Brake Bias - Solved

[scrubs]

I am holding off closing the top of the footbox until I can solve this...

I have 2 reservoirs for the F/R brake systems.
Both have been bled x 4, no air.
I have moved the balance bar in either direction a fair amount.
I have moved/screwed the MC pushrods in/and out in various combos.

The best I can get is my fronts locking up a smidge after the rears. Any other ideas before I start looking at more aggressive front pads?

I still have not searched for the pad rec's, but if you have them off the top of your head, would be appreciated:)

thanks all,

j

[Railroad]

I would drive it some more. You did bed the pads per instructions?
Mine are 6 piston on the front, 4 on the rear. Not exactly power brakes, but will lock the wheels, if you put the press on them.
I decided, I too would like more stop, less effort.
Wilwood does not provide a street pad for the 6 piston caliper, IMO. I think the pads I found were D30 from Hawk.
The effort is reduced and you have strength left to modulate the stopping. Under heavy braking they do made a groaning sound, which Hawk replied, Normal.
I am happier.
If the auto cross guys jump in, you should be some good input and part numbers.
good luck,

[scrubs]

I would drive it some more. You did bed the pads per instructions?
Mine are 6 piston on the front, 4 on the rear. Not exactly power brakes, but will lock the wheels, if you put the press on them.
I think I decided, I too would like more stop, less effort.
Wilwood does not provide a street pad for the 6 piston caliper, IMO. I think the pads I found were D30 from Hawk.
The effort is reduced and you have strength left to modulate the stopping. Under heavy braking they do made a groaning sound, which Hawk replied, Normal.
I am happier.
If the auto cross guys jump in, you should be some good input and part numbers.
good luck,

Thx. They are bedded. I have the stock ffr set up.

Will test and stop some more and get it as close as I can.

[Rsnake]

I was not really impressed with the performance of the brakes either. Was like pushing on a wall. Changed to 5/8" master cylinders and it's night and day difference.
Highly Recommend.

[scrubs]

I was not really impressed with the performance of the brakes either. Was like pushing on a wall. Changed to 5/8" master cylinders and it's night and day difference.
Highly Recommend.

Thanks, Rsnake.

1) If you move both to 5/8" MC's, will the relative balance still not be an issue?
2) Is it just a pull and replace - ie same plumbing? - (edit: saw Wilwood site..appears they are the same)

thanks,

j

[MB750]

I know you're not asking me, but changing from 3/4" to 5/8" will put more leverage on the caliper pistons when you push down on the brake pedal. It will allow your brake pedal to move slightly more (for the same amount of brake pedal effort), but it will apply more force to the pads in your calipers.

And yes, pull-replace-bleed. I just did all that with my clutch master cylinder.

[scrubs]

I know you're not asking me, but changing from 3/4" to 5/8" will put more leverage on the caliper pistons when you push down on the brake pedal. It will allow your brake pedal to move slightly more (for the same amount of brake pedal effort), but it will apply more force to the pads in your calipers.

And yes, pull-replace-bleed. I just did all that with my clutch master cylinder.

I'm asking anyone:) How would this affect my balance if both are replaced? I don't care so much about the effort (not saying it would be nicer to use less), ratherr the balance/bias.

Going to go for another bleed session and messing with the pushrods, otherwise will think about the swap.

Curious, where does everyone have the pushrods and balance bar?

I started with pushrod ends flush with clevis (they were cut per the manual) and the bar centered. Trying to move things around to get those fronts to lock up first...

j

[Railroad]

Let me know how you adjust for bias. I was told by Wilwood, the threaded adjustment rod should be long on the master cyl side you want most bias.
A local, fellow builder got just the opposite answer. I have not gone back to check my adjustment and do have a remote adj knob.
thanks,

[scrubs]

Let me know how you adjust for bias. I was told by Wilwood, the threaded adjustment rod should be long on the master cyl side you want most bias.
A local, fellow builder got just the opposite answer. I have not gone back to check my adjustment and do have a remote adj knob.
thanks,

Ah, that clears it up:confused:

I suspect given my initial moves that it will be drawing the front MC pushrod back out of the clevis and the rear MC deeper into the clevis. Unless it only work when the pushrods are in the right places, I have found the balance bar to do zippo.

No car work for a couple of days, but will report back.

cheers and thanks, everyone.

j

[MB750]

The pivot of the balance bar (inside the aluminum casting of the brake pedal) moves closer to the MC you want to have LESS leverage. Another way to say what I just said is the longer end of the balance bar is on the SAME side as the MC you want to have MORE bias.

If you have two MC's, both the same size, and the balance bar is biased to give the rear MC more leverage (pressure) than the front, hitting the brake lever will push the rear MC's rod further than the front's MC. This proves more force is going into that cylinder.

Basically, listen to Wilwood on this one.

[Hoooper]

What brakes front and rear do you have?

[scrubs]

What brakes front and rear do you have?

Stock ffr.

Plan wildwood bleeding protocol tomorrow and will report back.

[MB750]

I'm asking anyone:) How would this affect my balance if both are replaced? I don't care so much about the effort (not saying it would be nicer to use less), ratherr the balance/bias.

Going to go for another bleed session and messing with the pushrods, otherwise will think about the swap.

Curious, where does everyone have the pushrods and balance bar?

I started with pushrod ends flush with clevis (they were cut per the manual) and the bar centered. Trying to move things around to get those fronts to lock up first...

j

Sorry, I missed answering this question.

My balance bar is turned 5 rotations to give more bias to the front MC. This gives me around 70/30 bias to the front MC. Be advised, only adjusting the pushrod length isn't altering the bias. All that does is moves the brake lever forward or backward (depending on adjustment). If your balance bar pivot is centered and you only move the pushrods, you haven't altered the bias at all. If you want to test this, push the brake pedal. If both pushrods go backwards the same distance, you've got 50/50 bias.

Think of two kids on a seesaw, only one's fat and one's skinny. In order for them to balance you need to move the fulcrum towards the skinny kid because the fat kid puts more leverage on the lever (seesaw). This is the same logic, you want the fat kid on your front MC side. Turning the balance bar moves the fulcrum towards the rear MC which puts more leverage on the front MC. I believe Wilwood says about a 4% bias comes from one full turn on the balance bar.

[MB750]

Here's a decent video from Wilwood on the subject, although they still don't go into much detail regarding moving the balance bar and what physically happens to the master cylinders. More of "you can move it to adjust bias..." with no more detail:

https://www.youtube.com/watch?v=ZYK4VEOae6w


https://www.youtube.com/watch?v=ZYK4VEOae6w

[scrubs]

OK, just like with almost every snag you run into, start from scratch and check your work. The fronts now lock first. Thanks to all that gave tips and special shout out to MB750 for helping me think this through. I think he needs a write up, but his posts on the subject in his build are perfecto.

1) rechecked the gap between my clevis and the center pivot. Even though the Wilwood manual says 0.2-0.25" gap, the video said 1/8"....I was at .25 so removed the rod, gave the clevis 1 spin and wound up a smidge over the video's "2 quarters" gap.

2) placed balance bar in the center (measured from outer edge of edge clevis to end of bar)

3) made sure rods were flush with clevis opening as per FFR manual

4) performed the bleeding procedure as per Wilwood: https://youtu.be/jELllXdtjdc (it went as they said).

5) took the car out noted even lock up.

6) moved the balance bar so more threaded rod was towards the front MC (where I wanted more bias).

7) Simultaneously with #6 (I think necessary to get the bar loosey goosey), I advanced my rear push rod deeper into the clevis and front was backed out of the clevis an equal amount. As MB750 notes in his thread, this results in a situation where your side of more desired bias rests further from the MC when no pressure applied. The bar will be angled. When you depress the pedal, you will note increased excursion of the "longer" side and it may come even or pass the other clevis.

8) test -> front lock up first.


I admit, I got a few bubbles from the front with the first pump of the new bleed procedure, so that may have been the primary issue, but bottom line was: if things aren't adding up, go back to the start. Will be happy to close that footbox up and move to body fitment.

My father's day win: my son got his first lesson in driving stick today and he successfully got going from a standstill and completed shifts to second. He will eventually be the owner of this thing, so it was time.

Happy Father's Day to all the rest of you.

j

[MB750]

Awesome! Glad you squared it away, and glad I could help.

[CraigS]

A couple of thoughts. 1-Regarding the length of the pushrods. Many recommend that they be adjusted so that, w/ max pressure on the pedal, the bias shaft is perpendicular to the pushrods. This usually requires adjusting the pushrod length so that, pedal at rest, the bias shaft is at an angle. 2- Regarding the gap on either side of the pedal to the clevises. This is needed so the bias shaft can go to an angle w/o binding on the side of the pedal. I was concerned about the gap being too large thinking that the bias could shift as the shaft moved around in normal driving. I think the 2 quarter's gap is correct. 3- Regarding how far the pushrods move. this is determined by MC size vs caliper piston size. IE for a given MC size, a larger caliper piston w/ need more pushrod movement. 4- I would be concerned about going to a 5/8 front MC. My front stayed at 3/4 but over the years I had 4 different rear brake setups. At one point my 5/8 rear MC was not large enough to supply sufficient fluid to fully activate the rear brakes. It was not a catastrophe as I discovered it on test drives but it only happened on full max braking. It could be much worse if the fronts had that problem though.

[MB750]

Craig

Regarding the bias changing during driving, that won't happen regardless of how much the balance bar slides back and forth. Think of how the forces apply through that bar. The leverage (bias) is dictated by the distance from center of clevis (pushrods) to the balance bar pivot. The brake pedal sends forces through the balance bar pivot regardless of where it is inside the casting of the brake pedal, and since your bias is set based on distance from clevis (pushrods) to balance bar pivot, bias is locked down.

I'm surprised you had issues with the 5/8" MC. Pushing the brake pedal does move some fluid, but it's peanuts compared to the fluid transfer in a clutch system. Brakes are more "pressure transfer" than fluid transfer. My brake pads release from the rotor maybe 1/64th of an inch. That's not much volume of fluid if you back out the math based on piston diameter.

[BEAR-AvHistory]

Think it would be a great service to the group if someone who knows what they are doing made a short video of the setting up the spacing & bar in a FFR Roadster. Also setting F/R brake bias.

When it comes to this system I an in the stumbling around group so not qualified to do it.

[Dgc333]

Think it would be a great service to the group if someone who knows what they are doing made a short video of the setting up the spacing & bar in a FFR Roadster. Also setting F/R brake bias.

When it comes to this system I an in the stumbling around group so not qualified to do it.

The videos and instructions provided by Wildwood and Tilton do a very good job of showing/explaining how to set up your brakes.

[MB750]

The videos and instructions provided by Wildwood and Tilton do a very good job of showing/explaining how to set up your brakes.

Respectfully, I beg to differ. I've watched them all and the best I could conclude was that, "You can adjust your bias by turning this rod, or buy this knob thingy to turn it from the cockpit..." but NOTHING was said about how the balance bar specifically transfers load depending on where it's positioned. Regarding the Wilwood video, I even got the impression the guy doing the video had no idea how it works internally.

Case in point, look up a few posts where someone heard two different answers from two different sources.

[BEAR-AvHistory]

Respectfully, I beg to differ. I've watched them all and the best I could conclude was that, "You can adjust your bias by turning this rod, or buy this knob thingy to turn it from the cockpit..." but NOTHING was said about how the balance bar specifically transfers load depending on where it's positioned. Regarding the Wilwood video, I even got the impression the guy doing the video had no idea how it works internally.

Case in point, look up a few posts where someone heard two different answers from two different sources.


Agree otherwise would not have mentioned it.

[scrubs]

Think it would be a great service to the group if someone who knows what they are doing made a short video of the setting up the spacing & bar in a FFR Roadster. Also setting F/R brake bias.

When it comes to this system I an in the stumbling around group so not qualified to do it.

It seems to click quickly for some, not for me:)

I was so focused on getting it dialed in that it never occurred to me. Luckily, this forum has been plenty friendly in helping me baby step through issues.

If you need help, feel free to PM me and we can connect.

j

[Dgc333]

Respectfully, I beg to differ. I've watched them all and the best I could conclude was that, "You can adjust your bias by turning this rod, or buy this knob thingy to turn it from the cockpit..." but NOTHING was said about how the balance bar specifically transfers load depending on where it's positioned. Regarding the Wilwood video, I even got the impression the guy doing the video had no idea how it works internally.

Case in point, look up a few posts where someone heard two different answers from two different sources.

This video by Tilton Racing gave me all the info I needed to go about setting up the brakes in my 33.
https://www.youtube.com/watch?v=ISLqGf0sMX0&feature=emb_title

[BEAR-AvHistory]

It seems to click quickly for some, not for me:)

I was so focused on getting it dialed in that it never occurred to me. Luckily, this forum has been plenty friendly in helping me baby step through issues.

If you need help, feel free to PM me and we can connect.

j

Thanks for the offer but we're good. Replaced the braking system, except for tubing, on the car I built in 2014. Took me longer than I expected as I forgot some of the things I did before. Chasing down specific points was a pain in the butt. Thought a good DIY from the point of view of the FFR user as opposed to the brake manufacturer would be useful.

[CraigS]

Craig

Regarding the bias changing during driving, that won't happen regardless of how much the balance bar slides back and forth. Think of how the forces apply through that bar. The leverage (bias) is dictated by the distance from center of clevis (pushrods) to the balance bar pivot. The brake pedal sends forces through the balance bar pivot regardless of where it is inside the casting of the brake pedal, and since your bias is set based on distance from clevis (pushrods) to balance bar pivot, bias is locked down....


Thanks, that is a very good point.