'77 disc brake booster on a '71

[75Denver]

I'm about to tackle a factory disc brake swap after finally sourcing all the OE parts. However, without really thinking about it when purchasing, I bought a '77 booster/bracket/MC and didn't even think about the early fender shape interfering with the booster.

My ultimate goal is to have a stock (looking) '71 with all the factory amenities of a '77. Sticking with that theme, has anyone tired using an OE disc bracket and swapping to a smaller diameter Bendix booster? I'm curious what my options are now and if it's worth the hassle or just simply settling for an aftermarket PDB setup.

If aftermarket, what's the best out there that resembles the most stock factory look?

 

[72Sport]

2badrotties installed the factory unit in his early Bronco. I think he just cut a vee on the top inside of the inner fender and then turned the cut piece upside down, added a couple pieces of metal on the edge of the vee and welded up the vee. With the booster in place the vee cut was hardly visible and what you could see looked factory. I did a search and couldn't find the picture. Send him a pm and see if he can can send you a link to the thread and picture.

 

[DirtDonk]

I think I've read where some members put spacers under the lower edge of the bracket to angle it up a little bit. But I believe that it's a very fine line between clearing the wheel well and hitting the hood.
Should be able to be done though, since our brackets (aftermarket look-alikes of the factory setup) do not need clearancing of the wheel well.

But every other dimension is the same, so all of your factory booster and stuff will bolt on to the aftermarket brackets.
We used to sell them separately, but not sure if we do any longer. It's not listed that way specifically on our site, but a quick call during the week would settle that.

Good luck whichever way you go. I would try to avoid a smaller booster if you could, unless you know it's got the same equivalent area on the diaphragm so you don't lose some assist.

Paul

 

[75Denver]

72Sport- thank you for the suggestion. I’d definitely consider that option if it had already been messed with. In my case, it’s way to original to start cutting and sectioning panels. I’ll keep that in mind for future builds if I face the same hurdle.

Paul- thank you for the spacer tip. I’ve yet to pull my manual setup but will play with the bushing idea...assuming it isn’t too close to the hood. I was just reading about other members installing simply the disc brakes and not adding a booster. If the shimming doesn’t work, I might toy with that idea until I find the right booster. Correct me if I’m wrong, but the power is still in the stop with the disc brake setup...the booster is only an assist in the pedal and does not correlate to the stop at the wheel? Who knows, maybe the pedal feel will be “classic” enough while still gaining stopping power AND maintaining a stock factory look under the hood??

 

[DirtDonk]

Yes, using no booster is perfectly fine for many of us. Including me. I never put a booster of any kind on my Ford disc brake swap in the '71. And I love those brakes.
I like the simplicity too, which is what I was actually shooting for when I decided to do just the brakes first, then add a booster later if I needed it.

The real need for a booster comes if you use a master cylinder with a larger piston size.
If you stick with a master between 7/8" to 1" bore size, manual brakes seem to be fine. Go over an inch though, and your need for extra boost increases.
You can still stop of course. It just takes more and more leg strength as the size of the master piston increases. Just as it takes less and less leg power as the size of the wheel cylinder/caliper size gets larger.

What size tires are you going to be running?
That can have a difference on overall feelings about boosters too. Even Ford offered manual brakes on '76 and '77 Broncos. The power assist was still the option.

Paul

 

[75Denver]

That’s great news! Thank you. So is it safe to say that if I go with a 7/8” bore size it’ll be easier at the pedal? Or would the increase power be so nominal it would be hard to tell? I’ll be running the same tires (30” BFG ATs) and have already noticed a HUGE decline in brake performance and take off (running 3.50’s). They aren’t light tires.

 

[DirtDonk]

So is it safe to say that if I go with a 7/8” bore size it’ll be easier at the pedal?

Yes, but... There's always a "but" though, right?%)
Although I believe that 15/16" and 1" would be fine, the 7/8" might be a bit small. Not from a power standpoint, but from a soft pedal standpoint.
It's another circle dance, where one thing effects another. Too small a bore will move less fluid, which means the big piston disc caliper needs more pedal travel to get the fluid it needs.

In this case then, a stock size master is your best bet. Whether that was 1" for your year or not, the stock size works very well, as I can attest.
I'm still using the first replacement master cylinder that I put on the Bronco when it had drums in the late seventies. I'm sure by now with all it's sitting, it's not long for this world, but the point was the one I had worked fine for years.
Good firm pedal in fact. Hardly even noticed the slight increase in travel. It was VERY small.

Or would the increase power be so nominal it would be hard to tell?

No, you can tell the difference in 1/8" increments. The more sensitive you are to this stuff, and/or the more you drive a rig, the more easily you will feel the difference. If you don't drive it as much (maybe in your case?) it might be a bit harder. But you can feel the difference in both power needed for a given amount of braking, and the distance the pedal travels.
Neither is a bad change if you stick with stock size master cylinders though.

I’ll be running the same tires (30” BFG ATs) and have already noticed a HUGE decline in brake performance and take off (running 3.50’s). They aren’t light tires.

Yep, heavier is harder to stop for sure. And harder to get going!
But they're a great size to give you mucho leeway when designing the brake system. Just make sure you take into account any potential future changes.
I ran mine with 32" then 33" tires and they stopped fine for an old truck. Not at all well by today's standards probably, and certainly pushing the limits where with larger tires I would have wanted more power. But better than the old drum brakes ever did. The discs were not a huge increase in power per sé, but a vast improvement in stability, consistency, tunability, control and ease of servicing.
So totally worth it. Even without the booster.

If I was going to be running consistently with 33x12.50 or larger tires, I would consider either a booster of some kind, or a larger brake type.

Paul

 

[75Denver]

Thank you for clarifying. At most, I’ll bump up to a 31” but seeing as I’m just about to install your guys stock suspension kit, it’ll be a while before I make a change. If I prefer a shorter pedal stroke, then I’ll stick with a 15/16”-1” bore. Just curuious, what size wheel cylinder/caliper and master cylinder bore size was standard for the ‘76/77 DBs?

 

[clarrance]

Are you swapping the entire front axle and steering, or just from the knuckles out? either way I hope you know you will need all new steering linkage and a pitman arm too in order to use the 77 disk brakes. If your swapping from a D30 to D44 you will need a D44 Trac bar too. You might possibly need wheel spacers or new wheels too. The Chevy disc conversion is waaay simpler.

 

[DirtDonk]

Good to bring that up. If it's a knuckle-out swap from a Bronco, then your wheel choice has to have less than 3 5/8" backspacing and you'll have to bore out the tapered holes to allow for the (normally larger) T-style rod ends. You'll need a longer tie-rod as well (compared to a '66 to '75 version) but it's possible that both the tie-rod length and rod end size (to avoid reaming the holes) is fixable with a new steering linkage setup.
We sell our #2390 to work with the '76/'77 style knuckles and pitman arm.

If your knuckles are from an F150 then you would use the #2382 tapered sleeves.

Paul

 

[75Denver]

Are you swapping the entire front axle and steering, or just from the knuckles out? either way I hope you know you will need all new steering linkage and a pitman arm too in order to use the 77 disk brakes. If your swapping from a D30 to D44 you will need a D44 Trac bar too. You might possibly need wheel spacers or new wheels too. The Chevy disc conversion is waaay simpler.

Mine came from the factory with a D44. Through my hunt, I searched high and low for a 4turn box but then decided to go 6turn after driving a '76 (too squirrely!!) I was able to pick up a '76 pitman arm. I'm hoping that the WH T-linkage I bought can be scuffed and painted to look "stock enough". I REALLY wasn't happy with the shinny chromoly mid-section and the cast tie-rod ends but after reading about the wheel spacers, I just settled for the bling. Can't win them all;D.

 

[DirtDonk]

Good question. I never committed the caliper piston size to memory, but it's printed around here somewhere. Been mentioned in threads many times as far as the caliper piston size, but not sure I remember seeing many references to the rear wheel cylinders.
Usually comes up when comparing the truck/small car calipers (what we use mostly) and the "T-bird" calipers which were for the larger size cars and had larger pistons.

For the rear wheel cylinders my book says the stock early rears were 13/16" for all rears and the later models were 15/16 inch.
I installed slightly larger rear wheel cylinders before I even knew the '77's had a larger size to (I assumed) bring back some semblance of balance to the system. Seemed to work for me, but it's been so long I don't remember what size cylinder I used. I want to say 13/16 to 7/8 but that's just a wild-assed guess.

For the master you can simply order a stock replacement for manual brakes for whatever year you want. I believe that they used the same piston size throughout the entire model run of Early Broncos, including power and manual brakes at 1" bore size.

Remember one more change though, which is that the ports on the power booster versions of the master come out on the driver's (fender) side, while the standard non-power assist master cylinder's ports are facing the passenger (engine) side.
This simply means that if you do go with the booster bracket later, you would need to swap masters or at least make some custom lines. I see a lot of custom lines when opening Bronco hoods, so it's quite common either way.

Paul

 

[DirtDonk]

You'll need to paint/coat that thing anyway Denver. It's just polished/machined and not plated in any way, so it will rust very quickly when out in the real world. Here in CA (not always the real world) they might last a couple of seasons before you see rust. But in any other part of the country where moisture happens, you'll see rust happen quickly.

For those that actually like the bling I recommend a simple clear coat. For those like yourself that don't particularly care for it, black paint is your friend.

Paul

 

[75Denver]

Good to bring that up. If it's a knuckle-out swap from a Bronco, then your wheel choice has to have less than 3 5/8" backspacing and you'll have to bore out the tapered holes to allow for the (normally larger) T-style rod ends. You'll need a longer tie-rod as well (compared to a '66 to '75 version) but it's possible that both the tie-rod length and rod end size (to avoid reaming the holes) is fixable with a new steering linkage setup.
We sell our #2390 to work with the '76/'77 style knuckles and pitman arm.

If your knuckles are from an F150 then you would use the #2382 tapered sleeves.

Paul

All my parts are from a '77 Bronco knuckles out. I'm hoping I don't run into any issues with the steering linkage (don't remember the part) but at the time, you guys didn't have the 77 T-style with the '73-75 drag link. I settled for the '77 linkage and continued searching for a '77 pitman. Will I be running into any issues? I'm running factory 15" wheels. Don't know the backspacing.

 

[75Denver]

DirtDonk to the rescue again! Thank you. I'm hoping a scuff and a heavy etched primer will do the trick of blending the two materials. As picky as I am, I will say the heft and build of that linkage is amazing!! I'll search around for those sizes and when my rears need addressed, balance the system if it's not meeting the requirements.

 

[DirtDonk]

Your stock '71 steering linkage will not bolt up safely. The tie-rod adjuster does not have enough extension to let the rod ends reach the new, wider spaced steering arms.
And then the tapered holes are smaller on the Bronco disc brake knuckles.

And no, we don't know what Ford was thinking when they did that!
Well, for the spacing they were trying to improve the ackermann angle and road feel (and pretty much succeeded at that) but why they chose to use a smaller taper on the rod ends is a mystery.

So yes, you will have issues...
Using stock early linkage is a no-go, unless you decide to use stock '77 "Inverted-Y" linkage.

Paul

 

[75Denver]

Your stock '71 steering linkage will not bolt up safely. The tie-rod adjuster does not have enough extension to let the rod ends reach the new, wider spaced steering arms.
And then the tapered holes are smaller on the Bronco disc brake knuckles.

And no, we don't know what Ford was thinking when they did that!
Well, for the spacing they were trying to improve the ackermann angle and road feel (and pretty much succeeded at that) but why they chose to use a smaller taper on the rod ends is a mystery.

So yes, you will have issues...
Using stock early linkage is a no-go, unless you decide to use stock '77 "Inverted-Y" linkage.

Paul

Okay, for me in this instance, I plan on replacing my stock '71 linkage (same for D44 '71.5-'75) with all new WH '76/77 T-style linkage. The biggest concern at this point is, will I need to ream out the '77 knuckles to fit the WH T-style linkage or were they designed for the stock knuckles? This damn flu season has drawn out my conversion! I don't even remember what the selling points were for buying the new setup?:?.

 

[DirtDonk]

Selling points:
1. Bolt-on
2. Stronger.
3. Much more adjustability.
4. Can be considered a "conversion kit" in your case, to ease swapping to non-stock knuckles. So yes, no re-tapering of holes.
5. Less expensive than stock, when it comes time to replace at least some of the parts. Specifically the original long driver's side tie-rod (long side) and draglink.
6. For some, it's also easier to convert to a tie-rod over (TRO) arrangement because you don't have to modify the tie-rod.

In your case, rather than just the straight swap for a '76/'77 Bronco, you would combine parts from both early and late models. In this case, for your '71 with '76 knuckles you would use the #2403 tie-rod, and the #2379 Draglink for the '75 and earlier models.
This way the ends fit the later knuckles and the early pitman arm.

You can ask at the time of the order to make sure that the pricing is the same as if you were buying them in "kit" form. At a quick glance that will save you about $30 or $40 bucks if I remember.

Since you're not raising the suspension height you do not need a dropped pitman arm or trackbar bracket. But if you ever lift over 3" (or 2" as far as I'm concerned) you can add those items later to keep the overall angles more street friendly.

Paul

 

[DirtDonk]

Oh, and as we just discussed last night in another thread, the tie-rod comes bare, but looks really snazzy so it's tempting to leave it as-is.
But you do need to coat the center tie-rod to keep it from rusting in the outside world.

It's a really cool machine-polished looking chrome-moly steel rod. But unlike what it looks like, it is NOT plated.
As in the other thread, if you like the bling you just clear coat it. If you think it's a little to bolt of a statement for your Bronco, just paint it black.

And make note of the angle of your stock tie-rod and set the new one up the same way. Because the new one is fully adjustable, it will not automatically just fall into place like the non-adjustable stock one. But it's easy enough to mimic the stock one when setting the new one in place.

Paul

 

[75Denver]

Oh, and as we just discussed last night in another thread, the tie-rod comes bare, but looks really snazzy so it's tempting to leave it as-is.
But you do need to coat the center tie-rod to keep it from rusting in the outside world.
Paul

If I do go this route, what product do you guys use in-house to properly seal the bare metal?