no power brakes

[ocbaud]

ever since switching to longtubes and from my edelbrock avs to the demon 650, my power brakes suck big time.

going around a neighborhood its like i dont have any power assist.

on the highway its much better, until i get off and use up the assist.


i guess i need a vacuum canister? why would it change so much from just swapping carbs?

[1974ChevyC10]

when you hit the brake pedal do you hear a hissing sound(kinda sounds like psssh)and does it seem to take longer to stop and your pedal sinks a little to the floor.if so it is your vacuum canister for the power brakes.i had the same problem with my 78 last year it failed suddenly one day on the drive home from work good thing i only lived a mile or so from my job at the time.depending on your braking system if its heavy duty or not it will cost a little more for a new booster and possibly be prepared to order a new one i ended up having to because no stores in town had a JB5 booster in stock.

[BLE 'BURBAN]

Start with the one way check valve that the hose connects to on the booster. They are notorious for failing on the older trucks. Fortunatly, NAPA auto parts carries such an item. Part number is 89000 Line code is UP (United parts). It's about $10.00 for the part. Start with that before going for a reman booster.

[ocbaud]

the brake booster isnt bad

its that it isnt getting enough vacuum to it. the combination of my cam and new carb is causing it i'm sure

[Pyrotechnic]

Have you driven around with a vacuum gauge to verify a low vacuum condition ?

[Ivan D.]

Originally Posted by ocbaud

the brake booster isnt bad

its that it isnt getting enough vacuum to it. the combination of my cam and new carb is causing it i'm sure

Well, in that case, you know the solution:



I like that system so much I'm about to throw one in my Lincoln next summer when I replace the PS pump. It's a bolt-on upgrade too, especially since you already got power brakes.

[1974ChevyC10]

Originally Posted by ocbaud

the brake booster isnt bad

its that it isnt getting enough vacuum to it. the combination of my cam and new carb is causing it i'm sure

i stand corrected it sounded similar to a problem i was having with my truck last year i guess i should have read a little better before answering.i would go with ivans idea and get powerboost.i used to have a car that had powerboost assisted brakes and man that for being as large as it was stopped way better than any vehicle car or truck ive owned with vacuum assisted brakes.

[swb85]

What are your cam specs? How much vacuum at idle? Unless you've got some wicked cam, it sounds like a vacuum leak somewhere IMO. The cam in my truck has 13* overlap at .050" and I only pull 9-10" of vac at idle......power brakes work perfectly.

[454HO]

Originally Posted by ocbaud

ever since switching to longtubes and from my edelbrock avs to the demon 650, my power brakes suck big time.
.
.
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why would it change so much from just swapping carbs?

It shouldn't. Where are you getting vacuum from? The brake booster should recieve full manifold vacuum at idle. You need it to be attached to true manifold vacuum with at least a 3/8" line. If you attached it to a 'timed' port on the new carb, that would explain why it seems to work better on the highway.

[Ivan D.]

Greg, do they even make carbs with ported 3/8" vacuum? All 3/8"s I've seen have been manifold vacuum, at the base of the carb. The ported vacuum is usually 1/4" or so, way too tiny for hooking up a power booster hose.

[454HO]

Originally Posted by Ivan D.

Greg, do they even make carbs with ported 3/8" vacuum? All 3/8"s I've seen have been manifold vacuum, at the base of the carb. The ported vacuum is usually 1/4" or so, way too tiny for hooking up a power booster hose.

That was kind of my point. The brake booster needs to use the largest manifold vacuum port on the carb. I am not at all familiar with the Demon carbs, so I don't know what it would look like. If I remember correctly on a Edelbrock carb it is either a 1/4" or 3/8" NPT fitting between the secondary bores in the base of the carb.

[ocbaud]

found out why my brakes suck

i'm running the pcv and booter off a T coming off the vacuum port on the back of the carb. i guess they dont like sharing the same port? ha

so where the hell can i run my pcv to? the fitting on the back of the manifold is taken up by: tranny and hvac controls. there isnt another spot to put a large pcv fitting at

[454HO]

According to this Demon carb manual that carb only has 3 vacuum ports. Two on the right front, one of which is ported or 'timed', the other is direct manifold. Then a large one in the back that is for the PCV valve.

My recomendation would be to run the HVAC controls off of the carb's front direct manifold port, then use the port directly in the intake manifold runner for the brake booster and transmission modulator valve. Hook up the PCV valve to the port on the rear of the carb. The vacuum advance for the distributer would go to the carb's timed port.

[BLE 'BURBAN]

No vac port on the front of the carb for the pcv valve?
If push comes to shove, drill and tap the manifold for a fitting

[ocbaud]

Originally Posted by 454HO

According to this Demon carb manual that carb only has 3 vacuum ports. Two on the right front, one of which is ported or 'timed', the other is direct manifold. Then a large one in the back that is for the PCV valve.

My recomendation would be to run the HVAC controls off of the carb's front direct manifold port, then use the port directly in the intake manifold runner for the brake booster and transmission modulator valve. Hook up the PCV valve to the port on the rear of the carb. The vacuum advance for the distributer would go to the carb's timed port.

i'm running full manifold for my timing

[xtreme80]

Originally Posted by ocbaud

found out why my brakes suck

i'm running the pcv and booter off a T coming off the vacuum port on the back of the carb. i guess they dont like sharing the same port? ha

so where the hell can i run my pcv to? the fitting on the back of the manifold is taken up by: tranny and hvac controls. there isnt another spot to put a large pcv fitting at

Weird. Im running a T in the back of my carb as well, and don't have any problems. Unless my brakes suck compared to yours and I'm just used to it?

Im also not running as big of a cam. It's pretty mild too.

[PhilaTruck]

I have my PCV running into the front of the Q-jet, at the base. But that's my carb.

[Ivan D.]

Originally Posted by PhilaTruck

I have my PCV running into the front of the Q-jet, at the base. But that's my carb.

Yes, but you have two 3/8 ports, front one for the PCV and rear one for the brakes, he only gots the rear one.

[ocbaud]

i fixed it

running the booster off the fitting on the rear of the carb

and using a smaller hose from the pcv to the 't' fitting on the back of the manifold. the smaller hose was a pita to get on, but its working great now

[Ivan D.]

Eric, if the PCV now goes to the manifold T-ee, what did you unplug from the T-ee to make space for the PCV, and where did you move it to?