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How to?: more flex, no front driveshaft issues?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by dyeager535, Feb 22, 2005.

  1. dyeager535

    dyeager535 1 ton status Premium Member

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    Wondering if anyone can comment on how much flex you can get with a stock setup before things start to hit other things? :)

    I've got stock 3 leaf springs up front, with the "pinion snubbing" bump stop already removed. Still have the rear (still talking front spring) bumpstop that hits the spring, and the other one that hits the top of the spring plate that the u-bolts are bolted to. Both of these have left obvious evidence that they are hitting constantly, I hope only when I'm off road though. There are a few inches between them and the spring with the truck at rest on flat ground. I don't *feel* it hitting the frame as an obvious event (no noise, no feeling that "oops, theres the spring bottoming out), but I'm thinking that is part of the jarring ride the truck has...it's enough that even with the dust and mud that coated the underside of the truck from one week of hunting, the spots are bare where the bumpstops were hitting.

    I noticed after switching to poly body mounts that the body seemed more prone to popping sounds and general binding around doors, etc., than before with the stock rubber mounts. I figured that was all there was to it. But my friend that was over working on the truck with me (well, watching is more like it lol) yesterday said that the springs bottoming out were a more likely cause of the body issues. Makes sense to me.

    From what I understand, any issues with additional flex in the front is going to be on the passenger side. My exhaust is a good 1.5" away from the driveshaft/axle, etc., so that should never be an issue.

    Only thing I can think of as being a real problem is how much additional travel (compresssion obviously) can be had before the driveshaft starts bottoming out? I know the splined section of the shaft is the limiting factor here, but is there enough there to get another 1-2"(?) of travel without a stock one bottoming out? I know that 1-2" of travel isn't going to equate to 1-2" of compression, but testing how much is possible seems tough without damaging something...I've tried a floor jack outboard as far as possible on the front axle, but it didn't bottom the springs out before the other tire lifted.

    Just looking for thoughts and experience with this or similar. I suspect the right way to do this is to bolt up the stock shaft, get some bumpstops from the wrecking yard, trim them a bit at a time, bolt them in, and find somewhere I can flex the truck out enough to see if the driveshaft is getting close to bottoming out the splined section.

    What is the purpose the rearmost bumpstop, the one that hits the spring midway between the shackle and the axle/spring mount? My suspicion is that it is there to keep the front spring from contacting the frame because of axle/spring wrap? When I'm hard on the truck, it's in 2WD, so spring wrap in the front should never be an issue. Besides, if it's just to cushion the frame from that unlikely event, couldn't a MUCH shorter piece of rubber be placed there?

    Is there more to consider than just driveshaft splined length if I try and get a couple more inches of compression on the front by trimming the bumpstops, or even removing one or the other? It seems that everything else has plenty of clearance for more travel, just the bumpstops and splined section of the driveshaft being the limiters.

    If driveshaft splined section is the only concern, is that simply (but more $$ of course) solved by running a longer splined section which is something easily accomplished? I have the broken rear shaft out of my truck, which has a good splined section that appears to have a lot more travel than the front one...
     
  2. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    I think the rearmost bumpstop is supposed to work like having longer shackles and keep from bottoming on frame , but I am not certain .

    As for the passenger side , driveshaft , and flex . Stock I was fine , 4 inch lift I was rubbing the crossmember . I had to take a piece of crossmember out , not enough to compromise it , but a little square where it rubbed . I have to move my exhaust now that I am lifted , but it doesn't rub much to worry yet , only on pass droop .

    The driveshaft is working for me , but that may be different from truck to truck and trans/case etc. Maybe a little longer shaft overall , but leave the splines alone .

    For bumpstops up front I am running Mopar car bumpstops from Help section at Autozone , which is just a hair longer than the ORD swaybar holdup bracket . I can hit the inner fender sometimes now that everythings broken in .

    I would run bumpstops anyway , it won't hinder flex much if at all if they are short . Stock springs maybe just run the really thin or really short ones , like control arm bumpers from cars :k5: :k5:
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    My thinking with the rear bumpstop is that if the front one is doing it's job, since the spring arches "consistently" you wouldn't need a rear one...make the front one long enough, under regular suspension compression, the spring would never hit along it's entire length...but if you throw axle wrap into the equation, the spring could easily negate the front stop. Just my idea anyway...they used pinion snubbers stock on cars to keep from twisting the pinion up too far under acceleration, doing a similar thing with the spring (for the same or different purpose) makes sense to me. Not saying you are wrong, just wondering if having two bumpstops do the same thing would make sense to GM.

    Of course, my thinking is solely based on spring travel and axle wrap, not any issues the shackles create, etc., so I may not be seeing the "big picture" on spring movement. I'm listening though. :)

    Now on your suspension travel experience. Before the lift, did you change the bumpstops out for shorter? Since I have no plans for a lift, that part is most important to me.

    It *sounds* like you did do some bumpstop mods before then, if so, did you actually measure/test everything, or just run it and nothing broke? Nothing wrong with that, but as you mention, every vehicle has differences, I know bottoming out the shaft is a bad idea. :) Definitely not interested in hitting the fender, but with 33's, I think I'd have to get a LOT more flex out of the axle than will be possible with the stock stuff I've got to have problems.

    I'm hoping that my u-channel crossmember is workable. It should end up narrower than the stock crossmember. (probably only as wide as the "raised" portion of the stock crossmember, not the lower edges on either side) With no lift it doesn't sound like the driveshaft angle will be very extreme, so hopefully no issues. If I make it, it will be 3/8" lower in the area yours rubs as well, so thats a bit more extra space.
     
  4. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Yes I ran very short bumpstops on the stock front , the ones I used were the short Energy suspension ones that looked like a step pyramid you could trim those easily . I actually still have them , I can get a part number when I get home .

    Look closely at your crossmember , it will appear that the backside is a little lower where the driveshaft sits above it , stock you can probably get away blending the front half into it . On mine we just cut it out .

    I don't understand why they came like that , it would off been easier to have the stamping machine flat in that spot :dunno:

    I got pretty good flex out of the stock suspension while I used it . I actually popped out swaybar bushings , before I knew of the aftermarket kits .

    If you look at this early pic , you can see what I did stock on 31's . I couldn't get much more without removing the inner fenders , lloks like the tire is on the ground to boot :k5: :k5:
     
    Last edited: Oct 5, 2007
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    I appreciate the info. Sounds promising that I should be able to shorten the bumpstops at least some without causing problems to myself.

    If those are 31's and they were close to rubbing, with 33's I won't be able to get away with nearly that much bumpstop trimming I'm sure. But at least it will get some more travel. Be interesting to see what kind of difference that makes. Has to make some, or I wouldn't be bottoming out all the time as it is now.

    Did you by any chance try trimming the stock bumpstops? The front one looks to be hard enough material that it could stand some trimming, rear doesn't look that promising. As long as there is no reinforcing metal too far into the stop, should be able to trim and run as is, no? Poly probably a better bet since it offers more resistance and the stop will be thinner.
     
  6. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    I couldn't trim the stock ones , too many AZ summers prior to my ownership . They tore up the first time I put it in low :D
     
  7. Hossbaby50

    Hossbaby50 3/4 ton status

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    The reason bump stops are good things is they help keep springs from going negative on uptravel. Going negative will kill springs very quickly, especially lift springs.

    The only other thing I would worry about beside the driveshaft splines bottoming out and spring life, is if the springs uptravel more is the stock steering. Just make sure you don't bind it to much.

    Beyond that just ckeck for pumkin to oil pan clearence, and the stuff like that.

    Harley
     
  8. jarheadk5

    jarheadk5 1/2 ton status

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    I don't know about Dorian's truck, 'cause he's got 3-leaf front springs... but my '87 K5 has stock 2-leaf front springs that are already negatively arched, sitting on flat ground. I've only got about 1" between the bumpstop and spring plate; yes that's 1" measured clearance, and when it was still road-worthy the spots under the 4 bumpstops were the cleanest parts of the underside of the truck.
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    I have more clearance than you do between the stops and springs, but the spots are way too clean for a truck driven as "lightly" as mine, at least IMO. There have to be a lot of painful jolts that can be attributed to riding on the bumpstops I would think.

    My stock 3 leafs are flat, perhaps a hint of negative arch, so I don't *think* flexing them a bit more is going to hurt...they have to go negative during normal suspension travel, I just want them to move a bit more.
     
  10. ntsqd

    ntsqd 1/2 ton status

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    Bumpstops are a good thing. IMHO you should hit them, it means you're using the suspension to it's fullest potential. In desert racing the urethane bumps die an early and rapid death. Use rubber when you can, they'll live longer.

    From what I've seen the stock springs are designed to be neg arch. The Rauncho prerunner front springs on my Sub also appear to be designed for this. Few others are and driving them to bend backwards will kill them pretty fast. FWIW, those Rauncho springs made the ride WAY better. Does lift the front though.

    Roger Brown came up with a trick for articulating a truck in the driveway that really works well. Put a car ramp or similar at opposite corners. Check the ramp weight ratings first!
    What he used the trick for was to diagnose articulation. Drive onto them and check for teeter-totteriness. Space up the front until the truck lifts a wheel like on an RTI ramp. Stand back and look at the axles vs the body. Which ever axle the body has less angle to is the stiffer one.
    Can also use it to do what you want, to look at where things are when crossed up. Since you're crossing both sides on flat ground (assuming your driveway is reasonably flat) the truck should be stable enough to climb under it and look things over.

    I would check the drive shaft plunge with this trick. Cross it up and then pop the U-bolts loose. See if the shaft has any compression travel left in it.
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    From the pic that was posted, there is a HECK of a lot more travel left in the stock suspension, the bumpstops seem to be the limiting factor. I can see them as a "safety" device for driveline issues, etc., and thus not completely remove them, it sounds as if shortening them will do no harm. You'll still hit, something has to stop the compression, I just think more travel is good.

    Ramp idea is good, may have to try that one.

    I should state that my shocks still work, it's got quad shocks up front, which will eventually be tossed for a good single shock. I will also be marking the bumpstop with grease or something, just to make sure that it isn't hitting in street driving, speed bumps, etc. It shouldn't, but if it is, something more to correct.
     
  12. jimmy88

    jimmy88 1/2 ton status

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    Don't forget about axle wrap caused by hard braking and how that will twist the pumpkin and effect driveshaft length. Might that be part of the reason for the rear bump stops?
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    I can see hard braking causing wrap, but IMO, your shocks should take up a large majority before you hit bumpstops, and secondly, on the street, I would hope the spring was far enough away that it wouldn't come close to hitting.

    I believe this is probably a fine line between driving style/use, and how much of the stops you can trim. Going to be interesting to see, thats for sure.
     
  14. ntsqd

    ntsqd 1/2 ton status

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    Ideally a bumpstop has lots of travel. That way you don't hit it & stop immediately, the stop acts as a HUGE rising rate spring to slow down the suspension's compression over a longer distance.
    Rather than shortening it, I would suggest that you give it more of a taper while leaving it the same length. That will make it easier to compress while still having a decent distance to stop in.

    Failing that, shave the bumps real short and install hydro-bumps! :)
     
  15. jarheadk5

    jarheadk5 1/2 ton status

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    Exactly what I'm talking about, too. My truck saw far more street miles than offroad miles, especially in the last 2 years it was driveable. I've known about 2 of the broken bodymounts since early 2001, so I only 'wheeled once after that.
    Incidentally, my rear springs have definitely sagged quite a bit, because I had the same clean spots where the rear axle bumpstops hit (on the axletube, I think). But with the front sag, it all kinda equals out. My truck actually sits level, no "K5 droopy butt".......
     
  16. jimmy88

    jimmy88 1/2 ton status

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    Just throwing it out there. I was thinking more about steep rocky decents where you might be on the brakes while running into rocks or dropping off ledges. Figure there will be a few issues: axle twist combined with rearward movement of the axle and compression of the suspension, all of which will want to shorten the driveshaft. Might want to make sure you have some extra slip for those conditions.
     

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