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only complaint about rear discs...

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by mike reeh, Jul 25, 2003.

  1. mike reeh

    mike reeh 1/2 ton status

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    ... is that they dont release instantly like they should.. they work excellent but if I get on it hard (say, hard enough to lock em up) I can let off and its a few milliseconds (I wouldnt say its more than 1 full second) before they release.. Anyone else experience this?

    every single part of the brake system is new or rebuilt. I wonder if it could be master cylinder related though because its a kragen M.C. and it leaks like a SOB. I will replace it soon, hopefully with a higher quality one.. but I have a feeling its not because of the m.c.

    I thought maybe there should be some sort of spring retraction system to make it release instantly like you might find on rear drums, but.. its just an idea..

    anyone?

    mike

    77 K25 swb 400/700/205
     
  2. white-rhyno

    white-rhyno 1/2 ton status

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    I believe it has something to do with the proportioning valve. Its designed to hold some pressure on the drums. I cant remeber who but someone here has a welth of knowledge on this subject. I have just got used to your problem. It dosnt bother me all that much.
     
  3. Blue85

    Blue85 Troll Premium Member

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    I don't have this problem and I don't understand why you do, either. Rear discs are the same as front discs and nobody ever complains about them not releasing right away. There is nothing in the prop valve that would cause noticeable hanging of the rear brakes.

    My guess is that the rear calipers or caliper pins are hanging or that it is not your brakes at all but the classic T-case slip-yoke bind.

    Just my opinion.
     
  4. RootBreaker

    RootBreaker 3/4 ton status Premium Member

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    from my understanding ... if you converted from drum.. you need to replace the portion valve with one that is adjustable... cuz the drums tightened and released differently.. so now you need a adjustable portion valve to get it tuned in....
    but that is all hearsay as i havent done the conversion .... YET /forums/images/graemlins/thumb.gif
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    [ QUOTE ]
    Rear discs are the same as front discs and nobody ever complains about them not releasing right away.

    [/ QUOTE ]

    IIRC, one of the features of the front disks is that when the pedal is released after application, the shoe (my mistake, pad) *should* be pulled away from the rotor a bit. Almost like a reverse action...you clamp the rotor when you push the pedal, unclamp as the pedal travel changes direction.

    There is no spring to pull the disk pads away from the rotor like there is with drums.

    However, I have a feeling this is done for economy and longevity, not out of necessity to prevent the problem that is happening here.

    I doubt the proportioning valve is the problem, but my suspicion would be, whatever the cause, that the rear line pressure is not "bleeding off" fast enough. The lines running to the rear are smaller, but that would probably affect rear application as well, and be more common among people that have swapped rear disk setups.

    Still somewhat interesting how different peoples problems are with this swap. No one seems to have exactly the same issue.
     
  6. Stoopalini

    Stoopalini 1/2 ton status

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    Which calipers are you using? I used the caddi calipers in my rear swap, and the pads are just a hair too big with the new rotor. I have to take my pads and run them down a belt sander for a few seconds and shave enough off to fit the pads in.

    Then, for a few miles (100 - 200?) they are a little sticky, but they loosten up after a few applications.

    Thomas.
     
  7. Blue85

    Blue85 Troll Premium Member

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    The adjustable proportioning valve will reduce the bias to the rear. How much you need it depends a lot on how big the calipers are that you put in the rear. However, it will not speed the disengagement of the rear brakes.

    I am actually considering putting a residual pressure valve in my rear brake line. My thought is that it will give me higher pedal action since less fluid will flow back after each application. As long as the pressure is right, it won't cause hanging or dragging. Usually these are about 2psi for disc and 10psi for drums.

    In my experience, all problems with pulling or hanging brakes have been at the calipers. My list of suspects would be in this order:
    1) sticking caliper slide bolt
    2) caliper piston sticking in it's bore
    3) master cylinder holding too much residual pressure on the rear circuit.
    4) Slip-yoke bind
    5) phase of the moon
    6) proportion/combo valve

    What Master Cylinder do you have?
     
  8. fad2blk99

    fad2blk99 1/2 ton status

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    If you don't have one already I'd get the adjustable proportioning valve. Wilwood makes one...
    You can buy them at www.summit-racing.com
     
  9. woody9

    woody9 1/2 ton status

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    aw shucks.... (a bit long) and a poll!

    i've been lurking on this subject for long enough! /forums/images/graemlins/smile.gif
    I've got a 91 1/2 ton sub, originally with the 10 bolt/3:42 axles in it and factory disc/drum (11"). /forums/images/graemlins/confused.gif
    For towing reasons, i jumped over to a 14FF (rear & matching front 10 bolt) with 4:10's in it from an 80 pickup.
    Clean & easy swap! u-joint/u-bolts, and brake parts (with the 80 13") and (percieved?) more 'swept area' on the front with the 3/4 ton 'top-hat' disc's. /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif
    That was an IMMENSE improvement in braking!! /forums/images/graemlins/thumb.gif Especially when towing. (pricey with new hardware, 1 new 13" drum and such)
    Time passed, and i felt the effectiveness was fading away. Hmm, could this be my excuse for the rear disc? I thought so! /forums/images/graemlins/smirk.gif I slowly began collecting the parts. Brackets on the board, calipers when they were on sale, pads as well, new hardware again (yeah, the bill was adding up, but done over time, and less than the previous drum hardware was with that pesky 13" drum replacement!!)
    Finally the day came to make the swap! Fearing issues with clearances, i popped the new pads on the front and took the lightly-used ones and moved 'em to the rears. I started in and was done in no-time flat.
    Mamma got REAL tired of being the 1st mate on brake bleeding, but that too passed in time. Still i wasn't getting what i thought was right results from the conversion. /forums/images/graemlins/thinking.gif
    Took it down to the PROFESSIONALS /forums/images/graemlins/deal.gif, and they did the power bleed on it, and still, not what i thought was right.
    Was able to retain the original ABS stuff, as it's primarily x-case driven (i think.. nothing out on the old axle anyways...), and NEVER have locked the rears. /forums/images/graemlins/ooo.gif
    I've done the complete fluid change as well now, and still, not what i expected. (cheby calipers, not the caddy's btw).
    I don't 4-wheel it like i originally planned /forums/images/graemlins/frown.gif (Wis is fun, but not quite like the rockies of Colorado!! /forums/images/graemlins/thumb.gif)... so for my use, towing braking is what i'm looking for.
    The M/C checks out a-ok, and no other issues with the pro-valve.
    I'm really about ready to go back. /forums/images/graemlins/shocked.gif I discovered that part of my issues with the drum setup was more a leaky seal, than degrading performance, so.....................
    Have thought about the 'residual pressure' setup, maybe the 1 ton M/C (if no line issues!!), or maybe even jumping back to the drums, where life was good with 13"! (so to speak!!??)...

    what's ya'lls recommendations? /forums/images/graemlins/ears.gif
    Bail out and make a he!! of a deal to someone on the disc setup? (plus shipping of course!!)... or invest more in this? /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif
    I'm looking @ $50-$75 (new shoes & misc hardware)to go back. Lord knows what i'll continue to spend to improve the disc setup.
    ????????????????????????? /forums/images/graemlins/thinking.gif /forums/images/graemlins/thinking.gif /forums/images/graemlins/thinking.gif <FORM METHOD=POST ACTION="http://coloradok5.com/forums/dopoll.php"><INPUT TYPE=HIDDEN NAME="pollname" VALUE="1059181125woody9">


    What to do?
    <input type="radio" name="option" value="1" />Keep disc and experiment?
    <input type="radio" name="option" value="2" />Jump back to drums and make me a deal? (check is in the mail!!)
    <input type="radio" name="option" value="3" />Go have another beer and ponder this ??
    <input type="radio" name="option" value="4" />Other?
    <INPUT TYPE=Submit NAME=Submit VALUE="Submit vote" class="buttons"></form>
     
  10. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Re: aw shucks.... (a bit long) and a poll!

    Go hydro boost with the one ton MC. I run the D44 calipers, D60 calipers up front and on 40's it stops like nobody's business. The brake bias is excellent and I can threshhold brake easily with both front and rear tires on the verge of lock-up.

    I use the stock prop/combo valve too.

    Vacuum boosters are for cars.../forums/images/graemlins/grin.gif

    Rene
     
  11. camiswelding

    camiswelding 1/2 ton status

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    Re: aw shucks.... (a bit long) and a poll!

    this should help...
    http://subtopics.freeyellow.com/Brakes.htm
    I am very interested in what you all have to say about the conversion... I moved all the one ton stuff to my blazer.. it was all nearly new.. I wanted to do the disc conversion but I was waiting for Az's ebrake setup which is still in R&amp;D... I still hope everyone agrees this is the best way to go and the one case it isnt working is an anomoly with that vehicle...
    let me know how it works for the rest of you
    cam
     
  12. woody9

    woody9 1/2 ton status

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    Re: aw shucks.... (a bit long) and a poll!

    had thought about that, but wasn't sure the $$$ involved in dumping the 'car' brakes and getting those MAN-LY Truck brakes. (would need complete setup... and time... and... hmmm), but i shoulda added it to the poll!
     
  13. woody9

    woody9 1/2 ton status

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    Re: aw shucks.... (a bit long) and a poll!

    I read a lot of that stuff on 'free-yellow' (dang popups!! /forums/images/graemlins/angryfire.gif ), and about figured the LARGER drum thing in the rear really DOES fit what i was looking for.
    He!!, this thing don't see dirt roads hardley except when i'm in the driveway! No more stream crossings, etc. Almost criminal use for such a truck! /forums/images/graemlins/frown.gif
     
  14. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    Re: aw shucks.... (a bit long) and a poll!

    I don't mind the rear drums myself, huge difference in braking compared to the 11" drums. I can't justify the expense of doing the disc swap not to mention the e-brake I need...maybe when the drums are shot I will.
     
  15. fad2blk99

    fad2blk99 1/2 ton status

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    Re: aw shucks.... (a bit long) and a poll!

    I got a 14b rear disk setup on my Blazer....
    What do I need to go to hydro boost?
    A buddy of mine has a mothballed 2wd Diesel I might be able to get the parts from....
     
  16. SUBFAN

    SUBFAN 1/2 ton status

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    Re: aw shucks.... (a bit long) and a poll!

    Take it all....
     
  17. fad2blk99

    fad2blk99 1/2 ton status

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    Re: aw shucks.... (a bit long) and a poll!

    What exactly do I need???
    Of course the hydro boost cylinder and hydraulic lines...
    What about pump? I assume it runs off the power steering pump. Will my pump work or do I need one from a hydro boost application? And the master cylinder.... I think the donor truck is a 3/4 ton.... should I go get a 1 ton M/C?
    Just need a little help fillin' in the blanks....
     
  18. SUBFAN

    SUBFAN 1/2 ton status

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    Re: aw shucks.... (a bit long) and a poll!

    Sorry can't help with particulars, just telling you what I would do....That way I would have two of everything, and I wouldn't have to go back either....
     
  19. SF87K5

    SF87K5 1/2 ton status

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    Re: aw shucks.... (a bit long) and a poll!

    Take everything from the MC down to the pump. i.e. pump, MC, hoses etc.
     
  20. wrathORC

    wrathORC 1/2 ton status

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    Re: aw shucks.... (a bit long) and a poll!

    You can steal the hydroboost setup off a car too. Just about all diesel cars had them. It's a little more girly than the truck one but it'll work. It puts out about twice the assist pressure our powerboost booster does.

    I've been thinking about getting one so I can run a little more wild cam. I can easily lock up all four discs right now so it isn't necessary but it'd be nice. Plus, I should have a little more room.
     

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