Calling brake EXPERTS
#2917299
05/01/21 11:01 AM
05/01/21 11:01 AM
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Joined: Jan 2007
Posts: 401 Norway
General 68
OP
mopar
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OP
mopar
Joined: Jan 2007
Posts: 401
Norway
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Hi! I am working on a 70 Challenger. Has poor brake performance with all type parts tried. Different boosters, MC's, calipers etc. Currently has 2-3/4" (or so) chrysler slider calipers, 11,75" rotors front, Bendix style booster and a proper MC for the set-up (all from Dr.Diff). Rear discs from Ssbc. Wilwood adjustable prop. valve in rear line and a disc-disc combination valve.
Brake feels normal and grabs great for light breaking, but when pushing the pedal further it is like hiting a wall. Rock hard pedal and not nearly able to lock the brakes on loose gravel! Flat out dangrous to drive in traffic.
I have tried all different settings on the prop. valve without change. Brake warning light works , but does not illuminate, so I don't think the valve gets tripped.
Feels like the rear brakes are hydro locking and prevent pressure to the front.
Bleeding fron brakes is easy and normal. Pedal will bottom out when pressure bled. When bleeding the rears I noticed that the pedal not will bottom out but stop where it stops when all is bled, about half way through total travel.
What am I missing here? Only things not changed is combination valve, prop. valve, hard lines front and calipers, hard lines and hoses in the rear. All boosters tried worked great and I even plumbed in a vacuumn pump that pulled 20hg to make sure there was no problem in that eria.
Had the combination valve open but could not spot anything obvious wrong.
Really ned help with this one!!!
Thanks
Last edited by General 68; 05/01/21 01:22 PM.
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Re: Calling brake EXPERTS
[Re: DoctorDiff]
#2917353
05/01/21 01:19 PM
05/01/21 01:19 PM
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Joined: Jan 2007
Posts: 401 Norway
General 68
OP
mopar
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OP
mopar
Joined: Jan 2007
Posts: 401
Norway
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Thanks Doctor😀 -Maste cylinder push rod is adjusted like you describe. There is no signs of the MS bottoming out.
-The adjustable prop. valve has been there since I got the car. Can they be troublesome? My believe was that it should not come into play when fully open. I might very well be wrong😋
-The combination valve has also been in there from the start. It is the disc-disc type with no metering valve for the front, but a proportioning valve to the rear and ofcourse the pressure differential valve with the connector for ground signal to the brake warning light. My understanding is that the prop. valve only delays fluid to the rear when panic braking. Am I wrong?
-I will check parking brake cable tension, but I thing I got that covered already.
-Can you explain "ratchet the parking mecanism"? I am Norwegian an might be a little slow😂🤣 I heard something about the rear calipers that are adjustable could cause trouble and adjusted them pr Ssbc's instructions for a gap between pads and rotor to 1/6 to 1/32".
All parts I got from you are great and out of the question😀 But they did not solve the problem. They were only purchased to optimice the system.
Front lines, rear lines and hoses, rear calipers, comb. valve and adjustable prop. valve is what is left in the system from when I got the car. To me it boils down to problems with valve(s) or rear calipers. Why will the pedal go to the floor when bleeding fronts but not the rears?
Hope yo hear from you 😀
Last edited by General 68; 05/01/21 01:27 PM.
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Re: Calling brake EXPERTS
[Re: Andrewh]
#2917460
05/01/21 07:07 PM
05/01/21 07:07 PM
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Joined: Jan 2007
Posts: 401 Norway
General 68
OP
mopar
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OP
mopar
Joined: Jan 2007
Posts: 401
Norway
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Aha! Thanks. I have not ratched the parking brake before bleeding the rear. I need to investigate more around the rear calipers.
For the MC: I have checked for freeplay but I will check again. I doubt this is the cause because I have tried three different MC's and always checked and adjusted for correct freeplay. What exactly happends if the rod is a tiny bit too long? Will it only cause pressure to stay in the system and finally create a drag? Or can other things happen?
Last edited by General 68; 05/01/21 07:12 PM.
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Re: Calling brake EXPERTS
[Re: General 68]
#2917514
05/01/21 10:38 PM
05/01/21 10:38 PM
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Joined: Dec 2007
Posts: 18,157 Mass
DAYCLONA
I Live Here
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I Live Here
Joined: Dec 2007
Posts: 18,157
Mass
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Rear discs from Ssbc. Wilwood adjustable prop. valve in rear line and a disc-disc combination valve.
You might want to keep the adjustable proportioning valve in the rear line if you can't maintain a (front/rear) 60/40 - 70/30 brake bias based on the existing caliper sizes you have, ditch the disc-disc combination valve, as far as the SSBC rear calipers, make sure they are centered on the rotors when installed, most people just bolt the calipers to the brackets, unaware that the caliper must be installed centered on the rotor, the SSBC kits use washers to shim the caliper where it's required, unfortunately SSBC kit install instructions neglect to mention this.... MikeG
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Re: Calling brake EXPERTS
[Re: DAYCLONA]
#2917568
05/02/21 08:23 AM
05/02/21 08:23 AM
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Joined: Jun 2014
Posts: 1,329 VA
dragon slayer
pro stock
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pro stock
Joined: Jun 2014
Posts: 1,329
VA
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If the rod was too long wouldn't that just block the compensation ports when brakes were off keeping residual pressure on and start to drag brakes because piston did not return fully?
Can you post a picture of your combination valve? If a late model that combination valve has metering and proportion all ready. You state you have a proportion valve in rear with brake light warning? What about the combination valve warning?
I think you just need a distribution block as mentioned. That just distributes flow and it will have warning light for failure of one side. Then with your adjustable proportion valve you can set your balance.
A Mopar MC has the primary piston for the front brakes at the rear of MC (large reservoir). The smaller secondary piston is at the front of the MC. If you open the front brake bleed valves and press brake petal the front piston can collapse to the rear piston and full travel. When you go to bleed rear, and the pedal stops that is because the front piston seems to lockup before it collapses enough to move the rear piston sufficiently.
So either you have issues with the combination valve or some other problem preventing sufficient pressure build up at either set to even lockup a wheel in gravel. Pressure gauge can help you determine where the issue is. But your statement car never had good brakes and you still have your combination valve original, would lead me to get rid of it, and get the plain distribution block in.
You can gravity bleed and I use a small inexpensive vacuum pump kit to bleed brakes.
Last edited by dragon slayer; 05/02/21 08:24 AM.
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Re: Calling brake EXPERTS
[Re: General 68]
#2917584
05/02/21 09:17 AM
05/02/21 09:17 AM
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Joined: May 2019
Posts: 6,290 nowhere
Sniper
master
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master
Joined: May 2019
Posts: 6,290
nowhere
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I jus wonder if the rear calipers can play a part here. They are adjustable and rests with a gap between rotor an pads. I
There should be no gap between the pads and the rotors.
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Re: Calling brake EXPERTS
[Re: General 68]
#2917596
05/02/21 09:51 AM
05/02/21 09:51 AM
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Joined: May 2019
Posts: 6,290 nowhere
Sniper
master
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master
Joined: May 2019
Posts: 6,290
nowhere
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Pr Ssbc's instructions it should be set between 1/16 and 1/32". SSBC instructions are incomplete or wrong. That section is the parking brake adjustment. That is where you START to properly adjust the parking brake, not where you end up. You need to cycle the parking brake several times till that clearance goes away and the parking brake actually functions. then you should have brakes.
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Re: Calling brake EXPERTS
[Re: dragon slayer]
#2918769
05/05/21 09:26 AM
05/05/21 09:26 AM
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Joined: Dec 2007
Posts: 18,157 Mass
DAYCLONA
I Live Here
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I Live Here
Joined: Dec 2007
Posts: 18,157
Mass
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Pressure gauge and test at various points can help you divide and conquer. We are arm chairing this at this point. Agreed, when I set up a 4 wheel disc brake system of my own design or pre-assembled kits for customers or myself, regardless of the manufacturer's claims I employ a high pressure gauge at each caliper to test how biased/balanced the system is rather than seat of the pant's guessing/trail and error, Summit Racing offers an affordable testing gauge kit for those on a budget as 2000psi gauges aren't exactly cheap if you want to make your own 4 wheel testing system Mike
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