Questions on a dlm alignments.

[abe_05]

How do you find the centerline of a dlm?? How do you square the rear end to this centerline?? Is that something you want to do?? New to this stuff and when I ask car builders, all I ever get is just measure the rods, square the rods to the Rearend tubes (just eyeball that!) and set the J-bar. Everything is fine after that. I would like to know more. We had a Rayburn and CJ did tell me the the right frame rail was set at 2 degrees. I got on ACAD and did some measurments and found a way to square the rear end to the right side rail. It made a huge difference in the car! We have had several 4 bar cars and I have never been comfortable not knowing this info. Am I worring about nothing??

Your must had a pull bar in Rayburn, very critical to square rear end with pull bar. If rear end moves left to right very slightly it changes pinion angle. It seems like your are talking about left to right on 4-bar. Start with recommended length of j-bar you can change it by just lengthing or shorting j-bar 1/4-1/2". I would shortin j-bar 1/2" on real slick track, this is moving rear roll center and helps with side bite in our case. To answer your main question it is not near as criticial as Rayburn but it is always smart to make notes, simply putting angle finder on j-bar is easy way to watch changes like by increasing lr bite will move angle more than one might think. In setup always make note were j-bar is mounted on pinion (measure or what hole), frame, and then measure the angle. A lot setups sheets tell you were to start on j-bar but they are just giving a good starting spot. Example if you start j-bar on pinion just say on bottom hole and on frame 4" up, j-bar angle may be 10 degrees with 50 lbs of bite in car, change bite to 150 lbs angle may go up 20 degrees. May not sound like a lot but by just simply adding bite to car and not checking j-bar angle, now you making more adjustments than what most racers think about.

[late96]

This is how we were showed years ago,tell me if I'm wrong. We would set front caster to zero, drop plumb bob from grease zert, plumb bob rear end draw a line, set birdcages zero, than adjust bars to get square. Be sure to re-check bird cages as you adjust.Don't know if this is at all correct, but no one has shown me any differant.

[Egoracing]

This is how we were showed years ago,tell me if I'm wrong. We would set front caster to zero, drop plumb bob from grease zert, plumb bob rear end draw a line, set birdcages zero, than adjust bars to get square. Be sure to re-check bird cages as you adjust.Don't know if this is at all correct, but no one has shown me any differant.

Most dirt late models are built with the RF further forward than the LF some as much as 2 inches. This helps the car turn into the corner.

[abco]

Just do yourself a favor, when u figure out where ur axle is square and everything is happy put some center punch marks on the frame and center of the axle tube for a quick refrence! (16" or a 20"#) Saves alot of time at the track !

[late96]

So how important is it to have your birdcages alligned or indexed?

[twisterf5]

So how important is it to have your birdcages alligned or indexed?

very!! it can put the rear in a bind if they are going the wrong way

[hpmaster]

I run an 09 bwrc and the book Barry gave me at the seminar I went to days the cross member in front of the radiator is square to the rest of the car and to drop plumb bobs off the front of that bar on each side then run a string across the two strings hanging down out past the front tires and be sure it is tight. Then get about a foot and a half of 1/2 inch threaded rod and take the axle caps off and screw the threaded rod into the axles. The measure from that string to the rod on each side and that should give you your lead or trail on the reared. Also you can take the grease zerts out of the lower ball joints and screw small bolts in that hang down and measure from the string to that bolt and it will give you your lead on the front end. I run my lower ball joint on the rf about a quarter inch ahead of the lf. It seems to help it steer in a touch better.

I agree with this statement. I heard this many years ago and have measured all cars from this point since and found it gives the most consistant measurements of all suspension pick up points and chassis attachment points.
Measuring a car chassis from a part mounted in a chassis by 4 welded tabs and in most all cases AFTER the entire chassis has been completed makes no sense at all if you just take a minute to think about it.
As for lead on the RF I have played with for it for over 5 years and using too much lead on the RF, .5 inches or more can make a car turn well but hurts drive off traction, why I am not really sure of.

[late96]

very!! it can put the rear in a bind if they are going the wrong way

Well I hav'nt seen a new car with bars set to specs. that they are straight up and down. So what's the best method without changing a lot? Thanks

[twisterf5]

Well I hav'nt seen a new car with bars set to specs. that they are straight up and down. So what's the best method without changing a lot? Thanks

the way we do it could be wrong but it works for us. we made a level that we touch both hiems i set the right just towards the rear and the left just forward of level.

[chasingthatedge]

I agree with this statement. I heard this many years ago and have measured all cars from this point since and found it gives the most consistant measurements of all suspension pick up points and chassis attachment points. Measuring a car chassis from a part mounted in a chassis by 4 welded tabs and in most all cases AFTER the entire chassis has been completed makes no sense at all if you just take a minute to think about it. As for lead on the RF I have played with for it for over 5 years and using too much lead on the RF, .5 inches or more can make a car turn well but hurts drive off traction, why I am not really sure of.

this is how we set up the car mostly....over the years I have squared rear to midplate ...then lined up left side tires and adjusted at track from there....many diff ways to set up car.....mainly go with chassis builder recommendations and then adjust car to what the car is doing as per the driver...no 2 cars are exactly the same and every driver is diff.....as far a birdcages , the idea with the level is a good one....timing can affect the way car gets up on bars and car acts...just remember to give the car what the car wants....conditions change and so does how a car acts...hope all this helps some....you have to think about the whole picture

[F22 RAPTOR]

NOT!!!

most all late are built square on a jig.but engine are off set most of the time and you will get a longer reading on one side.do to different fronts and offsets you can not go off wheel base. use the rear bars like they said on the rears the rear has been squared on the jig to those bar lengths.

for example our new car that is on the jig now is set up with the rear squared but has a shorter left bottom rod then the right. and with the lower we are using the left side wheel base is 3/4 inch longer that the right. this is built into the chassis to tighten the car. and do to were the engine is there is no way to tape the left side back you could never get to the tube. so in short call the builder and go by there bar length.

Why the engine being offset would have any bearing on squaring the rear axel makes no sense. You can project a line across the back of the engine plate to square the rear axel to. Secondly I have yet to see a squarely built frame in probably 20 years, almost all builders splay the frame rails to some degree going back to the leaf car days. Now Barry Wright cars are splayed back to the main hoop and the rear clip steps in and squares, but the engine plate idea would still work for the axel. The engine plate idea is the simplest, you simply drop a plum bob off back of engine plate at both ends, project a line thru both points the width of the car. Do the same with the axel and now you can square the rear to the engine plate, easy.

[dirty white boy]

according to joe garrison a GRT chassis 4 link mount brackets are square with front cross member

[zeroracing]

I agree with this statement. I heard this many years ago and have measured all cars from this point since and found it gives the most consistant measurements of all suspension pick up points and chassis attachment points.
Measuring a car chassis from a part mounted in a chassis by 4 welded tabs and in most all cases AFTER the entire chassis has been completed makes no sense at all if you just take a minute to think about it.
As for lead on the RF I have played with for it for over 5 years and using too much lead on the RF, .5 inches or more can make a car turn well but hurts drive off traction, why I am not really sure of.

Why does it not make sense? It is not mounted by 4 tabs, there are also to major front engine mounts, so up to 6 points. If all 6 points mount up, chances are it is not bent in that area. This area is centrally located, so not as prone to routine damage. As far as being completed after the chassis, why again would this be bad, so they places them post welding, so the heat warping has already been completed. Final note if the motor is out of skew typically the driveshaft will bind, or tail of trans hit the x brace, often when this area becomes unsquare you have signals. Using a bar across the front infront of the radiator makes little sense to me, since the front end can easily be hit out of square with much more hard to see signs. For example a rear facing strut rod car, the front maybe unsquare but you would never know or care(infront of radiator).

[ALF401]

I got some great ideas and advice from this thread. I appreciate the input. Check out this link from Longacre on squaring the rear end. I believe the process is for a pavement car mostly, but you will get a great idea on how they recommend to square the rear end.

http://www.longacreracing.com/articles/art.asp?ARTID=29

Thanks