HOW TO DO AN ADVANCED SEARCH.

Mon Jul 08, 2013 3:56 pm by Admin


For the benefit of 944Hybrids users there are two search functions available for you to use.
The purpose of this sticky is to explain the "Advanced Search" function because it is much more powerful and is the best choice when researching information.

When you log on to the site a list of options is shown in a line at the top of the page. One option is labelled "Search", use this option (NOT the search box lower down on the right).

After you click on the upper search option, a drop down box appears. At the bottom of this box is a radio button marked "Advanced …

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Brake Line Pressure

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Re: Brake Line Pressure

Post  87-944S on Mon Nov 28, 2011 7:26 pm

Here's what I have so far,

The first measurements did not have the bias bar adjusted as I think it should have, but any way:
Pedal Ratio 6.65:1

Front:
1 Inch M/C Caliper pressure M/C pressure
600 PSI 800 PSI

Rear (second pressure is with bias valve closed)
3/4 Inch M/C
400/300 PSI 950 PSI

I am not confident with the above numbers, but very confident with the ones below (above were with a Wilwood gauge, that appeared flaky, and I think I blew it out with the next measurements, I used another gauge with a range to 3000PSI)

I put in a 5/8 and a 13/16 Wilwood M/C, since I am a glutton for punishment, so another $170 invested in the experiment (we won't discuss brake fluid and absorbent clay costs)
With a comfortable foot pressure the 5/8 put out 1500 PSI, the 13/16 was about 1000. If I pressed it really hard (not sustainable in driving conditions) the 5/8 went to 2300 and the 13/16 went to 1600. I wasn't able take a drive and see how the pedal travel is, hope to do that this week. These measurements were at the M/Cs.
From what I have researched, 1200PSI is pretty typical of required disc brake pressures at the calipers, and 1400PSI should lock up a caliper. As the low pressures from the first experiment barely stopped my car, I tend to side with what I have read. I will have the opportunity to test this out, and I may slap the gauge on my Ford Escape and see what pressures I have there. In any event, what I need to feel now is the pedal travel with the current M/Cs, I expect to achieve full brake about mid pedal or so, and lock up at 3/4 or a smidge more. Lockup must occur before full pedal, I will kepp you posted on results.

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Re: Brake Line Pressure

Post  87-944S on Sat Dec 03, 2011 2:53 pm

Success, sort of. After bleeding the brakes I measured 1500 PSI at the front calipers with a decent amount of foot pressure, not as much as what I would expect to do in a panic stop. I took a quick drive down the street and was able to lock them up, but still doesn't feel quite right, a bit too much pedal travel. Currently there is a 5/8th front and 13/16 rear M/C. I will try the 0.70 unit next, that Arthropraxis lent me. Getting tired tired of bias adjustments and bleeding brakes!
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Re: Brake Line Pressure

Post  Lemming on Sat Dec 03, 2011 3:26 pm

87-944S wrote:Success, sort of. After bleeding the brakes I measured 1500 PSI at the front calipers with a decent amount of foot pressure, not as much as what I would expect to do in a panic stop. I took a quick drive down the street and was able to lock them up, but still doesn't feel quite right, a bit too much pedal travel. Currently there is a 5/8th front and 13/16 rear M/C. I will try the 0.70 unit next, that Arthropraxis lent me. Getting tired tired of bias adjustments and bleeding brakes!

I'm about to swap my front master cylinder, will intall a 5/8 in place of the 3/4 and will leave the 3/4 on the rear. With my current set up (3/4 on both ends) I cannot lock up the fronts (Turbo S brakes with Hawk DTC 70's running Hoosier R6 275's) and have to use very soft pads in the rear (rear calipers are 968 fronts).
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Re: Brake Line Pressure

Post  87-944S on Sat Dec 03, 2011 3:43 pm

Hey Lemming,

How do you have your bias bar setup? Thanks,
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Re: Brake Line Pressure

Post  Lemming on Mon Dec 05, 2011 9:46 am

87-944S wrote:Hey Lemming,

How do you have your bias bar setup? Thanks,

I had the balance bar turned heavily towards the front. New 5/8 master (front) is on but need to redo a hard line before I can test it.
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Re: Brake Line Pressure

Post  948 on Mon Dec 05, 2011 9:39 pm

Wow, I am slow to the party on this one...seems to be the story lately. Embarassed
I would like to share some calcs I did back in 2009 when I was trying to determine if dual master cylinders were the way to go. USE AT YOUR OWN RISK!!!! TRUST BUT VERIFY Smile

The comparisons are as follows:
1. Stock boosted, line pressure. 5/18 bias valve, Assumed 50/50 force split
2. Stock manual, line pressure. 5/18 bias valve, Assumed 50/50 force split
3. Balance-Bar A manual dual, line pressure. 5/18 bias valve, Assumed 60/40 force split
4. Balance-Bar A manual dual, line pressure. 5/18 bias valve, Assumed 40/60 force split

As you can see, the dual cylinder system "A" can be set-up to match the original front output. The rear falls short when the stock Bias valve is installed; if removed the pressure would be linear and close to the original rear pressure. Set-up "B" seems to fall short in both front and rear, but is more balanced?? Pushing harder would yield higher pressures.

I have been told by Tilton that pedal travel should remain less than 3" and pedal ratio should be less than 7:1.

Master Data Sheet


Front Comparison


Rear Comparison




Last edited by 948 on Mon Dec 05, 2011 10:51 pm; edited 3 times in total (Reason for editing : Added #4 Balance Bar)
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Re: Brake Line Pressure

Post  Arthropraxis on Mon Dec 05, 2011 10:03 pm

Good info. The Tilton tech recommended for stock turbo brakes 5/8in front and 13/16in rear with a 6:1 pedal ratio and a balance bar. You have the larger MC in the front circuit. Which works better?
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Re: Brake Line Pressure

Post  948 on Mon Dec 05, 2011 10:33 pm

Arthropraxis wrote:Good info. The Tilton tech recommended for stock turbo brakes 5/8in front and 13/16in rear with a 6:1 pedal ratio and a balance bar. You have the larger MC in the front circuit. Which works better?
I can't say better, but it does closely match the stock pressures for the front circuit.
Either my calcs are off or there is some other variable I am missing......
I have updated the data to include the set-up you mentioned.
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Re: Brake Line Pressure

Post  Lemming on Tue Dec 06, 2011 7:50 am

I finished up the hard lines last night and was able to do a prelim assessment (no driving yet). So, new setup is 5/8F / 3/4R running Turbo S calipers in the front, and 968 front calipers in the rear.

Pedal travel is increased and it does not require as much force to move the pedal. I will need to move the pedal up some to compensate and make heel/toeing easier. I'll be at the track this weekend to test and tune.
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Re: Brake Line Pressure

Post  948 on Tue Dec 06, 2011 11:27 am

Lemming wrote: having a rear brake proportioning valve in a race car is critical. I change my brake balance based on fuel load and track conditions.

Most 'race cars" do not use hydraulic proportioning valves as they usually have a properly set-up balance bar, MC, caliper combo.
When you watch a NASCAR/Indy car etc driver crank away on his bias knob, before doing his victory burnout, he is simply moving the balance bar. They too also make adjustments during the race using just the balance bar.
I would suppose that we see the hydraulic units in lower level racing with street cars because it is more cost effective and allows us to make adjustments without having to own two dozen different master cylinder and caliper combinations.

Do you have the pressure regulating valve installed also?

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Re: Brake Line Pressure

Post  Lemming on Tue Dec 06, 2011 11:51 am

948 wrote:
Lemming wrote: having a rear brake proportioning valve in a race car is critical. I change my brake balance based on fuel load and track conditions.

Do you have the pressure regulating valve installed also?


Yes, I have Wilwood valve on my TT tunnel. My DMC is on the other side of the firewall and I did not want to try to run a controller to it from the cockpit. Since I already had the wilwood valve, I left it in place.
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Re: Brake Line Pressure

Post  xschop on Tue Dec 06, 2011 11:53 am

I always thought the larger piston calps (36x40) on the rears were too big. 86T calps are 36x38 which are a little better on the pedal throw. That's why I went with the RX7 calipers 36x36 with bigger pads. I am still running the Rx7 calipers rear and Lexus Calipers up front (43x43). I have a 5/8" master up front and 1" on the rears and can lock them up at 3/4" pedal travel. Only way to improve besides the Carbo-tech pads installed in the Lexus calps is to run a 330mm Cayenne rotor, which BTW can be done with 6.5mm spacers on the Lexus calps.
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Re: Brake Line Pressure

Post  reclaimer on Tue Dec 06, 2011 6:47 pm

I'm sure it's been covered in one of the other threads, but for anyone that has not done the math on the brake pedal they are actually using... be warned, early verses late pedals have different ratios.
Just measuring up from the existing hole and drilling a new hole may yield a less than desirable ratio. I've measured a solid 1983 pedal and a hallow 1987 pedal. The 83 had a 4.88 ratio and the 87 had a 4.15 ratio.

I'm just putting this info out for the guys coming along later... After all the master cylinder pressures have been posted like this, someone is going to order a pair and then be disappointed because of a simple math mistake on their brake pedal.

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Re: Brake Line Pressure

Post  Arthropraxis on Tue Dec 06, 2011 7:10 pm

That has not been posted before. Do you know the difference in the actual position of the clevis hole for a late vs early pedal?
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Re: Brake Line Pressure

Post  948 on Tue Dec 06, 2011 8:01 pm

reclaimer wrote: I'm sure it's been covered in one of the other threads, but for anyone that has not done the math on the brake pedal they are actually using... be warned, early verses late pedals have different ratios.
Just measuring up from the existing hole and drilling a new hole may yield a less than desirable ratio. I've measured a solid 1983 pedal and a hallow 1987 pedal. The 83 had a 4.88 ratio and the 87 had a 4.15 ratio.

I'm just putting this info out for the guys coming along later... After all the master cylinder pressures have been posted like this, someone is going to order a pair and then be disappointed because of a simple math mistake on their brake pedal.

Just to be clear, and add to what reclaimer has shared, the calcs above were based on My stock 1986 944 Turbo, which has a solid brake pedal with a ratio of ~4.25. The relocated hole has a ratio of ~6.00....this information is shown in the first data sheet.
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Re: Brake Line Pressure

Post  948 on Tue Dec 06, 2011 8:04 pm

Lemming, how much does your car weigh and what is the balance?
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Re: Brake Line Pressure

Post  Lemming on Tue Dec 06, 2011 8:13 pm

948 wrote:Lemming, how much does your car weigh and what is the balance?

Race weight with me in the car coming off track is around 2700. 51/49 on the balance.
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Re: Brake Line Pressure

Post  reclaimer on Tue Dec 06, 2011 8:44 pm

Arthropraxis, the pedal from the 83 measured 2.2 inches center to center on the pivot and clevis holes. Also, from the pivot center to the center of the foot pad was 10.75 inches.
The one from the 87 measured 2.525 center to center and then 10.5 inches to the center of the foot pad.
I feel sure there were small running changes during the model years on top of the major changes between early and late. There may be half a dozen or more ratios... who knows.

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Re: Brake Line Pressure

Post  948 on Tue Dec 06, 2011 9:42 pm

Lemming wrote:Race weight with me in the car coming off track is around 2700. 51/49 on the balance.
So your car is ~500Lbs lighter than a street 944?...Impressive.
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Re: Brake Line Pressure

Post  Arthropraxis on Tue Dec 06, 2011 9:42 pm

Thanks. Everyone is providing such useful information. It didn't even cross my mind the ratios of the pedals would be different.
948 did you reverse the force split ratio on the dual MC B chart? It has .4 on the front and .6 on the rear. Those are great graphs to compare the force created manual vs power.
Using your formula a .70 front and a .625 rear with a 60/40 F/R balance adjustment would be close to the factory boosted setup. How do you think the pedal travel would be?
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Re: Brake Line Pressure

Post  Lemming on Wed Dec 07, 2011 7:11 am

948 wrote:
Lemming wrote:Race weight with me in the car coming off track is around 2700. 51/49 on the balance.
So your car is ~500Lbs lighter than a street 944?...Impressive.

Not really, I had to add weight to stay in class Suspect Also, 2700 is with me in the car in full race gear, so the car is closer to 2520. My 924S with 968 engine was under 2400 lbs.

You also have to remember that racers generally inflate the weight of their cars, but I would never do that lol!
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Re: Brake Line Pressure

Post  xschop on Wed Dec 07, 2011 2:46 pm

Reclaimer, That is great info on the pedal differences. Has anybody considered chopping the pedal and re-welding the foot pad lower for more leverage?
This Christmas break I am going to make adapters for the rears so the Forged Wilwood radial-mount Dynapro calipers will mount up to stock turbo rotors. They come in 4x32mm and 4x35mm piston sizes and bigger pads than the Turbo front calipers...best of both worlds for a stock MC. Very Happy
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Re: Brake Line Pressure

Post  948 on Wed Dec 07, 2011 6:02 pm

Lemming wrote:
948 wrote:
Lemming wrote:Race weight with me in the car coming off track is around 2700. 51/49 on the balance.
So your car is ~500Lbs lighter than a street 944?...Impressive.

Not really, I had to add weight to stay in class Suspect Also, 2700 is with me in the car in full race gear, so the car is closer to 2520. My 924S with 968 engine was under 2400 lbs.

You also have to remember that racers generally inflate the weight of their cars, but I would never do that lol!

My street car is just a tick under 3000Lbs on its own, so it is about 500lbs heavier than you car at race weight....
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Re: Brake Line Pressure

Post  948 on Wed Dec 07, 2011 6:16 pm

Arthropraxis wrote:948 did you reverse the force split ratio on the dual MC B chart? It has .4 on the front and .6 on the rear.
Yes, as indicated in the data chart, "B" has to have a 40/60 split; if you don't apply 60% of the force to the larger rear circuit the PSI would be much lower than even the stock manual boosted system.....

Arthropraxis wrote:Using your formula a .70 front and a .625 rear with a 60/40 F/R balance adjustment would be close to the factory boosted setup. How do you think the pedal travel would be?
The travel with a .70 would be more than with a .75. If you wanted to you could estimate the pedal travel with a calculation. You would need to know your caliper piston sizes.
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Re: Brake Line Pressure

Post  Arthropraxis on Wed Dec 07, 2011 6:37 pm

I missed the explanation of the force split front to rear. The first two manual systems I found, one on rennlist the other on the old site, both had the bigger MC on the front circuit. Why would the Tilton rep suggest to put the smaller MC in the front?
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Re: Brake Line Pressure

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