1946 chevy truck build.

[joedoh]

if your bar measurement of 13" was related to the bar measurement of the lowers as 21", you still have the problem. measuring eye to eye isnt going to make it better. fix these problems:

your upper bars point down while the longer lowers are straight, this will always cause pinion/roll steer problems. you want them to be close to level when at ride height.

your upper bars are way too short. looking at them from the top this is visible, the upper length looks to be less than half the lower length. you can only measure their length STRAIGHT ALONG THE FRAME, it doesnt really matter what the actual length of the bar is. the effective length, measured straight along the frame, that is how long the bar is. not eye to eye, not just the bar length, all of that is irrelevant. mark two spots on the frame, the centerline of the axle and where the upper bar attaches to the frame and measure straight between those two points. that is the length of your upper bar. if it helps, imagine it as a big rectangular piece of steel instead of an angled bar. even though you can draw a long line from corner to corner of the rectangle, how long the rectangle is measured along one side is how long the rectangle is. thats it.

the upper arc of operation will be a much smaller diameter circle than the lower arc of operation, so the lower mount will stay roughly stable in up/down motion while the upper will not, it will move forward and back dramatically.

having the lower bar mount kicked forward of the axle centerline is pretty standard for 4 links, especially with a shock mount on the rear.

edit: I just rotated and enlarged your picture so I could see better and it looks like you are welding to the cast part of the rearend. this will probably break under use, welding to cast is possible if you preheat it with a torch and get it cherry red but it takes special rod too.

[dillonv2008]

Originally Posted by joedoh

if your bar measurement of 13" was related to the bar measurement of the lowers as 21", you still have the problem. measuring eye to eye isnt going to make it better. fix these problems:

your upper bars point down while the longer lowers are straight, this will always cause pinion/roll steer problems. you want them to be close to level when at ride height.

your upper bars are way too short. looking at them from the top this is visible, the upper length looks to be less than half the lower length. you can only measure their length STRAIGHT ALONG THE FRAME, it doesnt really matter what the actual length of the bar is. the effective length, measured straight along the frame, that is how long the bar is. not eye to eye, not just the bar length, all of that is irrelevant. mark two spots on the frame, the centerline of the axle and where the upper bar attaches to the frame and measure straight between those two points. that is the length of your upper bar. if it helps, imagine it as a big rectangular piece of steel instead of an angled bar. even though you can draw a long line from corner to corner of the rectangle, how long the rectangle is measured along one side is how long the rectangle is. thats it.

the upper arc of operation will be a much smaller diameter circle than the lower arc of operation, so the lower mount will stay roughly stable in up/down motion while the upper will not, it will move forward and back dramatically.

having the lower bar mount kicked forward of the axle centerline is pretty standard for 4 links, especially with a shock mount on the rear.

edit: I just rotated and enlarged your picture so I could see better and it looks like you are welding to the cast part of the rearend. this will probably break under use, welding to cast is possible if you preheat it with a torch and get it cherry red but it takes special rod too.

I understood what you mean. Not length of the actual bar but from centerline axle along frame rail to the link where it attached to the frame. That was indeed 13inchs. I was just saying the specs of the bar itself in post about length of lower and upper bar actual spec length. But I removed the upper bars and going to be re angling them around 30sih degrees or so and parallel with lower bars at ride height. I'm ordering new tab links because old ones didn't make the tear down haha. So when New ones come in I'll go ahead and do what you said. Also I'll mount them on the axle them self not the pumpkin part as you are saying can't be done unless special measures are taken.

Would I get a better pinion angle stability of staying still if I was to just do a reverse 4 link? And order longer upper bars?? Or if I do what you are saying of pushing angles not so wide and level I will see a much better and practical ride. I want to be able to drive at it slammed for shows or streets. So all angles id like no issues with driveline u joints going out

[dillonv2008]

Originally Posted by joedoh

if your bar measurement of 13" was related to the bar measurement of the lowers as 21", you still have the problem. measuring eye to eye isnt going to make it better. fix these problems:

your upper bars point down while the longer lowers are straight, this will always cause pinion/roll steer problems. you want them to be close to level when at ride height.

your upper bars are way too short. looking at them from the top this is visible, the upper length looks to be less than half the lower length. you can only measure their length STRAIGHT ALONG THE FRAME, it doesnt really matter what the actual length of the bar is. the effective length, measured straight along the frame, that is how long the bar is. not eye to eye, not just the bar length, all of that is irrelevant. mark two spots on the frame, the centerline of the axle and where the upper bar attaches to the frame and measure straight between those two points. that is the length of your upper bar. if it helps, imagine it as a big rectangular piece of steel instead of an angled bar. even though you can draw a long line from corner to corner of the rectangle, how long the rectangle is measured along one side is how long the rectangle is. thats it.

the upper arc of operation will be a much smaller diameter circle than the lower arc of operation, so the lower mount will stay roughly stable in up/down motion while the upper will not, it will move forward and back dramatically.

having the lower bar mount kicked forward of the axle centerline is pretty standard for 4 links, especially with a shock mount on the rear.

edit: I just rotated and enlarged your picture so I could see better and it looks like you are welding to the cast part of the rearend. this will probably break under use, welding to cast is possible if you preheat it with a torch and get it cherry red but it takes special rod too.

I took a 2ft framing square and set it on my axle center. Along frame rail to link and measured 13"

[dillonv2008]

Originally Posted by joedoh

if your bar measurement of 13" was related to the bar measurement of the lowers as 21", you still have the problem. measuring eye to eye isnt going to make it better. fix these problems:

your upper bars point down while the longer lowers are straight, this will always cause pinion/roll steer problems. you want them to be close to level when at ride height.

your upper bars are way too short. looking at them from the top this is visible, the upper length looks to be less than half the lower length. you can only measure their length STRAIGHT ALONG THE FRAME, it doesnt really matter what the actual length of the bar is. the effective length, measured straight along the frame, that is how long the bar is. not eye to eye, not just the bar length, all of that is irrelevant. mark two spots on the frame, the centerline of the axle and where the upper bar attaches to the frame and measure straight between those two points. that is the length of your upper bar. if it helps, imagine it as a big rectangular piece of steel instead of an angled bar. even though you can draw a long line from corner to corner of the rectangle, how long the rectangle is measured along one side is how long the rectangle is. thats it.

the upper arc of operation will be a much smaller diameter circle than the lower arc of operation, so the lower mount will stay roughly stable in up/down motion while the upper will not, it will move forward and back dramatically.

having the lower bar mount kicked forward of the axle centerline is pretty standard for 4 links, especially with a shock mount on the rear.

edit: I just rotated and enlarged your picture so I could see better and it looks like you are welding to the cast part of the rearend. this will probably break under use, welding to cast is possible if you preheat it with a torch and get it cherry red but it takes special rod too.

I think I'm starting to under stand a little so I want from a side view. my upper bars to be around 20-30% less then lower bars. so if I was was to measure from axle to the link on the frame staying along the frame rail and my lower bar was say 30" id want my upper bar to be around 25" say. BUT the actual spec length of the bar doesn't matter only what you measure from a center axle to the link along the frame rail. and where ever that mark lands I go out 30* + to axle. idk if this is really really confusing or not haha in the picture I want lower bars to be longer then uppers but measure from side view not top.

[joedoh]

Originally Posted by dillonv2008

I think I'm starting to under stand a little so I want from a side view. my upper bars to be around 20-30% less then lower bars. so if I was was to measure from axle to the link on the frame staying along the frame rail and my lower bar was say 30" id want my upper bar to be around 25" say. BUT the actual spec length of the bar doesn't matter only what you measure from a center axle to the link along the frame rail. and where ever that mark lands I go out 30* + to axle. idk if this is really really confusing or not haha in the picture I want lower bars to be longer then uppers but measure from side view not top.

nope you got it. look from the side and that is the length that matters.

[dillonv2008]

[QUOTE=joedoh;8041849]nope you got it. look from the side and that is


Awesome thank you so much

[dillonv2008]

Originally Posted by joedoh

nope you got it. look from the side and that is the length that matters.

Also for setting pinion angle am I setting it up +* or -*? Since at ride height I'm only 6 inches off ground the transmission is angled down lower then the axle is gonna be. I guess what I'm asking what did you set yours at at ride height. My motor isn't installed yet so I can set that to what I'd like aswell - something

I do understand you want it to be opposite. -3 tranny +3 axle yatta yatta yatta. So if my axle at ride height is as high or higher then transmission angle am I still going +??

[Kermitt47]

Hi, I am going down a similar route so this thread is interesting. If you wanted to make the side view equal length then the top bar would have to be longer than the bottom bar? Is there an acceptable ratio to aim for or is it just to keep the pinion change to a minimum over the suspension travel?

[joedoh]

Originally Posted by Kermitt47

Is there an acceptable ratio to aim for or is it just to keep the pinion change to a minimum over the suspension travel?

its the latter, unequal lengths will keep the pinion angle and rear steer to a minimum. Just like upper and lower control arms are unequal length, equal length control arms will have MORE camber change, and it will be wacky camber too.

a good way to check this stuff out before even ordering bars is to scale model it with paper first. figure out how far apart (y axis) the bars will be at the front attachment and at the rear axle. then cut some paper strips and use round head fasteners (office supplies) and a hole punch to make an "axle" and "bars" and a "frame"

then you can use a pencil to trace the pinion angle at different heights.

[dillonv2008]

Originally Posted by joedoh

its the latter, unequal lengths will keep the pinion angle and rear steer to a minimum. Just like upper and lower control arms are unequal length, equal length control arms will have MORE camber change, and it will be wacky camber too.

a good way to check this stuff out before even ordering bars is to scale model it with paper first. figure out how far apart (y axis) the bars will be at the front attachment and at the rear axle. then cut some paper strips and use round head fasteners (office supplies) and a hole punch to make an "axle" and "bars" and a "frame"

then you can use a pencil to trace the pinion angle at different heights.

So why does this set up work if from side view bars are equal length. Id Like to redo mine a little so I can run bags on bars.

[dillonv2008]

Originally Posted by Kermitt47

Hi, I am going down a similar route so this thread is interesting. If you wanted to make the side view equal length then the top bar would have to be longer than the bottom bar? Is there an acceptable ratio to aim for or is it just to keep the pinion change to a minimum over the suspension travel?

from what ive read about the lower and upper bar lengths is you want the upper bar to be about 70-80% of the lower bar length from a side view. dont just cut the bars and make it shorter. its all from a side view. so in my drawing I did the lower bars are parallel to ground and example 30" long center of axle to end of bar link. so my upper bars need to be in the 70-80% range. but the upper links are going to be at an angle so cutting them to early before measuring like I did will make them possibly under that 70-80 range. you have to consider the angle they will be at in your measurments forgetting them in that 70-80 range. so in the example if lowers where 30" center axle to end link. 30-25%= 22.5 but they will be at an angle so you have to add for that angle in your measurments.so the bars them self might really be 25" but with 30* angle or whatever it will from a side view be 22.5 which is 75% of the length of lower bars .. ?? get it kinda I might of made it more confusing haha

[dillonv2008]

Originally Posted by joedoh

nope you got it. look from the side and that is the length that matters.

one more question just got the new upper bars in when I go to do the measureing from side view and upper bars need to be the 70 - 80% range. when measuring lower bars length. my lower tab as we talked sticks them forward because they are the shock mount style. question is do I measuring from center axle to front bar link to get my measurement or do I just measure link to link. my lower axle link is forward a few inches from axle.

[dillonv2008]

[QUOTE=joedoh;8041759]if your bar measurement of 13" was related to the bar measurement of the lowers as 21", you still have the problem. measuring eye to eye isnt going to make it better. fix these problems:

your upper bars point down while the longer lowers are straight, this will always cause pinion/roll steer problems. you want them to be close to level when at ride height.

your upper bars are way too short. looking at them from the top this is visible, the upper length looks to be less than half the lower length. you can only measure their length STRAIGHT ALONG THE FRAME, it doesnt really matter what the actual length of the bar is. the effective length, measured straight along the frame, that is how long the bar is. not eye to eye, not just the bar length, all of that is irrelevant. mark two spots on the frame, the centerline of the axle and where the upper bar attaches to the frame and measure straight between those two points. that is the length of your upper bar. if it helps, imagine it as a big rectangular piece of steel instead of an angled bar. even though you can draw a long line from corner to corner of the rectangle, how long the rectangle is measured along one side is how long the rectangle is. thats it.

nvm I reread this and understand center of axle to center link on axle

[dillonv2008]

Great progress tonight have front all tacted in place and rear tacted in with only maybe 1 degree change from ride height to on the ground about 6.5 inch of travel