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4wdb questons *Yes, I searched*

Discussion in 'The Garage' started by BigCountryx, Oct 16, 2005.

  1. BigCountryx

    BigCountryx 1/2 ton status

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    I've read 'till my eyes hurt, but mostly theory, and most posts tell about everything that they tried and failed with and very little about what actually has worked for them. Am I to believe that most on here have very poor bbraking after the "upgrade"?

    Here are my specs:

    1990 w/ factory MC (not hydro)
    Factory Prop Valve
    D60 Front W/ new Calipers
    14ff Rear W/ Front calipers off of my 1/2 ton 10 bolt

    I have read before that this combo has worked as is for some.

    I am still waiting on my d-shaft so I haven't driven it yet, but I have bled the system over and over and get good flow from every bleeder. My front Pass Bleeder gets a bubble from time to time, but otherwise, clean clear fluid. With the engine off I get a hard pedal that holds. When I crank the engine I get virtually no pressure and the pedal goes to the floor.

    Has anyone run a similar combo?
    Has it worked for you?
    If not what changes were made to make it perform better?
     
  2. dcubb

    dcubb 1/2 ton status

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    Location:
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    I,m using: '90 1/2t burb vac booster, '77 caddy m/c (mainly because its the old style cast iron one and I already had the right adapter for my pressure bleeder), wilwood adjustable bias valve, electrically operated "Mico" line lock solenoid, 3/4t calipers on both ends. Initially I tried to use the factory prop valve but really wasn't satisfied with the end result. One issue I ran into is that GM used different "ratio" brake pedals (On auto tranny trucks for sure, I'm not sure on the manual trucks). The first pedal that I installed, (since I went from sm465 to 700r4) had the m/c rod anchor point approximately 2.75" from the pivot. With this setup I had a somewhat soggy pedal with little effort. Got to searching around in the junkyard and found a pedal from a '87 burb that had the m/c anchor approximately 3.375" from the pivot. It made a ton of difference in pedal feel. Nice high firm pedal with slightly more effort. This 4wdb setup works great in my rig. Oh, another thing, the tight pedal with engine not running but very soft with engine running indicates to me that there is still air in the lines (most likely in the 1/4" line that runs to the rear) I had to pump almost a gallon thru with the pressure bleeder to clear out all of the air. With a line of that diameter and length sometimes a air bubble just moves back and forth in the line when you use the old "pump the pedal and crack the bleeder method". Hope this helps, Dave
     
  3. mouse

    mouse 1/2 ton status

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    I think you still have air. Try tapping the MC and everything else lightly to help the bubbles escape. Keep bleeding...
     
  4. darenofears

    darenofears Registered Member

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    you need to change to a different mastercylinder for four wheel disc brakes
     
  5. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    3/4 ton D44 rotors and calipers on my 14 bolt, 'stock' D60 front disks.

    MC is from an '83 C30 pick-up (had a 6.2)

    Booster is Hydro-boost from same '83 C30

    Stock prop/combo valve still in place, no aftermarket proportioning valve.

    Braking is exceptionally good, and is very easy to threshold brake with. In a panic the rears lock up just a half sec before the fronts do, and I doubt it'd be easy to get a manually adjustable system that close to perfect. It will lock all four 39.5's (I've done it twice now...)

    Pedal feel is somewhat firm, with no real dead area at the top of the pedal. Much better pedal than the old vac brakes with rear drums.

    I bench bled the MC, then gravity bled the rest of the system. A lot of MC's get ruined by manual bleeding. If you have to manual bleed the brakes I'd recomend a piece of 2x4 under the brake pedal to keep from going too far and wiping out the seals inside the MC.

    Rene
     
  6. mouse

    mouse 1/2 ton status

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    I've seen this a couple of times too. Your setup should work, not as strong as hydroboost, but make sure to bleed them carefully.
     
  7. BigCountryx

    BigCountryx 1/2 ton status

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    Allllllllllrighty then, this would have been good to know before Bleeding by pushing the Pedal to the floor. lol If I have screwed up the seals in my MC, What would be a good vehicle to get a new one off of? Are remnans OK? I assume one with a 4wdb system would be best. I really don't want to go hydro, so I am looking into a way to keep my vac system. And would like one to be plug and play if possible. Thanks guys, I thought I did my homework............think again :doah:

    Another thing is the rear ABS. Has anyone just bypassed the system? Any probs? If I end up replumbing w/ new proportioning valves etc. I would like to get rid of the ABS as I'm sure it's useless w/ the new configuration.
     
  8. mouse

    mouse 1/2 ton status

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    I tried a couple of MCs with rear discs and a vacuum booster. The stock one was not as strong as the 3/4 ton unit I used that was for a truck with the smaller rear drums. I still had to use a lot of foot to lock them up - thats why I went Hydro...

    I used (still use) reman MCs with no problems. And at $20-$25 a pop, they are not what I would call expensive.


    ABS, whats that?....Sorry, my old truck cant spell words like that!
     

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