low idle vacuum options ; Vac canister vs. Vac pump

Hubbarocks

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Hi gang !
Can i get some opinions on this? I'm running about 7-8" vacuum at idle. I'm in need to add something to the brake booster to function consistently , it was fun at first (jk) but i almost smacked someone in the arse the other day & not in a good way....:praying:

so i gotta spend some money and fix.

any one use vacuum canister and wish they would have spent the extra money on something else. vacuum pump or even hydro boost ?

$40~60 bucks for a vacuum canister , I'm hoping keeps the vacuum for the booster sufficient or do they not work as advertised?

i see vacuum pumps are $300 ~600 , so quite a price difference

-hubba
 

diesel_lv

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Manual brakes!! They work amazing on my '67 4dr. Pedal is not difficult at all.
 

Rusty knuckles

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Is this because of a cam? If not I'd say you need to chase down your vacuum leaks. But I'd seriously look at a different cam if I'm street driving very much.
 

diesel_lv

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You do have 4 wheel drum brakes? Disc drum manual combo makes for interesting braking.
Yes, disc front, drum rear, the standard since late 60's in almost every car/truck. Nothing "interesting" about it. No wheel pull left or right, no rear lockup before fronts, my daughter who weighs 110 can use them easily. Unless you're on a racetrack to hi speed straights with hard braking for turns, no brake fade.
 

steve340

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Hydro boost is your best bet in my opinion for a first time fix - and the least ugliness.
I believe there is a silent vacuum pump that sounds OK. But you have to mount and wire up that funny looking thing.
Whatever you do you will probably end up spending and adding some component or other in the engine bay. Low vacuum is hard to get around - and a canister only stores more of the 8 inches - it does not magically make it 20 inches.
Plenty of posts try all sorts of band aids and then a few months later another post "my brakes are still shit"
 

Geoff 2

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A vac canister does NOT increase vacuum, it only stores it. So if you have crap brakes now, with a vac canister you will have crap brakes for longer....
Logical solution is hydroboost or a vac pump.
 

F4R/T

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Try giving more initial timing at idle to cover up or smooth out the cam. Put a vac can on it and go.
 

Wietse

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I am using the stock Bendix brake booster and it works fine with 6-8" vacuum.
I have front stock discs and 10" rear drum brakes.
 

steve340

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The Bendix dual diaphragm style unit is definitely far better than any single diaphragm pancake booster and they do work well on engines with much lower vacuum readings.
You could fit one and still not be happy. It really depends on what you really want.
I like power assisted steering and brakes and I know some folks do not.
The fact of the matter is disc brakes have no mechanical advantage so some type of assist does make sense.
 

Hubbarocks

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thanks everyone for their input. i got some decisions to make.
i believe its the cam (gross lift .545 int & exh) i wasn't sure what to expect with this & high rise single plain intake as far as vacuum. However, i will re-visit the timing and check for any vacuum leaks. it's a good idea regardless. i had it pretty dialed in i thought before i put in hibernation last fall.

she's coming home this weekend (hurrah! )
 

MoparGuy68

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I am using the stock Bendix brake booster and it works fine with 6-8" vacuum.
I have front stock discs and 10" rear drum brakes.
Is your Bendix booster a single or dual diaphragm unit?

My system is 11” disc front / 10” drum rear. I have a large diameter single diaphragm Bendix booster, that I just had rebuilt by Karps in CA. Today, when hooking a vacuum gage up to my intake manifold (with the booster disconnected) I measure 8” to 10” Hg (fluctuating) at idle 850 RPMs. My car has 383 with a cam (specs unknown, probably not stock) that gives a bit of a chop to the idle.

I’m worried that I don’t have enough vacuum to operate the booster properly..

Before the rebuild, when driving the car, I don’t recall the brake pedal being soft or going down to the floor. I even had to make a sudden stop, once, at lower speed, which resulted in all four brakes locking up. Though the car stopped quick!

Unknown to me, the booster’s hub was cracked open and leaking vacuum the entire time I was driving the car (180 miles) prior to the rebuilt. Jeff, at Karps, said he was surprised my engine would even idle at all, with the cracked booster hub.. After he told me this I did tell him the engine idled roughly around 1500 RPMs, It would be smoother at lower and higher RPMs..

After removing the booster (to send it to Karps) and plugging the vacuum port on the intake manifold, the idle was much smoother at 1500 RPMs.

604E84D4-0884-4838-9C38-9501D18BFC34.jpeg 452B73FC-CCE7-4161-B83B-9AA9A9984F2B.jpeg
 

Hubbarocks

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i went through all the vacuum lines & timing. everything checked out.
i retested the idle vacuum from the manifold port and it's 6~7-ish at best.

i decided to purchase the summit vacuum pump. i actually got it last night. immediately tested it and it's 20" vac and shuts off. Kicks on at 15-17". There is an adjustable switch, which i thought was nice.

they said i could mount it any ware in any position. i decided to mount it in the trunk adjacent the battery. i have an open switch on my switch box that's tied to a relay. so i'll pull the 12v off that and just have to plum it all in. i picked up some 3/8 steel tube to run under the car and 3/8" on each end.

going to be garbage weather out here this weekend. so i'm going to tackle it and see if it improves my brake issues.
 

Wietse

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The unit you show there on the picture is a single diaphragm, i think for the disc/drum setup they only used the double unit.
That vacuum pump will do the trick i guess, i also considered one but since the brakes work i decided to leave it as it is.
 

MoparGuy68

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The unit you show there on the picture is a single diaphragm, i think for the disc/drum setup they only used the double unit.
That vacuum pump will do the trick i guess, i also considered one but since the brakes work i decided to leave it as it is.
It’s my understanding that power disc/drum 383 Magnum cars came with a single diaphragm Midland-Ross (much more common) or Bendix booster in 1971.. I do know the single diaphragm Bendix Booster that I posted two photos of is RARE!! Karp’s, in CA, was the only place in the country that had a replacement hub for that booster.. Even Booster Dewey did NOT have a hub to fit that booster. The original hub was cracked and leaking vacuum.
 

MoparGuy68

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Here are two photos of my 383’s vacuum pull at idle (8 to 10 inch hg fluctuating) and at a bit over 2000 RPM (17 inch hg). These vacuum readings were made with the booster disconnected.

CF3D318B-5A7D-422E-A9E8-7E4E0327593D.jpeg 03634827-F4E3-4523-8184-A0F9CE25A79B.jpeg
 

kiwigtx

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But I'd seriously look at a different cam if I'm street driving very much.
Best thing I ever did to my GTX was to replace the stupid cam and get some vacuum back into the brake system, and air grabber.

It's no fun when you have power disc brake front end, and you get maybe one good stab at the brake pedal every 10 minutes.

:thumbsup:
 
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