Ditching the power brakes, but keeping ABS

[Ipassgas]

I'm interested in keeping ABS. I have a feeling some less experienced or overly aggressive people may drive my car at some point, so I think ABS is a good idea.

But, since I'm expecting 2100-2200 pounds, power brakes are overkill, and to quote the manual will be "touchy".

Is there a reason that I can't think of why I need power brakes if I'm keeping the ABS module?

Thank you.

[DMC7492]

Hi look this thread over. Lots of ABS info
https://thefactoryfiveforum.com/showthread.php?15282-Any-ABS-updates-Anyone-have-it-working

[Hindsight]

I have working ABS without power brakes. The ABS works great. The brakes overall are not great. Pedal effort is too much and that's even with my moving the master cylinder pushrod clevis hole up even higher on the brake pedal than the FFR manual calls for. For street use, it's ok - with the right brake pads, I guess. But not for track use.

Different people have different opinions on brake pedal effort though so maybe you wouldn't mind it.

I know of only ONE person who has power brakes and that's the guy who bought the green FFR Wilwood car. I think I asked him his opinion at one point and he said it was ok - not that touchy - if I recall correctly.

If I had it to do-over again, I'd go full wilwood setup (pedals and calipers) with ABS. I'd probably use bigger rear wilwood calipers than come in the FFR kit though, if possible.

[phil1734]

Hindy - Do you run the same diameter tire front and rear? I'm still curious if a ~1 inch stagger affects the ABS or not. I've heard all sorts of hypothesis on what it could do but I'm very curious how it would actually behave on a track at the limit with all sorts of other slips and slides thrown in.

I always assumed the 15+ year old Subaru system was only looking for a locked wheel and pulsing that corner but others have said it might cut in much sooner. Could always depend on the year too... :confused:

[Hindsight]

Phil I was worried about that too but it didn't turn out to be an issue for me at all. I believe I'm running 265/35/18 rear and 235/40/17 in front, but looking on tire rack I don't see 235/40/17 anymore so it looks like they stopped making them, CRAP! closes they have is 235/45/17 which are a lot bigger. Just did some more searching and found the size is available in the V3 version of the tire. Whew.

So my rear is 25.4" and front is 24.5" diameter. That's 1" difference. ABS works perfect on the track and on the street.

[Ipassgas]

Thanks for the help. I'm a long way from that point, but I think I'll try to use both the power brakes and ABS.

I didn't get the Wilwood set up because FFR said it wouldn't work with ABS.

[Hindsight]

I don't see why the Wilwood brake setup wouldn't work with ABS. You would have to get a bit creative. Wilwood uses dual master cylinders. You'd need to change the line layout into the ABS pump. By default, the ABS pump line routing is such that one input line controls diagonal output lines - so one input line controls right-front and left-rear, and the other input line controls left-front and right-rear. You'd just change it so one input line controls front and one input line controls rear. You lose a bit of safety by doing so, in that in a worst-case scenario, your front master cylinder fails and you now only have rear brakes but I don't think it's a big deal. Anyway, after you route those input and output lines accordingly, you also have to update the ABS sensor wires to account for the change you made in the brake line routing. You would also have to fabricate a mount for the brake pedal switch onto the wilwood pedals. I think that should be it.

If you really don't want to go Wilwood, I'd probably try running the power brake booster, as you suggest. If you hate it, it's not a huge deal to remove the booster. Probably have to pull the windshield though. So figure out if you like it during go-kart phase. If you use the booster, don't move the master cylinder pushrod hole on the brake pedal. Keep it in the factory position. If brakes are too touchy, you can try move the hole DOWN a bit to reduce leverage and see if that helps.

[Ipassgas]

Thank you. I already made the hole, which is what got me thinking about it again.

I wouldn't have had the courage to try this project without guys (and girls) like you on this forum. I lurked a long time, to see what sort of community support there was.

[frankc5r]

I have working ABS without power brakes. The ABS works great. The brakes overall are not great. Pedal effort is too much and that's even with my moving the master cylinder pushrod clevis hole up even higher on the brake pedal than the FFR manual calls for. For street use, it's ok - with the right brake pads, I guess. But not for track use.

Different people have different opinions on brake pedal effort though so maybe you wouldn't mind it.

I know of only ONE person who has power brakes and that's the guy who bought the green FFR Wilwood car. I think I asked him his opinion at one point and he said it was ok - not that touchy - if I recall correctly.

If I had it to do-over again, I'd go full wilwood setup (pedals and calipers) with ABS. I'd probably use bigger rear wilwood calipers than come in the FFR kit though, if possible.

Hindsight,
The rear calipers that come in the FFR Wilwood kit are the same small calipers that are in the Wilwood WRX kit. I had to convince Wilwood to sell me rear calipers that have 2X piston size that give you
proper brakes. Some math will show you that the Wilwwod rears only generate about a 1/2 G stop with 50 # pedal pressure. All else same, the 2X Wilwoods I use generate a 0.82G stop at same 50 # pedal
pressure.

[Wayne Presley]

Frank, what part number caliper did you get?

[mikeinatlanta]

Power vs non power. My experience has been that inexperienced drivers often will not push manual brakes hard enough to lock in the first place. Seems they have muscle memory of their power OE car setups and will hit something rather than giving that extra pedal push. The MRS is that way. If inexperienced drivers were the driving force for my decision, I'd go power ABS. For me I prefer non power non ABS. I know it's a bit counter intuitive, but IMO the OP's first assessment of inexperienced drivers is backwards. Overly aggressive drivers will lock with less effort and hopefully have better control as a result.

[Hindsight]

Frank, what part number caliper did you get?

Yes, please share! Did you need to do anything else other than buy the calipers? IE are the mounts different, etc?

[frankc5r]

Frank, what part number caliper did you get?

Wayne,

I ordered kit 140-7006-CFG with the cfg meaning special config that allows swapping of parts. The kit comes with 120-9706 caliper and I asked it to be replaced with a 120-9703-RD caliper which has 3 in of
piston area.https://s6.postimg.cc/io535omrx/20171005_163043.jpg (https://postimg.cc/image/io535omrx/)

https://s6.postimg.cc/mkif1ofh9/20171006_104630.jpg (https://postimg.cc/image/mkif1ofh9/)

It comes with a paper template for cutting clearance of backing plate which is hard to use. I made a sheet metal template of caliper interference area. Picture attached. Hope that helps.

[frankc5r]

Yes, please share! Did you need to do anything else other than buy the calipers? IE are the mounts different, etc?

The kit , 140-7006, is designed to use 12.19 in rotors or 12.88 rotors for racing. It comes with nice offset adapters that position the caliper at the proper position for which rotor you use. I got e-coated rotors which
look great and eliminate corrosion. I did not check if they would fit stock rotors since I got whole kit.

[Hindsight]

Power vs non power. My experience has been that inexperienced drivers often will not push manual brakes hard enough to lock in the first place. Seems they have muscle memory of their power OE car setups and will hit something rather than giving that extra pedal push. The MRS is that way. If inexperienced drivers were the driving force for my decision, I'd go power ABS. For me I prefer non power non ABS. I know it's a bit counter intuitive, but IMO the OP's first assessment of inexperienced drivers is backwards. Overly aggressive drivers will lock with less effort and hopefully have better control as a result.

I agree with you, except in the 818, the pedal effort is just TOO high. At Road Atlanta, when braking into turn 1, and into 10a, I have to STAND on the pedal and push as hard as I can. My leg starts shaking when I do this by half way through a 20-minute track session. I could lock them up, but it's like I have to put 150lbs of pressure to get the braking I want, and 160lbs of pressure to get to full lock. You can't modulate the brakes when you are applying 150lbs of pressure on the pedal. All you can do is stand on them and let the ABS do it's thing - which isn't ideal. Plus your legs get blown out.

I do prefer the pedal feel of manual ABS brakes but only if the pedal effort is reasonable. In our 818 setup, it just isn't.

[Hindsight]

Thanks Frank!!

[frankc5r]

Thanks Frank!!

Bigger rear brakes will solve your pedal effort problem.

[phil1734]

At the expense of thread de-railing, I copied Bob and put stock front calipers on the rear. Requires a bit more trimming of the backing plate but I think for calipers, brackets, pads, rotors and hardware I was in less than $200 after core returns and you could go even cheaper if you find them at a junkyard or part-out. (And yes, Rockauto did accept the rear caliper for the front caliper core ;)) Rear rotors from a '06 Legacy GT, though there are other options if you want to go larger and spend more money.

Long story short you end up with the same piston area and reaction moment as Frank's kit and replacement parts are way cheaper and widely available.

Bob had enough pics on his build thread to get me started and I was going to do a write up on it and took pictures but the more I got into it I decided that if you can't figure it out as you go you probably shouldn't be frankenstiening your own brakes together.

In the end I went from an extremely high pedal effort (the fronts were pinched off almost all the way to try and balance the system) to one I can comfortably drive barefoot, though with a touch more pedal travel.

[frankc5r]

At the expense of thread de-railing, I copied Bob and put stock front calipers on the rear. Requires a bit more trimming of the backing plate but I think for calipers, brackets, pads, rotors and hardware I was in less than $200 after core returns and you could go even cheaper if you find them at a junkyard or part-out. (And yes, Rockauto did accept the rear caliper for the front caliper core ;)) Rear rotors from a '06 Legacy GT, though there are other options if you want to go larger and spend more money.

Long story short you end up with the same piston area and reaction moment as Frank's kit and replacement parts are way cheaper and widely available.

Bob had enough pics on his build thread to get me started and I was going to do a write up on it and took pictures but the more I got into it I decided that if you can't figure it out as you go you probably shouldn't be frankenstiening your own brakes together.

In the end I went from an extremely high pedal effort (the fronts were pinched off almost all the way to try and balance the system) to one I can comfortably drive barefoot, though with a touch more pedal travel.

That is a very good way too. I talked to Bob about what he did but decided to go the Wilwood way. Both get same results.

[Hindsight]

Thanks Phil and Frank.

Frank, to clarify, you went with the 4-piston front and 4-piston rear Wilwoods right? You did NOT go with the 6 piston fronts right?

[frankc5r]

I used the stock WRX fronts cause they are a good size
for front use. Wilwood on fronts would be fine but I thought
the stock were ok. The rears caliper piston size is THE problem on the 818. Thus I just
purchased the Wilwood rear kit with a substituded
bigger rear caliper. Good luck.

[Hindsight]

Got it thank you!

I have the 4-pot 06-07 WRX fronts so they should be adequate. Could save a lot of coin just staying with Wilwood rears instead of the full set.

[mikeinatlanta]

I agree with you, except in the 818, the pedal effort is just TOO high. At Road Atlanta, when braking into turn 1, and into 10a, I have to STAND on the pedal and push as hard as I can. My leg starts shaking when I do this by half way through a 20-minute track session. I could lock them up, but it's like I have to put 150lbs of pressure to get the braking I want, and 160lbs of pressure to get to full lock. You can't modulate the brakes when you are applying 150lbs of pressure on the pedal. All you can do is stand on them and let the ABS do it's thing - which isn't ideal. Plus your legs get blown out.

I do prefer the pedal feel of manual ABS brakes but only if the pedal effort is reasonable. In our 818 setup, it just isn't.

I think in a way we are saying the same thing. High pedal effort reduces control. Not terrible bad for the guy experienced with it, but actually increases risk of uncontrolled lockup.

[Ipassgas]

I'm going to try then with power and ABS.

As it turns out, turbomacncheese discovered the WRX booster/MC doesn't really fit with the newest 818 frame configuration. When he let me know this, I started to formulate a new plan. I MAY have hit on a way to have weak boost, in a package that bolts right up and fits. In theory, this is ideal. I have no idea if it'll work. If it does, I'll post details. But I'm still a couple of months away from knowing for sure.

[Hindsight]

Good luck and keep us posted

[turbomacncheese]

Yeah, I was a little disappointed there. I DID get it mounted, but it involved taking the firewall back apart. Maybe I had a goofy booster, who knows? The mounting studs were way too long to let the booster pivot into place.