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My Booster Mod - New Pictures!!

9741 Views 28 Replies 18 Participants Last post by  43AutoX
Spent the night doing my booster mod. Not quite finished yet but thought I would share a few pics. Still have to lower the steering shaft bearing by about 1/4" and either mod the original aluminium panel or make up a new one. Also have to move the brake pedal outboard about 1/8" at the top to get perfect alignment for the booster rod clevis and clean up/paint the booster and M/C. The booster rod clevis will attach to the brake pedal just above the current pin with a grade 8 bolt. This will give a slight mechanical advantage + the boost.

Cheers, Rod

[ May 01, 2005, 09:59 PM: Message edited by: dv/dt ]
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Is that a stock Mustang donor booster? I plan on running PB on my build, and am becoming increasingly concerned about "fit" in a MkIII. Apparently, what fits perfectly in a MkII doesn't fit so well in a MkIII. It looks like the Whitby frame mod will still clear the booster on the side rail, but the steering shaft looks pretty tight on the underside of the booster. Rather than space it down, have you considered putting a "divot" in the underside of the booster housing? What about "nudging" the entire pedal/booster assembly up a bit, splitting the difference? Which aluminum panel are you going to have to mod?

Sorry for the "dumb" questions, but I'm trying to plan as many details as I can in advance.


Nice work.

Here's mine with the original football-shaped booster. I used a ball-pin (round headed) hammer to gently tap a dimple in the booster where it would have rubbed the steering shaft bearing. I don't know if this approach would work for you. Is your booster stock? I went to replace my original and AutoZone had your style as stock so i kept the original since it looked to fit better.

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Hi Allen,
No, it is a booster from a '91 Sprint (believe it or not). I had to machine an adapter for the pushrod between it and the M/C due to differences in length and how the booster is set up compared to the Mustang. I've already moved it up about as much as I want to and I don't think moving the steering shaft bearing down a 1/4" won't be a big deal. I have also dented the rim as much as it can be without damaging the seal. The booster came with that clevis already on it.

Here is a pic of it beside the booster out of my '87 Mustang so you can see there is a big difference in how far the M/C is pushed forward.

I've seen other Mustang boosters that were not as long but much bigger in diameter and would not work on a Mark III due to the steering shaft location.

I figure the FFR will not require as much boost as the Mustang did so the smaller booster should work well. The only concern I have is that this booster only has about 1-1/4" of travel in the pushrod which is less than the Mustang booster but I'm hoping it will be enough. I'll find out once all the brake hardware is hooked up and bled.

It is, in other words, experimental at this point! :eek: :D

Cheers, Rod
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The picture of your old donor booster looks virtually identical to DMW's 1990 booster. Was the goal just to get the MC closer to the firewall, or am I missing something? Logic tells me that if I can keep all the brake parts the same on the build as they were on the donor, everything should work "perfectly". The brakes on my 1993 donor are flawless, and I'm figuring "why mess with a good thing?".


If I read your post correctly, other than the frame mod (and I am planning on using the Whitby bracket rather than hacking and welding the frame), all you did was put a dimple in the bottom of the booster to clear the steering shaft?

You got everyones attention now!!!!!! keep us posted!!!!!!! nice idea!!!

I did the following:

1) moved the steering shaft bearing to the inside of the footbox wall,

2) Dimpled the booster,

3) cut the frame tube and re-fastened it with a 1/8" steel plate.

That's it.

Some other thoughts:

Many parts stores sell solid steel square bar stock or "keys". I believe a length of 5/8" square bar stock fits tightly inside the cut tubes. As an alternative to the Whitby's bracket, you could put a solid bar in each tube and connect them with bolts and a couple of drilled holes. This is a much cheaper alternative.

One alternative to dimpling the booster may be to just put some spacers between the bearing and the footbox wall. This will move the bearing inward, say, 1/8" so you'll have no clearance issue and is a lot safer than potentially damaging the booster. I thought of this after I did the dimple.

A couple of related mods that you'll need to do with or without P/B:

1) You may have to trim some excess off the pedal box where it would interfere with the installation of the bearing/steering shaft. This excess is on the front face of the pedal box. You'll see when you test fit.

2) A good idea is to cut/grind a notch in the top of the pedal box facing the passenger. If you want to raise the steering column, the pedal box restricts this so by notching it you can get more lift on the column.

3) On your first test fit, the pedal box will not seem to fit. Don't worry, just bolt down the front end where it mounts to the booster and it will flatten out into perfect alignment on top of the bars where it rests.
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I did a similar power brake mod on my 1964 Ford Falcon. I used a booster from a Geo Metro, which is the same as the Suziki unit. It will have plenty of boost believe me! I was suprized how much that little booster would put out! You might run into an issue with the amount of travel, however, the Metro/Sprint master cylinder that is normally hooked up to that booster is alot smaller than yours. It might be OK though, try it! Good Luck

Jeep MC with donor proportioning valve...how does it work?
Very interesting! I'll be interested to see if the Sprint booster has enough travel for the tandem master cylinder.

Since you're running 4-wheel discs, you might want to consider the CNC parallel master cylinder that Mike Forte sells, which would have less stroke travel than a tandem m/c, and can be used with a remote adjuster so you can balance front & rear from the cockpit (which can be an issue otherwise). The guys using the CNC manually are running 3/4" front, 5/8" rear cylinder diameters, but you could probably go up to 1" & 7/8" or 7/8 & 3/4" with the booster, which would need even less travel. This m/c setup is probably too long for the thick Ford booster, but the Sprint booster might work nicely.

Does the Geo Metro unit have a longer stroke, more like the Ford unit?

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Yes, his booster is the same as my donor booster. The goal was to not move the M/C so far forward into the fender and also just for looks. I had hoped that being smaller in diameter it would not require the frame mod. On a Mark II frame that might be very possible since you could shift it to the passenger side a bit which would most likely line up the clevis very nicely. The Mustang booster works fine for many and there should be lots of "search" info here but DMW laid it out pretty well above.

Ben, will do!

Matt, I found this booster just checking around at my friendly scrapyard but I did find a write up online of an install similar to what you describe. The available stroke is a concern but the 1-1/4" at the pushrod translates into 4-1/2" of pedal travel. That seems like it would be an excessive amount of travel to me which leads me to believe it will be OK.

Dale, That M/C and the proportioning valve are part of the old (discontinued) rear disk upgrade kit from Ford (M-2300-C). It has been gutted to take out the proportioning function but retain the shuttle valve function. If you look closely you will see that it also has an electrical connection to add back in the failure warning indication that was lost when switching from the stock M/C.

Forrest, Thanks for the info, that may be a very good solution if the stroke is an issue. Not to mention a very good looking solution.

Thanks for the feedback!!

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Interesting modification and choice of parts! Looks like you're doing a really nice job with it. All I can say is that it makes me feel better about how easily the donor hydroboost unit fit into my MKIII!

Cheers, John
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Here's mine, do you have a welder handy?
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Hi John, thought about the hydroboost setup since I will be running PS but I enjoy the challenge. For $15 I figured I give this a try. I want to do a little more checking on the alignment and clearances because it may be that if I can move the booster up a bit more I can avoid both the steering shaft and the frame mod. If that is the case then it would be a matter of drilling 6 holes (4 to mount the booster, one 2-1/4" and one in the brake pedal).

AkFreeFlyer, the welder is ready if I need it but will most likely do a bolt in splice.

Cheers, Rod
A lttle more adjusting and, bingo, no more requirement to to do the 3/4" frame mod or move the steering shaft. Everything worked out great!

Frame tack welded back into place.

About 1/8" clearance between the booster and 3/4" frame. I have since removed the boosted to ensure it was possible to do with the frame in place. No problem.

The steering shaft is in it's original location and has 0.010" of clearance at the closest point. I can get about 1/8" more clearance by just ovalling (is that a word) out the bolt holes. The main bearing hole will not need modification.

The clevis now lines up perfectly with the pedal arm and just above the existing pin. The arm currently floats freely in the clevis.

Quite happy at this point!! :D :D :D

Cheers, Rod
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Guess im having brain fade, but what is a 91 sprint??

nice work.

I did a small dimple on my Mustang booster and ended up not working properly. I would avoid dimpling.
Rod, could you "elongate" the booster mounting holes upward to make it clear the steering shaft a little more? Maybe place some washers under the mounting points of the pedal box.....
Have a good one,
'91 Sprint = Chevrolet econobox

Thanks Earl!

Ben, I have elongated my original holes almost 1/2" to get where it is now (up and to the passenger side). Don't know if i can go much more. I can get 1/8" by elongating just the bolt holes for the bearing retainer downward which should not result in any clearance problems.

Cheers, Rod

This turned out to be a pretty slick approach! I'd definitely lower the bearing a bit just in case. You never know if clearances will change slightly with temp differentials, etc.

I hope the booster works well once you get it going.
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