4/4 birdcage options

[dirtmod]

My new 4/4 modified has both brake calipers mounted directly to the birdcages. Both sides are floated, spring behind left rear, spring in front right rear. In my thinking, anytime I am on the brakes, it will be working against the 4 link bars.
Is there any time this set-up will be better or worse than something else?
Would the left rear be the same as running a left rear brake floater since it is integrated into the birdcage?(If so,I would clamp the right rear caliper to the housing).
Please explain in detail and type slow since I am trying to learn this 4/4 deal as much as possible before I run it.

[profab00]

Used to have a latemodel 15 years ago with that system. It didn't work well because I felt the brakes jammed the cages for a split instant and kept the car from giving as much instant traction. I questioned a guy I felt to be pretty intelligent about going back to that and he recommended against it due to bind. But, if you go up on top bar on right rear you are tightening into the corner, but also giving rear steer afterward. Rasing the left rear top would push upward on that corner of the frame and in theory would help keep the left rear loaded, no, keep it up on the bars.

[dirtmod]

I actually pretty much understand what the bar changes do, but if I am at a big disadvantage with the calipers mounted to the birdcage I want to change to something better. A lot of the 4/4 cars I have looked at have the calipers clamped solid to the housing and the birdcages are seperate from the brakes.

[profab00]

I would actually feel better for one of the more educated in this area to talk because I thought what you bought would be the hot ticket until I asked

[Rocket Bonehead]

If you're running a lot of slick tracks, then that setup will not hurt you much if you know how to use the brakes. When the track has grip, I'd recommend clamping up the RR brake to help free the car on the brakes. The car should turn better on corner entry and late entry if you drag the brake to keep the car on the bars with the LR floated. Note that if you get too extreme on the LRT bar angle, you will run into issues of maxing out your travel and breaking LR traction.


My advice would be to make an option to clamp the RR brake. I'd start off clamped all the time, even in the slick, but if you need to be tighter on entry, and you have no more bar adjustment left to improve that, then go ahead and float the brake. Whenever you are floated (either side), I would NOT advise stabbing the brake at any time as that will drastically upset the car. It will take you a few races to get used to driving the car with the brakes floated, but if you're smooth on the pedals and wheel, then you should be fine.


I know a number of modified guys who float the LR brake all the time, as it helps the car turn if the brake is used properly, so I don't think that will hurt you much if any.



RB

[profab00]

Hey RB, are they floated on the same birdcage or are they on a seperate brake floater all to them selves?

[Rocket Bonehead]

Hey RB, are they floated on the same birdcage or are they on a seperate brake floater all to them selves?


Most cars I see, that are floating the LR brake, are running a seperate floater. You don't see too many birdcages made now days with the option of floating the LR on the cage. The last company I saw that used this was GRT, but I don't think they're doing it still on their new cages.


Most cages now days, with few exceptions, have the option of floating the RR on the cage. I haven't seen anyone run a seperate RR floater in a long time.



RB

[profab00]

A GRT latemodel was the chassis I was running so long ago with the claipers mounted to the cages. When I questioned on combining them back together I was told if I trail braked into the corner to keep the chassis up on the bars, then I didn't have a need for the brake floater on the left rear. However, not all have that ability and quite frankly, I'm not sure I do. I suscribe to Billet Bird Head's analogy of himself and believe it applies to me also, I used to think I could shoe until I met a few real shoes.

[billetbirdcage]

I'm not going into great detail here but here is a little:

Whether the brake is floated on the cage or a seperate floater basically works the same with some major differences but the principle and the way they work are the same. Since the 4-bars will generally always have a uphill thrust angle, when you are using the brakes they will apply a rotating force to the cage/floater and push on the bar/bars (running uphill) and will push down on the tire. This causes that tire/tires to have additional wieght on it (traction) thus will make it decellerate or excellerate the car more with that perticular tire.

Yes, this inheritly binds the car up. Bounce on the back of the car and see how freely it moves then have someone sit in the car and hold the brakes, the car will become very stiff and locked up when you try to bounce it.

Difference between brakes floated on the cage and a seperate floater is pretty basic but some things most people don't realise:

The caliper is mounted so it is in center contact with a 11.25" rotor so that puts it 5.625" away from the axle center. Most cages have the bars mounted 4.5" away from the axle centerline, so when the caliper has 1000# of force trying to rotate the caliper that translates to 1250# at the cage (5.625 / 4.5 = 1.25 times the caliper force). This now has 1250# of force rotating the cage which is going to be spread between the bars or to the average thrust angle of both bars (basically a line from the axle centerline to half way between the two frame mounting points - that is the average thrust angle opf both bars).

With a brake floater, the thrust is soully the angle of the bar from the floater to the frame. However the height that the bar attaches to the floater may be different then the 4.5" of the cages bars, alot are around 6" on the floaters. So if the floater is 6" that 1000# of force on the caliper is only 937.5# instead of the 1250# of the cage (5.625 / 6.0 = .9375 times the caliper force). You can see that if the average thrust of both bars on the cage and the single bar of the floater were the same that you will have a different amount of force on the thrust angle causing diffferent amounts of loading of the tires. Since you will have less force on a 6" floater you will need more thrust angle to achieve the same desired loading of the tire.

I see NO reason to float the brake on the cage over a seperate floater, except out of simplicity or just what you have. Anytime you move a 4-link bar you are altering the thrust angle, so you are changing the braking thrust on the brakes as well as. You can not adjust them independly, you move a bar to affect the brakes you are changing the acelleration thrust angle also as well as rollsteer. A seperate floater allows you to seperate these two items and be able to adjust them without effecting the other.

There are alot of other things going on that I'm not going to get into.

[claybuster]

BB, thats a lot to digest day after newyears. My gears are starting to turn slowly.

[dirtmod]

billetbirdcage, I didn't think it was a very good design, would you recommend just clamping the caliper mounts to the housing or putting brake floaters on? I need to buy new birdcages and cannot afford to do it wrong again. Thanks (P.S. this a modified with a torque link)

[billetbirdcage]

I would not have the brakes on the cages with no way of clamping them down. If I had to choose only one way or the other, I'd go clamped as it is the most consistant and good on a wide array of conditions.

If I wanted the option of floating a brake, I use a seperate floater that locks up, that is what we do. This way if you wish to float it just unlock and add the bar and you are floated.

In some contraction to all, that most LM's had the brakes on the cages until around 1995 or 1996 when most switched to clamping them to the tubes.

With clamped brakes you will need something to control or dampen the pinion movement. On a LM with brakes on the cages we used a solid chain to the torque arm, when you switched to clamped brakes you needed to add a 6th coil to that chain or it would overly loosen the entry. So you will need some time of control on the pinion like a 6th coil, bumper on 90/10, or a 2 way pullbar.

[profab00]

There! Glad I got that off my chest!:D

[LM14]

.... The caliper is mounted so it is in center contact with a 11.25" rotor so that puts it 5.625" away from the axle center. Most cages have the bars mounted 4.5" away from the axle centerline, so when the caliper has 1000# of force trying to rotate the caliper that translates to 1250# at the cage (5.625 / 4.5 = 1.25 times the caliper force). This now has 1250# of force rotating the cage which is going to be spread between the bars or to the average thrust angle of both bars (basically a line from the axle centerline to half way between the two frame mounting points - that is the average thrust angle opf both bars).....


I'm not so sure that statement is 100% true. I believe if you do an annalysis of the forces on the uper and lower 4 bars, you will find that under braking the top bar will be in compression and the bottom bar will be in tension. Wouldn't that possibly negate the "average angle" you mention? Under throttle the thrust angles could be averaged because they would both be in tension, not under braking. Am I wrong?

SPark

[billetbirdcage]

I'm not so sure that statement is 100% true. I believe if you do an annalysis of the forces on the uper and lower 4 bars, you will find that under braking the top bar will be in compression and the bottom bar will be in tension. Wouldn't that possibly negate the "average angle" you mention? Under throttle the thrust angles could be averaged because they would both be in tension, not under braking. Am I wrong?

SPark

No, you have it right! I'm not sure that tension (I think of compression) is the correct word here (maybe extension is better) but I know what you mean as maybe I wasn't as clear as I could have been.

Yes, it is pushing on the upper bar and pulling on the lower bar. That is why I said 1250# at the cage. You would have to figure out the average thrust between the two bars which is pretty hard to do because you also (when on the brakes slowing the car) have both bars in extension also from the rear end slowing the car (multiple factors here). It would be less then the average (acelleration) thrust angle formula that I list and wasn't meant to be the actual braking thrust angle (I probably confused people with that).

If the lower bar was level then it would have no upperward or downward force to the tire as long as the bar stayed level and the upper (always having upward angle) is going to be pushing down on the tire.

You could also argue the 5.625" at the caliper as the pad isn't only contacting the rotor at it's largest diameter but over the height of the pad. I had to pick a number and that was the easiest.

The post was meant to show some of the differences in a seperate floater and on the cage with a major factor being able to adjust one side (braking only verse throttle) without effecting the other.

[billetbirdcage]

I would not have the brakes on the cages with no way of clamping them down. If I had to choose only one way or the other, I'd go clamped as it is the most consistant and good on a wide array of conditions.

If I wanted the option of floating a brake, I use a seperate floater that locks up, that is what we do. This way if you wish to float it just unlock and add the bar and you are floated.

In some contraction to all, that most LM's had the brakes on the cages until around 1995 or 1996 when most switched to clamping them to the tubes.

With clamped brakes you will need something to control or dampen the pinion movement. On a LM with brakes on the cages we used a solid chain to the torque arm, when you switched to clamped brakes you needed to add a 6th coil to that chain or it would overly loosen the entry. So you will need some time of control on the pinion like a 6th coil, bumper on 90/10, or a 2 way pullbar.


I should also state, that I don't have a big problem with the LR being on the cage all the time. It is having the RR on the cage all the time that I would not want on my car. It can cause an incosistant push in the middle bedpending on how the brakes are used or more importantly how consistantly they are used. I would at least want the option on clamping down the RR caliper for an average use and then might float the RR if I really needed too at certain times.

The LR isn't a real big issue to me, but I like options for different situations. Most of my point was if you wish to have floated brakes why not use a seperate floater so you can make 4-bar adjustment without effecting the brake side of things and then could lock them up if you wished to have the brakes clamped.

That was my point about floated brakes, just on the cages limits you to what you could do and seperate floaters allows you do do both and not have one adjustment effect the other so you don't have any disadvantages of the cage system.

Maybe that was more clear!

[2dumb2kwit]

Dang, I was just gettin' ready to explain where all those forces were being applied.

[dirtmod]

I pushed down on the back of the car today with no brake, then had my crew chief step on the brake while I pushed down on the back of the car again. I could tell absolutely no difference, I even bounced up and down on the rear bumper and it was very free. I thought it would lock up the rear of the car with the brakes on.

[billetbirdcage]

Wouldn't you know it, your car makes a liar out of me!

There could be a couple of reasons as to why you noticed little or no difference:

1: Very little indexing of the cage for the amount of travel you were inducing by bouncing the car. This just means that with the bar angles, U and L bar angle split, U and L bar lenght split, and/or ETC that for the amount the suspension was moving during bouncing that the brake (applied) was not really limiting the movement of the cage because it wasn't really moving anyway.

2. Limited brake: You could have not had alot of brake pressure on the rear brakes by either having the brakes adjusted to the front and/or M/C size split, that the brakes just didn't hold the cage from rotating. I doubt this would be the case but mods have stock calipers and therefore not as good of brakes as a LM and maybe they don't produce enough braking ability without really pushing hard on the brake pedal when bouncing to notice a difference.

3. Limited travel during bouncing: You may just not be getting enough travel while bouncing to make this show up. This could be anything from stiffer springs, stiffer wheel rate (due to spring placement, leverage, and angles), or pullbar/decell control devises. If the pullbar has tension/preload and depending on what you have for a decell devise it may be making the rear suspension stiff from ride height down making travel during bouncing limited.

I haven't ever bounced on the back of a mod with floated/non floated brakes so I can't say if it is easier/harder to notice the difference. However it will "TRY" to lock up the suspension as when traveling far enough the cage has to rotate/index and with the caliper attached to the cage (with foot on brakes) the caliper is trying to stay locked to the rotor therefore the cage doesn't want to rotate/index because the caliper is trying to hold it in that position.

I will say that if the car is on the hook (LR SPRING BEHIND) that you will likely not notice this on the left side anywhere as easy as if the LR spring was in front. The right side is the most easily noticed side if the LR is behind. So if you on the hook just bounce on the RR corner of the car with and without the brakes on.

If you have your bar angles on the right side so it has little indexing (I.E. little upper bar angle and the lower uphill) you will have a hard time noticing it unless you are able to move the suspension a fair amount while bouncing. On a LM with typical bar angles and lengths this shows up somewhat fairly easy if you are on the softer side on the RR spring.

If you are bound and determined to see if I'm right: Jack the car up and put on stands and remove the shocks (both sides) and the spring on the RR, then lift the RR up and down (simulating travel up and down)by grabing it and see how easy it moves then do so with someone smashing on the brakes. It would probably be easier to notice if while you are moving it up and down to have someone apply the brakes while your moving it. That sould be pretty noticiable. I would look to see how much the cage is indexing, by putting a mark on the cage and a corasponding one to the retaining ring, that way you can see if the marks are moving away from one another. If they stay lined up then the cage isn't indexing (due to above reasons) and you will not see a difference.

[dirtmod]

Thanks, that makes sense. I am just going to clamp brakes both sides and run it.

[grunt4]

I pushed down on the back of the car today with no brake, then had my crew chief step on the brake while I pushed down on the back of the car again. I could tell absolutely no difference, I even bounced up and down on the rear bumper and it was very free. I thought it would lock up the rear of the car with the brakes on.

I believe this test needs to be more dynamic like the brake rotor needs to be stopped to apply or remove force to the floater/birdcage/bar location.