pullin truck breakage

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

Skips how? Is the whole truck coming off the track, or just one end or the other?

Before i added weight to the front the whole front end wanted to bounce bad. Now it seems as if the whole truck just "skips" or hops at the end. It doesn't techinally leave the track. Kinda like the tires miss a beat and break loose. Does that make any sense?

and the class i run doesn't allow ladder bars unfortunately

do you have any video so we can see exactly what it is doing. i have built an upside down traction bar before that stops spring wrap for rear but def help if could see what it is doing
gary

youtube.com/watch?v=rnqWpru6VDc&feature=youtu.be

i hope this helps. I can only post the link... sorry

I think something happened with the link. What have you tried to remedy this problem so far?

sorry for some reason i can't post the link in its entirety. cuz i'm new i guess.

What is the title of the vid on youtube?

lol sorry i shoulda thought of that. its thunder carroll co

Back in the day when dad was pulling "Hopping" broke stuff if you didn't get out of the throttle. Not sure what the remedy would be however you may look into taking weight off the back and moving it towards the front i.e. look for ways to take some weight off the back like removing the entire breaking system (drums etc...) and just use the front breaks. Remove some metal in the bed etc....

The more weight you can hang off the front the better....

Looks to me like your getting axle wrap. Your rear-end pinon is trying to stand up as the traction is applied. Check you spring perches make sure they aren't bent or rounded. then make sure your u bolts are dame tight. I use to start with the pinon at the negative angle so when you put the beans to it, it would go to inline with the drive shaft. what you got going on is the angle it straight with the drive shaft then as you put the beans to it the pinon points up and pulls the shaft apart or bust the u joint .


Dan

ive been puttin more weight in the front between the frame rails behind the bumper and it does help alot.

dan I put the rear in it last year after snapping every 60 axle i threw at it. And got to thinking about the pinion angle. what would be a good starting point for setting it negitive? i.e 15 degrees? more? less?

I think I set my highboy at 12 degree. If your rules allow clamp the springs together tight.

i have 2 clamps on each side on the rear now. ill have to check to see what degree i have in it when i get back but i can tell you it sure isn't 12... lol

You dont have a big stack of springs in the front do you....?

just 2 on each side. the main and a buddy. i did it like that to give them some negative arch and more movement... is that a smart move?

Make sure nothin is keepin that front axle from drooping.... shock, steering linkage etc, stiff springs. you want that axle to be able to droop 6 inches or better .... if not .... there is your hop.

that makes sense. Ill check it out. thanks everyone for the helpful tips and things to look for... ill post when i figure it.

Check your driveshaft angle at the transfer case too. With that short shaft in the rear that could be why it breaks. Might need to lower the transfer case some.

I looked this morning after work and noticed my rear perch on the pass side is crushed and i have less than 6 degrees in the driveshaft angle at the pinion. plans for building some new perchs that wont give way are already in the making.

I looked at the front this morning and it appears to move freely. Does anyone think running a quad shock set up with those stiffer shocks in the front would help?

If it is legal in your class, air bags on the front can offer some adjustability to how the front reacts to different tracks. There is a guy here in Nebraska that is using them on the front of his pulling truck with great success.

what tire pressure are you running in the rear, and how much hitch height do you have..If your airing down in the rear it could be waddin the tires up and makin you hop, also on a biteing track, I always take an inch or two out a the hitch ... good luck

thats not really an option where i run... good idea though

i usually run about 40 to 45 in the rear with about 26 inches on the hitch height