Ladder Bar Disaster

[GTX JOHN]

Jon Jr took his 3000 Lb Big block ladder bar car out first time.
Pinion angle looks about 3 down/ 0 Preload in bars. No apparent
binding in heims and everything is moving smoothly.

Making easy pass not using brake, the car makes immediate sharp right
turn almost hitting the tree. Once Jr. lifts shifts to 2nd and gather it up....
It goes down track OK and straight at 130+ with no drama.

It is a S and W built back half car with tubular front and has been raced forever I'm told with no drama.

I have not had a ladder bar car since the 60's but it looks very simple
with just IC/Bar Preload/ Pinion Angle to check. Nothing looks wrong/bent
but it acts like one bar is unhooked or someone sawed right axle in two
for first 50 Ft.

Tried the 14/32s from 10 to 12 Lbs.with no difference. Sidewalls look good on launch not bunching or anything weird(Tires look fairly new).Front end rises OK. Track is sprayed and Jr. is right in groove

After 3 Passes, scaring the starting line crew to death every time, they told us
not to bring it back again until it is safe.

Any thoughts appreciated!

[Jim B]

On the checklist don't overlook possible tire rub (I would think tire slippage on the rim has been eliminated) on the leave or a broken/partially stripped heim socket or end/weld or chassis/housing attaching bracket that may not look broken but actually is. Also double check the posi/spool/axle spline condition paying close attention to the side that the car pulls to on the leave. Keep in mind I've seen failures that only produced a symptom in the lower gears at first (gear multiplication factor) until the failure got worse. Then the symptom occurred in the higher gears. Of course, you want to find the problem before it gets to total failure and is becomes obvious at that point.

[V M Kauffman]

Needs preload as best I remember at least 75 more RR CANT REMEMBER how much left front 100? With driver in seat.

Originally Posted by GTX JOHN

Jon Jr took his 3000 Lb Big block ladder bar car out first time.
Pinion angle looks about 3 down/ 0 Preload in bars. No apparent
binding in heims and everything is moving smoothly.

Making easy pass not using brake, the car makes immediate sharp right
turn almost hitting the tree. Once Jr. lifts shifts to 2nd and gather it up....
It goes down track OK and straight at 130+ with no drama.

It is a S and W built back half car with tubular front and has been raced forever I'm told with no drama.

I have not had a ladder bar car since the 60's but it looks very simple
with just IC/Bar Preload/ Pinion Angle to check. Nothing looks wrong/bent
but it acts like one bar is unhooked or someone sawed right axle in two
for first 50 Ft.

Tried the 14/32s from 10 to 12 Lbs.with no difference. Sidewalls look good on launch not bunching or anything weird(Tires look fairly new).Front end rises OK. Track is sprayed and Jr. is right in groove

After 3 Passes, scaring the starting line crew to death every time, they told us
not to bring it back again until it is safe.

Any thoughts appreciated!

[Wade Mahaffey]

Sounds to me like the possibility of an enlongated bolt hole in the ladder bar mount on the rear housing. This condition occurs when one or more bolts has loosened up. It gradually wears from perfectly round bolt hole, to oval bolt hole. This will allow a big change in the preload on a hard launch. Take the bolts out of the rear on one side, then measure the bolt hole from the 6 o'clock position, to the 12 o'clock position...and then the 3-9 o'clock position using a vernier caliper. Make sure you measure just the bracket and use care not to reach the caliper into the rod end, because it would show perfectly round. Just the bracket holes on both sides of the rod end. You will be checking 8 holes in four brackets. If you find a bad hole, make up two sleeves of tubing with an inside dimension of the bolt 5/8 or 3/4 whatever you have. The tubing needs to be at least .125 wall and about 1/4 to 3/8 long. use a slightly longer bolt with the sleeves in position on both sides of the bracket (like where washers would be) then pull the bolt up tight. Tack weld the sleeves in perfect position, then remove the bolt and rod end and complete the weld all the way around the sleeve to the ladder bar bracket. These sleeves make bolt hole deterioration a thing of the past, if you find wear in a set of holes, you would be smart to take the rear out and sleeve all of the holes. Good luck

Wade Mahaffey

[ab5098]

This may sound dumb but be sure to measure the roll out on rear tires I had a set of tires that was 3/4" difference from side to side and caused the same problem. I went through every thing and found this to be the issue .

[jims5600]

Originally Posted by ab5098

This may sound dumb but be sure to measure the roll out on rear tires I had a set of tires that was 3/4" difference from side to side and caused the same problem. I went through every thing and found this to be the issue .

I experienced the same thing

[jmcarter]

All good things to check but does it have a track locator bar? If so I'd be sure it's okay, and as said here, make sure the heim joints have good thread engagement.

[Jim B]

You seem to imply the car is an acquisition that you don't have first hand knowledge in the build or history. Basically, what has changed since the last known trouble free operation? Such gremlins as actual or transport damage or component swap can enter the picture in a purchased car scenario. (ie, axle housing centered and square in chassis, rear wheels same width and offset, etc.?) A one in a million past encounter was sand/water spilling from a bodyframe cavity after a winter sandblast/caught in a rainstorm caused a pull on the leave although it wasn't as severe as you described.

[Ed Carpenter]

Originally Posted by Wade Mahaffey

Sounds to me like the possibility of an enlongated bolt hole in the ladder bar mount on the rear housing. This condition occurs when one or more bolts has loosened up. It gradually wears from perfectly round bolt hole, to oval bolt hole. This will allow a big change in the preload on a hard launch. Take the bolts out of the rear on one side, then measure the bolt hole from the 6 o'clock position, to the 12 o'clock position...and then the 3-9 o'clock position using a vernier caliper. Make sure you measure just the bracket and use care not to reach the caliper into the rod end, because it would show perfectly round. Just the bracket holes on both sides of the rod end. You will be checking 8 holes in four brackets. If you find a bad hole, make up two sleeves of tubing with an inside dimension of the bolt 5/8 or 3/4 whatever you have. The tubing needs to be at least .125 wall and about 1/4 to 3/8 long. use a slightly longer bolt with the sleeves in position on both sides of the bracket (like where washers would be) then pull the bolt up tight. Tack weld the sleeves in perfect position, then remove the bolt and rod end and complete the weld all the way around the sleeve to the ladder bar bracket. These sleeves make bolt hole deterioration a thing of the past, if you find wear in a set of holes, you would be smart to take the rear out and sleeve all of the holes. Good luck

Wade Mahaffey

That's what happened to mine several years ago. The holes got enlongated my car went dead left everytime at the hit. Got that fixed and its been fine since.

[XSTOCKER]

What type of rear? Axle tube slipping in the housing?