AP Trunnion Balance Bar (CP5520)

[BryanZH]

Hi Guys,

I am designing the brake system for the new car and planning to use AP Trunnion Balance Bar, CP 5520, but I am not quite sure how it exactly functions.

Firstly, the brake bias is still change purely by changing the moment arm of the balance bar? From the installation guide, it said 5 turns max on the left and right, so am I right to say the moment can be change on the left or the right independent of each other?

It also do not have any jam nut, anyone has any idea how it the bias bar setting secure?

The initial setting of the balance bar can be shrew at an angle of max 13 degree. This angle adjustment is for the difference of stroke length between the front and rear master cylinder as a result of the difference in piston bore size. This help to remove cocking effect?

Hope someone can give me some guidance here, I want to clear the unknowns before I decide to put in $$$$ into it.

Thank lots in advance!

Link to Trunnion Balance Bar Installation Drawing (http://www.apracing.com/car/drawings/cp5520_3cd.pdf)

[terra_dactile]

Hi Brian,
With a trunnion style bias bar the master need to be manufactured with a spherical at the end to allow them to pivot, you can not use fixed master so rthe concept does not work,
On a standard cheap bias bar usually the rod ends on each master do not move and the center section or spherical inside the tube that is welded to the brake pedal moves towards one of the two master inorder to give more load to that side since the moment arm decreases.

On the trunion set up the masters always stay the same distance from each other how ever if seen from the top view of your car they will moveleft to right as a pair, as the masters on the other end can move becaus ethey have a pivot. The ideal setup is to have your brake system designed so that when the bias bar is setup at 50:50 or no bias, that the your system has enough bias to be close to the range you desire, ways of doing this are different sized masters or caliper bores. The idea behind the 50:50 being ideal is that as the bias bar is adjusted away from centered, the efficiency dereases substantially.

In our 2006 car we used a cheap standard bias bar that you can buy from chassis shop or any other race store for abot 60 $ US

Testing and data aquisition of the pressure in the front and rear lines showed to us that the bias would vary anywhere from 57-65 % this is very big and could cause serious implications for vehicle dynamics as depending on the force applied the bias did not stay constant. There was less variation at higher loads.

The system we use on our current car uses tilton masters and bias bar mechanism, its probably 8-9 times the price just for the bias bar but, believe me it is worth every penny.

The feel of the pedal compared to last year just using the tilton 77 series masters compared with tony Kart masters is day and night.

I hope that i have clearly explained how the AP Racing bias bar works if you have any other question feel free to post again or contact me directly.

Jude Berthault
ETS FSAE 2003-Current
Team Captain & Vehicle Dynamics Leader

[skillet]

or you could look into manufacturing your own bias bar

[Pete Marsh]

Hi Brian,
The angled setting of the bar at rest should be so it is as square as possible when under typical load. This should help to reduce the losses, espesially with the cheaper tube style bars.
The bar you have may be intended for remote cable opperation and there is normally a detent in the remote knob, just a possibility.
We make our own bar in a variation of the trunion style that works well.

Pete

[BryanZH]

Thanks guys, I think I have a better idea how the trunnion bar work. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Actually, we are trying to make our own pull type master cylinders, which we are now manufacturing our prototype for testing, and we plan to use AP pull master cylinder as our back up in case our self made master cylinder don't work out at the end of the day. So, we are trying to design the pedal box around the AP master cylinder, hence we decide to use the particular trunnion balance bar. Anyone tried having a pull master cylinder brake system before? Packing seems to be a big problem.

Pete, you say you guys did your own trunnion style balance bar, mind sharing a bit more in sight? Did you use needle bearings also?

[markocosic]

Pull type cyilnder work well for overhung pedals/top hinged pedals packaging wise. Push tends to work better for floor hinged pedals.

If you can live with the packaging (more difficult than the spherical at each end jobs) the CP2623 master cylinders from AP are an absolute steal at $140 the pair - exactly the same performance as the others, gorgeous short cutoff, and provided that the pushrods are kept long no issues with linearity either.

The AP trunnion is gorgeous, but well pricy for what you're getting! http://fsae.com/groupee_common/emoticons/icon_redface.gif

[Pete Marsh]

Hi Brian,
No, we used a DU bushing on the pivot.
The masters are also pull type in a floor mounted sled which packages pretty good I thought. I don't have any pics (and the car is on the water) but plenty were taken in the US if someone wants to put one up.

Pete.