Reverting back to stock from t-bird calipers- banjo fitting

[chuzie]

So are those Corvette calipers the 5.5" hole pattern metric style like the s-10 calipers?

 

[toddz69]

So are those Corvette calipers the 5.5" hole pattern metric style like the s-10 calipers?

No - they have a different mounting configuration.

Todd Z.

 

[chuzie]

Bubble =burst :-(

I wonder if my adjustable can get me from 53/47 to 70/30. Does anyone have experience with the range of these adjustables?

 

[broncnaz]

I would probably just go with stock off the shelf calipers for there price. Then use a adjustable prop valve to dial in the rear brakes. No sense in spending a lot of money on a setup that can be hard to get if it ever needs to be replaced. Plus you still need to get the new setup functioning. While its always in your best interest to size your brake system so you dont really need any valving sometimes its better to have off the self stuff. you may need to research other calipers that may work or could be adapted.

Not sure on your current adjustable valve when you say 53/47 what type are you running? Maybe thats the issue with your current setup. A adjustable valve should only be reducing pressure to the rear brakes not both front and rear. Thats why you have a dual MC and two brake line ports fronts more or less get full pressure and the rear should be reduced. Most will reduce pressure up to 57%
Brake bias is tricky to pinpoint a exact number to shoot for and thats where adjustable valves come into play. You want as much rear braking as you can get without locking them up. Your foot is the "valving" for the front braking as you reduce or increase foot pressure as required.

 

[chuzie]

Agreed. Readily accessible parts are important for me especially as a driver.

I am not running any prop valve at the moment. 53/47 is what the proportion would be if I paired t-bird fronts with s-10 rears. I would need to employ adjustable proportioning valve to get to 70/30 but now I'm leaning toward trying the 53/47 to see how it feels. Most disc/disc setups are 50/50 anyway, right?

 

[Apogee]

No, most disc/disc setups are not 50/50, but rather more like 65/35 to 80/20 depending on the application. As was stated before, a short wheelbase coupled with high CoG tends to mean a lot of weight transfer from the rear to front under braking, increasing the need for a higher front bias than say a sports car might require.

While the adjustable proportioning valve can certainly reduce the rear brake bias somewhat, that's not what it was designed to do. It's much more effective as a fine tuning device, not a band-aid for otherwise improperly sized and/or mismatched components. The valve itself is quite simple where it basically does nothing up to it's set point, and after that set point, it reduces the outlet pressure to 57% of the inlet pressure. When you adjust the valve, you're just moving that set point up or down the pressure curve. A low deceleration rates, you generally want more rear brake since you're not transferring a significant amount of weight forward, however at higher deceleration rates, you then want the valve to reduce the pressure to the rear discs since more weight is transferring to the front tires from the rears.

FWIW, the D154 calipers are 5.47" [139mm] pin to pin to be more accurate.

As Todd stated above, the C4, C5 and C6 calipers options are all a pin-guided floating caliper design, the new industry standard, and have their own mounting requirements.

 

[chuzie]

Is there a program out there I can plug my cg and other pertinent data into and it provide a recommendation for bias?

 

[Broncobowsher]

Is there a program out there I can plug my cg and other pertinent data into and it provide a recommendation for bias?

Not that I have found.

 

[chuzie]

Smallest metric caliper I found was only 2" What would you do if you went back to standard front calipers? That really is, what rear caliper would you need in back?

Where did you find a 2" metric GM caliper? I didn't see one on speedwaymotors.com.

Reading about how brake bias is calculated, I think I have been doing it wrong. I have just been dividing the piston area of the rear by the front. Multiple sites bring into account multiple variables. Am I wrong in my simple calculation for caliper selection or is that good enough to get me in the ballpark?

Here are two calculator sites I found:
http://brakepower.com/index.htm
http://www.tceperformanceproducts.com/bias-calculator/

and I found a very involved Excel sheet on Pirate
http://www.pirate4x4.com/tech/billavista/Brakes/Brake_System_Design_by_BillaVista.xls

and a great article explaining it here
http://www.pirate4x4.com/tech/billavista/Brakes/

Gonna comb through it and see if it helps. I just want to make the right choice and make this the LAST brake system iteration for my Bronco.

 

[broncnaz]

Yeah I think your calculating wrong. At least as far as bias goes. Kinda what I touched on before your front brakes are really the ones doing most of the work. The rears just help reduce the amount of work the fronts have to do and help slow the vehicle down faster. Which will help reduce pedal effort. As was said correctly sizing the system is your best bet as you really dont want to have to use valves but the valves do work.

Here's my take could be wrong but it makes sense to me. You really want the front brakes to be able to lock up in a panic stop. That makes the front bias almost 100% Next you add in the rear brakes which you dont want to lock up during that same panic stop but you want them close to locking up so they are sized or propotioned so they wont lock up. When in that panic stop now both sets of brakes are working the rears are pulling there say 30% and now the fronts only need to do the other 70%.
The biggest issue with lifted vehicles is the rears may need to be backed way off due to weight transfer and soft suspension so you may see/need way less than 30% bias in the rear.

I think the TEC link is fairly basic and should get you in the ball park. The pirate link looks a little easier with more info. but comes up with different numbers. so who knows. But they should be workable. The first link needs a lot of info and some of that is guess work on a bronco.
I think even with the t bird calipers it still works out that the explorer size calipers are close to what you need. Bigger calipers in the rear only mean you'll have to reduce pressure more to them. You also have to consider that a lot of master cylinders dont push the same volume or pressure out to the rear brakes. even on disc /disc setups. So in effect you may already have some built in proportioning.

 

[chuzie]

Good point.

According to some of these calculators, in a max braking situation, the bias would shift to 96/4 and that is taking into account my center of gravity, lift, etc, etc.

Here are the results for my current setup (T-bird/Explorer) if it was actually working.

Front

Required Brake Torque (front) (in. lbs) 43,504

Calculate Clamping Force (front) (lbs) 18,153

Calculate Brake Torque (front) (in. lbs.) 39,936

Rear

Required Brake Torque (rear) (in. lbs) 2,040

Calculate Clamping Force (rear) (lbs) 6,668

Calculate Brake Torque (rear) (in. lbs.) 12,668

That is 64/36 with regard to clamping force.


And for the proposed new setup (T-bird/S-10):

Front

Required Brake Torque (front) (in. lbs) 43,504

Calculate Clamping Force (front) (lbs) 22,976

Calculate Brake Torque (front) (in. lbs.) 50,548

Rear

Required Brake Torque (rear) (in. lbs) 2,040

Calculate Clamping Force (rear) (lbs) 15,003

Calculate Brake Torque (rear) (in. lbs.) 22,505

That is 65/35 with respect to clamping force.

Seems like the actual clamping force is close between the two setups. But I really don't want to have to employ the adjustable proportioning valve to such an large degree to achieve the theorized 96/4. Heck, according to these numbers, I would need a significant reduction to get the rears from 22,505 to 2,040.

I think before I do anything I really need to look into my pressures. Calculations show I should be in the ballpark of 1,500psi not 750psi as I currently have.

Does anyone have a multiplication number for the large aftermarket vac booster?

I also need to verify with CPP if there is any built in proportioning in their MC.

 

[Apogee]

I don't know which calculator you're using, however many of those are designed for race applications and assume you're running a dual master cylinder setup with a balance beam, so you'll need to compensate for that if you're running a more traditional tandem master cylinder (like you are). The calculator will basically double the required input force for the same outlet pressure with a 50/50 balance beam bias versus a tandem MC if you assume same size MC's in the dual setup.

Most vacuum boosters generate a maximum gain factor between 2-4 times, however that's progressive based on pedal effort/position and will vary depending on vacuum level supplied, size/configuration of booster, etc.

CPP makes a master cylinder with a built-in proportioning valve, their MCPV-1...is that what you're running? They also sell several without.

 

[chuzie]

Well my vac is around 13. I think that is low but have been told by others it is fine so I don't really know.

Here is the data from the calculators...

The booster number is a guess. Still waiting for Wildhorses to get back with me on the data. Also confirmed with WH that there is no integrated proportioning in that MC it is 50/50.


I attached a pdf of the excel sheet calculations from pirate. Wish we could upload excel files here. grrr.
Also attached the CG calculations too. Just ignore the word Jeep.

This one is located here http://brakepower.com/index.htm and allows options for single, tandem or dual MC.

 

[broncosbybart]

Chuzie, I had a Heep with an Explorer 8.8 in it and discs. They worked ok but the GM calipers I used on the racer work much better. I used an adj prop valve and the early 80's 'metric' style calipers from a Malibu, Monte Carlo, etc. Super cheap and they work great for me.

 

[chuzie]

Thanks for the info bart. I think GM is the way to go, just have to decide on what size caliper.

Gotta wait till I get home to do some more pressure tests though.

 

[ntsqd]

I've got to take issue with the statement that tandem M/C's don't always output the same pressure front and rear. That can only be true if there is a difference in bore size or one side is leaking. Differential bore m/c's do exist, GM used them for a few years that I know of.
Otherwise there is a slug of brake fluid captured between the front piston and the rear piston, it will apply the same force on the rear of the front piston as is applied to the rear of the rear piston. Not possible for a non stepped-bore m/c in good working order to have different output pressures.

I also don't want my front brakes to lock-up first. You loose all steering when that happens. I'd prefer to have a shot at steering around what I'm trying not to hit than slide into it.

I think brake bias considerations are over-rated. Get the maximum from the front brakes first. THEN bring the rears up to the point where in the worst case situation they just barely lock-up before the fronts.

 

[broncnaz]

There are other things to consider about some tandom MC's a lot of them have a spring between the two pistons which in effect delays secondary pressure slightly. Also rear brakes tend to use larger lines. So more volume is used before pressure builds. Yes eventually front and rear pressure may equalize. Its just a factor to consider. Small differances like these make a differance. Theres a reason that when people hook there front brakes to the wrong port on the MC they get poor braking. If all was equal it wouldnt matter what port you hooked the front brakes to.

If you look at just about any brake system you can always lock up the front brakes. Your foot needs to modulate the pedal or in the case of todays cars they have Anti lock brakes so you dont have to modulate the brakes its done for you.. Again Im talking about panic stops where foot pressure is above normal. If you dont get lock up your brakes are not at there optimum.
It really comes down to knowing how to drive older vehicles yes you have to use your brain.

 

[chuzie]

What if you have a tandem mismatched with the wrong calipers. Say the front calipers are smaller than the rear (unlikely I know). In this case you would not necessarily achieve front lockup, depending on weight, size, etc. More importantly, you will max out the fronts before the rears and the pedal will not be able to continue to travel enough to produce full pressure in the rear.

Even with a larger line, I don't think it will delay and use more volume. Sure, it will take more at initial fill, but the fluid is not compressible. Whether I have a 3/16 line or 1" line, as long as the output is the same, the pressure and fluid to achieve that pressure will not vary with line size.

 

[ntsqd]

The spring is only there to maintain the distance between the front and rear pistons inside the m/c when at rest. The front piston is driven by the compressed slug of brake fluid between the two pistons. So yeah, there is a *slight* delay between the front and the rear, on the order mirco-seconds. The two pistons only come into direct contact if the system plumbed to the rear port has a leak. In that case the fluid won't compress enough to drive the front piston and they come into intentional contact.

Locked brakes are not optimum and neither is the ability to do so. Better to be *almost* locked-up, it stops the shortest then. I learned this on my coaster-braked bicycle at the ripe old age of 9. Being able to lock the brakes is not any indicator of anything. Where within the whole brake performance envelope they lock is. Ideally only in the worst possible combo of circumstances should you be able to lock the brakes. Predicting exactly what those circumstances are too complex and missing means leaving some braking on the table. So bring locking them back a bit into closer to normal operation.

Optimize the front paying no attention to the rear. Then you'll have the major portion of the work done. Since the rears rarely account for even 50% of the braking force, then with the front optimized you can start to dial-in the rears. Unless you are using a balance bar system (please, DO NOT!) the m/c bore optimized for the front is what you're stuck with for the rear. Adjust the piston area of the rear calipers to get the most ideal brake bias without any p-valve or LBS in the system. Then "tune" the system to the best that it can be with either or both valves.

 

[chuzie]

I think that is a great plan. Optimize front and size rear for ideal bias.

So does the 94/6 bias really sound reasonable?