Brake bleeding experience

[Duvalof]

Hi Friends,

Finishing my rear brake upgrade i am still concerned by a bleeding problem. Pedal remains spongy and very long (touch the firewall). Any of you experienced that in the past and solve it ? /ubbthreads/images/graemlins/confused.gif

I have the following setup:

-GTD pedal box upgraded with 5.1 pedal ratio
-2 Girling 0.625" MC with brake bias
- Front set: Wilwood Superlite 4 pots
- Rear set: AP Racing 4 pots
- Hydraulique hand brake with Girling 0.7 MC (correctly connected = input at the rear output near the lever)

I tried to bleed with the old 2 men method, no bubbles any more in the circuit but i suspect some in the MCs impossible to flush. Is it necessary to prefill them before car assembly?
Does the easy bleeder with pressure inside the brake circuit better than the old method ?

I must say that i am a bit lost, i checked each nipple, everything is brand new, so where is the trouble?

Tx in advance for your advice /ubbthreads/images/graemlins/flehan.gif
Cheers
Fred

 

[Paul W]

I had the same problem on mine and found that raising the rear of the car 6 inches or so helped the air escape to the rear.

 

[ChrisL]

Fred,
The rule of thumb that I use for determining if there is air in the system is to pump the brake pedal quickly. If the pedal rises as I do this and then drops again after I stop, then I take the view that there is most likely air in the system. If not, then I take the view that there is probably a mechanical or design issue.

Also as a long shot, if for some reason your pads are not sitting parallel with your rotors, then you will feel sponginess, but they would have to be way out to have your pedal drop to the firewall.

 

[Howard Jones]

How about you try this, bleed rear system with bias set to full rear, then bleed front system with bias set to full front.

If that don't work then bleed masters thru with out the rest of the system(s) hooked up. You will need to disconnect the peddle so that you can pump one at a time.This will get all the air out of the masters. Then go to the rears. Make sure the bleed valve on the caliper is up, you make need to disconnect them from the hub. Then do the front same thing bleed valve up(top of the caliper). Also the wilwoods need both sides of the caliper bled. Do not assume that doing one side does the other. I don't know about the alcons. But if they have more that one bleed valve then use them all.

Good luck.

 

[Frank Catt]

Fred, you may also have a problem with incompatable components in your braking system. 5-1 PEDAL RATIO/0,625 MASTER CYLINDERS/WILWOOD SUPERLIGHT FRONTS/AP RACING REARS ETC. are you running servos ? and are the rear calipers underslung on the upright ? Frank

 

[Sandy]

I had the same problem with my 65' Mmustang when I replaced all the lines and calipers with Willwood stuff. Went out and got one of the $25 'Mighty Vac' hand pumps which came with fittings for the caliper bleeds. Topped off the masters and 'sucked' out a bunch more air then by the pedal pumping method. Also didn't need 2 people for the job. Did waste a bit more of brake fluid, but brakes came up rock hard after doing it a couple times.

Sandy

 

I newer use the pedal when bleeding brake system. I fill the master and use a radiator perssure leakage checking handpump. Those pumps have a pressure guage. Select a pump cap that suit the brake fuid reservoir, those pumps have a number of caps. I pump up a 10 psi pressure that is held by a back valve in the pump. I then bleed the caliper in a normal manner.
Use no higher prssure than 15 psi, the fluid wil rusch in the line and may create steam that gives the same effect as trapped air. And it appere like newer getting rid of the air in the system. A extern pump also have the advantage of not create reverse suction in the system. IF, using the pedal, NO more than hand power should be used.

While driving there is no problem using any leg force, since the fluid hardley move in the lines. System is not pressure sensitive, only fluid-rusch sensitive.

Of cours, on may use an air system, just whatch the pressure.
Goran Malmberg

 

[Duvalof]

Gents,

Firt of all, thank you for your replies and sharing your experiences. So points i want to highlight for a better understanding:

Rear calipers are on the bottom (old GTD uprights) but i disassemble them for the bleeding to put the valves on the upside.

I don't use anymore servos (bad feeling)

As Franck metionned, i was wondering if 0,625 MCs are not too small for a 5.1 pedal ratio. I made a quick calculation on my setup and discovered that i need 12mm travel of the piston MC for a 0,2mm travel on the pistons calipers ! I don't know exactly how far the pads are from the discs but it makes me wondering...

Other point, the hydraulique hand brake is very efficient and hard, so i think there's no air trapped into the rear calipers. When the handbrake is "on" if i pump 3 times on the pedal it comes also very hard and short (i think it's logical as the circuit is closed).

The last solution i see is to use Goran's solution by putting the circuit under pressure, my only concern is to find a cap for my brake fluid reservoirs. I want to drill a cap and put a tire valve on it to achieve my task. If it doesn't work the last thing i see is that my MCs are too small ...

I'll keep you informed ... /ubbthreads/images/graemlins/banghead.gif

 

[Bill Musarra]

How old are your master cylinders? Could they need rebuilding from worn seals? Just a thought.

Bill

 

[BenL]

[ QUOTE ]
The last solution i see is to use Goran's solution by putting the circuit under pressure, my only concern is to find a cap for my brake fluid reservoirs. I want to drill a cap and put a tire valve on it to achieve my task.

[/ QUOTE ]
You can make a "universal" adapter by taking a bicycle inner tube (get the fattest tube you can find) and cut it in half opposite the tire valve. Tie a knot in one end and place the open end over the open reservoir. Use a hose clamp (jubilee clip) to hold it in place. Then use a bicycle pump to inflate the inner tube.

(Don't forget to periodically remove the inner tube to check the fluid level)

 

[Rob]

Food for thought guys... if you are using air over hydraulic pressure for bleeding you MUST keep a close eye on fluid level, as you can easily introduce air into your system if the fluid runs short. For this reason it is generally suggested that you use fluid pressure (i.e. hydraulic bleeder ball) or a vacuum system with a drip feed.
I personally have a "Vacuula" system with the drip feed. It was much cheaper and takes up less garage space. It works awesome, saves a tone of time, always have a rock solid pedal first time out and best of all I don't have to yell in from the garage "honey can I borrow your foot for a minute to bleed the brakes again".

 

[Duvalof]

Gents,

Some news about this braking trouble. As Franck Catt mentionned upper it seems that my master cylinders are too small. I used 0.625" Girling MCs and the pedal travel was very high, i changed one of those by a 0.7" (previousely bench bleeded), incredible how such few increasment in Ø MC can change the feeling ! Now travel is reduced by half and pedal is strong.
Now i only have to buy a new 0.7 to fix defenitly the problem.
If my experience can help !
Furthermore thank you all for your advices and your experiences. /ubbthreads/images/graemlins/beerchug.gif

 

[Murray Cowley]

Good to know you have it sorted Fred. /ubbthreads/images/graemlins/banana.gif

 

The caliper has a big influence on pedal-master cylinder lever. If we got 4x1,3/4 caliper, there is a 6200mm2 pistonarea. For two calipers we got 12400mm2 then.
A 4x1,5/8 caliper makes for a total of 10700mm2 area.
A 5/8 masrter is 198mm2 and a 3/4 is 285mm2.
12400/285=43,5.
12400/198=62,5
10700/285=37,5
10700/198=54,0
A pedal ratio of 1:5 makes for a total of...
5x37,5=187,5:1
5x43,5=217,0:1
5x54,0=270,0:1
5x62,5=312,5:1
This is for on single axle.
Then we must figure that this total ratio should match the weight distribution of the car under braking condition.

I should suggest the ratio to be in the order of 150:1 to 200:1 for a manual system for a 2500 pound car.

There are a lot factors that influence the firmness of the pedal. However, witha pedal to caliper ratio of 175:1, the pedal should be a rock, or else there is something wrong within the system.

312:1 ratio makes for a almost powerassisted pedal effort feeling. And is not recomended for a sportscar, and dosent exactley gives a brick pedal.

Goran Malmberg

 

[Duvalof]

Some comments after this first run test tonight /ubbthreads/images/graemlins/driving.gif, the car didn't run since last May now !

I was a bit desapointed to discover that my rear brake upgrade didn't give as much satisfaction i was expecting for /ubbthreads/images/graemlins/frown.gif After a modification of the pedal ratio (5.1 now); new master cylinders 0.7 front & 0.75 rear, big calipers AP racing 5200 at the rear with Ferodo DS 2500 pads and 305 mm AP discs (still the Wilwood superlight on the front /ubbthreads/images/graemlins/mad.gif) the brake feeling remains the same !!! It is written somewhere that this car won't never stop as a good race car .... /ubbthreads/images/graemlins/banghead.gif

My best thing was to discover the improvent of the steering by adding 1 cm shims under the steering rack, the car is much more precise now, and it cost me nothing compared the 1600€ thrown in the brakes /ubbthreads/images/graemlins/cussing.gif

 

[Frank Catt]

French Fred, just pop over the channel and come and see us, Belgium Fred does it all the time and we usually sort his problems out ! Frank

 

[Tim Kay]

Fred,

With an upgrade of my own in mind and similar to yours, what size wheels are you running. If 15", I would like the part numbers to the Wilwoods you are using. Both caliper and rotor as well as the AP's. If your using larger wheels then chances are your brakes are to big to fit inside a 15" wheel.

Thanks in advance.

 

[Howard Jones]

Fred are you saying that you have larger rotor/calipers on the rear than the front?

I have superlight 2A's on my car. I have used the same size calipers/rotors on all 4 corners and have been able to get a very good ballance with a proportioning valve in the rear line.

I have used wilwood HD curved vane 12.19 X 1.25 rotors all the way around.

At this point I am going to leave the "stock" GTD master/sevros/peddles on the car as all seems to work pretty well.

I havd planned to go with a complete peddle box and twin masters later. We'll see, maybe later when the funding gets better.

Back to your car. Are the brakes/peddle spongy even if you pump them up? Or do they pump up and become firm? Do you think all your physical mounts like the caliper adapters, peddle box mount, masters mounting to peddle box, are good and strong? Maybe you have something bending under load.

Is the peddle box bolted thru the floor? Or is a hanging type? The floor of GTDS are only sheet metal and fiberglass unless you have added some sort of frameing to bolt the peddel box to.

I would try pluging one end of the car at a time and then evaluating peddle feel.

Lastly I would have though that the larger master would be on the front brakes. could you review for us the cylinder sizes. Masters front and rear and calipers front and rear?

What size rotors are on the front?

What kind of brake fluid is in the system? Did you mix types? Silicone and regular mixed will really screw things up.

 

[Duvalof]

Ok Guys i'll try answer all questions, first of all Frank if think about coming and seeing you in UK with the car !

Setup is as follow:

Original GTD pedal box with brake bias and twin MC, the barke pedal is modified for a 5.1 ratio. Fitted as original, not on the floor.

MCs are 0,7 Girling front and 0,75 Girling rear, hydraulique handbrake is 0,685

Fornt brakes are Wilwood Superlignt 4 pisotns 4x44 mm (first generation w/o steel bar to maintain the pads) rotor are 305 x 32 mm Wheels in 15"

Rear brakes are AP Racing 5200 4 pistons 2x44 2x38 first pistons are the 38
rotor are 305x28

No drilled rotors only vane vented.

PADS are DS2500 on the rear and can not say on the front

Brake fluid is Ferodo Dot 5.1, AP 600 is too boring to bleed regularly

Pedal feel is good , but deceleration is not hard enough

The last thing i see is to change front pads after that ....only god knows !

 

[Sandy]

Did you use the supplied SL pads from Wilwood? I made that mistake with the 65 Mustang. It has Wilwood SL6's (same pad size as the SL4's) on the front wtih 13" Rotors and they got spongy almost immediatly on the track. I changed them out with one of the 'J' Compound Pads which made a huge difference in fade and pedal feel. They are more race then street, but should not be a problem on the street (Might squeel a little). The guy at Wilwood's tech department said to throw out the pads that come with them /ubbthreads/images/graemlins/smile.gif

I'm running Dual CNC 3/4" Masters with residual presure valves on the end of the masters. The masters use a balance bar for adjustment not the presure valve, not sure how that might factor in. The fronts are Wilwood SL6's with the J compound and the rears are Dynalites (much smaller) I think with the less grabby street compound due to the axle hopping nature of the mustang.

Not sure if this at all relates /ubbthreads/images/graemlins/smile.gif The front pads were the most dramatic change in any case.

Sandy