Back in 2006 I designed an adapter that was a direct bolt in, to add adjustable rear brake proportioning. However I decided at the time that I didn't want to sell outside my local area, but I have now changed my mind. I have four adapters for sale which are the last of my stock. Two are for the (Edit to read 13/16" or 21mm End Cap) model year and the other two are for a (Edit to read 3/4" or 19mm End Cap) model.
********* Edit for End Cap size instead of year of car *********** The 13/16" / 21mm (early model) adapter allows you to add upto 3 times more rear brake bias The 3/4" / 19mm (late model) adapter allows you to add upto 4 times more rear brake bias
The price is $120 plus $10 shipping (This is the revised shipping price) or if you want a tracking number $25 shipping (Edit shipping charges: $25 was for UPS and since it seems there will be also COD required to cover the US tax and UPS USA shipping (brokerage fee) I will ship these though Canada Post/USPS instead for $10)
Latter I will upload a youtube video showing the installation, which is a 15 minute job.
[This message has been edited by aaron88 (edited 01-23-2013).]
I was just going over my notes from 2006 and it seems as though some of, if not all of the 87's use the newer valving. My notes say in order to determine if you have the newer or older valve you can tell externally by the size of the end cap (nut).
Check the size with a wrench or socket: 21mm or 13/16" is the older valving
19mm or 3/4" is the newer valving
Thant's what I need to know when you order an adapter, instead or the model year.
The only question I still have after watching the video is how to calibrate the bias? It seems there isn't much you can do except stand on the brakes and readjust until the rears lockup, then back off a little. Too much rear bias can be a bad thing but that's what we get with old technology.
That is basically it. The only real way to know is to use it in the exact conditions you want it to perform in. However there is a good fast way I found that allows you to get a very close calibration in short order.
Use an parking lot, and a friend watching from the outside on the passengers side (the passengers front tire is usually the first to lock up). Get upto about 20mph (30kph) hit the brakes hard. What I do is increase the braking pressure so that the wheels lock up only once I'm almost stopped. That should stop the tires from flatting off. The first run should tell you what tires lock up, and in what order. Your spotter from the outside will tell you that. If the front locks up first dial up the rears, if the rears lock up first back off the adjuster a bit.
Everyone is going to have a different comfort zone when it comes to how soon after the fronts they want the rears to lock up. For me It's very close.
Also, something else you should consider is adding an adjustable link to one end of your front (and rear if you have it) sway bar. That way you can make adjustments to the side to side weight distribution so that both front (and rear) wheels will lock at the same time. A threaded rod is all you should need (usually on the drivers side). To check the weight distribution you use the same method.
If you look carefully at your tires and markings on the ground you can do all these adjustments by yourself. That is another reason I like to use low speeds and have the wheels lock just before stopped. You don't even have to measure. You should be able to see it clearly.
It's winter here so I can't make a video, but maybe in the spring. Or maybe I can find something else on the net somewhere to link in.
All good idea's. However, in my case the 20mph test wont work. I'm running the car for autox only and have done a lot of mods. One is the tire size. I'm running 225/17 front and 255/17 rear with very sticky tires. I also have the 16" corvette rotors. With the rest of the system stock I can't get the tires to lockup except when I transfer weight during a turn. And it's funny you should say the passenger front tire is the one that usually locks up. That's the only tire I currently have a flat spot on. With the extra weight in the rear (3800 eng) and wider tires I'm sure I could use more rear bias. I'm just not sure how I'll know the setting is right except maybe under race conditions.
All good idea's. However, in my case the 20mph test wont work. I'm running the car for autox only and have done a lot of mods. One is the tire size. I'm running 225/17 front and 255/17 rear with very sticky tires. I also have the 16" corvette rotors. With the rest of the system stock I can't get the tires to lockup except when I transfer weight during a turn. And it's funny you should say the passenger front tire is the one that usually locks up. That's the only tire I currently have a flat spot on. With the extra weight in the rear (3800 eng) and wider tires I'm sure I could use more rear bias. I'm just not sure how I'll know the setting is right except maybe under race conditions.
I purchased one of these to play around with on my LS4/F40 car.
I already have an air cylinder setup that I can use to load the brake pedal with a consistent and measurable amount of force along with a break fluid pressure gauge for the calipers to measure the pressure at the calipers. With these two tools, I plan to collect the brake pressure (front/rear) for the stock setup for this car (I already have it for another 88), then install the tool and start measuring the % change based on flats (turn the nut 1 wrench flat) and whole turns. Once I have the gain scale figured out, then I will start testing for lockup conditions. I will be looking for 3 settings: stock for daily driving/rain, moderate increase for braking while turning on dry pavement (autocross/road coarse), and maximum rear braking for stop box type competitions. Once I know the # turns/flats to obtain these 3 settings it will be quick to dial in the optimal bias setting for what I am doing at the moment.
Since the stock fiero calipers are the same diameter front/rear brake pressure difference = brake bias. On the 88's the low input pressure results in about 75% rear braking, but that number drops to 55/56% and stays there past a certain input pressure. This devise should not change the 75% starting point or the 56% ending point, but it should allow the 75% level to remain for higher pedal input levels before tapering off.
On my 88 when I had stock brakes, wheels and tires my setting was 4.26mm or .168in compression, which was 3.02 full turns in (about 400psi rear pressure at the knee point). More information than that is isn't useful because that number changes with different brakes, calipers, tires, driving surface, width of tires, weight, on and on.
By my calculation the stock proportioning knee point starts at 230psi on older combination valves. My add on allows you to adjust that upto about 740psi on the late model combination valve the stock proportioning knee point starts at 200psi. My add on allows you to adjust that upto about 870psi My pressure numbers however are all calculated not measured.
Firoguru; I'm assuming that your input peddle pressure is psi on the cylinder not peddle load (lb). Is that correct?
My1stMidEng; If you can't use 20mph to test, just incrementally increase the test speed until you have a speed that works for you. But even after you have that one calibration you may want to make adjustments depending on your application. If you truly only use the car for autocross and can't lock up the tires, just crank the adjustment all the way down. Your not locking up and your maxing out the adjustment. If you are always flatting on the same tire you know there is more braking to be had by balancing your left to right weight as mentioned above.
Here is a graphical representation of the data fieroguru posted above. Thank you.
It's easier to see this way that the front brakes are doing twice the work the rear brakes are doing. Notably; I added the point "n" which is the stock knee point for the separation of the two system pressures. Also the limitations of the vacuum assist are more easily seen in graphical format. My adapter moves that knee point at 200psi upto the figures posted previously.
Also the limitations of the vacuum assist are more easily seen in graphical format. My adapter moves that knee point at 200psi upto the figures posted previously.
I was thinking that the front numbers levelled off with increasing pedal load. This is what you're referring to?
Yes, where the number level off around 1200psi (and about 700psi for the rear). After that point doubling the input force only increases the system pressure by 15%
Yes, where the number level off around 1200psi (and about 700psi for the rear). After that point doubling the input force only increases the system pressure by 15%
Originally posted by coady: ok a stock 85 gt with stock break set up, how much with this thing help?
Assuming that you also have recently rebuilt calipers, stock tires and a properly functioning vacuum brake booster. Once adjusted you should expect about 10% total system aid. Larger gains can be expected if you have brake upgrades that miss match rotor sizes and/or caliper piston areas (front to rear).
You mean as in keeping the hydraulic steering pump from an engine conversion and using that? I'd probably rather increase the rotors size, increase the booster size, decrease the MC size or maybe even try a vacuum pump before adding hydraulics. No offence to hydraulics but their messy and inefficient....work well though.
My stock is now sold out, and I have a waiting list for new manufactured units. I will order in the springs and seals that I need and make more. So to be clear, I am taking orders.
You mean as in keeping the hydraulic steering pump from an engine conversion and using that? I'd probably rather increase the rotors size, increase the booster size, decrease the MC size or maybe even try a vacuum pump before adding hydraulics. No offence to hydraulics but their messy and inefficient....work well though.
Yes, that's what I meant.
Bigger rotors (improving the input pressure to torque relationship of the system) lowers the pedal load necessary to induce lockup back into the vacuum booster's linear range...
BUT
Hydroboost pedal feedback is MUCH more linear than vacuum booster pedal feedback.
My main concern with the hydraulics is the weight. The vacuum booster weighs 2-3 lbs (must include the vacuum tube that goes through the cockpit in the system weight) while the complete hydroboost system from pump to booster could weigh 20 or more, especially considering the length of hose/tube necessary to put the hydraulic power at the front of the Fiero.
Also, the Fiero firewall needs to be stiffened significantly in order to reduce deflection at high pedal loads.
Assuming that you also have recently rebuilt calipers, stock tires and a properly functioning vacuum brake booster. Once adjusted you should expect about 10% total system aid. Larger gains can be expected if you have brake upgrades that miss match rotor sizes and/or caliper piston areas (front to rear).
sorry ive checked you post a dozen times since i asked that question and never noticed your response. if you get a free moment can you pm me with the process id have to go through to up grade the system thanks
Most supplies are in but, one supplier tells me that they don't have any more stock for the spring I'm using, so they will have to make more, which will take 4 to 5 weeks. However they have lots of the same spring .25" longer which will work with a temp re-design. So I think I'll get a several of those while I'm waiting for the rest of the springs to be made and shipped. All that being said I should be able to ship more soon. There will be no change in the appearance or operation of the adapter with the longer spring.
That is with a fierostore big brake front kit, big bore master, dual diaphram booster, new lines and hoses, and new oem rear brake calipers/rotors/pads (87gt).
Interestingly, half the adapters I have sold have been for 88's. I was expecting the ratio to be 10 to 1, but it's nowhere near that. I'm interested to see how the final numbers look. I have plans and provisions to make 100 so that should be a good census pool.
