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By Kingfisher - 3 Months Ago
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1956 Mercury. As you can see in the photos, the brake booster somewhat dominates the space under the hood. I can't even remove the valve cover without first unbolting the booster.
Disks on front, original drums on rear. What can I do to take less room and improve on this arrangement? 
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By KULTULZ - 2 Months Ago
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Is the MC/BOOSTER part of an aftermarket kit? If so, can you give the vendors name and PN's ?
Do you know or can measure the booster diameter?
How much additional room do you think it needs (booster) to remove the rocker cover?
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By Kingfisher - 2 Months Ago
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The car is in Australia now, but the brakes were upgraded in CA back in 2018. I can't see any identifying marks on the booster or MC. However, the invoice quotes 5474009, which appears to be a very common booster code. And NMC1481 which I'm guessing is Napa Master Cylinder and again, 1481 seems to be a common MC code.
The main booster body diameter measures 8" but that increases to 9" with the flange. The flange only clears the valve cover by about 1/2", an extra inch would be nice. Of course if the whole (smaller) unit was flush against the firewall, that might help also. And then I see the Wilwood setup with no booster and wonder if that is an option.
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By Deyomatic - 2 Months Ago
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I have a set of those Valve Covers, too. I love them...
You'd gain the most room if you went to manual brakes, but I'm sure you thought about that already.
I just googled "thinnest power brake booster" and a bunch of skinny ones popped up- they probably work the same way- build vacuum and just help out. You'd just have to adapt your Master.
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By miker - 2 Months Ago
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7” dual diaphragm boosters are fairly common. In my limited experience they don’t make as much boost as the larger units. If the car has power steering, there’s also hydroboost units available. Check the Mustang resto mod sites. And the electric ones, I’ve only seen adds and references, never actually held one.
Many of the front disc conversions for the early birds use a dual master with the old oem remote booster on the front disc only. Same unit that did all 4 drums originally. Not cheap, but there are some aftermarket units available.
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By KULTULZ - 2 Months Ago
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Does your booster the the bracket and linkage at the rear as shown in the lower illustration -
  It s used to raise the booster assy to clear an engine and/or exhaust manifold.
Like mentioned, either a 7 or 8 inch dual diaphragm, hydro boost (will give stronger line pressure) or there is a remote booster available that would work like a 1954/57 FORD/BIRD MIDLAND apron mounted assy. Or you can go with manual DISC/DRUM.
You have a minimum of 17-18 hg intake manifold vacuum? |
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By Dave V - 2 Months Ago
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Summit part# OER-B10518 for 66-70 Fairlane or Torino which raises the booster 3". I did the conversion on my 56 Victoria and does what you're trying to accomplish. Great look and lots of clearance all around it. You'll only have to elongate 2 of the mounting holes less than 1/16"
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By Kingfisher - 2 Months Ago
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Thanks all,
I've considered manual, but am not confident in getting it to work.
Kultutz, I have the adaptor you show. Vacuum is down a bit, around 15, but that will hopefully remedy with some other work being done.
Dave V, The current bracket gives a lift of about 2 1/2", so not a lot of difference.
I reckon I'll go for a dual 7" and hopefully the flange is a little more compact also. The current setup looks a bit rough so a new one will at least will be nice and shiny.
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By KULTULZ - 2 Months Ago
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You need a minimum of 18in HG for the booster, especially a dual diaphram.
Big cam? Did the car come though with power (TREADLE-VAC) or manual?
How does the car stop now?
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By Kingfisher - 2 Months Ago
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KULTULZ (6/3/2025)
You need a minimum of 18in HG for the booster, especially a dual diaphram. Big cam? Did the car come though with power (TREADLE-VAC) or manual? How does the car stop now?
Vacuum comes up to 17 or 18 with at about 2000rpm. I'm assuming my gauge reads correctly of course.
Just a mild cam. I can't be sure of original brakes but probably manual.
Car stops well currently. Not too sharp, not too soft, easy on the leg.
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By KULTULZ - 2 Months Ago
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I guess it would be best to leave as is if it is working correctly. If you loosen the booster/MC assy, can you somewhat slide/tilt the assy over to clear rocker cover removal without disturbing the brake lines too much? ? If not, the only cost effective choice would be a double diaphram booster.
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By Kingfisher - 2 Months Ago
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New 7"double diaphragm unit in place. All seems to work well. It requires a little more push than the old one, but quite acceptable. And the valve cover clears easily now!
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By KULTULZ - 2 Months Ago
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Vacuum comes up to 17 or 18 with at about 2000rpm.]
What is vacuum @ curb idle (AT in gear)?
Nice looking install.
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By paul2748 - Last Month
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If you can, running those spark plug wires like a stock yblock might give you more room.
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By Kingfisher - Last Month
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18 at idle out of gear 770rpm. 15 in gear at 620rpm.
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By KULTULZ - Last Month
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"New 7"double diaphragm unit in place. All seems to work well. It requires a little more push than the old one, but quite acceptable".
"18 at idle out of gear 770rpm. 15 in gear at 620rpm"
Well, there may be a problem (don't let me get you worried).
It takes @ a minimum of 18Hg to properly operate a booster @ all times (to keep the booster fully charged) and that also is considering the brake type, MC bore size and pedal ratio.
The vacuum tank portion can only hold what the engine gives it in Hg. So say the engine only supplies 15" @ idle (in gear) manifold vacuum. It (vacuum canister) may not recharge itself (with low vacuum supply) enough for several back to back stops @ speed (the pedal becoming harder to push).
But this is less likely a hindrance with four wheel drum as they are self activating (not as much line pressure required as disc). Once the primary shoe makes contact, you will then have full brake application.
As long as you are satisfied with it and the pedal feels good, I wouldn't worry too much. It is the multi-stops that may get to you but you would still have manual application requiring a heavier foot.
An exercise if you wanted to know for certain is to tape a vacuum gauge to the windshield and see what vacuum the engine supplies at differing RPM's while driving.
If too much vacuum or too large/strong a booster, you may get the touchy pedal syndrome to whereas it wants to throw you into the windshield. It is all a fine balance.
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By KULTULZ - Last Month
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Paul is right. You may want to tie those IGN WIRES down as they are routed over the exhaust manifolds -
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By down-the-road - Last Month
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Kingfisher (6/30/2025)
New 7"double diaphragm unit in place. All seems to work well. It requires a little more push than the old one, but quite acceptable. And the valve cover clears easily now!
That looks like a good fit. What are part numbers for the booster and master cylinder that you selected?
Thanks!
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By Kingfisher - Last Month
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The ignition wires are normally tied back to the brake lines under the MC, but it's a fairly messy arrangement. I've taken your collective advice and have started to reroute them. It gets fairly busy down there, particularly with all the header pipes.
The MC is part # CAL-4478 and the booster CAL-4483 from https://performancewarehouse.com.au/
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By RB - Last Month
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I dislike those retrofit setups immensely.. They use that heavy bulky corvette master and a booster and bracket that is extended way away from the firewall. Your brake lines end up nearly up to the end of the valve cover.. This setup was installed on my 56 Vicky when I purchased it. I ripped it out and replaced it with a booster from a Ford ranger and a mustang master cylinder. Much tidier setup
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