I have a 66 F100 with single bowl master cylinder . I am planning to upgrade it to a dual bowl for non power drum brakes. Some of the things I have looked at incorporate an adjustable combination valve or distribution valve to fine tune rear brake pressure. Videos I have seen which have been converting similar era Falcons and Mustangs do not seem to use this valve. Does anyone have experience with this and know if the addition of this adjustable valve is necessary or if it makes a major difference in the outcome.

 

You will NOT regret it if you DO add the power booster at the same time. IMO, not necessary to have an adjustable proportioning valve. Having all drums within spec, new hard lines/hoses/ shoes, wheel cylinders and hardware - for a daily driver you’ll be good to go. Racing it, maybe a different story. These old trucks will, however, absorb as much money as you want them to.

 

Thanks so much for your input on this. I’ve been pretty lucky so far with the $’s on this truck but I definitely see the danger haha

 

If you have original four wheel drums you shouldn't need an adjustable proportioning valve- the stock wheel cylinder sizes determine the front to rear brake bias. Make sure the master cylinder has internal residual valves to keep pressure on the wheel cylinder cup seals. Having or not having internal residual valves is the difference between disc or drum master cylinders.

If you have disc/drum you need a prop valve, and an adjustable one is best. You also need a "hold off valve" (sometimes called a metering valve) in the front line so the discs don't immediately apply while the back wait until pressure builds enough to overcome the shoe return springs. The rear still needs a residual valve whether its internal or external.

If you have disc/discs you'll still want an adjustable prop valve to dial in the front to rear bias. You never want the rear to lock up before the front does; an adjustable valve allows you to get the most rear braking possible without locking up too soon. Generic non-adjustable prop valves are just that- generic; who knows what they're calibrated for.

Adding a booster to a non-abs truck isn't always as great of an idea as it sounds... you don't want too easy of a pedal that locks the brakes up easily. **You** are the abs system, so you need to be able to modulate the brakes and a manual system makes that much easier than a boosted system. If you can't lock up the wheels with a manual system, something is wrong with the brakes, its not because it has "weak" manual brakes.

A smaller bore master cylinder will have a similar effect as a booster- increased line pressure while decreasing pedal effort, except you can tune the pedal effort with different master cylinder sizes. You can't really do that with boosters, you're stuck with however much assist the booster adds- often too much for a non-abs system.

 

Thank you for the great explanation. I am planning to stick with manual drum brakes all around with no booster. When the time comes to do the conversion I will be sure to source the correct master for non power drum brakes. I appreciate your time to explain all the configurations.

 

There’s nothing wrong with a booster on a drum/drum truck.

 

[QUOTE=theastronaut;21250013)Adding a booster to a non-abs truck isn't always as great of an idea as it sounds... you don't want too easy of a pedal that locks the brakes up easily. **You** are the abs system, so you need to be able to modulate the brakes and a manual system makes that much easier than a boosted system. If you can't lock up the wheels with a manual system, something is wrong with the brakes, it’s not because it has "weak" manual brakes.[/QUOTE]

Poppycock Balderdash. In other words - Nonsense.(There’s another commonly used phrase, frowned upon in polite company: It’s initials are BS)

This is a great , economical brake upgrade, one commonly done by members with no reported problems, and one of the best for upgrades for daily driven trucks , that won’t “brake” the bank.

I will say this: If you happen to be “one of those guys”, i.e. the kind that wants to change out only one wheel cylinder per axle, thinks dried-out, cracked 60 year old brake hoses are good enough, sees no need to replace rusty old lines, and thinks periodic flushing of the entire system is for suckers - well, you’ll reap the rewards of your philosophy.

Astronaut, I am funnin ya, BUT this upgrade has been done so many times with no problems. It’s a non-issue.

 

Poppycock? Race cars almost exclusively use manual brakes, should we tell them that they're doing it wrong? There is much more to upgrading the braking system than just throwing a booster on it. Making lots of line pressure easily is great for modern cars/trucks that have discs with ceramic pads that have a lower coefficient of friction, and grandmas with weak legs, and abs that keeps the wheels from locking up when you stab the pedal. But when you make a lot of line pressure easily without ABS it very often makes it too easy to lock up the tires, which just makes you slide uncontrollably. That's not safe, and its definitely not an upgrade.

Non-boosted brakes are easier to modulate at the limit of traction; this isn't something I came up with on my own and it's a pretty easy concept to grasp. But, boosters have forever been marketed as an upgrade to make marginal old/worn out brake systems "work better" (ie easier pedal effort, but not actual shorter/more controlled stopping distances) for so long that saying otherwise makes you the "bad guy" that doesn't know what he's talking about. Just listen to what the magazine articles/ads and TV shows and the guys selling parts tell you, they always know best... didn't you say these trucks are money absorbers? Those guys know that, and market certain items accordingly. Nevermind that most of the time when an older non-ABS car is modified for track use (where actual braking performance and stopping distances matter) the booster is eliminated and a smaller bore master cylinder is swapped in to make modulation easier and more precise. Again, YOU are the abs system so you don't want to make a brake modification that makes it harder for YOU to modulate the brakes. Muscle memory development when braking at the limit of grip (how to stop the shortest/safest) is much easier to learn with manual brakes. If you shrug at this then just say you don't care about actually stopping shorter/safer with a non-abs car/truck, and say instead that you enjoy less pedal effort no matter the downside. This is an item that doesn't matter that much until it does matter, so most people get away with a less than ideal brake setup.

Aftermarket boosters often add more assist than is needed or is beneficial, which makes it hard to modulate the brakes in an emergency stop situation- they just lock up and slide because pedal effort is so low that you can't modulate the pedal force accurately enough. When you don't have ABS to sort it out for you you don't want an overly easy pedal. We have a $200K+ 1966 truck coming into our shop in the next few weeks to go over the braking system because it's overboosted and the pedal feel/response is garbage. It has a booster and all the brake parts the owner was sold... it should be good to go according to the people that sold the owner the parts, but in reality it's simply overboosted/overassisted. I spent two minutes diagnosing it and comparing it with my '66 and they have the pedal ratio all wrong for a boosted setup. Either eliminating the booster or reworking the pedal ratio to lessen the mechanical advantage of the pedal's leverage on the master cylinder will be needed to make the brakes feel like they should.

This is on the same level as uninformed people throwing LED bulbs into halogen headlight housings which ruins the beam pattern and always performs worse when tested for actual objective lighting performance, yet the guy that just installed them takes a few steps back and exclaims "they're so much brighter!" and goes and recommends it to everyone else. "I don't have to push the pedal as hard!!" is the same false sense of security or sense of added braking performance/shorter stopping distance as "my headlights are so bright people flash me all the time!"

I'm not saying to never use a booster, because my own autocross/track car has one (its a very small booster, and the pedal ratio and master cylinder size are designed to make the system easy to modulate). I'm saying that you need to look at the braking system as a whole and modify it in a way that increases driver control and actually makes it easier to stop shorter so it's actually safer. Just throwing a booster on it so the pedal effort is low is not an upgrade without abs, it's the opposite when it makes the brakes easy to lock up. So many people do these mods then barely drive their older car/truck and 95% never drive them hard enough to ever have to brake hard enough to ever know how poorly their brakes would actually perform when having to stop as short as possible in a controlled manner, so yeah they recommend what they did to everyone else because "the pedal is easier now".

If you're going to add a booster, the pedal ratio and master cylinder diameter often need to be adjusted accordingly. If you don't know what those two items have to do with adding a booster and don't know which way to go about making changes to the pedal ratio and/or bore size then you definitely don't need to be the one making decisions about brake parts on a truck you'll be driving on public roads without doing research first.

If you're going to say "poppycock", please back up your side of the debate with more than "a lot of other people have done it and they all say it works great". Lets get into pedal ratio, the effects of master cylinder diameter on line pressure, etc. Bring some actual data into the conversation, not just "other people did it". Lots of people add LED bulbs into halogen headlights as well, I know because I get blinded by them multiple times every night driving home while they light up the top of trees instead of having light aimed where it needs to go. Yet you almost never see bad reviews on led bulbs made for halogen headlights, people just don't know what they're doing except for "other people did it and said it works, and my own subjective observations make me believe that it's better now".

I could just say "add a booster" like everyone else, but its better to educate people on the effects adding boosters have and tell them that adding a booster by itself isn't a great idea- the brake system needs to looked at as a whole and adding a booster without altering the master cylinder bore size and/or pedal ratio is asking for trouble. Sticking with the manual setup and dropping the master cylinder bore size by around 1/8" will make more line pressure without making it overly easy to lock up the brakes, and will still be easy to modulate. That's cheaper than adding a booster (basically free in this situation because he's already replacing the master cylinder), makes a bit more line pressure, keeps the brakes easy to modulate, leaves more room in the engine compartment, and doesn't require other modifications like adding a booster would. There are no downsides besides not having a booster than everyone claims "you should have".

 

Well, not going to be so verbose as you. Less is more.

I’ll back it up simply by saying that drum/drum, with power booster, dual chamber master cylinder has been done countless times with no problems, if the entire system is otherwise up to snuff.Not even debatable.

See, that wasn’t so hard, was it? Short and sweet? Now, can YOU back your position up by citing even one instance of a member here that had problems?

 

I'll offer this; my 72 F100 came with four wheel drum brakes and a brake booster from the factory. It now has a disc brake swap. It's all about matching components. My 63 has a disc swap using D52 calipers, 76 disc/drum master, 76 non-adjustable combo valve and 76 brake booster.

 

I covered your question already, here it is again in case you missed it, and I've also added an example from the forum.



This thread is a perfect example of what happens when someone overboosts the brakes. The OP has touchy brakes after installing a booster, and people offered the same advise that I have here- that the entire system (pedal ratio, bore size, booster) needs to work together to work properly. Someone commented that drum brakes had a smaller booster than disc brakes because drums are self energizing and need less line pressure to work correctly.

https://www.ford-trucks.com/forums/1...ke-booster.htm


And again...

A lot of people did something and were happy so they can't all be wrong! And yeah, the factory did add boosters as an option but they weren't guessing on which parts to use together. Was the pedal ratio the same between boosted and non boosted trucks? Were the master cylinder bores the same diameter? Wheel cylinders the same diameter? Different size MC bore for discs vs drums? Different size boosters for discs vs drums? Like I've said, just throwing a booster on it might make it harder to modulate the brakes. Mixing parts with no knowledge of what your're doing is not a good idea with something as important as brakes. It shouldn't be a point of contention that I've pointed out that brakes are important and need to be assembled from the correct parts, instead of just saying "throw a booster on it, you'll love it!" and letting the OP wander off to possibly have overboosted brakes. Less info is not more when it comes to something like brakes.


I'll also add that pad compound makes a big difference in how well the brakes can be modulated. When I bought my current daily driver it took excessive pedal effort to stop it in normal driving. I did a thorough check, it was all 100% stock parts and everything worked correctly. I swapped to a set of semi-metallic pads with a F/F rating (coefficient of friction rating at cold and hot temps) and bedded the pads in, and the brakes started working properly with only normal effort needed to stop the car. If you're using pads with a lower coefficient of friction rating or have never bedded them in properly to establish a transfer layer so they make the amount of friction they should then you can probably get away with overboosted brakes because the pads aren't working to their full capacity.

 

More!? Yawn.

99%, my estimate, don’t race their trucks. No need to worry about rare exceptions to the rule(outliers) that almost never happen. It’s a time-proven , economical upgrade for almost all old trucks, with no drawbacks, other than a bit of work /money. I and quite a few others have, and will continue to heartily recommend it.

 

I answered your question with what you asked for- proof from the forum itself that simply adding a booster doesn't always automatically improve the brakes with no drawbacks like you claim it does.

 

Hmm, drum brakes all around with a 1966 F-100 power booster now. I wouldn't say it has made my brakes as easy to apply as my other cars with power brakes. Far from it. It happens to be a little easier now

 

I was in the same situation with my '66 F250 and I did a write up which might help you: https://www.ford-trucks.com/forums/1...onversion.html

I installed an adjustable block mainly because it comes with a brake light switch and it doesn't hurt for a drum/drum setup. I converted to an 8-lug disc/drum setup in the meantime and was happy it was already there.