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Old 08-08-2013, 01:50 AM   #1
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Default More on Chevy suspension issues

As more information has been coming in on new springs, shocks, wheels, tires, etc, you would think things would get clearer, but it seems to be going the other way. Harsh, not harsh, porpoise, no porpoise, springs fit, springs don't fit, shocks too short, shocks not too short, Tufftruk good, Tufftruk bad, Erb good, Erb bad. No real consensus on much of anything.

I was doing the bi-annual service on DW's CRV, oil, trans fluid, coolant, brake fluid, etc, so I had some time while things were draining, cooling etc. The Roadtrek is high enough for me to get under without jacking it up, so I crawled under to do some measurements. First I used a plumb bob to locate the lower control arm pivots on the floor, then the spring/shock centerline, and then the middle of the tire. Measured out to be 8" from the pivots axis to the spring/shock, and 20" from the pivot axis to the tire center. That means the spring and shock move 8/20 (40%) as much as the wheel. I then marked the shock at the bottom of the dust boot, so I could tell where it was in it's travel when loaded, after removing it. I took the shock out and checked how much travel was in each direction from the mark, which is at normal, light load height. It had only .4" in the extension direction, and nearly 4" in the compression direction. The .4" extension gives 1" at the wheel, which is about half of what I have normally heard is the proper droop at the wheel of 2".

At that point, I started to try to determine how much droop I could realistically have before the upper control arm hard stop hit the frame, metal to metal. I measured the wheelwell height at rest (37") and the camber of the tire (-.5*) and then lifted the van by the crossmember frame on the same side of the van in increments making the same measurements and also watching the gap close on the hardstop. Here is how the numbers came out:

37" / -.25* / gap at over 3/4"

38" / -1.5* / gap about 9/16"

39" / -3.5* / gap about 5/16"

40" / -5* / gap about 1/8"

40.5" / -- / upper arm on stop

From this it would appear that the most droop you would possibly be able to have would be 3", and that would put you awfully close to the stop, especially since the shock is in rubber and could possibly move further down if it dropped quickly. I already had 1" of droop, so if I wanted to go to 2", and stay about 5/16" off the stop, I would need the shock to be .4" longer, which would double the amount of droop. There was not enough thread to get .4", but 4 washers got me .320", and I could still get the nut tight enough to get to the locking section with one thread showing above the nut. After it was back in, I measured about 5/6" to the stop. Pretty close to what was predicted.

I didn't have a chance to take it for a ride to see if it makes any noticeable difference, but I am not expecting anything major, as I had not noticed the shock topping out in the past. We will see what happens in reality.

While it does appear that, at least in our case, a little more droop may be a good thing, and certainly doesn't hurt much, although the camber change does start to get pretty big, and seems to be the wrong way compared to what I thought it would be (I thought it would go to the positive).

The actual numbers also point out, if correct, that the posts wanting 2" longer shocks would be way, way, too much longer. Even 2" more droop at the wheel is possible, but getting very close to hitting the stops. You would wind up with more droop than compression travel as you would lose 1/2 your compression travel. It would also make contacting the hard stop on the upper control arm an almost certainty, if you hit a dip big enough. One wheel bumps would be much less of an issue, as the very large front swaybar would hold the wheel up a lot.

IMO, for our dimensions, a shock of .4-.5" longer would be the best. That would give 2-2.25" droop, which is right where folks say it should be, and it would still keep you off the hard stops. 3/4" longer would be getting you very near the stops, but give you another 3/4" droop to nearly 3".

It would be interesting to see if Bilstein makes this shock with a longer rod, so you could use a couple more washers. Even 3/16" longer would be enough to get you to 2+" of droop. (total of .480" in washers).

If folks had more overhang weight in the rear than we have, they may be lighter in the front and more likely to top out the shocks. That might also explain some of the porpoising issues. Large overhung weight, airbags up to support that weight, lighter front weight because of it, might give a rotation around the rear axle that would feel like front end bouncing.

Interesting stuff, but I still don't know what it all means or why the results are so different for folks.

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Old 08-08-2013, 02:11 AM   #2
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Default Re: More on Chevy suspension issues

I figured I would list this test separately from the first post. This is a test we ran last week on our first of the year outing to Perot State Park in Wisconsin. We knew some of the roads would be in pretty poor condition and possible be under construction.

There have been a few folks who have stated that the rear ride got harsher when they put in airbags, which is opposite of what we found on our C190P. Airbags are known for giving a better ride than springs in many industries, like trucking and railcars, so it was odd. I could see it if they were pumped up very high, giving a huge springrate, but not if used normally.

Without bags, we had found the van to pitch quite hard on compression bumps in the rear, probably due to being on the very high rate overload leaf. We found it to get smoother after the bags were in, as we were off of the overload leaf.

Going out, I inflated the bags just enough to get off of the overload by about 1/16", which is less than we usually would do. We found the ride to be less than stellar, as bumps of any real magnitude would start movement that would abruptly come to a halt, presumably when the overload contacted. It felt kind of like stepping off a curb you weren't expecting. There would also be a very noticeable "thump" heard and felt through the entire van. On the way back, I lifted the back a little higher to about 1/8"+ off the overload, and the ride got much better, and no noises. There was only about 10 psi difference in the bags to get that much higher.

This may also be a possibility of something that contributes to the rough ride and porpoising we have heard about. Bouncing off the overload in the rear, with a rapid change in movement speed of the body, could have more effect on the front than would seem logical, I think, making it bounce more.

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Old 08-09-2013, 10:02 PM   #3
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Default Re: More on Chevy suspension issues

Another step on the Chevy stuff completed today. This time to see if there could be some help for those who find the front ride too harsh with the Tufftruk, or other, springs.

I was at the Chevy dealer on Monday getting a couple of little parts for the Roadmaster wagon, and had them look up sway bars for our O7 Chevy. I had done the GM parts direct thing in the past, but they use non-official lists on occasion, with big disclaimers all over the place on returns. My biggest assumption had to be that a 3500 and 1500 used the same frame, or at least, all the same location points The parts lists showed only the bar and insulators to be different from the 1500 to the 3500. End links and insulator brackets stayed the same. The weight of the 1500 bar was less, so the guess was it was smaller diameter.

The parts were pretty cheap, at least compared to the other suspension mods, so I decided to order the bar and insulators (about $125). They showed up yesterday, and I put them in today. The bar is a different shape, without the bump out in the middle front, which made the insulators deform a little, but I have seen that on many bars in the past. Other than that, it fit fine.

The 3500 bar we had was 1.375" diameter, the 1500 bar is 1.295" diameter, which gives a rate change of about 23%. Not huge, but I don't think we want huge in this case.

I did notice when putting it in that the links did not have the same amount of compression on them, much like I found when I did the homemade rear bar with hand drilled hanger locations. I adjusted the rear at that time by shortening one of the link tube spacers until they both were even, with no load on the bar when level. I decided to do the same with the front. I leveled the back with the airbags, and had the normal 10 psi difference side to side that we always have had. I disconnected the front links and the rear went out of level. Releveled it with the bags, and now it did not need a difference side to side. At that point the front also came perfectly level. No doubt the front bar was doing some weight jacking. I wound up shortening the right front link by 1/4", and now it sits dead level, with same amount of air in each rear bag all bars tightened the same.

When the van was stock, the right front was always lower than the left, so perhaps this was the reason. I would also think that whichever wheel was carrying the extra weight probably be more likely to pound into bumps or react poorly to them. Maybe this is another variable that is causing such a wide range of results for the mods.

We took it for quick ride, very lightly loaded, and it still handled very well. Hard to tell, as you tend to find what you are looking for, but it did seem to be smoother on the front. Of course changing the bar rate will only effect one wheel bumps, not dips or rises of the entire front. It will take a bunch more driving to come to any real conclusions on ride quality.

I do think that the sway bar biasing the weight distribution might be something folks may be interested in looking at, especially if their front end sits with a side to side height difference.
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Old 08-20-2013, 03:20 PM   #4
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Default Re: More on Chevy suspension issues

Thanks for posting all this info.
We get tossed around a fair bit in my older van on rough roads and I know we could benefit from some upgrades. I just have to decide whether to spend any more money it.
Two bikes on sliding cargo box: & 1997 GMC Savana 6.5L Turbo Diesel Custom Camper Van Specifications:
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Old 09-22-2013, 09:30 PM   #5
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Default Re: More on Chevy suspension issues

I think this will finish off the suspension mods for us, finally!

We just got back from a 2500 mile, two week, trip through the UP, to London Ontario, Door county Wisconsin, etc. Lots of two lane, some freeway, lots of of wind everywhere.

We did get an improvement in the recent mods, back to and including the larger tires and correct offset wheels. The latest was a smaller front sway bar and a small amount of spacing on the front shocks to increase extension travel. The "bias" which was crossloading the front through the swaybar was also taken out. The rest of the suspension is Tufftruk springs, Airlift rear bags, Bilstein shocks, homemade 1.375" rear swaybar. We found by some testing this trip that 60 psi in the bags gets us up off the overload leaf enough to not ever hit it and smoothed out the rear better than lower pressures.

The van is now very carlike, except in sharp turns where you can tell it ways 9000#+. On two lane, freeway, fast or slow, it just feels right. Very little steering correction needed, even in 15+mph winds. We tested at 70+mph in 15-20mph winds on the freeway in Michigan, and it still was a 3 finger on the bottom of the wheel one hand drive, which is as good, or better, than our cars would do.

When we first put the larger Michelin MS2 tires on, they seemed to handle better at 65 psi in the front than at 60 psi, but now that they have a few thousand miles on them, there really isn't much difference in handling, but they ride smoother at 60psi.

The smaller front swaybar didn't seem to increase rocking or sway, or any other bad things. It does appear to have smoothed out front, one wheel, bumps somewhat. It also has contributed to the better steering response, I think. We will be keeping it in, but putting on better, greaseable, pivot bushings.

Mileage was down a bit from expected at 14.7mpg for the entire trip, but we did drive quite a bit faster on all the roads, and had lots of slow around town and parks driving. We did tests at 65 and 60psi front pressures, but the conditions varied so much we couldn't tell if tire pressure made any difference. Next time out, we will probably run 65/80psi like we used to on the smaller tires and see how the mileage looks. We have also added the solar, so that may be contributing to a loss ( I think I will add a leading edge deflector). The van has also not been aligned after the wheel change, so the toe could be out a bit and also reduce mileage.

All and all very satisfied, and we did not find it overly harsh anywhere.
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