forgive my ignorance, but in all my builds I've never really messed with steering geometry so its not something I've come across, but what is bump steer?
Build "The Milk Truck" FJ45 Preservation Sorta
- Thread starter Tank5
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- #982
Google will explain it better than I will but I understand bump steer is the result of different arcs of movement in the suspension and steering, that occurs when the suspension cycles creating unwanted steering input into the system as a result. I understand that the panhard bar and draglink generally need to move in the same or very close arch of movement when the suspension cycles up or down to prevent the effects of bump steer. What I don't know (well there is a lot I don't know) is how much the arch can be offset before this really becomes an issue. My research also found that the length of the drag link in comparison to the panhard also comes into play as might the other parts of the suspension.
Through my own trials I am finding my set up has 5 degrees of separation in the angle of the draglink and panhard and so far does not seem to be affected enough that the bump steer is felt at the steering wheel. More driving is needed though.
If anyone cares to correct anything I got wrong or expand on the topic please do, so I am not spewing miss information.
With limited up and down travel it will not be as noticeable as in a long travel suspension. In my race car for example I have 14" of up and down travel. I have both the panhard and drag link at the same length and angles to limit the bump steer. I do not get bump steer but over a long period of large washouts, 18"-24" or so at speed 60 mph ish, it will walk to the left, I have to input a little steering to keep it straight. I am talking over 50 yards or so. @tTank5 is correct. Google search and you will find out more, but yes it is important to have your angles and lengths correct.
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- #984
You probably just explained why I am not
experiencing bump steer. My suspension only has about 4.5 inches of up travel before all the compression is taken out of the bump stops. The down travel is about 5.5 inches. My total shock travel front and back is only 10 inches and I may only get about 9.5 inches of that due to bump stops and limit straps. From your shared experience I may not get enough travel in my suspension to produce significant effects of bump steer in my normal driving conditions.
With 5" of lift and traditional leaf spring suspension, it took hi-steer arms from Over The Hill and a slightly dropped pitman arm to resolve the bump steer on my 45, which has 13" travel shocks. I do most of my high speed off road driving on the washboards of Death Valley, where it suffers the same leftward pull on the whoops that @matzell mentioned. But the weight of the truck, the modest sized tires and most of all the wheelbase keep it pretty stable.
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Thanks for the explanation, makes sense to me.
So bump steer itself is just wandering or pull to one side within the steering when trying to drive straight? @65swb45 @matzell
Basically. When going over "bumps" it causes the steering to "bump". If you hold the wheel light you will see the wheel turn and then turn back as the vehicle goes straight. IF you hold it hard, the vehicle will dart side to side.
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- #988
We got some snow last night, so I took it out at the end of the day to test the heater and have some fun. The heater didn’t have any problems keeping the cab warm.
I played with the front, center, and rear lockers they all worked as I expect they should. Wish I had more time but it was getting dark and I was by myself.
I did find a spot for a good seasonal photo.
I played with the front, center, and rear lockers they all worked as I expect they should. Wish I had more time but it was getting dark and I was by myself.
I did find a spot for a good seasonal photo.
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- #991
I used the SGI-100BT unit to get it to work. I found that I was measuring the tach voltage incorrectly, so after finding it was low voltage I changed one wire on the SGI output from high voltage to low and it started working.
I have some things to do still. I just received a NOS lens for my dome light which I need to install. I am also waiting for a replacement switch for my wipers. The AC needs charged and tested but I want to have new lines made to clean up some of the fittings.
The steering needs to be revisited for a third time. After adjusting the pan shard bracket and getting more miles on it I notice the bump steer more. It is drivable and handles well but I would like to try and eliminate the bump steer if possible.
I plan to add some accessory charging outlets to my center console, so some more wiring eventually.
I would like to find some modern wiper arms and blades to fit the oem wiper motors. The original blades are a pretty weak.
I am sure there are some other tweaks I will make as I add miles to it but I am happy driving it as is for now.
I swapped in a set of VW Beetle(?) arms after reading about it here. Same spline as my ‘73 and common J hook attachment. Elbow was the wrong directions, but it was easy to modify. Now I have no problem getting replacement wipers at anytime.
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- #993
The steering is going for its 3rd iteration. The current version clears everything very well but I am noticing the bump steer the more I drive it.
On to round three. I bough this ruff stuff kit made for one of the heaps. It uses 1ton gm tie rod ends in a y-link configuration which will drop my drag link down so it is close if not in line with the pan hard bar. It only comes as a welded kit, so I am going to have to do a little surgery to make it fit. I hope the third time works.
While I waited on parts I installed the dome light and mounted my jack on the roll bar to gain room in the bed box.
On to round three. I bough this ruff stuff kit made for one of the heaps. It uses 1ton gm tie rod ends in a y-link configuration which will drop my drag link down so it is close if not in line with the pan hard bar. It only comes as a welded kit, so I am going to have to do a little surgery to make it fit. I hope the third time works.
While I waited on parts I installed the dome light and mounted my jack on the roll bar to gain room in the bed box.
Please remind me... what did you change from the OEM 80 series setup that you're having a hard time with your steering? I thought it was stock for the most part, but I can't remember.
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- #995
My front axle is made from an 80 series rear semi float housing, so I could run a 9.5” diff up front the same the 45 originally came with.
The 9.5” diff is low pinion, so I couldn’t use the 80 series stock tie rod location. I opted to go with high steer Hellfire knuckles with cross over steering to solve that issue.
I had to raise the panhard bracket to properly align the with the draglink. Which worked really well but was too close to the frame and was making contact on compression, so I dropped it back down to the stock location which has plenty of clearance but causes bump steer.
I had also started out with normal heim joints but they didn’t provide enough distance to clear the upper panhard bracket. I swapped them out for offset heims which solved the clearance issue.
Short answer I wanted a 9.5” diff up front and keep the 80 series radius arm setup. This has created my wormhole of adjustments. I am sure I can make it work.
If I was to start over I think the Slee high steer arm with stock knuckles might be a better option to keep the 80 panhard and radius arm setup with a 9.5” diff.
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That's right.... its amazing how you change one thing and it leads to another. The butterfly effect of vehicle building. It seems like everything is a tradeoff.
I'm sure you'll get it dialed in and be happy with the results.
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- #997
I finished installing the new steering setup tonight. I had to shorten the tie rod and lengthen the drag-link to fit my needs. I anticipated this and ordered some 1 in solid steel stock to insert inside tube to bridge the cuts.
After welding it up and painting.
I reemed the pitman arm to fit the 1ton tied end and had to drill out the knuckle arms to 7/8 to fit the sleeves to accommodate the larger tie rods. After putting it all together I learned the steering damper mount needed to be move to the passenger side 3 inches due to the extra length of the longer tie rod at the pitman arm. I pulled it apart moved the bracket and put it all back together. The clearance looks good and the alignment between the drag link and pan hard bar look much better. Should get to take it out for a drive tomorrow.
After welding it up and painting.
I reemed the pitman arm to fit the 1ton tied end and had to drill out the knuckle arms to 7/8 to fit the sleeves to accommodate the larger tie rods. After putting it all together I learned the steering damper mount needed to be move to the passenger side 3 inches due to the extra length of the longer tie rod at the pitman arm. I pulled it apart moved the bracket and put it all back together. The clearance looks good and the alignment between the drag link and pan hard bar look much better. Should get to take it out for a drive tomorrow.
Looks better, but I see two issues.
1. Ideally you want the drag ling and panhard the same length so they follow the same arc.
2. Can you raise the axle side panhard mount to be paralell to the draglink? need to look at mounting hole to mounting hole as the straight line
It should drive better but on big bumps with a lot of suspension travel it will still have some bump steer.
1. Ideally you want the drag ling and panhard the same length so they follow the same arc.
2. Can you raise the axle side panhard mount to be paralell to the draglink? need to look at mounting hole to mounting hole as the straight line
It should drive better but on big bumps with a lot of suspension travel it will still have some bump steer.
I am getting ready to build a similar bumper (flattery right!) and wanted to see if there is anything you would change about your setup?
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- #1,000
I can’t initially started with the axle side panhard raised but there was not enough room to keep it that way as it would contact the frame on compression and it only took about three inches of compression to get to do that. That is why I dropped it down.
I agree the drag link / panhard alignment is not perfect is not perfect but this makes it much better.
If this steering does not work I may have to swap the. Knuckles for stock and use the Slee arm with a double sheer configuration to go back to cross over steering or try to build a custom lower arm to do that with what I have.