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Brake problem #3053325
06/25/22 05:41 PM
06/25/22 05:41 PM
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Sweden , Enköping
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Rasmus Vestlin Offline OP
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Hello everyone!

I have rightstuff 4 wheel disc brake kit on my -70 challenger, the car is completly renovated and everything is new on the car. I use willwood booster and mastercylinder 1” bore. The problem is that the brakes dosnt work as good as i think they would..

I have done all this

:bleed the brakes 100 times, its no air left, if i pump the brakepedal it dosnt get firmer as it should if it still was air in the system.

: i have adjusted the parkingbrake arm as they recomend.

: I checked if the gap between the pushrod from the booster to my mastercylinder was to big. It was perfect gap there also.

The car stops when i brake, but it wont lockup the brakes even if i stand on my brakepedal. I am out of ideas now and would really appreciate help with this! Is it just bad quality or will it get better the more i drive the car and let it brake in the parts?

Please help!

Best regards Rasmus!

F8EB63FD-B0B6-41AC-A920-D054C46CF85C.jpeg
Re: Brake problem [Re: Rasmus Vestlin] #3053335
06/25/22 06:23 PM
06/25/22 06:23 PM
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Sniper Offline
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Wrong booster or wrong master cylinder.

What is the part number of the booster you used.

What is the part number of the master cylinder you used.

You need to put some pressure gauges on the front and rear brake lines to see what is going on.

Re: Brake problem [Re: Sniper] #3053395
06/26/22 12:47 AM
06/26/22 12:47 AM
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Las Vegas, NV
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chargerbr549 Offline
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That seems to be a common problem when people convert to 4 wheel disc brakes not having enough braking pressure to be able to make the brakes work properly. Master cylinder bore size becomes more critical as well as the rest of the brake system and the brake booster needs to be a very good dual diaphram style or some people have to convert to a hydro boost brake booster to make it work properly. Another option you could do, which most people don't want to hear is to go back to a rear brake drum setup and run the biggest diameter front rotors that will fit inside of your front wheels and adjust the brake bias by wheel cylinder/caliper piston size or use an adjustible proportioning valve and alot of times you can get away with not even needing a brake booster, you can save yourself alot of headaches that way.

Last edited by chargerbr549; 06/26/22 12:51 AM.
Re: Brake problem [Re: Rasmus Vestlin] #3053398
06/26/22 01:19 AM
06/26/22 01:19 AM
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Bend,OR USA
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Cab_Burge Offline
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You probably need a smaller bore master cylinder for 4 wheel disc brakes, bigger bore and piston master cylinders make less line pressure with the same stroke as a smaller bore M.C. twocents


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Brake problem [Re: Cab_Burge] #3053408
06/26/22 06:25 AM
06/26/22 06:25 AM
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Sweden , Enköping
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Rasmus Vestlin Offline OP
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Originally Posted by Cab_Burge
You probably need a smaller bore master cylinder for 4 wheel disc brakes, bigger bore and piston master cylinders make less line pressure with the same stroke as a smaller bore M.C. twocents



I dont think that gonna make it better, yes more pressure but then the brake pedal will need to travel even more and i already have it kinda low. Iam using a 8” dual booster and 1” inch bore MC with a adjustable proportionvalve, all from willwood. I have 19-20 vacum. I have bench bleed the MC and bleed the whole system back to front 20 times. Iam possitive its no air left. But i still cant get good brakes..

Going back to drums is no option. Iam thinking of change the pedal ratio to get more pressure and also make an adjustable rod from my brake pedal to my booster so i can adjust out all the play and get a better feel in my brake pedal. But i appreciate other tips aswell!

Re: Brake problem [Re: Rasmus Vestlin] #3053418
06/26/22 07:38 AM
06/26/22 07:38 AM
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Freeport IL USA
poorboy Offline
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I know you checked the measurement between the pedal and your booster and stated it was correct, however, if you have an adjustable rod already, maybe you should try adjusting the rod just a bit longer. I would give it a shot at about a 1/4 turn out and give it a try to se if it helps. As long as you don't go far enough to make the brakes drag, it will rise the brake pedal off the floor with each adjustment. The threads on that adjuster are very fine, a 1/4 turn (or an 1/8 turn) doesn't add up to much, but can make a big difference on the pedal travel.

The best part is, no money out of pocket, and if it doesn't work, you can go back pretty easily. The next step would be the pedal ratio, but that can get harry pretty quickly too.

Re: Brake problem [Re: Rasmus Vestlin] #3053421
06/26/22 07:42 AM
06/26/22 07:42 AM
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ruderunner Offline
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Is the pedal hard to push? Or just excess travel?

I'm not sure there's any adjustment that will fix your problem, I believe there's a basic mismatch in components.

What calipers are you using?


Angry white pureblood male
Re: Brake problem [Re: poorboy] #3053432
06/26/22 09:11 AM
06/26/22 09:11 AM
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Sweden , Enköping
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Rasmus Vestlin Offline OP
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Originally Posted by poorboy
I know you checked the measurement between the pedal and your booster and stated it was correct, however, if you have an adjustable rod already, maybe you should try adjusting the rod just a bit longer. I would give it a shot at about a 1/4 turn out and give it a try to se if it helps. As long as you don't go far enough to make the brakes drag, it will rise the brake pedal off the floor with each adjustment. The threads on that adjuster are very fine, a 1/4 turn (or an 1/8 turn) doesn't add up to much, but can make a big difference on the pedal travel.

The best part is, no money out of pocket, and if it doesn't work, you can go back pretty easily. The next step would be the pedal ratio, but that can get harry pretty quickly too.


Thank you! I Will try that and see if it gets better! Because a friend keeps telling me that my brake pedal is sittning to low. My brackets are behind the brake booster and not under dash like orginal. Its a bit of sloppy and play in the pins. I have adjusted max on the rod that coming out from behind my booster but it didnt do much.

I have the longest arm from the brake pedal but it should be adjustable instead, then i could adjust the height of my pedal and get rid of the play also. I put some pictures on what arm i mean. Iam thinking of cutting it and weld on a nut and bolt to each end so i can adjust it.

BCE7BDB8-CD32-4369-A257-3B05DB6ABDD8.jpeg
Re: Brake problem [Re: ruderunner] #3053434
06/26/22 09:19 AM
06/26/22 09:19 AM
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Sweden , Enköping
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Rasmus Vestlin Offline OP
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Originally Posted by ruderunner
Is the pedal hard to push? Or just excess travel?

I'm not sure there's any adjustment that will fix your problem, I believe there's a basic mismatch in components.

What calipers are you using?


If the sloppy play in the brackets behind the booster were gone, then i think the pedal Will feel alot better and get harder. Because right now i can move the pedal an inch before i actully feel its pushing in the mastercylinder. And the messurnent was good on the rod to the MC. Its a dual 8 brakebooster and 1” bore mc from willwood. Its coming asemblied from them, so it cant be a missmatch.. its not hard gå push, its more excess travel.


Its rightstuff 4 wheel disc kit, so its 1 piston calipers. Back is the normal ”Cadillac brake calipers style” not sure on front, but its 1 piston there aswell.

Last edited by Rasmus Vestlin; 06/26/22 09:19 AM.
Re: Brake problem [Re: Rasmus Vestlin] #3053446
06/26/22 10:38 AM
06/26/22 10:38 AM
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usa
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lewtot184 Offline
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when i did a right stuff front disc conversion the car wouldn't stop. i ended up getting rid of the 2.74" piston calipers that came with the kit for 2.47" piston calipers and a 1" master. car stops now but not good. i hate their junk!!!!!!!!!!!

Re: Brake problem [Re: lewtot184] #3053450
06/26/22 10:52 AM
06/26/22 10:52 AM
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Rasmus Vestlin Offline OP
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Originally Posted by lewtot184
when i did a right stuff front disc conversion the car wouldn't stop. i ended up getting rid of the 2.74" piston calipers that came with the kit for 2.47" piston calipers and a 1" master. car stops now but not good. i hate their junk!!!!!!!!!!!


Yepp, same here. Car stops but not good.

Re: Brake problem [Re: Rasmus Vestlin] #3053457
06/26/22 11:22 AM
06/26/22 11:22 AM
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Sniper Offline
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https://www.markwilliams.com/brake-system-pressure.html

What is your vacuum level? You might not have enough to use the booster properly, 18" is the recommendation.


Re: Brake problem [Re: lewtot184] #3053468
06/26/22 11:52 AM
06/26/22 11:52 AM
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TJP Offline
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I would not suggest modifying anything just yet. One has to identify the problem first.

Step # 1. Make sure the "L shaped" bracket rod is installed correctly as it will affect travel and pedal leverage. be aware that some cars have multiple holes in the pedal arm for power or manual brakes. MAKE SURE you are installed correctly
Step # 2. Eliminate as much play or slop in the linkage as possible .030 at the master over a 6 inch distance multiplies significantly
Step # 3. Install pressure gauges on the master and verify the pressures being generated. Panic stop should be ~ 1500lbs.
note the pedal travel required. With the gauges(s) preferably on on each port note the amount of travel required, it should be very minimal unless there is excess play in the linkage or adjustment, something is moving/ flexing under the pressure, the master is bad. If you don't have 2 gauges you can get by with 1 by plugging the second port. that requires retesting the second port.
test kits are available relatively cheap on AMZ BRAKE PRESSURE TEST KIT may also be cheaper elsewhere.
Step # 4. Once you have established the pressures are being generated at the master you can the move to the calipers preferably one end at a time while blocking the other port of the master. You should see the SAME pressures at the calipers. While doing so again look for any flex or excess movement
Step# 5. repeat at opposite end.

By this time you should have enough data to indentify the problem and or rport back as there are a few other gremlins that are possible. beer

Re: Brake problem [Re: Sniper] #3053469
06/26/22 11:52 AM
06/26/22 11:52 AM
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Sweden , Enköping
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Rasmus Vestlin Offline OP
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Originally Posted by Sniper
https://www.markwilliams.com/brake-system-pressure.html

What is your vacuum level? You might not have enough to use the booster properly, 18" is the recommendation.



I have 19-20 in vacum when i checked it , so it should be enough?

Re: Brake problem [Re: TJP] #3053472
06/26/22 11:58 AM
06/26/22 11:58 AM
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Rasmus Vestlin Offline OP
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Originally Posted by TJP
I would not suggest modifying anything just yet. One has to identify the problem first.

Step # 1. Make sure the "L shaped" bracket rod is installed correctly as it will affect travel and pedal leverage. be aware that some cars have multiple holes in the pedal arm for power or manual brakes. MAKE SURE you are installed correctly
Step # 2. Eliminate as much play or slop in the linkage as possible .030 at the master over a 6 inch distance multiplies significantly
Step # 3. Install pressure gauges on the master and verify the pressures being generated. Panic stop should be ~ 1500lbs.
note the pedal travel required. With the gauges(s) preferably on on each port note the amount of travel required, it should be very minimal unless there is excess play in the linkage or adjustment, something is moving/ flexing under the pressure, the master is bad. If you don't have 2 gauges you can get by with 1 by plugging the second port. that requires retesting the second port.
test kits are available relatively cheap on AMZ BRAKE PRESSURE TEST KIT may also be cheaper elsewhere.
Step # 4. Once you have established the pressures are being generated at the master you can the move to the calipers preferably one end at a time while blocking the other port of the master. You should see the SAME pressures at the calipers. While doing so again look for any flex or excess movement
Step# 5. repeat at opposite end.

By this time you should have enough data to indentify the problem and or rport back as there are a few other gremlins that are possible. beer



Thanks for your help! I Will check that, my L shaped bracket is correct mounted and i only have 1 hole at my brake pedal. I think next step first is to get rid of the slop and play in the brackets. Also try to adjust out the pushrod abit more to see what happens as someone pointed out.

Re: Brake problem [Re: lewtot184] #3053473
06/26/22 11:58 AM
06/26/22 11:58 AM
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Originally Posted by lewtot184
when i did a right stuff front disc conversion the car wouldn't stop. i ended up getting rid of the 2.74" piston calipers that came with the kit for 2.47" piston calipers and a 1" master. car stops now but not good. i hate their junk!!!!!!!!!!!


IF you went from a 2.74 piston to a 2.47 you actually reduced he amount of pressure at the the pads as the force generated byt the master is multiplied by the diameter of the caliper piston beer

Re: Brake problem [Re: Rasmus Vestlin] #3053482
06/26/22 12:18 PM
06/26/22 12:18 PM
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Sniper Offline
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Originally Posted by Rasmus Vestlin
Originally Posted by Sniper
https://www.markwilliams.com/brake-system-pressure.html

What is your vacuum level? You might not have enough to use the booster properly, 18" is the recommendation.



I have 19-20 in vacuum when i checked it , so it should be enough?


Yes, that level of vacuum should be more than enough.

Re: Brake problem [Re: TJP] #3053517
06/26/22 02:01 PM
06/26/22 02:01 PM
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lewtot184 Offline
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Originally Posted by TJP
Originally Posted by lewtot184
when i did a right stuff front disc conversion the car wouldn't stop. i ended up getting rid of the 2.74" piston calipers that came with the kit for 2.47" piston calipers and a 1" master. car stops now but not good. i hate their junk!!!!!!!!!!!


IF you went from a 2.74 piston to a 2.47 you actually reduced he amount of pressure at the the pads as the force generated byt the master is multiplied by the diameter of the caliper piston beer
NO!!!!!!!

Re: Brake problem [Re: lewtot184] #3053518
06/26/22 02:10 PM
06/26/22 02:10 PM
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I don't know, my four wheel drum brakes work just fine. grin


"We live in a time when intelligent people are being silenced so that stupid people won't be offended".
Re: Brake problem [Re: 6PakBee] #3053582
06/26/22 05:27 PM
06/26/22 05:27 PM
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ruderunner Offline
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Just to clarify, when I referred to mismatched components, I mean the whole system, not just the master and booster.

Iirc the Caddy calipers have fairly large pistons, we can assume the front are bigger.. I wonder if you're simply unable to move enough fluid to build enough pressure at the wheels. Either too small a master bore or not enough stroke.

Does the pedal seem to bottom out when pressed hard?

What happens if you disconnect the vacuum from the booster?

My point of reference is a 69 B body with 70 and up front disc, rear drum and no assist. I use a 1.25 bore master and have no problems locking the brakes up if desired.


Angry white pureblood male
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