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Discussion Starter #1
I need to build an air ride rear suspension for my 08 F350.

I'm thinking of building something similar to the Firestone R4 Tech setup.

I like it better than a 4 link because

- much less to fabricate
- no pan hard bar needed, thus there is room to keep a stockish exhaust system, ie rear exit
- leaf springs will locate the rear axle better side to side than a pan hard bar

I have a bunch of concerns

- finding an air bag to fit between the frame and the axle
- air bag having enough weight capacity at a reasonable pressure
- air bag having a decent spring rate at a reasonable ride height

Before I built the 4 link on my old truck, I tried removing leafs from the stock spring pack in the hopes of augmenting with an air bag. It rode terrible. However, I still had multiple leafs in the pack.

If I try this again, I will remove all the leafs except 1.

I have an email into Firestone requesting air bag information on the R4 Tech system.
 

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Discussion Starter #2
My stock 08 F350 is 8" from the axle tube to the frame, riding empty.

This will take a very short bag.

Here are some 1T14C-1 short bag candidates.



Note that one of the bags is used by Kelderman.

Here is a 1T14C-1 bag spec.




Note that the bag in the spec has about a 3.5" base, whereas the short bags listed above have 1.8" bases. Thus whereas the '5310 has a 9 inch design ride height for its characteristics, the '2119 and '2131 will have similar characteristics, maybe a bit softer at a ride height of about 7.5 inches.

8 inches frame to axle tube, minus 2 1/4" plates for bag mounting = 7.5".

The '5310 has a ride frequency of 1.43 ish Hz at various loads, which isn't bad. The single leaf is going to add a bit to that, but hopefully not too much. I'll do a calc on it later.

It would be nice to add a reservoir (ping tank) to the bags, but both of them have 1/4" NPT ports which don't allow enough air movement to be effective.
 

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Discussion Starter #3
Here is the rear leaf spring spec from the 08 Builder's Guide.



The spring rate for a multi leaf spring pack is static, ie add a bunch of weight and measure the deflection. In practice, the dynamic spring rate, ie hit a bump and measure the reaction, is much higher than this.
 

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Discussion Starter #4

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Discussion Starter #5
I spent some time under my truck measuring things yesterday. Whereas I previously said I had 8" between the axle and the frame, there is really 11" from the axle to the lip on the bottom of the frame.

So we now have room for a taller (softer) bag. Allowing for a 1/4" plate on the top and bottom of the bag,, the new bag should have a ride height of about 10.5".

A 1T14C-3 has a ride height of 10 inches.



Using that bag will result in a ride frequency of about 1.45 at 1500 pounds. (Between 1.35 and 1.53 anyway.) That is OK, but...

Goodyear builds a better air spring, for two reasons. 1) it has 2 bolts in the base and they will straddle the axle tube. 2) The bases on Goodyear air springs are hollow. This gives the bag more volume and thus a softer ride.

Here is the datasheet for a bag in the family I want to use.





Using a bag in this family will result in a ride frequency of less than 1.38 at 1500 pounds. I say less than because that number is for a ride height of 10 inches and my ride height will be 10.5 inches.

The 1R9-003 isn't the exact bag I want to use because the base is hard to work with. Instead, I want to use a 1R9-070. Here is a drawing for it.



It has the same max and min height as the 1R9-003 and a very similar base. In fact, the hollow portion of the base is slightly wider on the 1R9-070, thus it will be larger, thus this bag will be even softer.

I hope this all made sense. I documented how I did this so that people would understand that not all air bags are the same.

I have an email into 2 sources asking for the bag numbers for the R4 Tech kit for my truck. If the Firestone kit bag is better, I'll go with it. If not, I'll be ordering 1R9-070s.

BTW, I am getting this information from here.
Goodyear Airspring Specification files
 

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Discussion Starter #6
Some bag mounting parts. I'll get these cut at my local water jet shop.

Air spring top plate. This sits under the frame.



Air spring bottom plate. This sits on the axle.




Inside axle mount. This gets welded to the side of the bottom plate, nearest the diff carrier.



Outside axle mount. This gets welded to the side of the bottom plate, nearest the leaf spring and also to the spring block.



I ordered the 1R9-070 bags today. They might be here tomorrow.

You'll see how it all goes together as I fabricate it. I don't have a 3D drafting package !

You'll need 2 of each of these and they might or might not fit your truck. They'll fit mine though !
 

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Discussion Starter #8
The bags my supplier thought they had in stock were not 1R9-070s. The bags won't be here until next week.
 

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Village Idiot
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Nice, be sure and take some pics of the progress.
 

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Discussion Starter #10
I always do.

Its nice to see some people are interested in what I am doing. For a while there I was wondering why I was bothering.
 

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Thanks for posting this info! I've been wondering about the R4 setup vs a 4-link as well and for the same reasons as you. I had pulled most of the leafs out of the spring pack in a 3500 I used to have, but I just used the commercially available "air lift" bags. It rode great until I had to put any pressure in the tiny bags to compensate for a load. Now that I'm armed with more understanding and knowledge of air spring dynamics I'm ready to tackle my Ram 5500 before it send me to the spine surgeon! I'll be following and learning from this build just as I did on your last rig.
 

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i have also been thinking of building my own rear susp. i currently have new
'11 leafs ready to go in but am thinking of selling them and going a similar route as this. trust me, we are watching!! :bowfast:
clarence
 

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Discussion Starter #14
trust me, we are watching!! :bowfast:
clarence
Good stuff !

The bags will be here next week. I've got 2 trips out of town as well, so things will be delayed a bit.

But as soon as I am back I'll be working on things.
 

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Outlaw wrench
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:D. Definitely paying attention:bowfast:
 

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the stryker god
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i've been thinkin about goin with bags in the rear with a 4 link, but i won't be runnin any leaf springs at all. when i get home i can get the bed off and go to work
 

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4 Wheel parts sells the R4 Tech system and other firestone products.
 

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Discussion Starter #20
Can we please keep this thread for the build ? Please start another thread for selling the R4 systems.

The suspension system on my last truck was a 4 link air bag setup. It worked well, but the pan hard bar really limits the options for exhaust, ie there is no room for running anything over the axle and it also messes up the axle motion a bit.

I am hoping that using a very light leaf spring instead of the pan hard bar will alleviate those problems.

Stay tuned.
 
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