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| bomar76 | Brake bias spring | ||
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Guru Newb
 
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Son and I got his 87 out of storage temporarily this weekend to get a head start on spring projects....
MAN!!! I have to say the brake bias spring swap has to be the single best bang for the buck upgrade to do to a vette....the difference in stopping is night and day, and all for $20 or so. Holding that damn spring in while attempting to reinstall the clip appears impossible even with an arbor press, but somehow I got it on about the 3rd try. $20 seems insane $$$ for that little spring, but money well spent. It is worth $1000. |
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Posted on: 2009/3/8 22:01
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| bogus | Re: Brake bias spring | ||
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Grand Imperial Pooh-Bah
 
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I have it and really like the balance it provides.
Shockingly effective. |
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Posted on: 2009/3/8 22:54
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| Matatk | Re: Brake bias spring | ||
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Webmaster
 
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I still have to get one after my c5 upgrade. I've just been too lazy to order it. Thanks for the review.
Matthew |
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Posted on: 2009/3/8 23:06
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2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
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| Jeffvette | Re: Brake bias spring | ||
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Elite Guru
 
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Mine is still sitting in the MC which is sitting on the shelf.
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Posted on: 2009/3/9 0:44
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| flyboy | Re: Brake bias spring | ||
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Elite Guru
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I had a couple scary episodes before the spring install. My asphalt drive, downward slope, slick surface. I'd apply the brakes, the front would lock up, the rear tires would keep turning, skidding me toward my garage. I didn't know what was happening. Fortunately, I shifted to neutral before any damage was done.
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Posted on: 2009/3/9 1:17
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'91coupe, LT4Hotcam, some other stuff. If it's too loud, you're too old. "He works on old cars, then junks 'em" |
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| Dale1990 | Re: Brake bias spring | ||
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Senior Guru
 
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That's interesting. I really didn't notice much of a difference when I installed mine.
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Posted on: 2009/3/12 22:58
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86 Coupe: SR 383 90 Convertible: Stock L98 06 Z06: Stock LS7 |
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| Matatk | Re: Brake bias spring | ||
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Webmaster
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Jeff, you should send it to me so it can sit on my shelf. Matthew |
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Posted on: 2009/3/12 23:01
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2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
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| bomar76 | Re: Brake bias spring | ||
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Guru Newb
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Quote:
It was a night and day difference. |
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Posted on: 2009/3/13 1:31
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| CentralCoaster | Re: Brake bias spring | ||
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Senior Guru
 
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Quote:
After I put my huge brakes on front, the car wouldn't stop for shit. I half expected it, because I was screwing the bias up badly with the large piston sizes, but it was just terrible. My 60-0 braking distance increased from ~130 to 160 feet. I put in a new bias spring (stiffer than the DRM) and got enough rear brake to stop in 115 feet. Obviously don't do what I did in a car with stock brakes, or you'll probably experience rear lockup. |
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Posted on: 2009/3/13 1:47
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1985 Z51, ZF6 |
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| Dale1990 | Re: Brake bias spring | ||
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Senior Guru
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Quote:
I can see how there would be a significant difference in that case - you went way outside the stock specs. On my car, all I did was upgrade to J55s and refresh the rest of the parts - Hawk pads, new stock rotors, new (rebuilt) hydraulics. The BB spring was done last and all by itself, tho. I can't say there was a night and day difference in braking during spirited DD duty with the occasional panic stop. If I tracked the car, maybe I would have noticed. There is a little more dusting on the rear wheels. |
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Posted on: 2009/3/13 13:54
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| BillH | Re: Brake bias spring | ||
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The Stig Moderator
 
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CC.Where did you get a spring stiffer than the DRM? It would interesting to bench test the bias on your car to see roughly where it's at. Do you think your Wildwoods are a better setup than the C5 calipers? |
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Posted on: 2009/3/13 14:30
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| CentralCoaster | Re: Brake bias spring | ||
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Senior Guru
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I've tested the line pressures at the calipers, I have it written down somewhere. I don't have stock values to compare with.
I checked mcmaster carr for springs, and used the free length and initial compressed length to calculated the preload and make sure that was close. I bought a few different types and checked the spring rates relative to each other to try and determine the actual rate, because I know they can vary out of the box. I *think* the preload effects the knee point, and the spring rate effects the slope after that. An infinitely stiff spring would have no slope. http://www.stoptech.com/tech_info/wp_proportioning_valves.shtml This shows a bias curve on a truck where the bias spring preload increases as you load up the bed:  So, my bias curve probably isn't ideal at low braking levels, and probably gets me faster front pad wear. It would be nice to compare the bias curve and see what size spring has what effect. I wanted to bench test the various stock m/c's awhile back but only got one donation and it wouldn't hold any pressure at all. |
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Posted on: 2009/3/13 15:02
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| CentralCoaster | Re: Brake bias spring | ||
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Senior Guru
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My springs rate is 110 lb/in.
The DRM spring has 30% more preload than stock and is almost 50% stiffer. And mine's way beyond that. I have a few extras in between if you're interested. Ideally though, I'd actually need MORE pressure to the rears than front. Which is one reason I want to just put larger diameter rotors in back. Here's my bias curve. I don't know what the hell was going on at the high end of the curve, maybe the rear caliper was sticking or something. The orange line is an "equal force" line, meaning those pressures get you a braking force that is proportional to the weight available on that particular axle. So, at lockup pressures (generally 1400 psi or so) that ratio of front/rear would lock at the same time. My fronts lock at about 800 psi though, lol. I also figured out the ideal curves for other setups, but the spreadsheets a mess. Attach file:  110biascurve.GIF (6.72 KB) |
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Posted on: 2009/3/13 15:14
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1985 Z51, ZF6 |
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| BillH | Re: Brake bias spring | ||
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The Stig Moderator
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Yea, it's a ton of work when you're using a single master cylinder. Longacre makes a brake bias panel for racecars that has 2 pressure gages in it.
I've been kicking around, in my head, designing a dual master cylinder setup for C4s that could be used with the power booster. You'd probably have to eliminate the ABS. Does that heavy spring do anything to the function of your ABS? |
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Posted on: 2009/3/13 19:59
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| CentralCoaster | Re: Brake bias spring | ||
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Senior Guru
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1985, no abs. Although I'm not sure these early abs systems would be smart enough to know any different. I think they just look for wheel slip and then dump the brake line pressure, whatever it happens to be.
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Posted on: 2009/3/14 7:27
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1985 Z51, ZF6 |
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| BillH | Re: Brake bias spring | ||
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The Stig Moderator
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That's cool, wish mine had switch,like the ARS, to turn it off. ABS is fine for my Silverado on the street but, I hate it on the track. |
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Posted on: 2009/3/14 15:39
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| CentralCoaster | Re: Brake bias spring | ||
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Senior Guru
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I wish I had it on the track. All it takes is a few mistakes to flatspot and destroy $400 worth of tires. The ABS really limits rear brake though.
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Posted on: 2009/3/14 17:56
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1985 Z51, ZF6 |
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| BillH | Re: Brake bias spring | ||
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The Stig Moderator
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True but, that's part learning how to threshold brake. And learning this is one of the last skills that newer track drivers master (if they do at all). And the older ABS on C4's isn't that good = slower lap times. We spend a lot of time working on the bias, setting it up static at the shop and doing threshold brake runs on a test day. Flat spotting a set of tires is part of the learning curve, I'll bet you haven't done it the second time. Kinda like, you didn't kick butt the first time at the kart track, but now????? |
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Posted on: 2009/3/15 13:11
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Every man dies but not every man lives. |
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| CentralCoaster | Re: Brake bias spring | ||
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Senior Guru
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Did it once at an auto-x practice, then twice at the track a year later. A few times I even blew the entire turn. Basically everytime I get better at the turns before it, I'm carrying more speed down the straightaway and have to relearn the braking zone. I was trying to run it at 10/10ths though, it's not as if it caught me by surprise.
I flat spotted it at say, 12 oclock and 2 oclock, so there was two low spots with a high spot in the middle. Felt like driving on squares. It's tricky, because i have to nail the brakes hard at 100+ mph, and then actually ease off them once the car starts slowing down in order to prevent lockup. Most other people ease "into" the brakes, which is a waste of time. |
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Posted on: 2009/3/15 14:57
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1985 Z51, ZF6 |
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| BillH | Re: Brake bias spring | ||
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The Stig Moderator
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Quote:
Tricky, yes. Most of the HPDE drivers either brake too early (some way too early) and "ease" into the pedal. The others stomp on the pedal which is almost as bad. Stomping on the pedal is a good way to get lockup, it also slams the front end down & screws up the handling just before corner entry. Threshold braking is almost logarithmic in pedal application. If you're easing up to prevent lockup, you may be doing threshold already. Most guys don't understand how important braking is to your lap times. What's nice about an open wheel car is that you see the way the front tires are behaving every time you hit the brakes. they start to "strobe" just before lockup. |
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Posted on: 2009/3/15 15:30
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