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Old 04-30-2020, 11:39 PM   #1
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Question Need Advice on Chevy Coachmen Suspension Upgrade

Hi All, I'm the proud owner of my first Class B...a '95 Chevy Coachmen RD on a G30 chassis. Mechanic gave his blessing on the 53k mi engine and tranny (phew) so the next thing on my list is the suspension.

The van takes bumps and potholes very hard and sags in the front which causes wheel rub on tight turns. I reckon I'm in need of new front coil springs at the very least and will likely replace all four shocks as well.

When choosing coils, I took the manufacturers front axel Gross Axel Weight Rating (GAWR) of 3,880# and matched that up with the load rating of Moog coil springs that fit my vehicle. I want to strike a balance between enough support but not too firm a ride.

The coils I landed on are Moog 6560s with a load rating of 3,788#. Is this the right approach?

If anyone has reccos on suspension shops in the Northeast, would love to hear them. The first 2 shops I called couldn't even fit my 10' tall rig in their garage!
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Old 04-30-2020, 11:45 PM   #2
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Originally Posted by ChevyCoachmen View Post
Hi All, I'm the proud owner of my first Class B...a '95 Chevy Coachmen RD on a G30 chassis. Mechanic gave his blessing on the 53k mi engine and tranny (phew) so the next thing on my list is the suspension.

The van takes bumps and potholes very hard and sags in the front which causes wheel rub on tight turns. I reckon I'm in need of new front coil springs at the very least and will likely replace all four shocks as well.

When choosing coils, I took the manufacturers front axel Gross Axel Weight Rating (GAWR) of 3,880# and matched that up with the load rating of Moog coil springs that fit my vehicle. I want to strike a balance between enough support but not too firm a ride.

The coils I landed on are Moog 6560s with a load rating of 3,788#. Is this the right approach?

If anyone has reccos on suspension shops in the Northeast, would love to hear them. The first 2 shops I called couldn't even fit my 10' tall rig in their garage!

I think a 95 Chevy will have same front suspension as the slightly later years, so a thread by Markopolo about his upgrade suspension should be good information. Hopefully, he will jump in on the year questions and help you out. I don't think those are the numbers for the springs he used.
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Old 05-01-2020, 02:05 AM   #3
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Quote:
Originally Posted by booster View Post
I think a 95 Chevy will have same front suspension as the slightly later years, so a thread by Markopolo about his upgrade suspension should be good information. Hopefully, he will jump in on the year questions and help you out. I don't think those are the numbers for the springs he used.
Booster, thanks for the tip! I read Markopolo's thread and see that he used the Moog 81008 coil springs but unfortunately those springs do not fit my '95 Chevy. In fact, there aren't many options that fit my vehicle, especially when adding the "heavy duty" requirement. That's why I ended up choosing the Moog brand based on many people's positive reviews, and backing into what will fit my vehicle.
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Old 05-01-2020, 03:10 AM   #4
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Booster, thanks for the tip! I read Markopolo's thread and see that he used the Moog 81008 coil springs but unfortunately those springs do not fit my '95 Chevy. In fact, there aren't many options that fit my vehicle, especially when adding the "heavy duty" requirement. That's why I ended up choosing the Moog brand based on many people's positive reviews, and backing into what will fit my vehicle.

The specs I found on the 6560s are 3788# load, 1464 #/in rate, and .090" diameter wire.


The 81008 by comparison shows 4172# load, 1570#/in rate, 1.03" diameter wire.


The wire diameter difference won't count much because your springs are also smaller in diameter so can't use wire size for direct comparison. Marko's springs are a bit stiffer and with higher load capacity, so wouldn't get as much support as he did. How much lift you will get will depend on the actual weight on the front and how tall the new springs are compared to the OEM stock springs, which wasn't able to find easily. If you can find that out to compare to the 6560s at 13.59" tall, it would be useful to you.


How the Moogs turn out might be odd anyway, as the ones the make for the later Chevies have gotten very much stiffer lately but kept the same Part number.
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Old 05-01-2020, 05:27 AM   #5
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The specs I found on the 6560s are 3788# load, 1464 #/in rate, and .090" diameter wire.

The 81008 by comparison shows 4172# load, 1570#/in rate, 1.03" diameter wire.
Thanks Booster, I'm finding the same specs on Moog's nifty dimension chart.

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How much lift you will get will depend on the actual weight on the front and how tall the new springs are compared to the OEM stock springs, which wasn't able to find easily. If you can find that out to compare to the 6560s at 13.59" tall, it would be useful to you.
I did some digging and while I couldn't find direct specs from Chevy, I did find a set of AC Delco springs that claim to be "factory-original fit" and "engineered to exact OE standards".

Their specs are as follows:

Wire Diameter: 0.83 in.
Front Spring Inside Diameter: 3.7 in.
Front Spring Relaxed Length: 13.6 in.
Front Spring Compressed Length: 10 in.
Load Rate Front: 3841 LB

Could I use these specs as a proxy for the original stock spring specs? If so, it looks like the length is darn near perfect!
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Old 05-01-2020, 11:05 AM   #6
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Just summarized Moog coil options:

g30.png



The 1" install height difference would/could probably mean 2" van front height increase over the stock spring. (Booster could correct my guess if wrong)
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Old 05-01-2020, 11:45 AM   #7
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Looks like an in coil air spring add on is an option: https://www.airliftcompany.com/vehic...SE+MODEL#front
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Old 05-01-2020, 01:11 PM   #8
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Just summarized Moog coil options:

Attachment 9060



The 1" install height difference would/could probably mean 2" van front height increase over the stock spring. (Booster could correct my guess if wrong)




One, very often confused thing when we talk about this stuff is to always rememberthat the "load" the specs give is for the spring, at the spring location, and does not reflect the actual front axle or wheel load. The spring load has to be used along with the leverage to determine what the actual wheel load capacity is. You use the same ratio as mentioned later for calculating amount of lift.

I think that would apply approximately for the difference between the 6454 and the 6560S springs as they have the same load and free height. Free height is just the load divided by the rate to get the actual compression distance which you then subtract from the free height. Whether or not that gave 2" of lift would would depend on what the actual ratio of spring height to lift is. The later Chevies post 2002 have a 203 ratio. The 6560 is probably the exact same spring as the S version, just shorter which is what the do on the latter Chevies also. We have found in the past that predicting lift closely is very hit and miss as the specs seem to not be all that great or consistent. Measuring the actual ratio on the van would probably be a good idea as then we would be able to calculate the installed height more accurately based on actual front weight (measured) and ratio (measured) so only the spring rate would used from the specs. Once the ratio is known, it would also allow a guess of how much stiffer the springs would be compared to stock, although that may be a mute point as it appears to currently be full on the bump stops.

The van must have the shocks outside of the spring if the inside the spring bags are available, which could be very useful. Those are the same bags that I have on the rear of my old Buick and they have worked well for over 5 years now. They do perform a bit differently than the rear standalone bags do though. Since they aren't a free standing bag, they are restrained by the spring on the OD, they tend to be the same diameter and mostly the same height all the time. This makes them less useful for getting a wide range of height improvement compared to the rears. I think I get maybe 1.5" with them which about half of what the rear bags give. They would also need separate filling than the rears as they max at about 30psi IIRC. With the shocks out of the springs, you could also use airshocks or coilovers if there is room.
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Old 05-02-2020, 03:01 AM   #9
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Booster and Marcopolo, thanks for all the great guidance so far - I feel like I'm on my way to becoming a suspension expert!

Quote:
Originally Posted by booster View Post
One, very often confused thing when we talk about this stuff is to always remember that the "load" the specs give is for the spring, at the spring location, and does not reflect the actual front axle or wheel load.
I had the misconception that you could just match up the Front Axel GAWR with the load rating of the springs, but now know there's a lot more to it than that. The same spring will respond very differently based on control arm length, coil spring angle, and other weight factors.

I should have done this in my first post, but here is a side pic of my rig that shows the front sag:


All you have to do is look at the running boards to see a pretty steep decline in clearance from back to front. Here are the measurement I took from road to top of wheel well:

Rear Passenger Side: 38.5"
Front Passenger Side: 32.75"

I then took measurements of my control arm and coil angle as shown in this diagram:


A: 10.5"
B: 19"
Spring Angle: 80į

Here's a pic of the suspension assembly for reference:



Correct me if I'm wrong, but the last piece of the puzzle we need is the weight of the vehicle. Unfortunately I haven't been able to take it to a weigh station yet to get the measured weight, but here is what I know based on specs (Note: these figures do not account for Coachmen outfittings):



Do we have enough data points to do some preliminary calculations? If not, what else do I need to wrangle?

Thanks again for all the help guys!
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Old 05-02-2020, 01:10 PM   #10
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If you measured just like in the picture, you may not have gotten the most accurate dimension for what we are talking about, as the applied load to the wheel is normally a bit outboard of the lower balljoint. Using the centerline of the tire tread would normally be what you need. Our 07 Chevy is about an inch outside the balljoint based on how much the wheel moves forward and backward when turned. Wheel offsets can a big influence on this dimension, but on your year most of the wheels were around zero offset so probably not an issue for you. You will probably be somewhere above an inch further out to the tire centerline.
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Old 05-05-2020, 12:57 AM   #11
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If you measured just like in the picture, you may not have gotten the most accurate dimension for what we are talking about, as the applied load to the wheel is normally a bit outboard of the lower balljoint. Using the centerline of the tire tread would normally be what you need.
I called Moog technical support today to see if they had any additional information they could share on my camper. While they didn’t have any camper specific specs, they did tell me that my control arm ratio was 2:1. That confirms that I was off on my control arm length measurement of 19”. Adding an extra inch closer to the wheel would give me a 20” to 10” ratio or 2:1.

I also measured the bar diameter of the existing springs on my camper and they match up with the 0.83 OEM spring diameter. So I can now confirm that the springs are standard Chevy G30 factory springs and not heavy duty.

I found a scrap metal recycling yard that will weight my camper for $10. I’m bringing it there tomorrow and will report back on my findings.

Slowly but surely piecing the puzzle together...
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Old 05-07-2020, 06:03 PM   #12
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WOW! That 2nd pic of the suspension shows a serious rust issue. Suggest you have a frame and body shop perform a frame rust inspection and repair estimate. Some frame rust vehicle become unsafe to drive as total loss of steering can result from critical part failure. Your van might be a wreck looking for a place to happen!
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Old 05-07-2020, 06:19 PM   #13
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WOW! That 2nd pic of the suspension shows a serious rust issue. Suggest you have a frame and body shop perform a frame rust inspection and repair estimate. Some frame rust vehicle become unsafe to drive as total loss of steering can result from critical part failure. Your van might be a wreck looking for a place to happen!
Thanks for looking out Peder! I had my mechanic perform a full underbody inspection. While there is rust, it's all surface rust based on his inspection - no soft spots anywhere. Definitely something I'll keep an eye on though!
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Old 05-11-2020, 03:15 AM   #14
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Update on my progress:
The scrap metal recycler had limited hours due to the virus, so I brought my camper to a truck stop that had a Cat scale. Those things are great! Download the app, drive on, and it emails you front, rear, and total weights (also weighs your trailer if you have one).

Here is what I weighed in at:

Front: 3760 lbs
Rear: 4060 lbs
Total: 7820 lbs

Keep in mind, this was with a full tank of gas, full fresh water tank, 2 passengers (350 lbs), and typical cargo load for our camping trips.

I am within the GAWRs for each axel but would like my springs to support the full load rating. I found this spring rate calculator that I used to input all of my numbers. Here are the results it spit out:

SPRUNG WEIGHT: 1820
MOTION RATIO: 0.492
STATIC LOAD: 3,696.15
SPRING RATE NEEDED: 746.70
EFFECTIVE WHEEL RATE: 181.05

Based on the Static Load and Spring Rate Needed, the Moog 6454 springs look like they'll do the trick.



Am I missing something here or should I just go with the standard springs over the heavy duty options?
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Old 05-11-2020, 09:47 AM   #15
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Originally Posted by ChevyCoachmen View Post
Update on my progress:
The scrap metal recycler had limited hours due to the virus, so I brought my camper to a truck stop that had a Cat scale. Those things are great! Download the app, drive on, and it emails you front, rear, and total weights (also weighs your trailer if you have one).

Here is what I weighed in at:

Front: 3760 lbs
Rear: 4060 lbs
Total: 7820 lbs

Keep in mind, this was with a full tank of gas, full fresh water tank, 2 passengers (350 lbs), and typical cargo load for our camping trips.

I am within the GAWRs for each axel but would like my springs to support the full load rating. I found this spring rate calculator that I used to input all of my numbers. Here are the results it spit out:

SPRUNG WEIGHT: 1820
MOTION RATIO: 0.492
STATIC LOAD: 3,696.15
SPRING RATE NEEDED: 746.70
EFFECTIVE WHEEL RATE: 181.05

Based on the Static Load and Spring Rate Needed, the Moog 6454 springs look like they'll do the trick.



Am I missing something here or should I just go with the standard springs over the heavy duty options?

Being able to carry the load and being able to carry the load at the height you want are two different things and you don't always get them at the same time. How it all turns out is going to be based on the spring rate and overall free length of the spring. The 6454 and the 65620S are capable of the same load carrying capacity, but are different rates at the same free length, so you get the 10" installed height instead of the 11" you would have with the 6560S. An extra inch of installed height with a 2 to 1 ratio will give a 2" higher ride height. Your pix show the front quite low, probably a bit more than 2".


My guess would be that the 6454 is for stock vans (same as the Delco you listed earlier) so sized for the unloaded van to be at speced ride height. The later Chevy vans with stock springs sat about 2" low also in most class b RVs, so similar. It is probably very close to what you have in the van now, although the ones you have are also likely sagged, too. Again a guess, but you would probably get a small amount of lift, maybe 1/2" or so with the 6454 and maybe 2.5" with the 6560S.


It would probably be best to get the installed height on the what is in the van right know, although that is a tough one to do at home. You either need drive on ramps or a drive on hoist to be able to get at it to measure. That would give you a bit more insight.


Also keep in mind that the 6560S has 44% higher spring rate compared to the 6454, so it will be firmer riding, but the 6454 would probably be susceptible to some porpoising being as soft as it is. You are probably quite hard down on the bump stops now which firms up the ride a bunch and limits porpoising, but once you get off the stops it becomes possible. The 6454 may or may not get you off the bump stops.


Based on the Moog description of the 6560S being for the heavier diesel vans, it is likely the right choice for a heavy RV, I think.
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Old 05-11-2020, 03:50 PM   #16
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It's not an easy decision. The coils for the '95 van are relatively inexpensive - approximately $200 would get 4 coils, both the HD coils and the stock coils from Rock Auto.
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