adjustable rear axle

[tirediron]

has anyone built or modified a rear axle to be able to adjust camber/toe? I know it's probably of less importance in a rally car but on a circle track car it's pretty critical.

I bend mine a lot. ive been heating it and bending it back, but obviously this weakens it every time. pretty sure this axle is finished, RR has about 2" toe out...
would be nice to be able to adjust to compensate for slight bends. sometimes swapping an axle out is not an option, like when I hit stuff in the heat race and need to fix it for the feature.

[Geoff]

Building adjustment into the rear axle would probably be pretty tough and all the ideas that are popping into my head would weaken it. That's not to say it couldn't be done but there are other solutions to think about as well.

A number of rally cars over the years have suffered from bent rear axles. Some teams have replaced the axle tube with a larger, stronger one, by cutting the old tube out and welding a new larger one in. The silver 900 in the eEuroparts banner add above has one of these strengthened axles. Two years and no bent axle! I seem to remember that the strength of the new axle is over 300% greater than the old one. It physically looks big compared to the stock axle.

The guy who built the axle for the RallyHoMotorsports car built a jig to make sure that everything lined back up during reassembly. I've been thinking about building a jig and a reinforced axle myself. But, if there are a few of us interested I could look into seeing if Brett would want to re-assemble a jig and do a few axles. He's in central NH too.

[aero84]

I have been thinking the same about building an ajustable rearaxle.

I was thinking on using a flange solution in some way, with different wedges in different angles for camber and toe in / toe out.

[SwedeSport]

I kicked around a few ideas for the rear suspension on my new hillclimb car.

Would start by making lower arms with a spring perch for 5" Afcoils. Incorporate weight jacker upper perches into the chassis. This way you can open the trunk and use a ratchet to adjust ride height. Black Powerflex bushings in the forward pivot.

Next would be figuring out how to build a knuckle. I was thinking cutting them off a stock axle. Add a lower pivot shaft, with the ends drilled and tapped to bolt a pair of heavy ball ends to it. Attach a tab to the upper part of the knuckle to pick up a 3rd ball end.

the beam would consist of 3 pieces of tube, assembled like a truss with some cross bracing or plating placed strategically between them. The upper and front lower tube will be slugged, drilled, and tapped for reverse thread. The lower arm bushing socket would be replicated and will utilize Black Powerflex bushings.

The rear ball end for the knucke is fixed in place, and non adjustable. The forward and upper ball is adjusted by a short, fat turnbuckle. That is made from a fat piece of rod with a flat or hex so you can put a wrench on it . Opposite threads on either side of that.

Upper link mounts on the knuckle would be used as is, but the links would be replaced with adjustable ball end links.

The calipers would mount to the stock tabs on the knuckle. You could run stock calipers, or do the Wilwood conversion.

I dunno if it would be ideal for rally or dirt racing , but I would imagine it would hold up to pavement abuse.

[Sam]

There is a IRS kit sold for mustangs that converts basically any year car from 65 all the way up to 2013. I have often wondered if a 9-5 irs could be swapped by welding the two control arm types together. Surprisingly the c900 and 9-5 dimensions are quite close. The control arms mount in the same place and the shock mount arrangement is pretty damn similar. Most of the fab work would be in mounting the 9-5 rear subframe which can be unbolted from the 9-5.

[Crazyswede]

Sounds like a lot of work for minimal gain

[Sam]

Sounds like a lot of work for minimal gain

Can you really put a price on toe-in on an fwd car? This was the reason for all of the positive reviews on the focus ST.

[tirediron]

have thought of reinforcing the axle tube one way or another. in my application i think i could get away without a jig. measure, weld, measure and straighten accordingly. only issue i see is that i believe it is always good to have a fuse of some sort. axle is only as strong as what it's attached to. same reason i build my bumpers and brackets to bend before the body/cage. that being said i havent ever had any other rear end breakage aside from bending axles and ripping the panhard bar off one mount or the other.

my thought for building in adjustment was to cut the knucles off and weld plates to the tubes. gusset the hell out of it, run 4 bolts and use washers to adjust. pretty crude, but may work ok on the pavement. if i'm ever off the ground i have bigger problems anyways....

[gmreider]

have thought of reinforcing the axle tube one way or another. in my application i think i could get away without a jig. measure, weld, measure and straighten accordingly. only issue i see is that i believe it is always good to have a fuse of some sort. axle is only as strong as what it's attached to. same reason i build my bumpers and brackets to bend before the body/cage. that being said i havent ever had any other rear end breakage aside from bending axles and ripping the panhard bar off one mount or the other.

my thought for building in adjustment was to cut the knucles off and weld plates to the tubes. gusset the hell out of it, run 4 bolts and use washers to adjust. pretty crude, but may work ok on the pavement. if i'm ever off the ground i have bigger problems anyways....

That is really a good idea. I see that used on American car beam axles. In theory you could shim camber and perhaps toe in to some extent.

[Geoff]

Yeah, sounds like a good idea and is similar to how you can shim rear hub mounts on some cars (e.g. 9-5, NoGood900). I haven't run any calculations but I find myself pondering the bending resistance of a ~2" tube (not sure what the wall thickness is) vs. the tensile stress on say two 1/2" bolts... Washers might be a little thick for minor adjustments but for major adjustments they'd probably get you straightened out for the next heat around the track. If it were me I'd get some sheet metal in various thicknesses and make a bunch of slotted shims (like the front alignment shims) that can be quickly stuck in without having to remove the bolts. A plus to that is the thickness tolerance on a 0.052" thick piece of sheet metal is typically +/- 0.005". The tolerance on 0.050" thick washers is +/- 0.020". You'll get a lot better feel for what to expect when quickly putting in shims with tight tolerances.

[tirediron]

good idea Geoff, i have a pile of control arm shims lying around. strength wise, i'm not sure. i am clearly not an engineer most all my projects use the guess and test method.

one thing i find interesting after removing and cutting my old axle apart. the axle actually bent just inboard of both lower control arms. i would have expected it to be most bent outward of the arms, but i guess not. it is bent backward on both sides and slightly up, adding toe out and negative camber on both sides.

[DrewP]

I believe the hubs on 9-5's have 4 M12 bolts.

NoGood900

I have not had that hearty of a laugh in a while, that's damn funny.

[Geoff]

NoGood900

I have not had that hearty of a laugh in a while, that's damn funny.

I have to give credit to Snakes Malone for that one!