measuring flex

[will e]

I did a search... you know that drill.

I am SOA/SF. I have some Alcan springs. I have some rancho shocks but I know (suspect) they are 'too short'. I need to verify that and, if they are, determine the best shock length/range and also put in some bump stops.

So what's the smart way of going about this? My understanding is the axle travel will be limited by just three things (brake lines not included..)

1. Drive shaft length and range
2. Shock Length and range
3. Spring range

I suspect the first thing I want to do is know how compressed/extended the axles can get within the drive shaft range. Then put stops to reduce spring compression and use shocks or straps to limit spring expansion. If my spings don't compress/expand enough to limit the drive shaft then I just need shocks slightly beyond those limits (or limit if it is only one or the other).

Anyways, I would appreciate any thoughts on how to approach this. I won't be changing springs and would prefer not to have to mess with the drive shafts. That's not to say if in figuring this out a drive shaft is really limiting my flex that I wouldn't get it shortened/lengthened to make it better.

[j20brett]

I doubt you would use more than 14-in of shock travel. But as to how much exposed shaft you should have a ride height, you will have to flex it out to see how much you want it to stuff into the fenderwell. I am SUA with rancho 44044's and use up about 11" of my 12" travel shocks, 5.5-in of that being in uptravel. I have 5.5" of shaft exposed at ride height also.

Are you planning on changing your shock mounting points any? By changing the mounts, you can set your shocks up to do whatever you want them to and limit excess compression with bumpstops.

[Stuka]

Take the shocks off and measure flex (on a ramp or something). Unless you are running very heavy tires over drooping the springs is typically not an issue with leafs. Over compressing is certainly an issue though, so make sure you have bump stops in the right pace.

When on the ramp, measure the distance from shock mount to shock mount on all 4 corners. This way you get the compressed and extended lengths for front and rear. Then look around shocks that fit this. A lot of times it actually requires moving the shock mounts down on the upper side to get the most travel. As typically droop is greater than compression. So finding a shock that fits without moving that upper mount can be tough. But unless you really want the most flex possible, this is most likely not going to be required.

[ktmracer419]

I have a 78 j10, stock springs, spring over axle, GM dana 60 front.

My drivetrain is all chevy, but the stock driveshafts were perfect length for what i'm running, so its a moot point.

I had some 14" travel bilstein 7100s I wanted to run and needed to relocate my shock mounts so I got some f250 shock towers and bolted them in (they are like 15 bucks each at the dealership)



Using the stock dana 60 shock mount (about the same location as the factory dana 44 shock mount) This put the bilsteins at about 7" of uptravel and 7" down.

For bumpstops I had some airbumps lying around, Had to limit my uptravel to maybe 4-5" so my steering wouldnt hit my motor mount (go figure that hits long before the 38.5s)

Now the last issue i ran into was the front driveshaft binding. The leaf springs flexed plenty, but I had to limit droop by a couple inches To avoid the axle end U joint exploding. Sure I could have cut and rotated the knuckles then shimmed the axle, But thats a lot more work than adding limit straps.

fully drooped

This setup is really only temporary. I will be adding a little length to my driveline with a doubler which should help give me more droop with the driveshaft being at a better angle. I also plan on linking the front end shortly after. But Right now it just plain works, and flexes plenty.

[ktmracer419]

Originally Posted by will e

That's not to say if in figuring this out a drive shaft is really limiting my flex that I wouldn't get it shortened/lengthened to make it better.

driveshaft limiting flex has more to do with the binding like I said, and not making it longer or shorter. only lengthen or shorten it if the slip joint is pulled too far apart or it bottoms out.

[will e]

ok, I think I understand most of it.

One question though, how do I know I have reached my optimum spring compression? If I take off the bump stops/shocks then when testing compression how do I know I have not 'over compressed' the springs.

I guess the real question is.. how do I determine which length bump stops I need? My original thought was to make them long enough to stop the axle before the shock gets fully compressed.

[Stuka]

Thats kind of tough with leaf springs, as its different for every set. With coils its very obvious where the spring hits its max compression. But typically you do not want to push the spring too much into the negative arch area. Especially if your springs have some arch too them. Flat springs can go negative farther as they start out more neutral.

Also pay attention to any rubbing with your given tire size. For me my tires rub before my springs over flex, so its obvious where my bump stops should be.

[will e]

Tire rubbing doesn't seem to be a problem. I went wheel'n in Ouray and had no rubbing issues. I also didn't 'feel' my front suspension 'stop' except when I was strapping Tim down Corkscrew. I hit a drop a little faster than I normally would and had his weight pulling me down. (We were trying to make sure he had enough momentum to get over the next hill). Something stopped the front as it was going down. I don't know if it was the shocks, the springs or ?? I am pretty sure it wasn't the bump stops since they are stock.

I am going to go mess with it some more. It doesn't seem to be causing me a problem but I think my shocks are probably too short and not allowing 'enough' droop...

[78 Arizona Chief]

Mike,
hey, haven't been active on here for a little bit but I'm back. I break them down to front and rear.
Front: This will be entirely limited by the front driveshaft's CV joint binding. I think you notched your crossmember. I would support the frame on jack stands, remove the tires, shocks and brake calipers. I would then drop the front end down with the ds connects and keep lowering it until you can't rotate the front driveshaft since the CV will bind. I would then push the axle back up until you can now turn the shaft. Go up another 1/2 inch or so and that is the max length the front shocks can be. Buy those shocks, intall, then measure bs length to hit 1/2-3/4 inch before shocks bottom out. Finally, make sure the brake lines can accomodate that much travel. I doubt the steering will limit anything since you did full high steer.

Rear: A lot easier since the ds won't limit it (unless you need to lengthen it). I would again set the frame on jack stands and let the axle drop away with the tires off. Where is settles can be considered max. Measure for shocks at that point and then again set bs height accordingly.

Are the springs settling any? How did it ride on the highway and trail.
Kevin

[will e]

Kevin
That makes a lot of sense. You have me remove the calipers to avoid stretching the brake lines (if they end up being the limiting factor).

In your scenario I would, in the end, use the shocks to limit the downward travel.


I think it may have settled a little. Sitting flat I have 25" eye to eye on the front shock.. where are you sitting?

The drive to Ouray was much better this year. I got the front tow aligned at shop. The springs kept me from doing 'the dance' at 65mph. Tracks good on good roads but still likes to follow some lines. You have to pay attention.

Next step is to get a front sway bar back in.

[will e]

Okay, I did what Kevin suggested. Good plan. My front drive shaft starts to 'bind' just an inch or so below what the shocks I have would allow the axle to droop. It's amazing how 'actual' the bind feels. So I am going to keep the shocks I have. I probably need to start thinking about maximum compression but I can see how letting the front drop past the drive shaft binding would be a big problem.

PS Kevin.. I ground down the passenger side spring plate while I had it all apart...