Vacuum setup problem: pedal feels good, but braking is weak.

[JYLP]

I had the same problem when I did my conversion as well. Turned out to be my check valve was not good and neither was my vacuum source. So I bought a check valve from Summit, made up a Russel line, Taped my intake spacer and hooked it all up. Brakes work excellent now. Better then I expected. See pics below.

Summit Check Valve



Russel Line


Hook up to the check valve


Hook up to the Motor

I've been getting a bit of mixed information... My dad tells me that the pedal goes to the floor like it does because the cam size/valve duration doesn't allow the motor to create as much vacuum. My uncle tells me that if it was a vacuum issue, the pedal would be hard, not soft.

When I block the vacuum line, the brakes get hard. This car has a Wilwood brake system (m/c, 4 piston calipers, drilled and slotted rotors 10" up front, 12" in the rear and stainless lines). I don't know what booster is on it, the brakes were done by the previous owner. I checked the brake fluid and it looked more like old motor oil (very dark), so I sucked the fluid out of the reservoir, cleaned inside the reservoir with a clean dry rag and flushed the system with new fluid by bleeding each of the brakes until the fluid looked clear. When I was bleeding the brakes, I never seen any air.

The boost gauge reads about 10-13psi of vac at idle. When I pump the brakes repeatedly at idle, the RPM drops and it sounds like it wants to stall almost but never does no matter how fast or how many times I pump the brakes at idle. I did this after having just started the car, but I don't think it was fully warmed up.

The vacuum is coming off the distribution block on top of the dog house/upper plenum. It has the vacuum block for the vacuum brakes. Where were you getting your vacuum from before you moved it to the spacer plate? This car also has that same spacer plate.

How do you tell if the check valve is bad? I tried to blow thought it and it only allowed air to flow one way, but I'm not sure if it takes more pressure than that to test it. When the car off and having sat for hours, I pull the check valve out and can hear air.

I'm thinking I should take it to someone that can vacuum bleed the brakes, really flush the system and test the m/c to make sure it's working properly. The pads aren't that bad, so I'm pretty sure they aren't the cause of this problem. There are no fluid leaks from what I can tell.

I can make a video of this car and the issue if it helps.

Can you please explain how low vacuum would cause this problem?

 

[ttypewhite]

I had a distribution block behind my intake that I T'd it from before. Wasn't good enough. The Summit check valve is cheap and seals off the system very well with #6 Russel line and fittings. Your vacuum you have to your motor seems really low, almost like you have a vacuum leak in one of your lines or something. I get 17 inches of vacuum in my car. But low vacuum should give you a hard pedal not a soft one. Almost sounds like your booster or master isn't working properly if your foot goes right to the floor.

Need more info:
1) did this system ever work well since you have had this car?
2) When did things start going south with the brakes?
3) does it have the right brake pedal for the vacuum brakes? ratio is not the same as the power master
4) do you have a proportioning valve on the car? or are you running the stock one?

 

[JYLP]

I had a distribution block behind my intake that I T'd it from before. Wasn't good enough. The Summit check valve is cheap and seals off the system very well with #6 Russel line and fittings. Your vacuum you have to your motor seems really low, almost like you have a vacuum leak in one of your lines or something. I get 17 inches of vacuum in my car. But low vacuum should give you a hard pedal not a soft one. Almost sounds like your booster or master isn't working properly if your foot goes right to the floor.

Need more info:
1) did this system ever work well since you have had this car?
2) When did things start going south with the brakes?
3) does it have the right brake pedal for the vacuum brakes? ratio is not the same as the power master
4) do you have a proportioning valve on the car? or are you running the stock one?

I just found out that the booster doesn't hold vacuum like a booster on a newer car, so I'm pretty sure that's going to be my vacuum leak. Since I removed the check valve and put it back in a few times today, the boost gauge reads something like 7 to 10psi vac. at idle.

Since I've been driving it, the brakes have always been this way.

I'm not sure what pedal it has, but I measured about 4" from the hinge to the booster rod.

Using the stock proportioning valve.

I tried to see how hard I could stop today and the brake light on the dash came on and went out when I let off the brake. I then decided to gravity bleed the brakes. Once the brakes are up to temp, I'm able to do 60mph and come to a stop within about 65'. We made a 60' box on the street. I hit the brakes when I got to the first line and by the time the car stopped, the 60' line was at the middle of the door, so I'm guessing that's about 65'. It's actually making the seats fling forward, but the pedal still goes down too far.

I'm only able to hold about 7psi of boost with the foot brake, but the brake pedal is just about to the floor when doing that.

What cam do you have? I'm not sure what cam is in this car, but from what I'm told it's a 218-218 or a 224 something and it has 1.75 roller rockers with ported gn1 aluminum heads. From what I've been told, the more valve duration, the less vacuum you get.

Is it possible to modify the pedal that I already have?

 

[TexasT]

Sounds like you have a different pedal so maybe it go swapped In when the vac brakes got put on. Here is a pic of my pm/hb pedal.
Might be a bad booster, as you said pedal gets hard when you take vac off booster.

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[ttypewhite]

Yep, I got the wrong pedal in there. Swap that out first and give it a try again. You can modify yours to work. Do a search in this section, I remember someone posting how to do it. Your vacuum that your engine see's is still too low. I have a 224 cam in mine with 1.75 T&D's on TA aluminum heads and I have 17 inches of vacuum. Replace all of your rubber vacuum hoses under the hood and twist tie them all afterwards. Might want to also check the lash on your rockers to make sure that all valves open and close properly. You could have a valve hung open just a little that could skew your readings.

 

[JYLP]

Yep, I got the wrong pedal in there. Swap that out first and give it a try again. You can modify yours to work. Do a search in this section, I remember someone posting how to do it. Your vacuum that your engine see's is still too low. I have a 224 cam in mine with 1.75 T&D's on TA aluminum heads and I have 17 inches of vacuum. Replace all of your rubber vacuum hoses under the hood and twist tie them all afterwards. Might want to also check the lash on your rockers to make sure that all valves open and close properly. You could have a valve hung open just a little that could skew your readings.

A little smoke comes out the exhaust at idle, so I kinda figured the valves are probably hanging open a little. It also smells like it's running kinda rich at idle, but from what I'm told, it does have the biggest double pumper that would fit in the tank... I set the fuel pressure to 42-43psi and after driving for a while, I check it and it's way down at 30psi. Think that could also be due to vacuum?

Thanks a lot for all the help guys.

 

[ttypewhite]

I have the biggest Racetronix double pumper too. If you set it to 42 and come back to 30, you definitely have a vacuum problem somewhere or your fuel pressure reg is shot. Wherever I set mine, it stays.

 

[JYLP]

I did a compression test and all cylinders were at 130-135psi aside from #5 and 6 and they were at 120-125psi. They all held the highest pressure they reached. I'm not sure of the compression gauge is designed to hold highest pressure reached or if it will allow pressure back out if the cylinder doesn't hold that pressure.

I'm pretty sure the valves are floating, the car falls on its face at higher rpm and the valve springs look to be the ones that come on gn1 heads but aren't for a roller cam. I'm working on getting valve springs for it. Once I have them on the car, I will be sure to let you guys know if that helped with the vacuum issues.

In other news, the car actually broke the hotchkis rear sway bar and thus I'm also getting an hr sway bar.