Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Controlling brake dive

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BadDog, Dec 21, 2003.

  1. BadDog

    BadDog SOL Staff Member Super Moderator Author

    Joined:
    Feb 24, 2001
    Posts:
    7,777
    Likes Received:
    11
    Location:
    Phoenix, AZ
    Well, my son has totaled my wife’s prized Bonneville SSE/LE. So, now she is driving his K5 for the next month or two as this is resolved. Problem is, it has some serious nose dive, on heavy braking. Combine that with cross over steering and you have a quick right turn along with that panic stop.

    For me it’s not a problem, I had hardly noticed it and automatically compensated without a second thought. I pointed it out to my son and we did some parking lot “tests” to show him what to expect. He also seemed ok with it, and I saw him handle it fine in “real world tests” a couple of times. Now my wife is trying to drive a K5 after years of various Bonneville and sporty cars. The nose dive/steer scares her. And she nearly flipped it (her words, not sure really how close) when a stupid Mexican in one of those trash cars with the 12” wire rims sticking 10” out the side pulled out in front of her. Now she is really freaking out about driving it…

    So, I’ve been tentatively dealing improving the drivability over time, including this, but it just got elevated to “top priority, must fix”. Here is what I have:

    Basics - 88 K5 Blazer, TBI350/700R4/241/D60/C14/4.56/locked
    Lift – 4” Rancho Spring front, block rear.
    Shocks – Rancho 5012 x 4
    Tires – 35” BFG AT/KO
    Steering – Stock with cross over.

    I’ve already removed a 2” body lift. That made a HUGE improvement in body roll and some reduction in nose dive as well. Not enough though. The 5012s on the front have little resistance to up travel, very tight on down travel. I guess that helps soak up the bumps, but it sure doesn’t help control nose dive. If I put on a stiffer shock (particularly on compression), then that is going to hurt my ride quality which is quite good right now. But I don’t see much other option to further reduce the nose dive. More importantly, I need to reduce the brake steer, but short of ditching the cross over.

    Any suggestions for something I’ve overlooked?

    Any suggestions for what shock would make a noticeable difference without killing the ride? Preferably an affordable shock...

    Maybe I’ll just buy a block and put the stock drag link back on for a while…
     
  2. Paxx

    Paxx 1/2 ton status

    Joined:
    Feb 9, 2003
    Posts:
    1,405
    Likes Received:
    0
    Location:
    All Over Western Canada
    Didn't mention if the swaybar was connected or not. If it isn't that would make a huge difference I would imagine.

    All that I can think of anyway.
     
  3. BadDog

    BadDog SOL Staff Member Super Moderator Author

    Joined:
    Feb 24, 2001
    Posts:
    7,777
    Likes Received:
    11
    Location:
    Phoenix, AZ
    Dang, I thought I had covered everything possible. /forums/images/graemlins/rolleyes.gif /forums/images/graemlins/rotfl.gif

    No, the sway bar is not mounted. Right now the steering stabilizer has been mounted to the drag link. To reinstall I would need to move it back to the tie rod, but that's a problem because it is a 1.5 x 0.375 rock rod. I would have to build a clamp/bracket to move it. Also, 4" of lift causes some problems for the sway bar angles.

    I had originally planned on getting the sway bar back onto it when we bought it for my son to drive. But the body roll wasn’t that bad, and it’s not bad at all now that the body lift is off (still can’t believe how much of an improvement that made). I guess the sway bar might reduce that feeling of “I’m gonna roll!” during a panic stop/nose dive/steer situation, but I don’t think it would help with the nose dive and steer itself. Good idea though, I may try it if nothing else presents itself.
     
  4. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

    Joined:
    Jul 23, 2000
    Posts:
    36,175
    Likes Received:
    1,385
    Location:
    E-town baby!
    Maybe there is too much front brake bias as well. I think that would contribute to dive. Maybe an adjustable prop valve and some more testing?

    Other than that maybe some RS9000's or other adjustable shock as a band-aid until your wife gets another car...crank the shocks a little for her...crank em back down for you or your son.

    Rene
     
  5. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

    Joined:
    Aug 28, 2002
    Posts:
    9,097
    Likes Received:
    144
    Location:
    california
    I would add 2 more shocks up front if you have the quad shock package on it and a dual steering stabilizer. I have a 9" lift and no body roll problems and my sway bar is still connected. MIne swerves to thr left under hard braking too and I think it's a caliper or rear drum causing it, I would check out the brakes, our big 14BFF drums can really pull hard.
     
  6. 88Silverado

    88Silverado 1/2 ton status

    Joined:
    Mar 13, 2003
    Posts:
    2,664
    Likes Received:
    0
    Location:
    Quartz Hill, So. Cal
    It can be several things. Usually its a caliper or pads on one side that are sticking. Little bit of air on the left side caliper, try bleeding them. Porportioning valves usually dont change pressure side-to-side. Front to back, yes cuz discs run higher pressure than rear drums. A tow-out problem on the right can cause it also. Since your not running a swaybar could be a softer spring on the right side.

    My 88 had the same problem, Bad dive to the right on hard breaking. I installed the front lift and redid the brakes and replaced the calipers. Still has slight pull to right but I think its cus the new pads arent fully worn into the rotors yet (I didnt turn them). Nothing like before.
     
  7. BadDog

    BadDog SOL Staff Member Super Moderator Author

    Joined:
    Feb 24, 2001
    Posts:
    7,777
    Likes Received:
    11
    Location:
    Phoenix, AZ
    Sorry, one more thing I should have added. It's not brake pull, I'm sure of that. It's the same thing as the "bump steer" you get with cross over. Hit a good bump in the road (like the gutters at some intersections) and you'll notice a quick dart to the right. This is because of the angle of the cross over drag link. Same thing is happening here. Excessive nose dive is pushing the axle closer to the frame (just like a bump) which flattens the drag link, effectively pushing the knuckle to the right as it does so (because the pitman arm does not move unless you let/help it).

    I think Rene has it close though. These are 1 ton brakes on a short K5. I’m sure the power in those front calipers/disks is way high relative to the rear. A manual prop valve is likely my best fix...
     
  8. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

    Joined:
    Jul 23, 2000
    Posts:
    36,175
    Likes Received:
    1,385
    Location:
    E-town baby!
    Hopefully a prop valve will get it decent enough for your wife's comfort...cuz when your wife isn't happy nobody is happy (she'll make sure of it... /forums/images/graemlins/laugh.gif)

    Rene
     
  9. jms

    jms 1/2 ton status Author

    Joined:
    Jan 24, 2001
    Posts:
    1,683
    Likes Received:
    0
    Location:
    --
    From my own limited experience I'd say its: 1. brake bias fr >> rr; 2. front shocks.
     
  10. Blazinaire

    Blazinaire 1/2 ton status

    Joined:
    Mar 17, 2002
    Posts:
    1,262
    Likes Received:
    0
    Location:
    Santa Maria, CA
    Russ, all you need to do to almost completely rid the truck of bumpsteer (the brake steer that you are talking about) is make a trac-bar (panhard bar) that is parallel and equal in length to the draglink. The down side to that is that it will shift the entire axle to the passenger side as the suspension compresses... you won't feel it in the steering wheel and it won't have any adverse affects on handling, but it could potentially wear out your front spring/shackle bushings faster.

    Even if you only had rear brakes the truck would have brake dive, so I don't think that playing with proportioning will really help to reduce that. Sounds like you might want to look into throwing another leaf in the pack?
     
  11. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

    Joined:
    Jul 23, 2000
    Posts:
    36,175
    Likes Received:
    1,385
    Location:
    E-town baby!
    Actually with rear brakes only you get no front dive. Try it yourself sometime if you have a decent E-brake.

    Rene
     
  12. zcarczar

    zcarczar 1/2 ton status

    Joined:
    Feb 10, 2002
    Posts:
    2,495
    Likes Received:
    0
    Location:
    Apple Valley California
    I bet some decent high pressure gas shocks with a fairly stiff compression valving would also do the trick. I would say run a set of Bilstien 5100's with the appropriate valving. Maybe Jay can explain the shock valving for us that dont know much about it.
     
  13. Thumper

    Thumper 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    1,582
    Likes Received:
    0
    Location:
    Alberta Canada
    Tell me more about this bar! I have the same brake effect with my crossover. Could you make the bar quick disconnectable? Run it on the street and take it off for the trail?
    Where is the best place to mount it? Does it actually work?
    I have to get rid of this dive and dart syndrome... I will eventually be going to a high steer setup... hopefully this will fix it, but in the meantime...
    Does everyone have this syndrome with a crossover?

    Thanks
    Mike
     
  14. Pookster

    Pookster 1/2 ton status

    Joined:
    Nov 21, 2000
    Posts:
    3,195
    Likes Received:
    0
    Location:
    NYC, NY, USA
    Totally agree with you- Lack of or weak rear brakes cause massive brake induced steering. The truck will most likely still steer straight, (try it in a parking lot with your hands off the wheel). You'll see the wheel turn as you apply the brakes as the front springs compress.

    There isnt too much you can do- sway bar helps a lot, Sway bar disconnects are acutally a bit on the detremental side when it comes to this particular effect. The other thing is, you may have to try and limit rear spring motion-

    as the front is compressing, the rear is decompressing. You could try some limiting straps of some sort- Not too much, but I noticed that on my pothole soaked roads, I get 4" of shock compression in the rear, and about 2" in the front. Any flexy suspension setup will do that though.

    [ QUOTE ]
    Actually with rear brakes only you get no front dive. Try it yourself sometime if you have a decent E-brake.

    Rene

    [/ QUOTE ]
     
  15. BadDog

    BadDog SOL Staff Member Super Moderator Author

    Joined:
    Feb 24, 2001
    Posts:
    7,777
    Likes Received:
    11
    Location:
    Phoenix, AZ
    Yeah, after Christmas I'm going to run down a simple prop valve to see how that does.

    I may also go get some 9012s (or whatever the new number is, 9812?) or the long (don't know the number) gas charged Billstiens. I tried some DTs and some Rancho 7012s (thanks Allan!) but they are no better than the 5012s... Also got to redo the shock mount because the angle is all wrong and both 5012s have the loop bent about 30* and about broke off! /forums/images/graemlins/eek.gif

    If all else fails, I may put a moderately tight limit strap off the top of the housing (center) to prevent the rear jacking. But I’m afraid that will be harsh on the rebound. All I know is “Moma’s not happy and neither are we till this is settled…” /forums/images/graemlins/rolleyes.gif
     
  16. justhorsinaround

    justhorsinaround 3/4 ton status

    Joined:
    Sep 16, 2003
    Posts:
    6,798
    Likes Received:
    0
    Location:
    Northerish Phoenix, Az
    I didn't even think of your rear brakes effecting your nose dive prollem when you were over here the other day. I hate bein a dumb dumb head sometimes. Yea I'd look seriously into your back brakes and your proportioning valve. I'm thinkin I need to do the same thing on mine as I scared the pee outta myself the other day on the way home from Table Mesa. Good luck to y'all.


    Allan
     
  17. BadDog

    BadDog SOL Staff Member Super Moderator Author

    Joined:
    Feb 24, 2001
    Posts:
    7,777
    Likes Received:
    11
    Location:
    Phoenix, AZ
    Ok, speaking of prop valves, any recommendations? I’m thinking seriously about this Willwood unit.

    Willwood Prop valve at Summit

    Problem is, most simply reduce pressure passing through. I need more in the rear so I'll need to disable the stock prop valve to do this. What's the best way to do this without killing the residual pressure?
     
  18. Blazinaire

    Blazinaire 1/2 ton status

    Joined:
    Mar 17, 2002
    Posts:
    1,262
    Likes Received:
    0
    Location:
    Santa Maria, CA
    [ QUOTE ]
    Tell me more about this bar! I have the same brake effect with my crossover. Could you make the bar quick disconnectable? Run it on the street and take it off for the trail?
    Where is the best place to mount it? Does it actually work?
    I have to get rid of this dive and dart syndrome... I will eventually be going to a high steer setup... hopefully this will fix it, but in the meantime...
    Does everyone have this syndrome with a crossover?

    Thanks
    Mike

    [/ QUOTE ]

    Here's my thoughts on the trac-bar: it must be as close as possible in length with the draglink and also be parallel with it. The best place that I have found to mount it so far has been directly behind the steering box (just enough room to keep the pitman arm from hitting the bar) with a bracket that extends outwards a few inches off the frame (this is to compensate for the trac-bar not being able to attach to the knuckle on the passenger side but rather to the tube right at the housing end thus making it equal in length to the draglink) For attachment points on the tube simply weld a couple of tabs to the "C" of the tube near (but just below) the balljoint (try to make it the same height as where the draglink attaches to the steering arm.) You would probably want to make it a sleeved tube especially because it will more than likely have to have a bend in it and it will be taking ALL of the side load of the front suspension now. Heims or bushings can be used and other than that there really isn't anything to it.

    All that this bar is doing is forcing the suspension to travel in the same arc as the draglink nearly eliminating bumpsteer. It shouldn't limit your wheel travel much if any and I think that it wouldn't even be worth it to make it disconnectable... But if you so pleased, you could simply replace the bolts that run through the bushings/heims with hitch pins at both ends and completely remove the bar as you please (good luck putting it back in after a day of hard wheeling! /forums/images/graemlins/eek.gif)

    Histeer won't make a gnat's fart of a difference for this problem (ask me how I know)... it is just a simple matter of creating proper geometry and it bothers me how often people try to "band-aid fix" this problem and end up only with a lighter wallet /forums/images/graemlins/rolleyes.gif.

    As for shocks in the frontend Russ, just remember that all the shock is doing is slowing the movement of the spring. No matter how stiff the shock is, the springs will still compress just at a slower speed (spring rate remains the same) Stiffer shocks do help to control things like body roll and brake dive momentarily but if you're hard on the brakes for more than... oh say... 3 seconds... the front end will still dive /forums/images/graemlins/deal.gif.

    Most of the people on this board seem to be blind to the fact that 90% of the shocks available to us are made by one of two companies (gabriel or monroe) regardless of the brand name stamped on the side. Just because Jo Blo says that one is softer/stiffer than the other doesn't make it so. Adjustable shocks are another gimic (that I fell for), you will find that you will find an appropriate setting for your vehicle and leave it there rendering the adjustability pointless. Wouldn't it make more sense to just buy a shock that has the proper valving to begin with?

    Without going to a rebuildable/revalvable shock, hands down the best shock you could get would be a bilstein (I could write a book on why they are better but I'm sure that you are all tired of this book I've already written /forums/images/graemlins/blush.gif) the part number that I ASSume you are looking for (14'' travel 5100's zinc plated even ) is BE5-6250 (of which I have 4 of sitting under the christmas tree for my dad's truck /forums/images/graemlins/thumb.gif) feel free to ask if you want more info /forums/images/graemlins/deal.gif

    You may be on to something with the brake proportioning (I must admit, Rene let me see the light) but if that doesn't pan out as planned, I think it would be a good idea to restrict suspension movement (not just slow it down) by adding to the overall spring rate.

    Jay
     
  19. BadDog

    BadDog SOL Staff Member Super Moderator Author

    Joined:
    Feb 24, 2001
    Posts:
    7,777
    Likes Received:
    11
    Location:
    Phoenix, AZ
    Yeah, the drag link would be the best fix, but it's not really what I'm looking for since I think it would kill springs and bushings if changes were not made to allow the axle to move laterally without tremendous bind. The main point of a cross over is to allow extreme articulation while still allowing you to steer lock to lock. Extreme articulation with a track bar, with the passenger side down, is going to really put the hurt on some springs and bushings as the track bar tries to force the axle out the driver’s side.

    As for shocks only slowing the effect, I am aware of that and I agree. But I think her biggest problem is the rate of the effect anyway. When she nails the brakes due to some nit wit pulling out in front of her, the front drops very quickly causing the truck to dart dramatically to the right; faster than she can deal with. Slowing that from full dive in 0.5 seconds down to say 2-3 seconds was really what I was looking for out of shocks. That should make it much more manageable and, I think, reduce her fear of the truck.

    I’m not too keen on adding rate to the front springs even though I do have extra leafs lying around. They are nice and supple now, giving a good ride and all around work well. Still, might do it at least for the next month or two while she drives it. But that will be my last resort.

    As for the type of shocks, thanks VERY much for the numbers on the Billsteins. I’m leaning that way for now. Main reason for considering the adjustables is that I could crank them up for her to drive now and then down for me when she gets a new car.

    You also say:
    [ QUOTE ]

    Just because Jo Blo says that one is softer/stiffer than the other doesn't make it so


    [/ QUOTE ]
    But I think this is incorrect. Yes, regardless of stickers and colors, they are all made in just a few plants owned by a couple of companies. But, as I’m sure you know (and state later), they are made to many different specs and designs. Even among the same design of shock, you can have dramatically different rates due to valving, pressure, and relief specs among other things.

    So, my current plan is this.

    1) Figure out what to do about the brake balance. Still not sure about the prop valve. I’ve never been faced with needing to *increase* the rear brake pressure, usually it’s just a matter of putting in the valve and cranking it down. This time I would need to disable the main prop valve while keeping the residual valve functioning, and I don’t have a clue how to do that. I was talking to Dr 4x4 yesterday and he had a suggestion I had not considered. I have a prop valve on the buggy because the massive 1 ton rear brakes locked as soon I touched the brakes. The K5 has almost the smallest ¾ ton brakes made. If I swap them, that might be enough, but a freaking lot of work plus I would need new 1 ton shoes (not cheap) since the ones on the buggy are pretty beat.

    2) New shocks, particularly on the front. Maybe gas charged Billsteins since they have much stiffer compression rates. But still chewing on a set of the new adjustable Ranchos since that would give me the option of softening things up in the future when she is no longer driving it.

    3) If this is still not enough, last ditch will be adding a leaf in the front pack.

    Oh, and one more thing. It was slated for a shackle flip to eliminate the rear block and fix the pinion angle VERY soon. But that will be avoided until she is done with it since that will make the rear even more “loose” in all dimensions...
     
  20. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

    Joined:
    Jul 23, 2000
    Posts:
    36,175
    Likes Received:
    1,385
    Location:
    E-town baby!
    Lot's of good info there Jay. I'm not trying to hi-jack this thread (too much...) but wondered what you thought of the Doetch Tech shocks?

    rene
     

Share This Page