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DIY R4 Tech rear suspension.

58K views 122 replies 25 participants last post by  robs97z28 
#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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#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.
 
#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.
 
#4 ·
#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
 
#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 !
 
#8 ·
The bags my supplier thought they had in stock were not 1R9-070s. The bags won't be here until next week.
 
#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.
 
#11 ·
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.
 
#12 ·
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
 
#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.
 
#15 ·
:D. Definitely paying attention:bowfast:
 
#17 ·
4 Wheel parts sells the R4 Tech system and other firestone products.
 
#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.
 
#21 ·
How do you have the pan hard mounted, how long, etc.
The longer the better and straight at ride height. Now this depends on how much suspension movement you want.
Should be able to find a way to mount it to fit an over the axle pipe.
Another option is called a Watts Link Bar if you want a lot of travel.
 
#22 ·
My build thread is here.
Problem with air ride suspension... sort of... long - PowerStrokeNation : Ford Powerstroke Diesel Forum

Here is a picture of the pan hard bar setup on my truck.



I know all about a Watts linkage. Its fine for a hot rod, not so great for a Superduty pulling a 14K trailer.

Its very hard to set up a pan hard bar properly on a Superduty with the bags mounted behind the axle. It would be a bit easier if the bags were mounted between the frame and the axle, but its still not trivial.
 
#23 ·
The bags arrived. Unfortunately they were Firestone 5410s, not Goodyear 1R9-070s. Same bolt pattern, but the difference is in the bases. The Goodyear bags have hollow bases which hold more air, making for a softer ride.

I reordered genuine Goodyear bags. They should be here in a week or so.
 
#25 ·
You can answer that question yourself by looking at the spring rate and ride frequency of those bags. They are too stiff and way too progressive.

Take, for example, the 2B9-250. http://www.airsprings.cc/Goodyear/2B9-250.pdf The ride frequency is 1.6something plus, versus 1.3 for the 1R9-070. Firestone bags are similar.

Also, double convolutes don't have enough travel. They don't extend high enough. A triple convolute might work, ie http://www.airsprings.cc/Goodyear/3B12-325.pdf, but it has a diameter of 14 inches when pressured up and it will be expensive.

FWIW, I will be using Slam Industries RE7 double convolute bags in the front. They are OK for that application, but the 1R9-070s are better for the rear.

And just so everyone is aware, the 1R9-070 have a capacity of 3,300 pounds each at 100 PSI. Add 500 pounds capacity for the leaf spring on each side and the maximum rear axle weight will be 8,000 pounds. (3300 x 2 + 500 x 2 + 400 pounds for the axle itself.) I'm totally guessing on the capacity of the the leaf spring.

For people needing more capacity than that, you'll need to look at a larger bag. The Firestone 9422 comes to mind.
 
#26 ·
I've been thinking about the lower control bars while waiting for the bags to arrive.

The R4 kits use a spring link for the lower control arms. I believe they do this because if you use solid bars at extreme articulations they are going to tend to want to twist the diff in different directions. Its difficult to explain without going into a bunch of diagrams.

To avoid having to use springs for the lower bars and to make everything simpler, I am going to *TRY* to use a single torque arm going from on top of the diff carrier to somewhere forward on the truck frame.

This is how the torque rod is handled on a Class 7-8 truck. I may even use a torque rod from such a truck.

I'm going to secure the the torque rod to the differential by making a plate that bolts between the differential and the diff housing cover. Several suspension kits bolt various things to the differential this way, so I am going to try it too.

One advantage to using a single torque link is that it greatly simplifies (eliminates) the bracketry that goes under the axle perches and also the pieces that would otherwise be needed on each side of the frame. I believe I'll be able to re use the factory U bolts and everything.
 
#28 ·
That is not what I want to do. But I will give it more thought.

That torque arm forces the diff to go in an arc as it goes up and down. The pinion angle changes constantly. That works fine with small travel suspensions but not so great on longer travel suspensions.

The torque rod I am proposing keeps the pinion angle nearly constant through the travel, similar to how Firestone wanted it to move with the lower links in the R4 Tech system.

The R4 Tech system is like a 4 link system except that the upper link is a leaf spring. The leaf spring acts nearly like the upper link and the lower link handles axle wrap issues.

I want to take that a step further by removing the lower link and replacing it with a single link in the center of the diff.

The one bad side effect of putting the torque link in the center of the diff and above the axle is that the leaf springs go into compression instead of tension.

With the R4 Tech system, when the truck accelerates the front of the leaf spring goes into tension and the lower link goes into compression. This helps keep the leaf spring straight.

With a single torque rod in the center of the diff above the axle, the torque rod goes into tension and the leaf springs go into compression. This may cause the leafs to form an S curve when accelerating.

However, the forces are in the opposite direction when braking. So what *may* cause an issue during acceleration in one system will cause the same problem during braking in the other setup. So overall, I think both setups will work.

I guess I'll find out.
 
#29 ·
Question of the day. On the R4 Tech system, why are the lower links J leafs ? Why is the J in there ?

Obviously, the J is designed to push against the leaf once in a while. When will it happen ?

Will the leaf form an S curve during braking ?

Anyone have insight on this ?
 
#30 ·
Here is the reason I'm building my own R4 Tech system.

The ride quality unloaded is about the same as factory. If you drop the pressure to low in the bags(ie to keep a ride hieght) it will be VERY bouncy.
The bag is supposed to be inflated to 7" at all times.
FireStone R4 Air Ride Kits.... - Page 6 - PowerStrokeArmy

If you read that thread, the kit uses standard 1T14C bags, though it does appear to use a little better piston with more volume to get the spring rate down. 1T14C bags at 7 inches are pretty stiff.

I'm still waiting for my Goodyear bags to arrive. FWIW, I'm looking for a bag ride height of nearly 11 inches.

I also ordered an all in one welder, with a plasma cutter, so I doubt much is going to happen on this project until that arrives after Christmas.
 
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