I have a 74 f-250 high boy, dana 60 front axle 4.10 gears spooled, 14 bolt gm rear 4.10 gears locked. A 550 horse 477 mated to the factory np235 trans with a lakewood bellhousing and a single disk hayes clutch (got for cheap). the truck has a fat spring pack in the back locked dow33"n and 2 of the factory springs in the front to give it some negitive arch. I've got 33" at's on the back and mt's on the front. 1410 u-joints on 5 yokes and a 1350 on the trans yoke. For some reason i can't keep it from hoppin at the 280ft mark. Once it gets there it seems like it just skips and snaps the slip shaft on the rear driveshaft. I've tried numerous things and it still happens. I can't run ladder bars in my class either. Does anyone have any ideas what i can try? A dual disk clutch is definately the next thing its getting which i'm sure will help but i just wanna cover everything before the season starts. Has anyone had this problem? Any help would be greatly appreciated

 

My only thought is axle wrap and ladder bars will fix that, but as you stated you can't run them so maybe move up a class?
We have that problem with one of our tucks and this season we are adding ladder bars to it to hopefully solve it (along with losing a lot of weight off the truck but that is another story).

 

Have you tried playing with tire pressure?

Do you have any blocks in the rear suspension? If so, try to get rid of them as they will contribute to axle wrap.

Boxing the middle section of the frame might help. These frames flex more than you might think once they are torqued up.

What kind of shocks are you running?

 

I will eventually be moving up to altered stock but probably not this year unfortunately. I want to see if they will let me run some bars at the test and tune this year just for grins.. The truck weighs in right around 5200 without the extra weight. I have added about 700lbs in the front and 400 in a toolbox in the bed. It seems to work better with that weight in the front.

As far as tire pressure i run 40-45 in the rear and about17-27 in the front depending on the track. I have no blocks in the back. All spring with clamps and the overload stops flipped so they are maxed with the truck just sitting on the ground.

Shocks are a different story. I had blown out ranchos on the back last pull of last year and just moogs in the front. The front is pretty low so its hard to find a shock that will fit worth a dang. The frame pretty much rides on the front axle.

Anyone think clutch chatter or slippage may be a problem? I'm just tossin ideas around.
Thanks for the help so far!!!

 

I guess clutch slippage is possible, but not likely once you are moving. Usually if it is going to slip, it will slip at the hit. If it is slipping at the end, you should see some sparks coming out of the bellhousing.

Do you have any videos of one of your runs. A video may make it a little easier to figure out what is happening.

 

Carroll Co - YouTube

that does make since... like i said just kinda throwin ideas around.. thanx

 

I watched the video a number of times.
If you watch the front and not the back you will see the front starting to pogo first and then the whole truck starts. Try stiffer shocks on the front. You can also see the front bounce about 8-9 times after the driveline breaks and you let off the gas.

 

i know you said no ladder bars-does that include a panhard bar?

as 1wicked55 said: lots of oscillation in the front, at the end of your pull. like the front is trying to unload.

maybe the fronts trying to dig and the rear is pushing out.

would a 4.11/4.10 gear ratio work? try to spin the front slightly faster to plant the rear?

nice truck & cool video

my .02

kurt

 

check out the video right at 0:27. the front left wheel came off the ground and landed, that appears to have caused the truck to bounce and break

 

This isn't good. If the front doesn't have some free travel, then it's using the bumpstops and tires to do what the springs should be doing.
Like others have said, it appears the front started the hopping, and this could be the root cause.

 

i was thinking the same. if the front cant move- the rear gonna try its best to unload. all that flex and energy has to go somewhere

kurt

 

Ya i know shes a little bouncy. Ive got rancho adjustables on the way. lol hopefully that helps it out alittle.
As far as the panhard goes i'm not sure. i'll have to check on that.
And now that yall mention it i kinda notice the front comin off the ground.

 

the front has all the travel... i mean its free to move. the only time it sits on the frame to axle is if its just sittin... i may be confused on what your sayin to...

 

im thinking- as the she goes down the track and it starts to settle in on her suspension and the front tires try to dig, the frame is loaded like a spring, like bending a pencil. the first chance she has to straighten out...things happen.

this is quite the brain exercise trying to figure this out, thanks for sharing this dilemma with us. i have often wanted to get into pulling of some sort, but things never seem to work out. fear is the biggest issue lol

 

Will they let you run a pinion snuber to keep the axle from rotating up.