do you need a bigger booster with bigger brakes?

[G_Body_Enthusiast]

i'm looking at the C4/C5 kit from ed miller and i'm wondering if i need to upgrade the booster and master cylinder. currently i have a dual diaphragm g-body booster and stock master cylinder. im thinking of upgrading to the B-body dual diaphragm booster and master cylinder.

so for those who upgraded to much larger brakes, did you upgrade the booster and master cylinder? also if anyone has a before and after experience i'd love to hear about it. naturally i know the b-body booster and master cylinder will improve things but what i'm wondering is would they be enough or should i find something else to use?

i want all the brake parts to match as much as possible so i'm asking about this now so i can avoid some mistakes later.

 

[Bonnewagon]

I think the dual diaphram will be fine. The master needs to be sized to the brakes. Too small will decrease pedal effort, but increase pedal travel and in extreme cases the pedal will hit the firewall before the brakes are fully actuated. I like more capacity than needed to decrease pedal travel at the expense of more pedal effort, but with a booster, who cares? It can get mind boggling trying to figure out what size you need by using the formulas. Probably the Vette master would work. There's a terrific brake book by Fred Puhn. It explains everything you need to know about calculating brakes requirements..

 

[G_Body_Enthusiast]

would the vette master bolt up to the booster i have now? since i've not done much interchanging of parts on the car so far i'm just wondering. and because this is a huge safety feature on the car i want to make sure that things WILL bolt on and work together.

i know the g-body master wont cut it, the bore is too small and with the added volume in the caliper (two pistons Vs one) it's gonna need more volume from the master to get those pistons to work properly. i thought maybe the b-body booster and master would work better though i dont think they'd be a perfect match but a better one than what i have now.

what application would i look for when getting a vette master, C4 or C5? im guessing C5 since the calipers are C5.

 

[Bonnewagon]

That I don't know, just figuring most if not all GM's interchange pretty easilly. One easy way is to go on RockAuto.com and look up the parts. They usually give a pic and specs like bore diameter. Then you can make an educated guess and then go to a parts place and ask to see the one you think will fit, and compare to yours. Also see if the C-4,5 brake specs are there at RockAuto to compare to the B body stuff. You may find the B body master adequate. Also look at the 67'-68' Firebird master used with power discs. It was used with 4 piston calipers. I once put a 72' Catalina master on my 68' Firebird. Pedal travel was about 2" to lockup!

 

[86Cutlass383SR]

I bought the spindle brackets and had Ed Miller to modify a stock prop valve for my C5 front/LS1 rear disc swap. He suggested that the stock master would be good as is. My car isn't up and running yet so I can't tell you any results yet unfortunately.

There is a write up on MonteCarloSS.com about the b-body booster/master swap. Some say it was a good addition to the C5/LS1 swap. Others did the booster and left the stock g-body master.

http://www.montecarloss.com/community/u ... ber=757323

 

[malibu80]

I'm doing the same swap. Check out my post in general discussion under C5 Corvette brakes. There are some pix also. I haven't mounted them on the car yet because the 17" Torque thrust I bought don't clear the new assembly. In one of the posts here another member found out the same thing. Wish I had read that before purchasing the rims and tires.
I think your booster should be fine. In my case I'm going to be using a master cylinder and proportioning valve from a 81 Eldorado. The Eldorado came with 4 wheel disc brakes. This is ideal since I'm also adding S10 rear discs. The proportioning valve on the Eldorado even has the same electrical connector for the brake warning idiot light as the Malibu.

 

[G_Body_Enthusiast]

i checked out rockauto and found that the C5 master cylinder is only 1" bore while the b-body master cylinder was 1 1/8" x 40 (i guess the 40 is bigger bore in the back?)

clearly the b-body master cylinder has the bigger bore but if the C5 calipers are being pushed by a 1" bore then the stock g-body maser cylinder might work just fine as it is 24 x 36 mm. 24 is just under 1 inch .94 to be exact and 36 is 1.41 by my calculator. so that's in the acceptable range.

also the port for the lines are not the same size/thread on the c5 master cylinder but the B-body is the same as the stock one.

even though i have the stock dual diaphragm booster i feel like the pedal feel is junky. and after rereading the article on the b-body booster swap (i read it before but it's fun to read it again) i think the bigger booster is worth the hassle of replacing mine. i might even do that before i upgrade the rest of the brake system. at least i'll have better pedal feel and response in the mean time.

 

[Bonnewagon]

See that, research is key. Here's another tidbit. A 77' TA with manual brakes uses a 1" bore master while a 4-wheel power disc car got the 1 1/8th master. So for the same car, without a booster, they used the smaller bore to give less pedal effort, which also means more pedal travel. My Malibu came with a 7/8ths bore master and the pedal was close to the floor by the time the car stopped. I personally like less pedal travel and use the biggest bore available. I am using an 80' Firebird 1 1/8th bore master on my Bonnewagon, and with a dual diaphram booster, I have great brakes.

 

[G_Body_Enthusiast]

See that, research is key. Here's another tidbit. A 77' TA with manual brakes uses a 1" bore master while a 4-wheel power disc car got the 1 1/8th master. So for the same car, without a booster, they used the smaller bore to give less pedal effort, which also means more pedal travel. My Malibu came with a 7/8ths bore master and the pedal was close to the floor by the time the car stopped. I personally like less pedal travel and use the biggest bore available. I am using an 80' Firebird 1 1/8th bore master on my Bonnewagon, and with a dual diaphram booster, I have great brakes.

ok well a bigger master that would fit would be what you are using or a b-body master. as i said the ports for the c5 vette are not the same at all and i dont feel like making them fit.

what's the exact application for the master you're using? i'm thinking i want one bore, not two unless anyone can tell why i should use a two bore master.

i looked up an 80 firebird master and it's showing the primary port as 1/2-20 and the secondary as 9/16-18 but the g-body master is just the opposite. WTF?

and under the application of an 85 parisienne with a V8 i found a 1 1/8" bore master. apparently it's for non diesel and non HD cars, so it's more common on the V6 im guessing. and since those ports match up with the g-body it appears im looking at using the b-body master anyway.

 

[Bonnewagon]

I never heard of a dual bore master. It's the same, front and rear. The G-body aluminum master has the ports arranged exactly the opposite of a 2nd gen F body. So on a Firebird, the front big reservoir is the front brakes, and on a G, the big rear reservoir is the front brakes. I just re-reuted the brake lines, (those big coils below the master came in handy) the fittings are the same. I'm useing an 80' Firebird master for power disc, rear drum, and it is cast iron, which fits under the hood fine. Why? Because I had a spare new one and I needed the bigger capacity. The V-6 Malibu came with little-old-lady brakes, and I had a Pontiac 400 under the hood. It fit the Malibu booster fine.