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Discussion Starter · #1 · (Edited)
When building your gasser, what master cylinder have you used? Have you gone for just a duel circuit cylinder or have you added a power booster as well? I've got standard rear drum brakes with a disc conversion on the front along with a cylinder servo unit that I was told would do the job and I've ended up with a very bad feeling pedal.
To fix the problem I've been advised to take off the unit and go for a '69 Vette duel circuit cylinder and no power booster. I just wondered what set-up you guys have got and how good your brakes are?

Thanks,
Micky T.

P.S. Sorry guys, over here in the UK we call the power booster a servo, sorry to confuse?
 

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Hi Micky, your motor is pretty healthy, do you know how much vacuum you are getting to the servo? I am not for sure, but I think you need around 12 pounds vacuum (not sure what that is in kilos) to make it work properly. If you take off the servo, then it should be ok. Or you could put in an electric vacuum pump, just a thought. Also do you have residual valves in the brakes lines for front and rear and the proper master cylinder? The pressures are different for drum and disc brakes. You probably know all that, but I thought I would ask.
 

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I've used a couple 2nd gen Camaro (1970-81) master cylinders, and also master/power booster combos too. As maddog said, you need good engine vacuum to run the brakes with a booster, and in a disc/drum setup, the system needs a proportioning valve too. The 2nd gen Camaros had a prop. valve, so when using one from a donor car I always used the prop. valve with it, so it needed nothing else.
My present gasser is GM disc brakes, with GM drum brakes, and I was using a late 90's Subaru master/booster setup, with an adj. proportioning valve to the rear brakes. The new cam doesn't have enough vacuum, so I removed the booster, and adapted the Subaru master to manual only, and they work great now. Takes a bit more pressure to stop, but they are still very good brakes.
 

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Hey Mickey, I have front disc and rear drum on my 55 chevy street car, i used a 69 chevelle duel circuit master cylinder and the brakes work great. No power brakes just standard. Hope this helps.
 

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Discussion Starter · #5 ·
Yeah, thanks for the feedback guys, I've now got the car on the road and ironing out a couple of bugs I find while driving it, but still the brake problem is there. The more I ask round the more people I find not using a power booster and just going for a duel circuit master cylinder, adding to that the '69 Vette one seems to be the most popular so far. I've also been told that because of my engine being blown, it needs all types of stuff added to get the vacuum required and that the 7" booster will not be big enough anyway. I'm going to try one more tip I've been given and drill another hole 1" lower in the brake pedal for the push rod, if that doesn't work I reckon I'll take the power booster off and go for the Vette cylinder if you think that's the way to go?
After driving the car after nearly a 2yr build, I'm just desperate to fix the problem and drive the car properly, it's seriously looking like the Vette deal is the way to go though.

Thanks to all and I'll let you know the outcome,
Micky T.
 

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Drooping the rod lower will give you less leverage, and require even more foot power to stop. Need about 1 to 6 ratio for brakes, so whatever distance the rod is from the pivot point needs to have 6 times that in brake pedal length. I'm going to drill a hole closer to the pivot to increase pressure and allow for less foot pressure on mine now that I've removed the booster.
 

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I Run dual diaphram 7in booster with vet master cylinder and proportioning valve on a blown small block. It works well until I come to a complete stop,I loose the vacuum. If I shift to neutral as I stop, its ok. Im taking the vacuum off the intake,at the carb base its even worse. I am going to try a vacuum reservoir like the older cars had.I think this my help.Has anyone else had the same problem?
 
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