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Old 11-22-2020, 04:10 PM   #1
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Default Need a Basic Tutorial on Leaf Springs and How to Determine if Flattening has Occurred

Here is what I have: 2006 Roadtrek 210P. In 2011 I "lifted" the van with the old TufTruk coil springs in front and Firestone airbags in the back. I got 2" of lift both front and back (40-50 lb air pressure in airbags). Vehicle rides good as far as I can tell.

Then the other day a casual acquaintance of mine makes the comment: "looks like your rear springs have flattened". We didn't discuss further but got me wondering: how do you determine if your leaf springs are "flat" or not arched as they should be?
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Old 11-22-2020, 04:18 PM   #2
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Don't know if this is what you're asking, but mine have flattened on my '2012 Airstream Avenue (Chevy 3500 - similar to Roadtrek 190P). The upper leaf springs sit practically flat on the overload spring with very little to no daylight between them. Wheel arch height from the road straight through the center of the wheel hub is 34-1/2".

Because my van rides well, does seem to bottom out, and rear height is still 1/2" higher than the front, I don't ask any questions.
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Old 11-22-2020, 05:11 PM   #3
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Sorry, I should have provided more information. Just measured heights to the wheel arch.

Front Left: 36-1/8 Front Right: 36-1/8
Rear Left: 36 Rear Right: 35-1/8

Wow, why is the Rear Right so different??? Then I put a level on driveway and a level on flat floor below rear doors: both are level.

It does look like the right airbag is slightly lower than the left bag. Both bags are teed together so at the same pressure, about 45-50 lb.

I should take pictures of the springs with the wheels off but this is what I have for now. They look somewhat flat, but is that a problem? If they were more arched then the airbags would need to be at a lower pressure to maintain level. I suppose there is an optimal balance between the load carried by the springs and that carried by the airbags, but how would you know what is best?
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File Type: jpg Spring, Left Side.jpg (230.5 KB, 6 views)
File Type: jpg Spring, Right Side.jpg (241.7 KB, 7 views)
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Old 11-22-2020, 05:14 PM   #4
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Originally Posted by rowiebowie View Post
Don't know if this is what you're asking, but mine have flattened on my '2012 Airstream Avenue (Chevy 3500 - similar to Roadtrek 190P). The upper leaf springs sit practically flat on the overload spring with very little to no daylight between them. Wheel arch height from the road straight through the center of the wheel hub is 34-1/2".

Because my van rides well, does seem to bottom out, and rear height is still 1/2" higher than the front, I don't ask any questions.
Yes, sometimes asking questions can get you into trouble, but usually understanding what is going on works best. At this point I don't see a need to change anything unless someone more knowledgeable than I highlights a concern. Always fun to discuss things like this on this forum as usually a good discussion occurs.
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Old 11-22-2020, 06:33 PM   #5
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Any leaf spring will "go flat" if you put enough weight on it, and the 210 is certainly good at putting a lot weight on the rear with it's longer overhang.


I think you find that two things are going on with it.


The first is the weight it is carrying in stock Roadtrek form is plenty to put it right on the overload leaf, which is very stiff and will stop it from dropping much more.


The second is that the 210 comes with spacers over the axle to lift up the rear, which raises the back but doesn't change the load on the springs at all or how the sit for arch.


What that boils down to is that the van is sitting quite a bit higher than it normally would without the blocks.



You have the front springs in place which probably brought the front up to the factory stock trim height or a bit above. The rear is already "lifted" the amount of the blocks, so if you use the airbags to bring the rear up to get off the overload leafs, you probably will be at a higher wheelwell height at than you would be without the blocks, but the springs would be in a better position.


If you want to keep the wheelwell heights matching the front like they do now, you would need to remove the blocks and increase the airbag pressures, I think. This would raise the body above the axle and increase the spring arch and take it off the overload leaf.



Pretty much all the Chevies are uneven in the rear about 3/4", I think. You can even it out with the airbags. Or if you did take the blocks out from under the axle, just put in a smaller block on the low side only and you will come closer to being able run the same air pressure in each air bag.


Many people think a lot arch is good, probably from seeing lightly loaded trucks where they show a lot. I would prefer to have just enough arch that large, not huge, bumps will put it close the flat and then have an overload leaf or bumpstop to prevent much more travel.
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Old 11-22-2020, 06:58 PM   #6
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Quote:
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Any leaf spring will "go flat" if you put enough weight on it, and the 210 is certainly good at putting a lot weight on the rear with it's longer overhang.


I think you find that two things are going on with it.


The first is the weight it is carrying in stock Roadtrek form is plenty to put it right on the overload leaf, which is very stiff and will stop it from dropping much more.


The second is that the 210 comes with spacers under the axle to lift up the rear, which raises the back but doesn't change the load on the springs at all or how the sit for arch.


What that boils down to is that the van is sitting quite a bit higher than it normally would without the blocks.



You have the front springs in place which probably brought the front up to the factory stock trim height or a bit above. The rear is already "lifted" the amount of the blocks, so if you use the airbags to bring the rear up to get off the overload leafs, you probably will be at a higher wheelwell height at than you would be without the blocks, but the springs would be in a better position.


If you want to keep the wheelwell heights matching the front like they do now, you would need to remove the blocks and increase the airbag pressures, I think. This would raise the body above the axle and increase the spring arch and take it off the overload leaf.



Pretty much all the Chevies are uneven in the rear about 3/4", I think. You can even it out with the airbags. Or if you did take the blocks out from under the axle, just put in a smaller block on the low side only and you will come closer to being able run the same air pressure in each air bag.


Many people think a lot arch is good, probably from seeing lightly loaded trucks where they show a lot. I would prefer to have just enough arch that large, not huge, bumps will put it close the flat and then have an overload leaf or bumpstop to prevent much more travel.
Excellent comments and explanation. Much better to have a just enough arch than broken leafs. Having retired in a transporation career, I have seen lots of broken spring leafs before we went to air bags.
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Old 11-22-2020, 07:53 PM   #7
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I had typo in my response. The spacers are above the axle, below the spring pack so they raise the body.
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Old 11-22-2020, 08:19 PM   #8
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Excellent comments and explanation. Much better to have a just enough arch than broken leafs. Having retired in a transporation career, I have seen lots of broken spring leafs before we went to air bags.
Did the airbags replace the springs entirely or were they used in combination with springs?
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Old 11-23-2020, 03:30 PM   #9
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Did the airbags replace the springs entirely or were they used in combination with springs?
I was referring to Heavy Truck tractor trailers. Full airbags. I remember when every piece of equipment we had, had arched springs. The winter was so cold that almost all the rigs had at least on broken spring on the return run. We hauled gasoline and diesel, so the was two runs per day. That year they put us on the NY thruway! The "back roads" two lane highways were like corduroy roads of the old times, they had so much ice on them. After that winter, all the new equipment had airbags. Far less garage time!!!
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Old 11-26-2020, 03:59 AM   #10
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I have a similar set-up in my 2008 210V. Firestone airbags in the rear and Moog 81004 coils in the front, which provided the same 2" of lift.

I have found that 70 psi in the airbags provide the best combination of ride comfort and vehicle handling. I have a dedicated airline and fill valve for each bag. I think this helps counter vehicle roll in turns.

I did the upgrades to increase ground clearance, so I left the spacer blocks in place.
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Old 11-26-2020, 01:34 PM   #11
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I have a similar set-up in my 2008 210V. Firestone airbags in the rear and Moog 81004 coils in the front, which provided the same 2" of lift.

I have found that 70 psi in the airbags provide the best combination of ride comfort and vehicle handling. I have a dedicated airline and fill valve for each bag. I think this helps counter vehicle roll in turns.

I did the upgrades to increase ground clearance, so I left the spacer blocks in place.
For 8 years I had dedicated airlines and fill on each airbag. Slow and different leaks developed on both bags and I was concerned with having different pressures. I put in a compressor system and have the airlines connected together. I cannot tell any ride or cornering difference between dedicated and connected. I think that is because the airlines are small and the airbag volume is large so it takes long enough for the air to flow from one side to the other.

Here is the posting of my compressor and monitoring system.

https://www.classbforum.com/forums/f...tem-10328.html
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