Thread: 4-bar?

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As usual I am asking a novice question, so humor me a little and help out. I now have the front and rear four-bars installed (TCI) on my Brookville Model-A frame. When I put the bars on I allowed them to be almost fully threaded, but when I installed the Panhard bar on the 8" rear last weekend I noticed that it is out of line by about 10 degrees away from a right angle across the frame because the rear four-bars are fully threaded in. I realize that I will have to have the wheels aligned when I go for Inspection, but I need to "ballpark" the settings on the length of the bars. One idea I have is to count the turns on the full thread and then just set them at half so I get at least a half of the threads inside the bar. Even so, is there some other way to get the bars approximately the right length before a full alignment? I have wheels on order and will soon get tires and maybe (?) when the frame is up on the tires the four-bar angle will change and line things up better, but I don't think so because the frame is already sitting on the coil-springs.

Don Shillady
Retired Scientis/teen rodder

Set your front axle first. Work in the 5 degree king pin angle, use an "angle finder", or better known as a protractor. Then square it up to the frame by measuring at a diagonal from the top of the king pins to a fixed point at the rear of the frame. Use the same reference point on each side.

Then go to the rear. You'll need to set your pinion angle (start at 3 degrees, might have to swag a bit for rotation when you get a load on). Measure for wheelbase on each side, and square the rear with diagonals to a fixed point on the front of the frame. Double check the angles, squares, and wheelbase and adjust accordingly. Assuming they set the brackets in the correct places you shouldn't be bottomed or topped out on any of the adjusting threads.

Just to be sure I understand, you are saying that the 5 degree angle in the front is due to a slight difference between the upper and lower bar on the front and the 3 degree setting is the corresponding difference in the rear? Simplistically this might mean two more threads on the bottom bar on the front and maybe only one extra thread on the bottom of the rear bars?
It's great to get advice from experienced folks like you.

Don Shillady
Retired Scientist/teen rodder

That would be my tag team partner, the Masked Inspector!!

Thanks Richard.

Thanks Bob and Richard. That is another bit of tedium that has to be done, but I got my wheels from Early Wheels (Santa Barbara) today so I need to get the 4-bar straightened out so I can finish the chassis before I get the urge to put the body too soon. Since the rear tires are 15" and the front 14" I guess what "I am looking for in the drive line is close to a straight line from the trans output shaft to the yoke on the rear, I'll give it a try.

Don Shillady
Retired Scientist/teen rodder

Don,

Here's a sketch to illustrate what Bob and Richard are talking about.

On many street rods, where the engine is mounted low in the chassis, the transmission will be pointing slightly down, so the pinion will need to point slightly up - essentially the reverse of this illustration.

Basically, the output shaft to driveshaft angle should be equal to, but opposite of the pinion angle. In my case, the transmission is bubble down about 2.5 degrees, so the pinion us bubble up by the same.

Henry, the picture is a big help. I can understand why Richard was nervous. The link Streets provided is more refined and the vibration consideration will come later. While we are on this topic, should I look for a steel driveshaft like the original Maverick it came from and have a Chevy yoke welded into the other end (and balanced) or is it necessary to get a fabricated aluminum driveshaft? Thanks again for EXPERT advice from several folks!

Don Shillady
Retired Scientist/teen rodder

Aluminum necessary?? No. If you were a lower weight fanatic, maybe, but I'd bet 99% of the rods out there have good old steel. Any qualified driveline shop should be able to make up the Chev/Ford combo in their sleep since it's so common.

First of all, aluminum shafts are seriously expensive. You need to decide whether or not to spend the $$. I don't spend much time under my car looking up at the underpinnings, so steel is fine with me. I guess you could find a shaft from a donor car, but like Bob said, any driveshaft shop can make what you need. Most shops would rather work with new tube anyhow, and by the time you hunt down an old shaft, clean it up, have them cut off the junk, re-weld and re-balance, I've found the cost isn't much different than a whole new shaft.

Either way, check with the shop FIRST to made sure how they want you to measure the shaft length. Different shops have different methods. You may want to get a yoke from them first so you can stick it in the trans and measure the length. Also, make sure that you have enough slack on the trans end when you measure. You can't shove the yoke into the trans until it bottoms out. You need some slack to compensate for the effective change in length of the driveshaft as the rear axle moves up and down. To get driveshaft length, I usually push the yoke all the way in, measure for the shaft, then deduct an inch.

Tell them what rear-end you have, and what transmission, and they'll supply the yoke, u-joints, welding and balancing. They'll even paint it with some crappy, low-grade rattle can paint at no extra charge.

Also, bear in mind that there are many, many different sizes of u-joints. The trans end won't be a problem, since you're buying the yoke with it. However, make sure you know what u-joint goes on the differential end. I tend to use 1350 series whereever possible, because they are genuine hard-core strong.

Thanks to several experts. My son was able to help me since my arms are not long enough to measure both ends of the car. Well it was really out of line by almost 1 1/2 inches just using the length of the bars out of the box! Anyway we got the king pins triangulated exactly on the midpoint of the rear of the frame with the frame jacked up so the the flat part in the middle was level with a carpenters level. However the rear gave us fits but we finally got it so that the wheel base is within 1/32" equal on both sides and by the distance from the opposite king pin. It will still have to be aligned with one of those laser rigs, but we could only get within one turn on the threads of the four bar rods, so maybe it is as close as you can get? Anyway we will not drag a tire sideways on the way to the alignment shop! And (!) now the rear panhard bar is much more nearly parallel to the rear axle. Thanks very much for the procedure and the drawing. We did get the pinion aimed slightly up but it could be 3-5 degrees. We measured the Brookville frame several ways and it is really straight so I guess the problem is in the spring mounts and maybe that the brackets we welded on the rear axle are a little out of position, but anyway the adjustments are all within the thread length of the 4-bars. As Streets said the drive shaft will be pretty short so there would be little weight saving with an aluminum driveshaft and I learned from Richard that I can send for one made to order. Henry and Richard explained the need for slack in the splined part of the yoke. I will check into the National U-joints Streets suggested. Thus in one afternoon we got it lined up "in the ballpark" with a lot of help from several of you!

Don Shillady
Retired Scientist/teen rodder