4bar length question

chimp koose · February 08, 2013, 10:12:28 PM

I am about to build a 4bar front for my T coupe and was wondering if there is a reason why so many 4bar front ends are 20ish inches as I am considering building the bars @ 32" between centers. Is there a reason why they should be shorter? I plan on running a steering rack unisteer style so the long 4 bars will not be in the way of the steering box. Opinions?

Charlie Chops 1940 · February 08, 2013, 10:15:16 PM

I think some of the really short ones are for full fendered A's and 32's.

chimp koose · February 08, 2013, 10:29:52 PM

My coupe will be full fendered as well . I am using the same width frame as the T(23" to the outsides) which is quite a bit narrower than the A . Are you suggesting that the A 4bar is shorter because the frame is wider and there might be issues clearing the fenders and aprons? I will double check but I am quite sure the 32" bars will clear the T fenders. The roadster 4bars are longer than full fendered,I just never thought why other than appearance however they may be longer because of better geometry.Thanks for the reply. Anyone else?

Warpspeed · February 09, 2013, 01:27:03 AM

I suppose the trick here, is to first locate your steering box/half rack wherever it absolutely has to go. There are often really big issues with that...

Then arrange your four bar to minimize bump steer, by making the four bar lengths the same as the steering push/pull rod length.

enjenjo · February 09, 2013, 07:09:04 AM

I believe they are all about that length because that works well with most side steer setups. I can't see that it will hurt to go longer.

Charlie Chops 1940 · February 09, 2013, 08:41:43 AM

I started out with a tube axle, 4 bars and all the hardware from a '32 for my track roadster. The bars were short as the '32 had been destined to be full fendered. Those bars were nominally 21" eye-to-eye. They just weren't gonna look good on an open wheel car. I had a set made that ended up around 29-1/2" eye-to-eye. Much better.

The 4-bar set up evolved around use of side steer boxes like the early Mustangs and I guess needed to terminate before they got to where '32 -'34 fenders sweep along the frame. I'm thinking A's wouldn't have that problem but suppliers probably settled on a common length.

Just supposition on my part because at the time I was doing my cars with independent front ends.

Charlie

phat46 · February 09, 2013, 09:24:59 AM

I made a set that is 23" eye to eye, they could have been longer or shorter as there was nothing to interfere with them. I made them that length because I wanted them to pivot about the same place the drag link would pivot at the steering box. If you're using a rack or cross steer setup that wouldn't matter.

GPster · February 09, 2013, 09:55:38 AM

I seem to remember when "Pete and Jake" started with their 4 bar front ends they mostly used Mustang steering boxes turned on their sides with drag link steering. For "bump steer" elimination the drag links were near the same length as the 4 bars, the steering arm pointed up off the steering box and the steering box mount also served as a 4 bar frame mount keeping the bars and the drag link the same length. With this kind of set-up and "Super Bell" dropped axels all of this stuff had to be in front of the firewall and under the heigth of the top of the frame rails. Then when Vegas started nesting in the junk yards there was a better steering box to be had but they already had everything else designed. Seems to me that all of this might have been during a full fendered rather than a traditional period of this hobby. GPster

chimp koose · February 09, 2013, 09:44:26 PM

Thanks for the info guys. I didnt think this would be a problem but it pays to check. I will be going cross steer with a cut down rack. In order to keep bump steer in check I will be making the cross shaft from rack to tie rod as close to the same length as the panhard rod as possible. From the looks of things to this point I may be able to duplicate the length AND angle of the panhard rod.

Warpspeed · February 10, 2013, 03:34:02 AM

Quote from: "chimp koose"Thanks for the info guys. I didnt think this would be a problem but it pays to check. I will be going cross steer with a cut down rack. In order to keep bump steer in check I will be making the cross shaft from rack to tie rod as close to the same length as the panhard rod as possible. From the looks of things to this point I may be able to duplicate the length AND angle of the panhard rod.

That sounds like an excellent solution.