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Using an adjustable prop. valve w/ 4-wheel-disc?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by fortcollinsram, Nov 5, 2002.

  1. fortcollinsram

    fortcollinsram 1/2 ton status

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    This past week has brought with it some pretty ice roads in Northern Colorado...It gave me a good chance to see how unbalanced my brakes were after the rear disc conversion...I always thought they rears were a little on the strong side compared to the front..well on my first outing on the icey roads, I confirmed this when I hit the brake and the rear locked up before the front and the rear end skated side to side...it made for some interesting stops...

    So I got to thinking about plumbing in a Wilwood adjustable prop. valve...I was thinking I could plub the front line directly to the calipers and the rear line I could send through the valve...this would alow me to adjust the pressure going to the rears and alow me to ballance the braking habits on the truck...Any ideas?

    Chris
     
  2. Thumper

    Thumper 1/2 ton status

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    Yup. I have to do the same thing. I didnt notice it too badly in the summer on the dry, but now in the snow she really wants to come around. They are cheap (for you guys in the US) and should do the job perfectly. I also removed my stock combo valve from the fronts as well as the rears, and just need to find a adjustable valve for cheaper than 90.00 CDN!

    Later
    Mike
     
  3. Seventy4Blazer

    Seventy4Blazer 3/4 ton status

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    what i plan on doing is the adjustable valve and then a CNC cutting brake plumbed behing that for the rears. and a cuting brake would be FUN in the ice... on an empty road of course
    i plan on runnig the front brakes like the stock setup for the rear. one line down and a distribution block. then for the rear the cutting brake(one line in 2 out) routed down the middle of the rear axle(both lines) and out to each side.
    kinda long. yur idea should work well. but i just wanted to give you another idea...
    Grant
     
  4. TX Mudder

    TX Mudder 1/2 ton status

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    They sell brand new proportioning valves that are set up for front disc/rear disc (vs. stock front disc/rear drum.)
    If you look at Inline Tube you can see they list new valbes for front disc/rear drum for $85. I sent them an email and they said they make them also for front disc/rear disc also. I think it was the same price.
    Shoot them an email and see if they told you the same thing they told me.
    -- Mike
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    I'm just posting this in here because I'm thiniking (hoping) that someone has the time to check into a proportioning valve mod.

    I finally got a copy of the "stealth bolt mod" that the Impala SS guys use, which is "necessary because GM didn't change combination valves when they went to disks for those cars. Difference is, those cars are UNDER utilizing their rear brakes, whereas it sounds like everyone here has problems with them being over utilized.

    I figure if someone has the time to sit down and compare this document that I have (complete with pics) maybe there is a way to modify our stock proportioning valve to do the exact opposite of what they are trying?

    Hit me up privately if anyone wants to take a look at it, or I can put it on a web page for download if I've got any space left. It's a Word doc.
     
  6. MudFrog

    MudFrog 1/2 ton status

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    I was playing around on carparts.com looking at some prices for 1 ton master cylinder and booster. I saw they had a front/rear disc proportioning valve listed for the 1 tons. Maybe we could get that to work?
     
  7. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Sounds like the factory valve wasn't working at all. It should delay the rears in stock form to prevent lock up.
    I'll be finishing the first part of my conversion this week and most that I have talked to said to bypass factory valve. If you get too much rear then go to the Adj willwood in the rear circuit.
    I'll be doing a write on it in the next couple weeks. Need to get a CTM one done first.
     
  8. Flexy K20

    Flexy K20 1/2 ton status

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    Where would you go about putting this valve? Would you put it on the frame rail, or in the engine compartment?
    Thanks -Flexy
     
  9. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    It's an adjustable valve. You can mount it on the fire wall next to the Master or you could mount it on your dash. Then you can shut down all fulid to the rears and powerbrake till you blow the tires /forums/images/graemlins/smile.gif
    [​IMG]
     
  10. Thumper

    Thumper 1/2 ton status

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    Thats the one I need. They are like 35.00 USD right? Here in Canada, I cant get one for less than 80.00! Unfreakin believable. Wish I lived closer to the border. >:(

    Mike
     
  11. txbartman

    txbartman 1/2 ton status

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    I'm not sure if there are export restrictions, but try ordering from Summit. Here is a link to the Wilwood valve. If you can't get it for a decent price, let me know. Maybe we can work out a deal where I get it and then ship it to you. PM me if interested.
     
  12. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    It's the shipping and brokerage fees incurred at the border that make the cost go up to over $80 cdn...plus the cdn dollar is worth a fair bit less too. You sending it to Mike wouldn't help.

    I had someone send me something that was free via UPS. They had to declare a value for insurance reasons. I had to pay $35 to receive this free item...

    I do live close to the border so I recently set up a shipping address in Blaine WA. I can't get away from paying tax on my purchases but I do save a ton on 'brokerage' and 'handling'...

    As a rule of thumb, whatever the price I see in a magazine or catalog in USD...double it and thats about what it costs me to get in CDN $$.

    39.5x15 TSL...$434 CDN. /forums/images/graemlins/eek.gif /forums/images/graemlins/eek.gif

    Rene
     
  13. Blue85

    Blue85 Troll Premium Member

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    The factory delay is only supposed to delay activation of the fronts until the rear shoes have engaged. This is to make sure you don't end up using only the front brakes. Rear lockup is only prevented by the front/rear proportion.
     
  14. Thumper

    Thumper 1/2 ton status

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    Well, thats the problem. Crossin the dang border. Gotta love 'free trade' huh? I have a couple of work trips coming up. Possible Portland and/ or Denver this month, then definately New Orleans in Jan. so I can pick up one then. Thanks anyways.

    Mike
     
  15. Blue85

    Blue85 Troll Premium Member

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    I looked into a prop valve mod about a year back when I went to rear disc. The article that you point to just increases my confidence in making it work. Here is what our combo valves look like inside: [​IMG]

    The stuff on the right is the proportioning valve. As you can see, the fitting on the right (rear output) is threaded. It should be as easy as unscrewing that fitting and taking out the spring and metering piston and putting it back together. This gets you zero proportioning from the valve. The front and rear circuits will get whatever pressure the master cylinder sends them. This is all the Impala SS mod does, even though they never come right out and say it.

    Who wants to try this out?

    HOWEVER, as we already know, a K5 converted to rear disc has too much bias to the rear, so this would only increase the need for an adjustable prop valve. UNLESS you have a 4-wheel disc master cylinder. That may set the bias correctly already and this mod would just save you the money for a 4-wheel disc prop valve.

    The more important issues, in my mind are Residual Pressure and Brake Metering.

    Don't rear drums usually have a residual pressure valve in the system that keeps a little pressure on them to keep the shoes from moving too far from the drum when not engaged? We need to get rid of that. Isn't it in the master cylinder?

    With rear discs, we don't need Metering. This is built into the left-hand side of the combo valve. There may be a way to disassemble that end and remove the spring. This needs more investigation. It will definately be different than the Impala SS method.
     
  16. imiceman44

    imiceman44 1 ton status

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    I remember reading about that in a magazine once and someone correct me if I am wrong, there is a check ball somewhere in the MC for a disc/drum setup and they say you have to remove it if you are converting to disc/disc.
    I will try and find the article to confirm, so yes I believe you are correct about the check valve for drums.
    Did anyone that did the disc conv. know about that? how did you deal with it.
    Without dealing with it you might have problems with rears locking up, and not releasing, I remember reading a post about someone having this problem?
     
  17. Blue85

    Blue85 Troll Premium Member

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    I think that I am having this problem, which is why I brought it up as a big issue. Of course I'm not sure. I am very interested in any info you can find about this check ball.

    Anybody know of good MC applications for 4-wheel disc? IROC Camaro?
     
  18. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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  19. dyeager535

    dyeager535 1 ton status Premium Member

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    I wonder if part of the problem is different entirely... (although this is a copy, and it appears the master cylinder has alreday been touched on...I'm late : )

    Something I just thought of, I *believe* is master cylinder specific: front disk "quick take up"

    As I recall from the service manual, the front disks are retracted from the rotor slightly when the brake pedal is released. The drums, don't think this is the case.

    If the cars that were disk/drum AND disk/disk used the same prob valve, I'm thinking the master cylinder is different. (if the take up is caused by the MC) If the rears aren't "taking up" as you let off the brake, would they perhaps be too close to the rotor, thus applying faster?

    Cars have a problem with the disk/drum prop valve of too little braking. The trucks have a problem with the same setup valve, except now its too MUCH braking.

    Also as I recall, disks use much more fluid to move the piston than drums, which means that the rear disks on trucks should work less efficiently unless something else is different, right?

    I'm betting most of the problems can be resolved through the prop valve. I'd think delaying the rear brakes and changing the amount of fluid to them would both be accomplished through the prop valve, with mods.

    As to applications that would work, I'd personally probably want to try the Impala SS MC and probably even the combo/prop valve, but those master cylinders won't fit on mid 80's GM cars, so I'm guessing they won't fit the trucks either. The Cadi application might be a better choice. The 79-85 stuff should be cheaper due to how many years it was used, but I'd bet the master cylinder piston is much smaller for that application. I'd almost guess a Camaro one would be the same deal (smaller than truck), since AFAIK, the b-body (Impala SS, Caprice, etc) master cylinder has a bigger piston than the Camaro's.

    The 1LE Camaro was rear disked as well, but I *know* the rotors are pricey (early 90's stuff, maybe late 80's too) and you still have the issue of master cylinder bore size.
     
  20. Blue85

    Blue85 Troll Premium Member

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    The problem that I'm having is that the rear brakes seem to "hang up" when I start rolling. Coming to a stop, the truck leans forward a little (naturally) and after taking off again, I get a little "clunk" and then the rear seems to settle back down. Part of the reason I went rear disc was to avoid hanging brakes.

    As far as fluid volume is concerned, we can't ignore the fact that lots of us are running rear discs with the original master cylinders. I would guess that if there were 1-tons with 4-wheel discs, that would be the best MC to snag.

    Anybody have experience with the Eldorado or Camaro MCs?
     

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