Are there any disadvantages to a short upper arm on a 3 link rear suspension other than the rapid pinion angle change?

My rear crossmember is shot, I am building a new rear end housing, and I already have a watts link so I figured why not go for a 3 link. The only problem that I see is that without clearancing the floor plans on my '67, I am limited to about an 8-9 inch upper arm (stock length lower arms). Considering the angle of the stock arms, this arm length on a 3 link is actually a very slight improvement on the rate of pinion angle change compared to stock.

im not sure why you cant run a longer link. the 67's are longer than my 70 stock, and i was able to get mine to almost 12" c/t/c with a custom crossmember and no floor pan removal.

the SVSA will change much more with a shorter link. you'll have to run it through some programs with the estimated suspension travel for both launch and braking.

I thought you were still running a C4L. Did you switch to a 3 link? Do you have any pictures?

With the big 2.5" diameter of my Johnny Joints, it looks like I can only gain about 1 inch over stock on my SVSA before hitting the floorpan although my preliminary measurements were done without the rear end in my car so my estimates might be off a little.

im running the same jj's, and i converted to a parallel 4 link with a watts. my housing brackets do mount the arm inline with the rear of the axle tubing. it netted me about 1.5".

heres the only pic i really have

http://www.fquick.com/images/vehicles/full/23712235018.jpg?1234929054

I was able to get almost a 13" upper link in my 67, here is a link to a picture, its not real easy to see it.
http://www.chevelles.com/showroom/showphoto.php/photo/11517/cat/500/ppuser/26133
What I did was put the rear mount as far back on the axle housing as possible and the front mount is in front of the stock crossmember (with extra bracing). If the El Camino had more axle to floor pan clearance (it has less than Chevelles), I could have moved the rear mount back and up a little more for a 14-15" upper link.

Randy - I can't really tell from the picture, but it looks like you fabricated a bracket that mounts to the stock Chevelle housing ears. If that is true, do you have any better pictures? I am starting from an F-body housing and welding the upper arm mount, but I am sure there are others who would like to see a way to bolt on the upper mount without welding to the housing.

The main problem I have with the 2.5" JJs is when you put one on top of the center of the axle housing, it ends up being about 1 inch above the stock location in terms of side view height. In order to keep the same IC, I have to move the front mount up about an inch, which because the floor pan is set at about a 45º angle, I have to shorten my arm by about an inch. At that point, I only gain a little under an inch on the front and an inch on the back of the side view arm length compared to stock. I started off mocking up the arm with the front mount as low as possible while still clearing the driveshaft in full compression, but my IC ended up being just behind my front seat. I was advised to put my IC a little further forward than that for a general purpose corner carver so I went back to the drawing board.

I double checked my notes and it look like I have room for about a 10" arm (not the 8-9" I originally indicated - that is the stock side view length). Nevertheless, the 10" arm still seems pretty short compared to what I see in aftermarket 3 links for other cars so I thought I should double check before I start cutting.

I attached a better photo of the mount here. It was made from 1/4" x 2" steel (Lakewood driveshaft loop I had) and has 2 pieced bolted on each side of the ear and then a flat piece across to join them. Then I added tabs to mount the heim joint. It would have to be alot taller to fit a Johnny Joint, which could cause floor clearance issues on an El Camino, not sure on a Chevelle. Of course you can always clearance the floor.

As for the length of the 3rd link, you could try putting the axle mount further back to gain back some length or clearance the floorpan to allow for the longer link. Even with a back seat, the seat would allow for the link to come through some and still hide it, just don't have anyone sit in the middle. :D If you go a bit behind the axle, you can then you the cover bolts to help hold the mount if you want. Just a couple ideas.

Or you could just do what this guy did:
http://www.hotrodhomepage.com/gallerys/sire_performance/

that is maybe how I would redo my car, if I was ever crazy enough to dive in again. :clonk:

Sorry to resurrect this one but im in the same boat. i plan on a 3link/watts and just want an idea of the minimum length of the upper. Im in 70 2dr ht; how much do you think i can get. I plan on using the stock lower locations on the frame. Good Idea/Bad Idea?

No problem using the stock positions on the lower arms, that's what I am using. I would aim for the upper link being as long as you can make it, but a little shorter than the lower links. Mine is 13" as I limited myself to stay within the stock bodywork.