JTR BUMP STEER MOD - A MUST??

[Owen]

Perhaps if the laser pointers were pointing straight down instead of forward at a wall, you could get a visual of how the points are moving from their original rest point.

 

I too was thinking of jacking the control arms but thru my many converstations with Jon and re-reading of "How to make your car handle" it seems that jacking the car is the way to go? I remember somewhere in the book that care had to be taken to keep the car body from rolling, etc.

 

Now, I'm a ways from doing this (Jon, I finally ordered those caster/camber gauges!) but I love this type of discussion I don't mean to change the subject here, but before you do all this, does the car have to be level? Ride height I can understand but the book kept talking about making sure the car is level....where do you measure this? At the suspension pivot points?

 

Slotting the holes is a good idea, but my car is a street car mainly, I don't want to keep having to retorque the bolts, hence my desire to use tie rod ends for the steering rods.

 

Owen

[JMortensen]

The lasers are still going to move in and out while the suspension travels up and down, so you'd still need a way to measure the toe change independently of the track change.

 

Level really shouldn't matter as long as it is safe enough to jack the car up in the first place.

 

Slotting the holes is a good idea, but my car is a street car mainly, I don't want to keep having to retorque the bolts, hence my desire to use tie rod ends for the steering rods.

 

So slot the holes, figure out where the bumpsteer is fixed, drive straight to a muffler shop and have them weld the washers in place. Now its permanent and you don't have to worry about the bolts.

 

Jon

[Pop N Wood]

OK I have convinced myself. If is as simple as can be. With the wheel off and the spring removed, simply tape one of these

 

 

on the side of the hub. Raise the hub until the suspension is around the normal ride height. The laser will draw a line on the floor. This is the direction the wheels are headed. Snap a chalk line under the laser. Now raise and lower the hub and compare the new laser line with the chalk line. The two lines should be perfectly parallel. Just run a ruler down the lines measuring the distance between them. The angle between the two lines is the change in toe. Move the pivot and repeat the above until the lines stay the same distance apart.

 

This should be bulletproof.

[JMortensen]

I can't argue with your reasoning. That would work. No doubt. BUT-- you'll still be measuring on the floor with a ruler. I don't see how that could possibly be as accurate or as quick as using dial indicators, I've never seen a ruler that measures in .0001's.

 

Seems like you and Owen REALLY want to use a laser for this. IMHO it just isn't necessary and makes the job twice as hard.

 

I'm not trying to come off snotty or anything, but this is reminiscent of when I suggest that people can use an air hammer to take out stub axles. People just don't want to do it for some reason. I think I've told 50 people that method, and not a SINGLE person has actually done it that I am aware of. They want to make a special slide hammer instead. It's just not necessary, and they would have completed the job in the time it took just to go get the parts to make their slide hammer adapter thingy. Turns a 10 minute job into a hours long project.

 

Again, not trying to get bitchy with anyone, but I think you're going to make the job a lot harder than it needs to be.

 

I think you'll be pleased with the results regardless of how it gets done. If you're pushing the car really hard, this will make a noticeable difference.

 

Good luck with your projects guys... Sorry if that was a little preachy or self-indulgent.

 

Jon

[Pop N Wood]

Hey, I've actually passed on your idea of the air hammer! In fact, it was probably your post that prompted me to finally buy an air hammer. I have a 1970 240 and checking my stub axles is high on my list of to do's. The only reason I haven't tried it already is my Z is on blocks waiting for several other projects to get done first.

 

The reason I think the laser lines will work well is they have geometry working for them. Like I posted earlier, a 1/4 degree change in toe will cause a 52 thousands inch change across a 1 foot rotor. That same 1/4 degree of toe will cause a half inch shift along a 10 foot chalk line, and a full inch if the line goes out 20 feet. If I did the math right you could almost do it visually with a 20+ foot line.

 

My worries with the dial indicators is it doesn't take much of a shift in the position of the car to upset the positioning of the indicators. You had good results so I know it can be done. But the other thing to consider is I don't own a dial indicator, but I did get two of those laser lines for Christmas. The only other thing I need is some carpet tape.

[JMortensen]

OK, I'm sorry. I have been there too, so I guess I should be more understanding. Some times you gotta make do with what you have on hand. I can definitely understand that.

 

One thing though. If you attach the lasers to the hubs when you raise the control arm that will change the angle of the hub, and your line is going to go farther across the floor than the hub actually moves out. I don't think that will negate your measurements, but it might make your parallel lines farther apart and harder to measure.

 

Jon

[Owen]

You're not coming off the wrong way to me I'm just trying to get all the ideas out of my head and then to get feedback from others. I will use dial indicators and I will use the string method we talked about elsewhere.

 

The reason I mentioned my laser pointers is I ordered them cheap from Harbor Freight (4 months ago and they haven't arrived yet!). I think I'll get the dial indicators physically from the store instead of ordering them

 

Owen

[baddriver]

I like the idea of using the laser level to measure the angle, but I think there may be a flaw with your method. I've been trying to follow this thread for a few days and I love the discussion, so if I've misunderstood what's going on, forgive me.

 

The problem with measuring the toe by comparing the laser lines on the floor is that you are assuming the plane in which the laser line falls is perfectly vertical, when in fact, it will only be vertical for a given height, and then change with the camber of the wheel. I think you would be better off projecting a dot onto the wall in front of the car several feet ahead, and then measuring the (horizontal) movement of the dot. The wheel does move in and out a slight amount, the trick is to project the dot far enough away that the track change is less than 1/100th of the distance the dot moves, therefore making it insignificant in the measurement (at least to two significant figures). The ramaining movement should be entirely due to toe change, right??

 

Of course, I am assuming that the wall you choose is fairly straight and perpendicular to the car, and that the height of the dot remains constant. There are a lot of things to keep straight for this type of measurement.

 

I may be over-simplifying what is going on here, as I'm not sure I've followed this discussion completely, either way it's been very informative, Thanks, and keep up the good work.

[JMortensen]

OK, I either came up with something really brilliant or really really dumb, and I can't figure out which it is. Maybe you laserphiles can figure it out.

 

The problem as I see it is projecting a laser to the front only will show you where the wheel is pointed, and will also show track change, but it will not show the change in the angle of the wheel (toe change) as the suspension moves. So your dot will move in an arc, but how this arc relates to change in toe is difficult to measure, unless you measure front and back, and can relate the changes front and back to the centerline of the wheel.

 

So here's the idea:

 

What if you used a mirror to bounce the laser back to the wheel area, and then watched the change in the distance between the laser and the reflected "target" point on the wheel? My thinking is that if the toe changed the reflected dot will get closer or farther from the laser itself. The laser could be "aimed" to the target could be adjusted by giving a little toe in or toe out so that the reflection hits where it would be convenient, and that point is then the target.

 

Would take a little time to set up with the mirror; it would have to be perpendicular to the original beam, and the mirror would need to be flat for this to be accurate, but I think it could be done.

 

I still think the dial indicators would be easier (just had to throw another little dig there), but at least with this idea you could measure not just where the dot goes, but also the angle at which the laser hits the mirror (toe angle).

 

This should be pretty accurate because the toe angle will be magnified by the distance to the target and back, allowing for a really fine adjustment.

 

Jon

[Owen]

I agree, pointing forward, my guess is you'd only get track and camber changes. That's why I figured projecting the dots onto the floor would be better. You mount the lasers, draw a line or something between the two, then move the suspension and watch if the dots move from the original points.

 

Now the mirrors, that's way too much work for me! It'd probably take me longer to set it up . I seriously think the dial indicators are the way to go.

Owen