Greenhorn alert! I am building my first hotrod. Largely alone as i am out in the sticks. Pretty hard to get mates to pop over for a beer and a brain storm session! <O I am building what i call a 'tall rod'. That is, a stock model A repro frame with stock non dropped beam axle, spring and wishbones. So ride height is quite high. Nothing has been done to lower the car and i am not looking to unless i have no choice at the moment. <O I understand 'ackerman' and i understand 'bump steer'. Desire is side steer regardless of the pro's and con's i read. After trying all the usual steering box combinations we use in RHD Australia i have found what i hope/want to work for me. <O I have 2 concerns right now. <O 1. The stock wishbone ball hangs quite a way under the chassis rails. I have the front spring X member tilted back at what i was advised, 7 degrees and have the wishbones hanging at a position that does not bind the spring, although as high as i think i can go. Is this the normal amount of hang under the chassis for the stock 29 front? <O 2. The above suspension raises challenges for side steer as it is low down. I am trying to mount the steering box on the chassis rail, pitman arm 6 o'clock. With the box as far back as i can go, the draglink runs parallel (almost) to the wishbone. Some say that's ok, others, not. This places the arm about 3'' in front of the wishbone ball. Others say the draglink should run uphill in a perfect world, following the arc of travel the bones will make. To do that i would have to hang the box way under the chassis... not a good look to me. <O My steering arm is 1/2 '' shorter than the pitman arm and i plan to get it made a little longer to stop the tyre hitting the draglink. I have also had to place the tierod on the inside of the pitman arm to make it better also. <O I will post photo's in the next post with photoshopped diagrams of what i have, what i want and what our guidelines and principles of geometry demand for a reasonable ride. <O I hope i have given enough explanation so as to avoid getting to many questions! All i want is for people to look at what i have got, how it is set up and maybe help me either be comfortable with it for ffice:smarttags" /><ST1lace w:st="on"><?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-comAustralia</st1:country-region></ST1lace> and safety or work out how to make it right <O thankyou, Aussie
I hope these are enough to put us on the same page... i can move the pitman arm down and forward slightly as per the yellow line but i dont know that is enough or makes any real difference.
Just my opinion Aussie... Your set up will work OK with virtually no noticable bump steer. It is very similar to mine except I am running split bones, so I can say that from first hand experience. However it is not the ideal set up as you clearly understand. So it might come down to what you need to do in order to satisfy those who must be satisfied
Ideally, the steering arm should end as close to the 'bone pivot point as possible. With a wishbone attached solidly to the axle, not a parallel four-link, the steering link being parallel to it makes no difference. All that affects bump steer is the vertical distance from the pivot point to the rear end of the steering link, in your case, maybe 3". When the axle moves up and down a few inches, it's only going to affect the steering about 10% as much if the bones are 30" long. That ain't much. The ball socket on my "A" frame is about 4" below the rails, and it is a few inches lower than stock with a non-dropped axle, reversed spring eyes, and modified front X member.
Did something similar. No problems with bumpsteer. On normal roads your axel will only travel a small distance up and down. So no noticable problem there. On bumpy roads you will have to countersteer anyways
Aussie, your photo (first one) with the coloured lines introduces some parallax error to your arc calculations. With the wheels straight ahead the ball joint on the steering arm will be in line with the spindle axis. Having the ball on the pittman arm 3" ahead of the wishbone ball tightens the arc of the drag link a little but they should still be close enough to not cause any problems. Actually tightening the arc will probably help as the axle will be moving back due to the low mount on the back of the wishbone. I presume that the RTB won't let you cut the wishbone near the axle and move the rear pivot point up closer to the chassis. The best way to figure out the arcs is to make a stick model of the various parts and cycle it through the expected travel. We used to use icy pole (popsicle) sticks to work out four link geometry on drag cars back in the 70's. Now I use high end software but the stick version is lots cheaper. Roo
I don't see why you need the wishbone ball so low, and so far away from the frame? Just to get 7 degrees caster? You don't need 7, and even if you thought you did, you could pie cut the bones up front.
Before you get too far into it, consult the SA TAC to find out the local requirements are for rego etc. Could save yourself time & $$$. Draw on their experience because at the end of all your efforts you may find out it can't be registered.
Thankyou all! Striper, you give me confidence. R Pope, ball 4'' down with some lowing work, so i am guessing that Henry intended it to hang lower in stovk form then. Nielsk, thanks, i feel better! Rooman, off to play with sticks...photoshopping a photo didnt really work out too accurate did it? F&J, being a newbie i just do what i am told! Not sure about cuting the bones... will check if i am 'allowed'. Mgtstumpy. doing that all along. The problem as i am dure you are aware, every guy on the tac has a different idea! Am working close with one guy but he is 200 km away. So it appears my set up will work ok despite my ride height etc, just have to please the powers that be... aussie
It was hard for me to tell from your picture, but could you flip the wishbone over and get it to locate higher?
There suppose to be the same length and parallel Thats the best ,We can only do so much , The set up your using will do fine ,I described the perfect situation and that is hard to accomplish ,I have 2 cars that arent perfect . Go with your idea about steering box as far as you can ,,,,,,,And as level as you can make it with bending hoop arm down ........
well david, i never thought of that! I will go to shed and look... carcrazyjohn, thanks for the vote of confidence. as Rooman pointed out, my pics may not show it the best so i have done some more accurate ones. I did a 1:1 full scale drawing and set to work with string lines and the computer. what do you think. better or worse!?
You poor fuckers. My 2000 Ranger has worse bumpsteer characteristics than what you plotted and I bet they import them into Austrailia!
Hey Ozzie - whereabouts "in the sticks" are you. Also what is that pitman arm? I'm looking at a side steer seer set up as well but with parallel leafs along side my frame rails so wouldn't mind a bit of cross pollination of ideas Cheers Tony
HI Aussie, I dont think the pie cutting of bones is 'Allowed' here in SA without swinging it by an engineer unfortunately. even to regain correct caster I'm about to approach an engineer to see if i can extend my wishbone to clear my engine and to use the mount on the 40 ford X member in my 32 frame, I have seen a post here on the HAMB and am going to hunt it down and approach the engineer with diagrams I'll ask about the pie cutting too, IF and i say IF i have any remarkable news i'll let you know. Aaron MS
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