Technical Stumbles When Applying Brakes - HELP!

I have a 59 Coupe Deville that stumbles when applying the brakes and wants to die.

The vacuum check-valve appears to be working fine. I can suck through the end that connects to the carburetor but cannot blow the other direction (towards Booster/Vacuum canister). Also worth noting, when I remove the booster side vacuum hose from the check valve, I hear a release of air that was stored up in the vacuum canister.

One would think the booster has a leak (I did). So I just got done rebuilding the booster today. Tore it all down and reassembled with a new rebuild kit and used the supplied grease on the leather seal around the booster piston etc.

The master cylinder is also new, as are all four wheel cylinders and shoes (all done by myself last weekend).

So what gives? The exact same amount of hesitation/stumble is happening when I apply the brakes as it did before the booster rebuild.
The only way to drive the car is to turn the vacuum check valve around so that you cannot suck air from the carburetor end. Car still stops fine, but a little more effort is needed.

*worth noting*
New cap, rotor, wires, plugs and timing is all set. The only thing I have not done as of yet is rebuild the carburetor (which is next week).

Any ideas?

Here's the girl that has the hiccups

 

since booster is rebuild and not leaking,
i'm wondering how much vacuum you have at idle? 18?
possible your engine doesn't have enough "vacuum volume". maybe try a make/get a Vacuum Canister (with check valve) to store vacuum and possible help not depleting vacuum when brake is

just a thought.

 

Vacuum is pretty good (see image)

 

Your gauge says late timing, and the normal range is 17-22, you are at almost 16. Try adjusting the timing. What did you fix just before the problem started?

 

I have and to be honest, the car runs and starts the best where it is currently set. Don't know how much faith I have in that gauge as far as pinpoint accuracy, it's from Harbor Freight.

 

Try timing it with the vacuum gauge and see how it goes.

 

Current idle is at 520RPM (book calls for 450)
Timing is set at 5d ATDC (Book calls for the same)
I have tried advancing the timing to 10d ATDC which increases the idle and puts the vacuum gauge just in the green. The idle still has a stumble when applying the brakes though. This also causes the car to hard start. So I put it back to 5d ATDC

I have also tuned the carbs air screws via the vacuum gauge as well (adjusted until highest vacuum is achieved.)

I will say this, the car runs rich no matter what I seem to do and the idle screw has minimal effect on the idle speed when I adjust it. In fact, I have to turn it all the way in just to get the idle low enough to get near the books specs. This is why a carb rebuild is up next.

 

Have you looked for vacuum leaks all over the car? Try removing and plugging all the Vac hoses except to the distributor and P brake and see if it works correctly. If it does, connect the hoses back up one at a time to find the leak. Also look around the intake manifold and around the carb.

 

Stunning Caddy! Right color, wheels, and curb height.
Envy is running high here in Atwater...

 

I have not had a chance to have someone inside standing on the brake so I can check under the hoot for a vacuum leak (I understand that's on way to check things). I have checked for vacuum leaks around the carb and manifold. I will try your recommendations, although I don't hear any hissing sounds under the hood when it's running.

Thanks so much! The car is a dream to drive (normally) and it really is an attention getter? I flew up to Washington with a one way ticket and my girlfriend. Purchased it in the parking lot and drove it home to Southern CA over 4 days while stopping at B&B's. It was truly awesome!

 

So I went back out to the garage.
I blew out the air mixture screw holes with compressed air (gas came out those tiny top holes). So I can assume those air mixture screw passages are cleared.

I threw her in drive and checked timing and idle etc.
Idle is at 450rpm, timing is at 5degree ABTDC and vacuum is now at a measly 12 (should be around 20 from what I understand).
I plugged all the vacuum lines except the one going to the vacuum advance and the same problem is still there (stumbles when brakes applied and low idle vacuum)

I pulled a can of carb/choke cleaner and sprayed at the base of the carb. The car stumbled and the idle dropped to about 400. Brought the idle back and sprayed around the carb base again..same thing, idle dropped and car wanted to stall. I think it's safe to say the carb should be rebuilt along with the base gasket replaced.

I'll tackle this tomorrow and report back.

 

I think the master cylinder is leaking fluid into the brake booster. Pull and rebuild the master cylinder.

 

You should have a little better vacuum at idle. The specs call for 5* BTDC, not 5* ATDC. Late timing will drop the vacuum as you've noticed.

http://www.carnut.com/specs/gen/cad50.html

Does the vacuum advance work properly? Does it hold vacuum? Is it connected to ported vacuum or full manifold vacuum? Is the choke opening fully after warm-up?

 

i think that carb has the extra spacer under it, with a couple gaskets. i had one that the spacer was warped and leaked.

 

Please read my posts in this thread, it has been replaced, the fluid that was in the booster was from years past.

On the Harmonic Balancer I am timing it 5* to the right (clockwise) of top dead center (zero). The manual calls for 5* ahead of TDC. It doesn't say before or after, so I might be getting confused. Please clarify if I need to time it to the left of TDC or to the right.
When I advanced it to 10* clockwise to the right, it gained vacuum, so I assumed I was timing it correctly?

I don't have a vacuum pump to check the vacuum advance. It is connected to the factory spot at the manifold.

 

The carb has a gasket on the manifold, then a 1/4 -1/2" spacer, then gasket on top of that and finally a metallic shim type spacer on the very top that the carb sits on. I checked the manual and this is all factory correct.

 

did tha manual show them in that order? i had trouble finding the correct order for the one i did. it was a bunch of years ago.

 

Ahead of means before.

When you are using the timing light, standing in front of the car, looking at the engine, the line will need to appear to the LEFT of the 0° (TDC) mark.

 

Yes, this is the order the manual has it listed

Ok, I'll give that a shot. I'm a bit confused though as when I adjusted the timing in the direction you mention, the cars idle and vacuum dropped significantly.

 

Upon further investigation, I found a crack in the carb base plate. If you look at the pics, you can see a bulge in the gasket that was sat right where the crack in the baseplate was. It's a lot worse in person than the pics show. This was the same area that would cause a drop in idle when I sprayed with Carb/choke cleaner. I didn't hear any crazy vacuum leaks from that area though.

Quick look on feeBay and they go for $90 each. OUCH
On top of replacing this, I will double check my timing skills. Seems they are rather rusty from my Highschool Autoshop days back in 1995

 

yep, now that is see that picture i remember i found the same thing. at the time i blamed the order of the steel plate and gaskets. good find.
that carb has the big adjustment screw on the front of it right?

 

Yessir.
Two mixture screws on either end of the big idle speed screw smack dab in the middle.
I have the Carter AFB model. The same year also came with the Rochester version.
And of course, the 3 carb. version which sounds like a nightmare.

Further shopping I was able to find the riser plate for $77 shipped over at Cadillacparts ltd.
Caddy daddy wanted $100 and feeBay wanted $90. $77 is is I guess. Damn these classics aren't cheap.

 

Do you want everyone to own one?

 

there is a guy named dennis in pennslavannia that sells spacers for all kinds of engines/carbs. company name is cool something[?]

 

Good point

 

JB weld is a lot cheaper....

 

That "metallic shim type spacer" is to prevent exhaust gasses from burning a hole thru the carb base.... it is stainless steel. That is why it is critical to put them on correctly. If you are in a part of Cali that doesn't get that cold, I would plug the two holes in the intake to block them off (northern climate guys should ignor that statement). Then you could just get a 1/2 " thick spacer and a couple of gaskets to repair it.

Funny thing about the idle speed setting. My old Motors manual says to adjust to 450 rpm with a tachometer after adjusting mixture screws. If you don't have a tach availible, place the car in drive without the parking brake set and adjust idle speed up until car creeps forward, then back off until it stops creeping..... sounds like an exciting way to do it.... LOL

 

i found the guy, "cool carb".
http://www.coolcarb.com/how-coolcarb-works.html

 

Can you elaborate on the two holes that need plugging? I'm in the LA area of So CA so the coldest it gets here is like room temperature. haha

Great find! Thanks... never knew about this guy.

 

That does sound exciting, not in a good way.