve loop from the PVS. I go from PVS to distributor. 3-16A for the 4V is far simpler, but does not include the PVS, which I definitely have.

Looking at the diagram section of the image, not the drawing, my configuration omits everything on the very left (ambient temp sensor, normally open solenoid, a check valve and spark delay valve). Route from the middle port of the PVS direct to the distributor.

Vacuum for the power brakes comes from the larger vacuum stack on the back of the (original) manifold.

 

[RC92234]

Leeds

I believe Leeds makes a new unit that is bolt in.

Is this what you mean? This one is at Kentucky Mustang and is the slim profile 9"

https://www.kentuckymustang.com/cha...on-master-cylinder-1971-1973-leed-brakes.html

 

[70cobrascj]

Is this what you mean? This one is at Kentucky Mustang and is the slim profile 9"

https://www.kentuckymustang.com/cha...on-master-cylinder-1971-1973-leed-brakes.html

That looks like the one I bought.

 

[clevelandcoupe]

Amazon has them too and If you have prime, it ships free... Is it ever free !!!
Thanks ,Jay

 

[351c1971]

Is this what you mean? This one is at Kentucky Mustang and is the slim profile 9"

https://www.kentuckymustang.com/cha...on-master-cylinder-1971-1973-leed-brakes.html