Technical Flyinbrians post with brake issues, got me to thinking about something

In the thread there was a few replies about sizing brake components like the factory did.
So, say you pull an 8.8 from a newer vehicle. Just as an example

I had a ‘94 Explorer that something was amiss with the ABS thing. Reading up on it, says basically the ABS thing is bypassed and brakes work “normal”. Now when I had to hammer down on the brakes, no skids, etc and a nice stop before the light came on.

The first time I had to do a panic stop, the rear drums locked up.
So say I pulled that rear and used what Ford did for MC sizing and front rear caliper and WC sizing.
Wouldn’t it be better to size your set up pre-ABS brakes?


Just had me thinking

 

Yes

 

You can also tailor the rear brakes by using different wheel cylinder diameters, that have the same mounting bolt and hose specifications. If you want less rear brakes than what the original rearend application donor car had, find smaller diam. Say it had 7/8 diam wheel cyl as stock donor. For less braking find a 3/4 diam wheel cyl. Or for more rear brakes, find a 1 inch diam. These are just examples, but once you have a rearend and make some test hard stops, you can then get new wheel cylinders to adjust or tailor the pressure transferred to the rear brake shoes.

Note that the pressure inside the brake line is the same for all 3/4, 7/8 or 1 inch listed above. Since pressure is pounds/sq in (psi), the end pounds force is dependent on the sq in of the wheel cylinder. A larger diam gives more force: Pi x Diam(squared)/4 or Pi x Radius(squared).

 

I guess my point was, if you pull stuff off a modern vehicle, maybe not rely on what is all there, due to the gizmos that control things.

 

Not sure I can agree completely with that. Something I have been thinking about in the (preceding) discussion is the huge amount of variables that faces a vehicle/driver over time. Tire size and condition, road surface, weather and on and on. So, I tend to think all brake systems for production vehicles, certainly prior to ABS, are compromises.

The development of reliable and sophisticated ABS picks up where the prior system left off. Stated another way, brake engineers can do their best at guesstimating brake design and sizing, and the ABS covers the inevitable myriad of variables. My point being, I expect the OEM setup of sizing for the particular vehicle is likely well chosen for size and weight of the application intended. Our problem is choosing wisely (informed guessing ?) when we transfer that system to our vehicle of choice.

Ray

 

Master cylinders, wheel cylinders, and calipers all work the same way they always did. It's the ABS control module and all of it's little minion's that perform all the wizardry. When an ABS module goes out, you don't loose your brakes, you just go back to a conventional braking system as a failsafe. I guess what I'm trying to say is, no matter if it's modern or vintage part's, the same principal's apply to both.

 

Well, I never had an issue with some OT cars that were disc/drum, pre-ABS, with the rears locking up like I mentioned happened.
Maybe things improved since the early/mid 90’s?

 

I had a T rpu and when I nailed the brake pedal the rear would pass the front. I replaced the rear wheel cylinders with a smaller dia and that fixed that. But depending on tire size, weight distribution etc it might take a test dreive to see what it needs.

 

An adjustable proportioning valve might help as well.

Since when is ABS talk "traditional"?

 

most anything built that is a HAMB style its pretty much copy cat stuff, buy a set from a catalogue if you wish, it will work . Dont play with electronics, other than its off topic its designed to work on the car its fitted to and not a different car and at the moment its not tunable, maybe that will come.

 

nice , where were you in the thread where someone was doing weird things with a garden hose and a T piece to "prove" bigger lines and flow and stuff?

 

You missed my point. What I was saying, is if you looked at the vehicle I mention and pulled its rearend, then sized your front rotors and calipers based of that vehicle, sized your MC as well, you would wind up with a vehicle that locked the rear brakes. What kept it then from locking before was the gizmo controller. To be honest, I don’t know if it had a proportioning valve in it or not.

 

The reference to ABS in this thread seems to merely illustrate how modern brake system design deals with things like rear brake lock up. Nowhere did I see any suggestion that ABS should be incorporated in HAMB friendly cars.

An analogy might be carburetor fuel systems vs EFI. We (HAMB) exclude EFI systems because of the time period to which we limit our builds. However, it wouldn’t be a ‘violation’ when discussing fuel systems to say how difficult it is to get a carbureted system to fully compensate for changing operating conditions. Altitude changes when traveling for instance.

Remarking that EFI has made that a non-issue but we have to work harder/smarter with careful tuning of our carburetor systems to maximize their drivability is not the same thing as advocating switching to EFI.

Ray

 

A reasonable answer made in a reasonable manner ...... Thank you .....

 

@Hnstray did a better job of getting my thoughts across than I did

 

Yeah, Ray's good like that...

 

I sure would like to meet and hang out with Ray!

Ben

 

I've met Ray, and yes, he is a good guy!

 

awww shucks....thanks fellas...

 

The discussion may not be ABS specific, but the OP is talking about using a modern rearend. I understand it's more about braking theory. So what's the consensus answer? Most disc/drum setups I've seen required a prop valve, though I know they can be setup without one when attention is paid to the size/bore of the cylinders. I'm thinking the OP's experience with his wonky ABS setup locking up the brakes is more related to a faulty ABS system than the sizing of the brake components. I had faulty ABS sensors in a late model truck that would make the braking system do all kinds of weird things, including locking up the brakes.

 

This is why I keep copies of the Wagner brake bible. I have several vintages. They allow you to read the specs and match up a system that works.

 

It’s entirely possible that what I had was older tech, but the service manual I had (factory Ford) said when the light was on, the ABS was bypassed.

My intent was just to have folks think about what they are using, myself and I’m sure many others, don’t have access to the stuff that was plentiful in the 70’s when I was yard scrounging, so for me it’s pick and pull, the majority of parts like rearends are no more than 20 years old.
The reason I wanted to share my experience was because in the thread I referenced several noted “ using OEM designs”. Well, certainly I’m not putting ABS on anything I have, nor is anyone here on the HAMB either

 

If you take the modern OT ABS stuff out of the equation the brakes still work the same as before. Hydraulic theory has not changed. You still need properly match components, bore sizes, pedal ratios etc. Thats why I keep bringing up those actual spec books

 

X2

 

I am not real big on ABS personally. I have two vehicles with ABS and they work fine but you loose a lot of feel with them. I still find myself feathering the brakes, I know that is the wrong thing to do but it is a hard habit for me to break.

I could give you lots of reasons why I don't like them but that are not real relevant.

Most of us are not going to go ABS on our hot rods. I would think that if you had an ABS car and wanted to lose the ABS (some high end sports cars have a switch so that you can turn it off) the way to go would be to go with an earlier master for the same brakes.

We do a lot of things to balance out our brakes. First thing is to get the proper master. One thing that works for brakes that do not match (think 12" bendix rears and metric GM discs front here) is two masters. Wilwood makes a setup like that with a balance bar between the masters. Then instead of trying get odd ball slave cylinders to go with your disc size master you could just run two different size master cylinders.

Another thing that we can do is to adjust brake bias, with an adjustable proportioning valve. We consider for example that 60/40(front to rear) bias is good on a stock vehicle. On a lowered vehicle we can actually use more rear brakes because we don't have the leverage toward the front when we are braking. A lifted car may want even less brake bias say 7o/30 (nominal number) because they are more likely to lean toward the front under hard braking. The fact that our cars are commonly light in the ass end would put you in this situation as well.

There are a lot of ways to skin this old cat. They just take a little thought.

 

Not me, I hate being the inferior person in a room of two

 

......I can assure you, you would not be at risk. ​

 

Well, I’m glad my trials have people thinking. Here’s what I HOPE is the answer.


Sent from my iPhone using H.A.M.B.

 

Brake problems come up so often we need a forum just for brakes

 

The last sentence neatly sums up our problem... 'Choosing wisely' and 'system' are the operative words. Keeping matched parts together could eliminate some of the guesswork.

And the sentence right before it offers a 'guide' for your selection. Three things come to my mind when making that selection; vehicle weight, weight distribution, and tire contact area.
Vehicle weight is easy; simply make sure the brakes were used on a car equal to or greater than your vehicle's weight. If the donor is heavier, you just get better brakes for your weight.
Weight distribution is the critical one in my mind. Achieving a match on this will have a large affect on 'balance', assuming the donor had good brakes. It would probably pay to track down and read any 'road tests' you can find on the donor to see if they passed muster in the first place, as well as possibly having the needed specs.
Tire contact area can be either a non-issue, a big deal, or somewhere in between. All four tires the same? Non-issue as long as the donor had all the same size. A 185/80-15 on the front and 275/60-15 in the rear? A big deal, you better do some sort of calculation; same for any big/little combo but what/how you'd precisely calculate that I can't say. Strictly on a percentage basis is my best guess, but I'd think weight transfer under braking will have some effect...

And the inevitable flies in the ointment....

When working with a drum/drum or disc/drum system and pre-ABS, the engineer can vary drum diameter, width, shoe size, and wheel cylinder diameter to achieve 'balance' or get as close as they can, all fairly easily. Probably several dozen variations with changing no more than three parts, with drums being the only major one. This avenue is open to us and we should take advantage of it. When Ford first introduced discs in '64, they had two caliper sizes; big for the Lincoln and T-bird (and eventually used across all full-size lines), and small for the Mustang, also added to the other like-sized cars. They then tailored the rear brakes to achieve balance.

Disc/disc systems? While these have been around as standard equipment on some production cars since the early '60s, they weren't 'common' and the engineers usually went the extra mile to make them work well. But as discs proliferated into their general product line along with ABS, it seems like they did their best to settle on a limited number of 'basic' designs that they mixed/matched for their various cars to achieve balance. Any changes usually resulted in a whole new assembly. Understandable, it costs money to design/build/stock all those parts (and on the truly high-end brake systems, they use aftermarket parts). But with limited choices, did that degrade their ability to balance the system without resorting to ABS? Start mixing manufacturers and particularly eras, you're now in unknown territory...

We seem to have three choices; mix-your-own systems with most aftermarket suppliers using '80s GM calipers in front and all over the map for rears, buy a complete aftermarket system from somebody like Wilwood or Baer for big $$$, but to their credit I've noticed that Wilwood is offering a moderately-priced ($600) 4-piston front set-up for many cars that isn't that much more than some 'generic' GM-based conversions. Or roll-your-own, but that will require some skull sweat and shoeleather to determine what will work, and then build the parts to make it work.