Brake Booster Questionable........how much vac should it hold?? (1 Viewer)

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My '78 is exhibiting stall issues upon brake application again. I just replaced the booster and master a few months back and paid the shot with SOR!!! I am borrowing a vac gauge to hook up to the booster check valve and wondering if anyone can tell me what ammount of pressure it should hold on the gauge??? Thanks again............
 
It should hold whatever vacuum you apply. A typical F series engine will draw 18-21 inches of mercury depending on altitude. It should hold that for at least several minutes.
 
Thanks man.....will be checking soon. The OEM rebuilt unit from SOR only lasted a few months:bang:. I will check reciepts.......but very disappointing for sure.
 
Just curious, but do you know exactly what failed? ( I may be in the market for a new/reblt booster soon also). BTW, My 77 2F runs about 20.5 in Hg at idle)--when running~ 55 mph it holds around 16.--no change at all when applying the brakes-
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Thanks man.....will be checking soon. The OEM rebuilt unit from SOR only lasted a few months:bang:. I will check reciepts.......but very disappointing for sure.

Guys, if you've followed the various lengthy threads on brake boosters, you'll come to realize that there is no parts out there to rebuild the OEM booster. The so-called rebuilt units may not be much beyond cleaned up used units that still hold pressure. I bought one of these rebuilt boosters (by Centric) that lasted 3 months. The replacement unit made a hissing sound from day one.
 
Such a bummer as my rig WAS running so well, then the fuel pump and now the booster I suspect too-will get vac gauge on it tomorrow.........thanks for all of the great input buds!
 
So it took forever with the hand vac gauge, but got it to 10mmHg and in 2 minutes it was down to 5mmHg and in 5 minutes it was down to barely 2mmHG. So it looks like it is time for another booster????? Would love some opinions...............thx!
 
So it took forever with the hand vac gauge, but got it to 10mmHg and in 2 minutes it was down to 5mmHg and in 5 minutes it was down to barely 2mmHG. So it looks like it is time for another booster????? Would love some opinions...............thx!

How are you performing this measurement? Is this the vacuum reading at the end of the booster hose, where it plugs onto the check valve?
 
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Yes it is, I am removing the hose and checking at check valve on the booster.
 
Not pulling vacumn thru the hose, applying vacumn at the check valve.
 
I'm running a booster out of a 94, 80 series TLC. Along with the 80 4wheel disc master, brakes are now stronger than new (4wheel disc). I made in work without a spacer, but most use a 1/4" spacer from a mini-truck, Racer, or some other source, to move it out from the firewall a bit.

4Runner, 60 series, and many other Toyota boosters are all bolt in options.
 
Already took gauge back.................bummer. But, wouldn't I get a better reading with a shorter run, that is at the check valve?
 
Guess I could borrow it again but it wants to quit like every other time I apply the brakes................
 
In other words, measure it at the hose where it connects to union pipe on intake manifold, right?
 
Disconnect the booster, how does it run?

Start it up, let it run for a few, shut it off, go inside, have a drink, come out and pull the check valve.

Did it hold vacuum in the booster? Numbers aren't that important.

No, either a bad check valve or a bad booster. I ran at first with no check valve with the new booster... Motor didn't care! Braking was inconsistent. Your booster is likely bad.


Unless something else is wonky... At one point mine would almost stall if I stopped suddenly. In that case, the cam had 5 round cam lobes and several others almost round. After replacing the Cam, intake, and carb, the problem went away. A mechanic I knew saw the cam in the pile of recycling and commented it shouldn't have run... Much less run 1/2 decently.
 
Guys, if you've followed the various lengthy threads on brake boosters, you'll come to realize that there is no parts out there to rebuild the OEM booster. The so-called rebuilt units may not be much beyond cleaned up used units that still hold pressure. I bought one of these rebuilt boosters (by Centric) that lasted 3 months. The replacement unit made a hissing sound from day one.
I think this is a stopper--If your engine is running and you step on the brakes, then get a hissy sound from the left engine compt.--you prob. have a bad booster-you may or may not see this in your vac gauge(if you have one)
 
Never noticed a hissing sound. These low speed problems I have had on and off since owning the vehicle-could my mechanical advance not be working??? I cannot get it to idle below about 920 rpm. What RPM's does the mechanical advance effect? I know this is kind of unrelated but desperate to make this stupid thing run right. Also my ignition system has a Accel coil which delivers a spark that will jump an inch!!! And a red Mallory box on passenger side front fender. I do have the igniter but do not appear to have original coil.
 
Current booster in there was a big buck OEM rebuilt tandem booster from SOR; $438 before their famous shipping. Purchased in April 2012 and I believe I put it in in May. Hope they do something for me.....seems like a really short run for such a pricey unit, no?
 

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