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Installing a willwood for my disc swap, what line to rear?

Discussion in 'The Garage' started by 74kay5, Jul 30, 2006.

  1. 74kay5

    74kay5 1/2 ton status

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    I'm installing a willwood proportioning valve for my 14 bolt disc swap. Which line goes to the rear? The one closer to the firewall or the one toward the grill. All the lines going into the combo valve are throwing me off.
     
  2. sled_dog

    sled_dog 1 ton status

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    one towards the grill. The larger reservoir feeds the front brakes. Also, the master cylinder applies pressure to the front brakes first(seeing as they do more of the work).
     
  3. onetonbb74

    onetonbb74 1/2 ton status

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    i left my combo valve alone and ran the proportioning valve at the rear of the truck where the line necks down from 1/4 to 3/16ths. btw, i have the wilwood proportioning valve also. if you need help throw me a p.m. im in south san jose. as far as reservoirs on the master, mine has equal sized master cylinder reservoirs on it. My old half ton was front bigger, rear smaller. front being closer to fire wall and rear being grill.
     
  4. 74kay5

    74kay5 1/2 ton status

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    So the bigger diameter brake tubing is actually for the rear? Looks like the rear brake is 1/4 and the diameter for the front comming from the MC is 3/16? Does that make sense?
     
  5. 70jimmy

    70jimmy 3/4 ton status Premium Member GMOTM Winner

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    I was told to put in a resdual pressure valve in mine also when I went to disc. Supposed to keep the rear discs from backing off too far???

    Maybe somebdy else can chime in whether its necessary or not? I am curious myself. by the way I love 4 wheel discs and my adjustable proportioning valve is almost closed to the rear.
     
  6. bp71k5

    bp71k5 3/4 ton status Premium Member

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    I'm doing the rear disc conversion and thought you were supposed to remove the residual valve? The disc's are supposed to autoadjust so you don't need it. Maybe I'm not understanding it though, but if the front's don't need a valve, why would the rear?

    I'm just now debating going with the larger MC and booster while it's all apart. I have to bleed everything again anyway. the 3/4 booster is supposed to be pretty good at stopping.
     
  7. onetonbb74

    onetonbb74 1/2 ton status

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    the booster out of a 79 3/4 ton works perfect for mine.
     
  8. dremu

    dremu Officious Thread Derailer Premium Member

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    My understanding is that the factory combination valve is a proportioning valve as well as providing some residual pressure function.

    As I removed the factory combo valve, I have 5PSI residuals on both my front and rear lines right at the master ... I donno that they do much good, but they do allow me to switch the plumbing around, as I'm using the P30 hydro master which has the fitting sizes swapped front-to-rear.

    I also have an adjustable prop valve to the rear -- SSBC, as it's what my local speed shop had -- and I've found that yep, it works best when turned almosed all the way down. Still fiddling with it, mind you :)

    -- A
     
  9. 70jimmy

    70jimmy 3/4 ton status Premium Member GMOTM Winner

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    I removed the factory combo valve so its just lines out of the MC.
     
  10. sled_dog

    sled_dog 1 ton status

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    Residual pressure valves are for drum brakes, so THEY don't back off too far.

    One of the nice things about disc brakes is that they don't rub the rotor all the time. Frees up horsepower to the wheels. Spin a drum wheel vs a disc wheel(say on the back of a FWD car). A properly adjusted drum will stop shortly after starting to spin. Disc will just keep going until it runs out of energy.

    That and disc brakes pistons will only return so much anyway. They use a square cut seal inside that rolls and helps to act as a return spring for the piston. Think about it, when you compress the piston to install new pads, the first stab of the brake pedal is a lot of travel because the piston has to come out and size to the rotor/pads. The second hit, isn't nearly as much travel. The piston isn't returning all the way in, its just rolling back in a slight bit.

    We've had the residual valve discussion before. My understanding is that most are within the master cylinder. But many contest our trucks don't have them at all.
     
  11. stevos67k20

    stevos67k20 1/2 ton status

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    clearification....please correct if wrong....

    on my master cylinder, old 1/2 stuff, the rear brake line connects to the firewall side of the MC and the line is larger in diameter....(i think this is wrong)
    [​IMG]
    the front line is smaller in diameter and it comes from the grill side of the MC......are my lines flip-flopped?

    what i under stand from this thread, to make everything clear:

    --front lines should be larger,coming from the large reservoir on the MC(firewall side)

    --Rear lines should be smaller, coming from the smaller reservoir on the MC(grill side) proportion valve may be placed here to restrict flow to rear disc's.
     
  12. onetonbb74

    onetonbb74 1/2 ton status

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    according to the photo, the larger line is the rear brakes, and the smaller brake line is the front brakes. Sled dog was reffering to the size of the reservoir on the master and not the size of the lines. your picture looks normal. my halfton master is different, it has bigger reservoir for the front brakes and a small one for the rear.
     
  13. bp71k5

    bp71k5 3/4 ton status Premium Member

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    Your picture looks exactly like mine. My MC chambers are the same size. I swapped in a 3/4ton booster, but I had to use the pushrod from my old MC with the new booster.
     
  14. ntsqd

    ntsqd 1/2 ton status

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    Residual Pressure Valves (RPVs), as already stated, are mostly for drum brakes. The brake shoe retraction springs would pull the shoes in too far w/o such a valve. Commonly they are found behind the little brass tube seat in the outlet from the master.

    Drum brakes typically use a 10 lbs RPV while in some case discs will use an RPV, but those are only 2 lbs. Usually you only need an RPV with discs if the master is below the level of the calipers, but once in a while you'll run into a system with excessive piston knock-back and a 2 lbs RPV will cure the symptom.
     
  15. stevos67k20

    stevos67k20 1/2 ton status

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    one more question....

    i am putting a hydroboost on very soon. i have all the parts ready....
    do i want the big line for the rear brakes or the front brakes? currently there are big lines going to the rear.

    heres what i got: large reservoir on firewall side
    [​IMG]
     
  16. Desert Rat

    Desert Rat Fetch the comfy chair

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    I got a proportioning valve from Inline Tube (http://www.inlinetube.com/) that was made specifically for converting a Chevy truck to 4 wheel disk for $99. You just swap out the stock proportioning valve and put the Inline Tube on in its place. It is the identical dimensions as the stock valve.
     
  17. bp71k5

    bp71k5 3/4 ton status Premium Member

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    Do you have a link or picture? That sounds like it would work nice.
     
  18. Desert Rat

    Desert Rat Fetch the comfy chair

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    The link is in my reply above you. They don't have a specific pic of the one I bought, but it looks just like the stock one except brass.
     

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