Adding a rear stabilizer bar to a Dodge Caravan
According to the factory service manual, some of the Caravan models came with a rear stabilizer bar. However, I've never actually seen any Caravans (or Voyagers or Town & Countries) with rear stabilizer bars in the pull it yourself parts yard's I've checked. I've been looking for one for several months and haven't found one yet. They seem to be pretty rare.
Since I can't seem to find a factory unit, and I really want a rear stabilizer bar to reduce body roll and reduce understeer handling in our van, I decided to expand my criteria a little bit and search for a bar that I could make fit.
On vehicles with a solid rear axle, like the Chrysler Corporation minivans, there are two ways to mount the rear stabilizer bar. The stock bar is mounted to the axle beam and the end links are attached to the body. There are some disadvantages to this arrangement. The weight of the stabilizer bar is completely unsprung this way. However, it is easy to mount it up that way, and that's what Chrysler Corporation chose for their implementation.
Since I'm doing my own engineering here using other parts, I thought I'd try the other alternative. I want to mount the stabilizer bar to the body if possible, and connect the end links to the axle near the wheels. This has an advantage that it keeps the main (heaviest) part of the stabilzer bar on the body where it's sprung weight. This places less of a load on the shocks and springs and can result in better handling than having the additional unsprung weight of the bar on the axle.
I got under our van and looked around the back, behind the rear axle. There's a lot of room back there, and there's some extra bolt holes already prepared in the frame rails on the unibody. Those holes might be useful to mount the stabilizer bar to the body. On the suspension end of thing, out by the wheel, it looks like it wouldn't be too much trouble to stack some kind of bracket on top of the leaf spring, under the U-bolts, to secure the endlinks of a stabilizer bar to the suspension there.
So, I drew this little diagram outlining the requirements for a rear stablizer bar mounted on the body with end links on the axle.
Figure 1 - Plan for rear stabilizer bar
I guess this would be a good time to talk a little bit about stabilizer bars, or anti-sway bars, as they are sometimes called.
All stabilizer bars work about the same. They are like a torsion bar, but both ends are attached to the end of the axle or suspension near the wheels. Instead of supporting the weight of the chasis, they transfer weight from one side to the other in cornering.
The amount of weight transferred during cornering, and the ability of the bar to reduce roll and keep the vehicle level during cornering depends on the stiffness of the bar. The stiffness is related to three different characteristics of the bar.
Well, I got to the yard, and I thought I'd look at bigger rear wheel drive cars first. I was hoping to find a front bar from one of these that would fit. Front engine, rear wheel drive cars tend to have large, thick, fairly stiff front stabilizer bars. Unfortunately, front stabilizer bars on any vehicle have to be fitted to clear the wheels at full lock steering angles. Even the big mid 1970's Cadillac Fleetwoods and full sized vans and pickups only had about 36 to 38 inches of straight bar in the center between the bends. This won't clear the frame rails on the Caravan. The end links on these big cars were usually close to 48 inches apart. A bar with those dimensions would be guaranteed to interfere with the frame rail on the caravan. So these were unusable for me.
So, I was probably going to have use a rear stabilizer bar from something. There weren't too many available that would fit the dimensions required. I did find a few different potential donors, though.
I finally ended up pulling a rear stabilizer bar from a late 1980's model Toyota van and taking it up to the Chrysler section of the yard. I figured I'd put it under a minivan there in the yard and get a quick look at what I was dealing with.
So, I took that one home with me for only $15.
On the way home, I stopped at an auto parts place. The donor Toyota van was missing the whole rear axle. Whoever pulled the axle had removed the nuts and rubber bushings from the end links. The end links were still attached to the end of the stabilzer bar, but the end that attaches to the axle was just a threaded rod with no nut and no bushings.
I asked at the parts place for the end link bushings. The parts place could order the bushings, but they were a special order and would take 10 to 15 business days to arrive. So, I was off to see if the Toyota dealer could do any better. The end link bushing kits were only going to be around $5 per side from the parts place, so a dealer probably couldn't be too bad for the parts.
Here's a tip for all of us junk yard shoppers. If you take parts off of a strange vehicle (from a make or model that you don't actually own), write down the VIN # of the donor. When I got to the Toyota dealer's parts counter, they wanted to know the year, model, engine, transmission (automatic or manual) and some other information about "my" van. If you don't have that information, it's hard for them to look up the additional parts you might need (or replacement parts if rubber bits wear out down the road). Usually, if you say, "look, I don't know much about the thing, but here's the VIN number," they can get the info they need by decoding the VIN #.
The Toyota dealer also was going to have to order these bushings. Each bushing and keeper washer was less than $2, but there were 6 on each side, plus the rubber bushings in the bar where the endlink attaches to the bar. So it was going to be about $25 for everything. The parts took a few days to arrive, but once they were in, I was set. When installing mine, I found that I didn't actually need the center metal washer/keeper piece. The rubber bushings fit snug into the 1/2 inch hole in my flat bracket. I'm guessing that that keeper must be used on the Toyota where the surface the bushing is against isn't flat.
In the mean time, I mounted the thing on our van and fabricated the brackets to make it work.
First, I need to get the thing mounted to the body of the van. On our van, there were 4 holes on each frame rail that were conveniently located for this. They already had captive nuts in them, so I just had to find some bolts to thread in the holes. A M8x1.25 bolt seemed to be the best fit, though there was a little bit of surface rust and even that bolt didn't thread in the best. If I had a tap for that size, it would have been a good idea to run the tap through the hole to clean it up. I didn't have the right tap, so I just coated the bolts with antisieze/lubricant and did the best I could.
So, with the bar mounted to the body of the van, the next step is to attach the end links to the suspension at the wheels. In order to do this, I'll need a bracket that attaches to the leaf spring and has a hole in it for the end link to go through. I drew up this little diagram to show what I needed.
Figure 2 - Bracket to attach end link to the leaf spring/axle.
A couple of notes here. First, the brackets I made were slightly different from the diagram. I adjusted the diagram a little bit based on the clearances and angles I saw after installing my first version brackets. The diagram was updated to reflect this experience and will fit better than what I actually made.
The second thing is that if I had this project to do again, I'd seriously consider making the bracket out of 3/16" or 1/4" channel stock and using straight grade 5 or grade 8 bolts instead of the U-bolt. The bracket would have to be slightly longer in order to have a full hole on the outer end instead of the notch on mine. But this would avoid buying an overpriced U-bolt from the dealer, and I don't think grade 5 bolts on a channel stock bracket would be any weaker than the factory U-bolts. It might actually be stronger than the factory U-bolt, and the hardware and stock are easier to find and less expensive than the U-bolt.
Third, measure your U-bolts and make sure that what you are making will fit your car. When I first posted this page, I had a mistake on the bracket plan above. I've updated the pan now to show what I believe are correct dimensions, at least for our van. Don't assume my drawing will fit your minivan.
I used 1/8" by 2" cold rolled steel flat stock for mine. I'd recommend cold rolled stock rather than hot rolled because this part will have some stress on it in normal use. Also, it's much easier to prepare and paint cold rolled stock than hot rolled. With hot rolled stock, you have to sand/grind off the mill scale and surface rust first. I cut two pieces of flat stock, 4 1/2" long, and I drilled the holes necessary for the U-bolts and end links.
Tighten the nuts on the U-bolts to 65 foot pounds with a torque wrench. It will feel funny, almost like you're stripping the threads on the bolt. You're actually compressing the leaves of the spring together, so, it will take a lot of turns of the nut after it's snugged down to get to the 65 foot pound torque spec. I felt a lot better when I set the wrench to 35 pounds first. Then, after tightening to that, I stepped it up to 50 foot pounds, and then finally up to the final spec of 65 foot pounds.
The van can be driven at this point. Of course, you dropped the spare tire to make room to put the bar in, and now there's a bar across the spare tire area. I'm not sure what the long term solution to this is. I found that the spare tire will pull up snug against the bar. I just wrapped my bar in pipe insulation to prevent any rotation of the bar from wearing on the sidewall of the spare. I'm not sure how that will hold up for the long term. If it doesn't hold up, I'll make another cross piece from some aluminum tubing for the spare tire to rest against and to protect the moving bar from the fixed spare tire.
So, now that it's mounted, and the spare tire is back (close to) where it belongs, it's time to drive with the new stabilizer bar on. I was impressed the first time I drove the thing with the new bar installed. It is much more level in corners, and a lot of the understeer characteristics of the handling have been tamed. If you push it hard, it still understeers a little. But in everyday driving, it feels much more neutral than it used to.
The final verdict is in. I just came back from a trip up to visit some friends in Tennessee. I drove the van on U.S. 64 from Ducktown to Cleveland Tennessee, along the Ocoee river. On the way home, I followed Tennesse route 68 from Sweetwater to Ducktown. These are really fun, curvy, mountain roads. These are the kind of roads where I really enjoy driving our Miata. But for this trip, I needed the carrying capacity of the minivan. The van handled very well on these roads. It's not the Miata, but it was much better than I remember it on these roads in the past.
Also, while I was in northern Tennesse, near Norris Lake, I was following a VW Passat. The Passat was having fun on this twisty section of U.S. 441 near Norris Dam. I'm sure he was wondering why he couldn't seem to pull away from that Dodge Caravan that was following about 10 seconds behind him.