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Cowpatty69
Sitting Bull

USA
137 Posts

Posted - 04 Jun 2017 :  5:51:58 PM  Show Profile  Reply with Quote
Hello Guys- Been working on the '78/'70 frankenbird over the winter, and had the master cylinder, meter valve, and front brake lines replaced. The master cylinder and metering valve were bench bled, but the booster blew out. I ordered a manufactured booster and had it installed. We picked it up, and it just doesn't feel right.
The petal is very hard and feels like there is no power assist at all. The brakes work well, just takes a strong right leg!
i will be taking it back, but thought I'd check some things on my own first. The vacuum is great to the booster, and the filter is clear. There is no familiar "hiss" when you touch the petal, or anywhere in the petal travel. Any thoughts?
Thanks!

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cortcomp
Coyote

USA
5335 Posts

Posted - 04 Jun 2017 :  8:14:21 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
Maybe is a bad booster? This would be the third "new" one i've seen that didn't boost anything. Mfr's are getting sloppy as everyone is trying to sell disc conversion kits with the most margins at the cheapest prices.
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Blued and Painted
Chief PONTIAC

USA
3405 Posts

Posted - 05 Jun 2017 :  12:26:49 AM  Show Profile  Reply with Quote
Booster test: With car off, hit the brake peddal a few times to remove any available vacuum. Now with foot pushing moderately on brake pedal, start the car. Just after starting the brake pedal should drop one or two inches. This drop would confirm the booster is working/assisting.
Another possible cause. I"ve seen more than once, cheep pads loose there effectiveness after being overheated. It can have a rock hard pedal just like a bad booster.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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67drake
Sitting Duck

Azerbaijan
1501 Posts

Posted - 05 Jun 2017 :  09:05:39 AM  Show Profile  Reply with Quote
What Blued said.


71' GTO Original 400 M20 3.23 posi
13.95@102.1 MPH on street tires
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Bill Boyle
Horse Feathers (Charter Member)

USA
4794 Posts

Posted - 05 Jun 2017 :  11:04:22 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
Do you have the check valve in place?

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
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Cowpatty69
Sitting Bull

USA
137 Posts

Posted - 05 Jun 2017 :  9:23:38 PM  Show Profile  Reply with Quote
Thanks guys for the input. The booster passed the check test (same as painted and blue-thanks), We've swapped out the vacuum check valve with original, and no difference. The new proportioning valve has no adjustment (stock replacement) so moving on to rear wheels. Wheel cylinders seem to be in good working order, and we replaced the front calipers and all the fluid. Gonna check with my supplier next and see what they think- and will update. Keep the input coming! I appreciate it- Patrick

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cortcomp
Coyote

USA
5335 Posts

Posted - 05 Jun 2017 :  10:14:57 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
Maybe wrong bore size master for the application?

Edited by - cortcomp on 05 Jun 2017 10:15:09 PM
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67drake
Sitting Duck

Azerbaijan
1501 Posts

Posted - 06 Jun 2017 :  08:23:09 AM  Show Profile  Reply with Quote

Isn't there an issue that comes up if the wrong hole is used on the brake petal rod??? I've never run into this myself,I just remember reading about other people having this issue.
I'm not familiar with Cowpatty69's build,but a car named "Frankenbird" might have a few unorthodox parts in place?


71' GTO Original 400 M20 3.23 posi
13.95@102.1 MPH on street tires
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cortcomp
Coyote

USA
5335 Posts

Posted - 06 Jun 2017 :  09:59:47 AM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
Using the wrong hole (or not drilling one if needed) on certain cars, causes bind when the pushrod enters the booster, and also changes the advantage of the pedal (how much leverage you have.)

Manual cars had more leverage to help with pushing, so the hole was close to the pivot up top (if a hanging pedal setup.)

Power cars they moved the pushrod connection lower, because that much leverage would make the brakes too "touchy". Also, sometimes boosters were angled up to account for the lever now pushing at an upward angle.

I do know too, there are disc/disc and disc/drum prop valves and masters, although i'm not sure what the difference is in the masters. I'm also fuzzy on bore size (i understand what happens with different bore sizes, i'm just not sure, in a given setup, how to pick which bore size and what size brake lines.)

They make a gauge you screw into the bleeder port that shows pressure when you push the pedal, helps you narrow down where the issue is. (If you have good pressure, regardless if how the pedal feels, you should stop well. You could play with pedal leverage ratio, or bore size to change pedal feel. If no pressure, well, have to google i guess i don't remember.)
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Cowpatty69
Sitting Bull

USA
137 Posts

Posted - 08 Jun 2017 :  8:30:34 PM  Show Profile  Reply with Quote
Just sent questions to the company that i got the booster from to see if I might be missing anything. The car has the stock SBC350 that came with it. the master cylinder in the Delco replacement, and the proportioning valve is the stock replacement from Summit. It is not adjustable.
The rear brake cylinders work fine. At this point I think we may replace the front pads 'cause that's cheap- and see what the booster folks say.
The rod was reinstalled the same way as originally. When bled, good equal pressure at all 4 corners. Keep the ideas coming and I'll continue to update too. Thanks all-!

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67drake
Sitting Duck

Azerbaijan
1501 Posts

Posted - 09 Jun 2017 :  08:28:18 AM  Show Profile  Reply with Quote
Just curious is the caliper piston can be seated easily?
I had a car a few years back that I had to stand on the brake pedal to get it to stop. Caliper pistons were almost froze up. Just a thought.
But I would think by that point your rear brakes would be locked up if you have drum rears.

Never mind,I just read you replaced the calipers.


71' GTO Original 400 M20 3.23 posi
13.95@102.1 MPH on street tires

Edited by - 67drake on 09 Jun 2017 08:32:03 AM
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Cowpatty69
Sitting Bull

USA
137 Posts

Posted - 28 Jun 2017 :  8:47:19 PM  Show Profile  Reply with Quote
ok, so we have replaced the front pads and no improvement, but also have new rear wheel cylinders and shoes for this weekend. Will do a total bleed and see where we are

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DanM
Buffalo

80 Posts

Posted - 25 Aug 2017 :  10:04:02 AM  Show Profile  Reply with Quote
I upgraded from 4 wheel manual drums to front disk back in 1995. I moved the pushrod from the upper hole to the lower hole on the brake pedal. My main reason for doing this was so the brake pedal was in line with the gas pedal and thus I wouldn't have to lift my foot backward in order to go from gas to brake.

It's worked ever since.

Meanwhile: what's the status on your hard pedal? My brake pedal has always been kind of soft.

gas: heavy
brake: soft
steering: light
overall: fast

on new Charger
gas: light
brake: hard
steering: heavy
overall: fast
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Cowpatty69
Sitting Bull

USA
137 Posts

Posted - 06 Sep 2017 :  11:08:31 PM  Show Profile  Reply with Quote
Hi Dan, the petal is still pretty hard, but a little better. Initial breaking almost feels like there is no power assist at all, bug gets a little, very little better if you lightly let off a hair and reapply. New booster, metering block, lines, calipers, now wheel cylinders as well. We just keep plugging away. Thanks- Patrick

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