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Old 06-01-2008, 12:02 AM
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No power after brake upgrade

I recently clipped my 59 Suburban using a 74 camaro front end. I replaced the master cylinder with the master cylinder/booster from a 2003 Chevy Silverado. I plumbed new brake lines to the rear axle and the camaro calipers. The brakes bled out nicely and work but there doesn't seem to be any power assist.
We thought maybe the power booster was bad so we swapped in another but the result was the same. All I know to do is bleed the brakes some more but the pedal feels solid enough.
Any ideas?

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Old 06-01-2008, 12:18 AM
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I think some boosters have a external one way valve in the vacuum line. I can't think of the proper name for it right now.
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Old 06-01-2008, 01:00 AM
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I do not know if this relates or not, but.....

I installed a power brake booster and dual reservoir master cylinder (under the floorboard) in my 56.

The brakes and booster work great at highway speeds. It will lock the tires if you push a little too hard. I have a 272 Y-block V8 and apparently it does not produce very much vacuum at idle or even at slower in town speeds.

Around town the booster is useless. You have to stand on the pedal just to slow down a little. Definitely will not lock the tires..no matter how hard you push.

I just installed a vacuum canister (also under the floorboard) this week. I have not had it out on the road yet (this coming week), but it feel better just sitting here running. I am hoping that cures the problem with mine.

Also, I have vacuum wipers. Going up hill in the rain...they would just stop. Hope it helps with that problem also.

We will see.
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Old 06-01-2008, 09:06 AM
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I should have mentioned I also replaced the drivetrain with the 2003 Silverado. So the master cylinder/booster, engine and tranny all came from the same vehicle.
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Old 06-01-2008, 10:46 AM
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You did hook up the vacumn hose to the booster didn't you? One other thought that I have is....if you are still using the Suburban rear end with drum brakes? If you are then your setup is wrong...the 2003 Silverado has disc brakes front and rear I believe. If this is so...then your master cylinder is wrong for your application...also are you using the proportioning valve that was on the Silverado? if so then that is wrong also. You will need a master cyl that is designed for disc front / drum rear as well as a proportioning valve for the same. Another thing too...your pedal stroke may need to be adjusted.

Last edited by Henry Highrise; 06-01-2008 at 10:52 AM.
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Old 06-01-2008, 01:21 PM
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No proportioning valve. I will check on the rear axle to see if it was drum or disc. I modified the 2003 brake pedal assembly to fit in the 59 but the hinge point is the same.
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Old 06-01-2008, 11:00 PM
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HH is on the right track...You should be running a 1 1/8" or 1" bore master cylinder with the 74 camaro front brakes and 11" booster.. A 4 or 5 to 1 pedal ratio would be fine, so if you modified your pedal and made it have even less of a mechanical advantage it would have stiff brakes.


Check to see if the booster is working. With the motor off, step on the brakes about 5 or 6 times to bleed off any vacuum that might be present..The pedal should get firmer..then, while holding firm pressure on the brake pedal, start the motor...if the pedal gets easier to push and "falls" away under the firm pressure when the motor starts and runs for a few seconds, then the booster is working. If nothing changes when you start the motor, chances are that you need to check your vacuum connections, pedal adjustment or check valve...(part name for weirdbeard )


If your booster is working, then you need to check the sizes of your brake components and pedal ratio ..


Later, mikey
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Old 07-18-2008, 12:04 PM
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I'm finally tackling the brake issue again. The 2003 did have disc brakes so I'm going to advanced auto and pick up a master cylinder/proportioning valve to match the 74 parts.
After pushing the brake pedal then starting the engine the pedal does not move. It can't be the booster as we have tried 2 already.
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Old 07-19-2008, 01:36 AM
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Check your vacuum lines and where they are hooked up.. The Y blocks that I've worked on had plenty of vacuum. You should be running a 3/8 vacuum line,(not fuel line, fuel line that big could collapse under vacuum.) hooked up to a port either on the manifold or the carb at the baseplate. Make sure your checkvalve is installed correctly and there is vacuum present.


You need at least 16-18" of vacuum to run a booster properly.

Later, mikey
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Old 07-19-2008, 11:24 AM
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Using the factory vacuum line and booster. I checked it when running and there is plenty of vacuum.
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Old 07-20-2008, 01:54 AM
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Here's what the problem was. Looks like I routed a vacuum line to the wrong place and was killing the vacuum to the booster.
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Old 07-20-2008, 05:49 AM
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Glad to hear that you got the problem solved.
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Old 08-11-2008, 11:44 PM
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Not so fast. This would seem to be a complicated issue. I took the truck to the guy who programmed the PCM and he re-programmed it. His first attempt was way off, including having a manual instead of automatic tranny programmed. Now that the PCM is right the vacuum is up. At this point you could stop the truck but it still took a LOT of leg. I ordered new ceramic raybestos pads. This helped a little more. I could actually make the rear tires skid.
But wait! The front tires are supposed to skids first! I dug around the alldata files until I found a diagram of the entire breaking system. Guess what? The front line coming from the master cylinder goes to the REAR brakes! Great job Chevy.
So I switched the lines after the proportioning valve, bled the brakes and test drove the truck again. Now the back brakes don't lock up. BUT there is still way to much leg needed to stop this truck.
I'm thinking the master cylinder is angled down too much, causing a small leak in the booster when the brakes are applied. I noticed today the angle is suspect. I may have to do some sheet metal work on the firewall to get it straight. I can hear air hissing in the cab.
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Old 08-26-2008, 09:43 AM
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Final Post

After replacing the alternate booster with the OEM booster I have excellent brakes!! Evidently the alternate booster was leaking badly.
Thanks for everyone's help. Again, the big problem was the vacuum line routed incorrectly.
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Old 08-26-2008, 11:25 AM
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Glad you got it and thanks for telling us the fix. Happy rodding
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