Rack & Pinion Steering on a Chevy C-20 Suspension?
I have a question for the steering system gurus out there, and you know who you are. :P
A buddy of mine is building a '55 First, AD series 3/4 Ton panel truck project. He decided to go with the front suspension from an '81 Chevy C-20 3/4 Ton pick up as we don't think the MII kits would be strong enough for his purposes. Right now the project is still in the disassembly stages, and we figure he has 3 ways to go with this part of the build. One way is to machine the spacers for use between the '55 frame and the '81 crossmember, steering box, and idler arm like we've seen elsewhere online. Another way is to narrow the crossmember and try to use shorter tie rods to get the front end alignment right. And then I thought of a different idea. After narrowing the '81 crossmember, would it be possible to use a power rack & pinion steering system out of a later model sedan or something else on this project instead of trying to work out shorter tie rods? Would this be an option for use with the spacers between the '55 frame and the unaltered '81 crossmember?
This is a large panel truck with a 137" wheelbase (as it turns out, this is the same wheelbase as a late model Ford Expidition,) and it's based on a 1-Ton panel truck frame. The truck will use a Chevy 350/700R4 combo for power, and while it won't be a daily driver, it's being built to be driven often. It might see duty towing a flatbed trailer on occasion, and possibly a boat later on down the road, but mostly just for cruising around town, or the local highways. The panel will weigh somewhere in the 4200 - 4700 lb ballpark, depending on how crazy he goes with the interior accessories. We've done a little bit of looking online, and I've found the newer 4160lb Cadillacs and 4200 lb Dodge Magnums using R&P steering, so I'm thinking it might be possible, but I wanted to check with the gurus here at the board before I encouraged him to dig deeper for info. We have access to a full machine shop and a highly qualified machinist to run things, so slight modification of the ends of the rack or the C-20 suspension shouldn't pose a problem.
Basically, my questions are: is his truck too heavy for R&P steering? Just too durned big maybe? Any suggestions on a particular make/model of vehicle to look for as far as a donor rack is concerned?
As I said, the truck is still in the disassembly stage, and all that's left is pulling what's left of the stock suspension, and removing the body. He's got the '81 Chevy suspension sitting here, and is just making up his mind which way to go on its crossmember. Any help you could give us would be greatly appreciated.
Rack & Pinion
R&P steering should be fine on your truck. Providing you can find one that has the same pivot points as the inside bushing on the lower control arm at dead center.
If not, then you'll end up with "bump steer" and that is a NO NO. It also should remain parallel with the center line of the axle stubs or close to it for the same reason.
Study and measure the pivots on the center link on the existing steering, then study and measure those on given R&P's. Find one that measures the same and you should be ok.
Just dont' take one from a Chevette size car or import.
You are just opening a can of worms.... Especially if you start narrowing crossmembers and otherwise upsetting the designed suspension geometry.
The width of the suspension is a major player in how it works, narrowing it will upset it to the point that it will not be fun to drive.
Do a few searches on suspension design and get familiar with these terms.
Roll Center and Roll Center Migration
Side View Swing arm
Front View Swing Arm
Toe-in and Toe-out
All of these terms are involved in making a good or bad suspension. Cutting up a current suspension and moving things around, without taking all of these factors into consideration, will only make it an ill handling and unsafe suspension.
To determine a good candidate for a suspension swap measure the track width of the truck and then use that measurement has a quideline. Usually anything wider will cause problems with wheel and tire clearance. Anything up to a couple of inches narrower may work without looking funny. S-10's and second gen Camaro's, Firebirds or Nova's are excellant choices for these year trucks. They will go in without narrowing and there is a ton of aftermarket stuff avaible for them.
Sorry for the book but there is a lot of things to consider when you are doing this. Safety and drivability should be your first concerns...
No worries about the length of the reply. In fact my question was a lot longer than your answer. :D
Thanks for the replies. As I said, the truck is still being disassembled, so nothing has been done to the suspension of either vehicle at this point.
Ok, we have a lot to consider as far as narrowing the front crossmember is concerned. To be honest, I didn't feel right about going that far anyway, but it was an option, so I threw it out there for consideration.
So, I guess the only question remaining is whether or not there's a R&P unit out there that'll come close to the measurements of the steering system of the stock (un-narrowed) Chevy C-20 front end that won't require huge amounts of modification and is beefy enough to get the job done. We understand the ends of the rack that attach to the tie rods might have to be machined, or different tie rods all together might have to be used, but it's still possible to use R&P. His main question was in reference to the weight and length of the vehicle and the donor front end. I just haven't found anything online so far about those topics to help us determine whether or not his truck is even a candidate for R&P or not. And yes, we're still looking - and not just online.
He's eliminated the idea of using a front clip from a Camaro or some other passenger car for a couple of reasons. In talking to a couple of other people here locally who drive AD pickups that have been clipped, he just doesn't think it'll work for his needs. You also have to remember that this truck is on a 1-Ton frame, and that frame is different than the half-ton frame most people into the AD trucks are used to.
This is a long term project (he is figuring on about 5 years) so it's not like we're heading to the wrecking yard to search for an R&P unit today and bolt it in tonight. He's taking his time and trying to do things right the first time to avoid problems in the future. What I'm saying is we are researching things now and doing what work on the truck we can do while he's making up his mind about other things and checking into them. Lord knows there's lots of body work and an engine to build to keep him occupied for the next couple of years. This board is part of that research, and the input from both of you is greatly appreciated. :thumbup:
Please don't hesitate to add to your comments or point us in other directions. He wants a truck that is first of all safe to drive. He doesn't want to spend all day under it polishing things afterward. He wants to build it to drive. He'd rather have a more modern independent front suspension that incorporates disk brakes and power steering. The C-20 front end fits those requirements. If he ends up having to use the stock steering box and adapting it to work with the stock '55 frame and '81 crossmember, so be it. But it's worth asking about. Better to do that than go ahead and try it, then have to undo all that work. :smash:
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