square rear vs square wheelbase

[imca37]

Ok I'm not sure what to do. Rear end is squared off the motor plate 72 1/4 both sides. Plumb bobbed it, drew the lines and all that jazz. All is good there. Then when I measure the wheelbase from center of spindle to center of rear end, the left is 111 3/4 and right is 110 1/4. Any ideas or suggestions?

[hall99]

the only way you can square off of the front end is to set your caster and camber the same on each side. I usually square off of the manufacture recommendations, ex. motor plate, 4 bar plates, etc... Have also squared of off the front cross member of late models. You will also find out how much built in steer you car has... good to know.

[imca37]

Caster and camber is set. Caster is +6 right and +2 left and camber is -4 right and +3 left. Are those settings gonna change the wheel base? It's and old Harris so maybe it has a turned stub of about a 1/2 inch. So the real questions is do I just leave it or do I adjust rear links to to make even?

[twisterf5]

Caster and camber is set. Caster is +6 right and +2 left and camber is -4 right and +3 left. Are those settings gonna change the wheel base? It's and old Harris so maybe it has a turned stub of about a 1/2 inch. So the real questions is do I just leave it or do I adjust rear links to to make even?
yes the + caster on the right sets the wheel back compared to the left. you can not go off wheel base just square the rear and you will be fine as long as your front mounts are ok and lowers are both the same.

[HEAVY DUTY]

Don't measure the wheelbase. Most cars have the stub turned, as well as the tires offset in or out from front to rear, which will give you false measurements.

[JustAddDirt]

111 3/4 left to a 110 1/4 right is way too short on the right wheelbase.
what if you took a framing square, and had one side of angle on floor, and the other against the rearend. Take a tape measure, and hook the front on the lower ball joint grease zerk and measure back to framing square.
do that on both sides and see what you get numbers wise.

[Duckhnter83]

Some say go off the motor plate. Some say go off lower grease zerks on lower a arms. Some manufactures give you measurements from one point. But the question is what do you want the rear squared to if you don't have a manufacter notes. The motor plate? The chassis? Or the front end? I use the motor plate rather that's right or wrong it works for me.

[imca37]

Ok I measured from the grease fittings to the hole in the frame according to imca.com and measurement was 1.25 inches shorter on the right than the left and it didn't matter what hole I measured from. All measurements were 1.25 inches shorter on the right. I replaced the right lower A arm mid season last year with an A arm bought from SPEEDWAY. So now what? Go get a left lower from SPEEDWAY? Go to the junk yard and try and find a stock lower for the right? Or leave it and run it as is? If left as is what do I do to compensate? Thanks stock car driver for the measuring reference

[drtrkr244]

yes the + caster on the right sets the wheel back compared to the left. you can not go off wheel base just square the rear and you will be fine as long as your front mounts are ok and lowers are both the same.

Every car that I have checked,the wheelbase lengthened when more positive caster was set. Generally, every 1 degree of caster caused the wheelbase to increase 1/4 to 1/2 inch.

[HEAVY DUTY]

Every car that I have checked,the wheelbase lengthened when more positive caster was set. Generally, every 1 degree of caster caused the wheelbase to increase 1/4 to 1/2 inch. Not possible, unless you are running a strut rod car and are putting caster in by pulling the lower a frames forward. You might be reading the caster wrong. If you add caster by moving the upper balljoint back, the spindle pin has to move back although by a smaller amount. If you have pos caster, the upper balljoint is behind the lower, and negative means the upper balljoint is in front of the lower. If you turn your front wheels the wrong way when zeroing your caster guage, it will read pos , when it is negative. I have seen gauges that you are supposed to turn the wheel back from center to zero, and some that you turn forward from center . Not trying to start an argument, just trying to help.

[imca37]

Thanks for the input from everyone. Now to the next question. Since I had to do a lot of moving the rear end backwards to get it square and the J Bar bracket is now more forward than the pinion. What is the correct or ideal difference you want the mounting points. Such as you want J Bar mount on pinion to be XX from the motor plate and want J Bar mount on chassis to be XX from the motor plate. Any ideas?

[drtrkr244]

Not possible, unless you are running a strut rod car and are putting caster in by pulling the lower a frames forward. You might be reading the caster wrong. If you add caster by moving the upper balljoint back, the spindle pin has to move back although by a smaller amount. If you have pos caster, the upper balljoint is behind the lower, and negative means the upper balljoint is in front of the lower. If you turn your front wheels the wrong way when zeroing your caster guage, it will read pos , when it is negative. I have seen gauges that you are supposed to turn the wheel back from center to zero, and some that you turn forward from center . Not trying to start an argument, just trying to help.

I always shimmed my lca forward to get more positive caster.They were stock with some modifications. I did not shim the uppers to prevent any binding. I ran into the same problem with the gauges when I switched brands.Be sure to read directions when buying a new gauge.

[JustAddDirt]

drtrkr244
do you have a eccentric on your lower a arm mounts?

[powerslide]

I would think that the Wheelbase on a harris should be around 110.

[drtrkr244]

drtrkr244
do you have a eccentric on your lower a arm mounts?

No, they were stock Chevelle. I welded a flat plate to the mounts and bolted a 5/8 heim. Then i made spacers to adjust the caster. Real simple but effective.ran it for years with no problems.

[drtrkr244]

got any pics? cant picture how you would use a 5/8 heim on a stock chevelle lower a arm

No that was many years ago. I cut the stock mounts off and welded the flat plate perpendicular to the arm. Then I drilled a 5/8 hole in the plate and bolted the heim up to it. You will have to drill the frame mounts out to 5/8 also.We raced at an imca track and never got caught.

[JR. MECHANIC]

this might be a new topic, but what is the reason for turning the front stub anyway? Some say that it shortens the left side wheelbase and that helps the car turn... I don't think that's true because as long as the left front is parallel with the left rear and the right front parallel with the right rear, it will still roll straight... So what's the real reason?

[avenger1]

To sell cars

[Confused?]

But they aren't parallel in the turns, are they.

[JR. MECHANIC]

But they aren't parallel in the turns, are they.

What's your point?

[Confused?]

Read your own post. Parallel is for straight and most of the time, the wheels are turned. Drag racers have moved one of the front wheels back for years. You are correct in that it does not affect straight line driving, but we spend most of our time turning to some degree.

[Duckhnter83]

Drag racers do it so there tires stay in the lights for just a split second longer

[Ltemodel]

Turning the stub does quite a bit to the front end, especially with a drag link set up like on a modified. The biggest effects people often don't consider is the ackerman effect it has on the front end. Once you turn the stub and realign the front end with the tires pointing straight ahead, the arcs your tie rods and drag link run at will be different than with the front stub square in the car.

With all the changes the chassis manufacturers are throwing at these cars, the best thing to do is to tune your car to what you think it needs in handling. Basically, you'll probably pull your hair out trying square your car statically and never end up with a better handling car.

I would suggest getting your car to an attitude it runs at on the track and checking your right side tire alignment. Where your right side tires are running dynamically will trump any figuring you do while your car is sitting statically on the floor in your shop.

Then, with the in this dynamic state start turning your front tires and measuring your toe at various points. This will give you an idea on your ackerman and what is going on there. I will tell you that too much ackerman in counter steer will put your car into a stall when accelerating off the corner.

I hope this helps a little.

Good luck,

kevin