Author Topic: Brakes question  (Read 799 times)

Offline V12T

  • Jr. Member
  • **
  • Posts: 42
Brakes question
« on: December 07, 2019 - 07:17:10 PM »
I have installed a 4 wheel boosted disc brake disc setup on my 70 Challenger. Under normal conditions it stops beautifully with a very light touch but if I need to stop suddenly I need to press the pedal really hard. I have installed a vacuum tank and it is well above 18. Have I just got used to the featherlight touch needed on a modern ABS car (and this harder pedal is typical of an old classic) or could something else be wrong?




Online 70chall440

  • Sr. Resident
  • ******
  • Posts: 6186
Re: Brakes question
« Reply #1 on: December 07, 2019 - 10:25:54 PM »
Alot of factors here but first off, a non ABS car will lock up the tires if the brakes are slammed unlike ABS which will pulse (releasing and applying the brakes incrementally). That said, in your case I am not sure what you are expecting or what the car is actually doing. If the brakes are locking up and the tires are sliding, thats what an old school brake system will do. Ideally the front lock before the rear, but they will all lock nonetheless.

Have you changed the entire brake system (MC, proportioning valve, metering valve, etc.)?
Current Mopar
70 Challenger RT 440-6 EFI, 73 Cuda 416-6 EFI
05 Hemi Durango, 01 Ram 4x4, 14 Ram 2500 4X4, 10 PCP Challenger 6 spd RT, 01 Viper GTS ACR, 52 B3B w/330 Desoto Hemi, 70 Hemi RR (under const)
Past Mopars
9 x Challengers. AAR Cuda, 4 RR, 2 GTX, 4 Chargers, etc... (too many to list)

Offline V12T

  • Jr. Member
  • **
  • Posts: 42
Re: Brakes question
« Reply #2 on: December 08, 2019 - 04:41:29 AM »
All new system with proportioning valve. I have checked that it is centred. Wheels do not lock under heavy braking (at least so far)- it's just that I have to push hard - it feels almost as if I've lost the boost, yet under lighter braking it's perfect. I don't have excessive pedal travel, or a spongy pedal and my pedal ratio is 4-5. I wonder if the E brake system in the rear calipers is affecting anything although I have adjusted it carefully as specified and the E brake works well.

Online 70chall440

  • Sr. Resident
  • ******
  • Posts: 6186
Re: Brakes question
« Reply #3 on: December 09, 2019 - 12:23:52 PM »
I think I understand what you are saying; I do not it has anything to do with you E brake, it has to do with your MC bore size, I am think it might be on the large side.
Current Mopar
70 Challenger RT 440-6 EFI, 73 Cuda 416-6 EFI
05 Hemi Durango, 01 Ram 4x4, 14 Ram 2500 4X4, 10 PCP Challenger 6 spd RT, 01 Viper GTS ACR, 52 B3B w/330 Desoto Hemi, 70 Hemi RR (under const)
Past Mopars
9 x Challengers. AAR Cuda, 4 RR, 2 GTX, 4 Chargers, etc... (too many to list)

Offline V12T

  • Jr. Member
  • **
  • Posts: 42
Re: Brakes question
« Reply #4 on: December 09, 2019 - 12:48:37 PM »
That sounds possible except the whole kit was purpose supplied for the Challenger. Unfortunately I bought it over 3 years ago and the US supplier doesn't deal with tech queries (doesn't answer Emails and I'm in UK). Perhaps its just me and I'll get used to it as I drive it more.

Online 70chall440

  • Sr. Resident
  • ******
  • Posts: 6186
Re: Brakes question
« Reply #5 on: December 09, 2019 - 01:49:52 PM »
Understand, that is one of the problems with "kits"; if there is a problem many times it is hard to get corrected. So long as it stops you are probably good and it is true that old cars and braking systems are not like modern cars.
Current Mopar
70 Challenger RT 440-6 EFI, 73 Cuda 416-6 EFI
05 Hemi Durango, 01 Ram 4x4, 14 Ram 2500 4X4, 10 PCP Challenger 6 spd RT, 01 Viper GTS ACR, 52 B3B w/330 Desoto Hemi, 70 Hemi RR (under const)
Past Mopars
9 x Challengers. AAR Cuda, 4 RR, 2 GTX, 4 Chargers, etc... (too many to list)