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Discussion Starter · #1 ·
We are trying to set up the rear suspension of my pals 81 Long wheel base F100 and have major dramas. The engine makes about 900 hp on the spray and when it leaves the line the truck bunny hopps and actually lifts the back wheels off the ground . The changes we have made to the rear end are :flip kit has been installed to change the diff housing from sitting under the leaf spring to be now on top of the spring. Caltracs have also been installed which when raced with them seemed to affect the truck even more. The only way that the truck can take off with no bunny hopping is by not using the spray. The truck has gone 10 flat and 60 fts in 1.75 at 137mph with 200spray
Can someone please help us with some information as we are getting nowhere
Thanks
 

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my buddies 11 second ford shortbed did the same thing
he was running the factory leafs with caltracks
i would replace the leafs if it was me
we would crank the caltracks down until we ran out of enough treads on the joints and it would calm it down a little bit
 

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Discussion Starter · #4 ·
Well two things cause this, pinion angle from leaf sping wrap up and springs or shocks topping out.
Thanks Jeff,
Do you mean on initial launch the car body is seperating from the wheels and then the shockers or springs stop travelling upwards because they have reached the top of there travel causing the car momentum to lift the back wheels???. If so what would be the fix . The car seems to not squat at all but head upwards instantly on take off , as though someone has picked up the back of the car and slammed it down.Maybe aliens:confused::confused::confused::confused::confused:
 

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Discussion Starter · #5 ·
my buddies 11 second ford shortbed did the same thing
he was running the factory leafs with caltracks
i would replace the leafs if it was me
we would crank the caltracks down until we ran out of enough treads on the joints and it would calm it down a little bit
So we are not the only ones ;) We thought we were the originators of the back wheel stand!!! But seriously what leaf spring should we put under there? We thought by putting caltracs on it would stop spring wrap up, but is it because the springs are that long that it will still wrap up .So loading the spring helped .A suspension shop told us to go to a custom single spring we tried that and did'nt even make it to the track. On the street we tried it out without the gas and buckled the spring on the first launch and the truck dropped 4inches,so we went back to the factory springs which are still in there.
Thanks
 

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Thanks Jeff,
Do you mean on initial launch the car body is seperating from the wheels and then the shockers or springs stop travelling upwards because they have reached the top of there travel causing the car momentum to lift the back wheels???. If so what would be the fix . The car seems to not squat at all but head upwards instantly on take off , as though someone has picked up the back of the car and slammed it down.Maybe aliens:confused::confused::confused::confused::confused:

You need some good long double adjustable shocks out back. You've got to slow the rear separation down some. Also, putting the Caltracs in the lower hole on the side plate should take some hit out of it. I'm sure others will chime in with more details.
 

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The shock travel may be to short, but leaf springs will only bend on the shackle just so far, and they top out ,the reason the rear end of the truck is going up as the tire is being forced down, and yes when it tops out the truck will pull the rear tires off the ground because the spring or shock can not give anymore travel. When its this harsh a motion the pinion climbs like crazy also, if you had a good shock you could tighten it and slow it down but you may need the hit to hook. I would think a longer cal trac would be needed or some really low holes, because of the wheelbase you have its going to have to move out to get in front of the leverage point
 

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Thanks Jeff,
Do you mean on initial launch the car body is seperating from the wheels and then the shockers or springs stop travelling upwards because they have reached the top of there travel causing the car momentum to lift the back wheels???. If so what would be the fix . The car seems to not squat at all but head upwards instantly on take off , as though someone has picked up the back of the car and slammed it down.Maybe aliens:confused::confused::confused::confused::confused:

Yes exactly no not the Aliens, but the top part LOL
 

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JEFF is correct
(The shock travel may be to short, but leaf springs will only bend on the shackle just so far, and they top out ,the reason the rear end of the truck is going up as the tire is being forced down, and yes when it tops out the truck will pull the rear tires off the ground because the spring or shock can not give anymore travel. When its this harsh a motion the pinion climbs like crazy also)
like stated those truck were not built for racing but for loads
and like stated you need a different leaf spring
Here is a test then you will see.
unbolt the shocks and the caltract bars
so the leaf springs are the onlt thing atached to the housing
then jack the frame up and see how far it takes to pick up the tires from the ground then you will see how much seperation you have
and how much the shock gets toped out
 

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Discussion Starter · #12 ·
Well how did you go on the weekend?

What did you try different?
Thanks for your interest pistol ,but unfortunatley never had a spare moment to check it out will endeavour to do so this weekend.If you have a spare 1hr don't be shy to come around and get your hands dirty.
Anyway, you worry about getting your big banger going!!!!!!!!!
 

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Thanks all for the help, i will go and try these things over the week and report back.
Your information has been invaluable
Did u try what i told u

if u are un-sure bring it around and i will sorted it out for u -

Thanks

Nick--
 

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Discussion Starter · #14 ·
Did u try what i told u

if u are un-sure bring it around and i will sorted it out for u -

Thanks

Nick--
Hi Nick,
I was going to do what you told me but my oxy bottle was empty and a mate had my cutting torch. When i fill the bottle and get the torch back which way do you recommend cutting through the truck ????:confused:
Thanks for your advise:):)
 

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getting hands dirty

F100's are only good for towing real cars to the track!

Spare hour I dont have -sorry! Get my hands dirty - I dont think so...

Lets see how you go with testing with your truck pal this weekend...

Pete.

Thanks for your interest pistol ,but unfortunatley never had a spare moment to check it out will endeavour to do so this weekend.If you have a spare 1hr don't be shy to come around and get your hands dirty.
Anyway, you worry about getting your big banger going!!!!!!!!!
 

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Hi Nick,
I was going to do what you told me but my oxy bottle was empty and a mate had my cutting torch. When i fill the bottle and get the torch back which way do you recommend cutting through the truck ????:confused:
Thanks for your advise:):)
well theirs no right way or wrong way to cut up the thing-

The only mistake that i see is that the truck is a ford-

thats the problem right their--

i can only try and help u get this out of your life-

Let me know if u get stuck

Thanks

Nick--
 

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I had the same problem with mine when the bars were in the top holes. If you are getting a lot of separation you need to set the shocks stiff as they will go on extension. The other half of the problem was in the front suspension , after installing some f body trick springs and honing out and greasing up the urethane control arm bushings. It has gone a string of 1.32 60' which is down from midto upper 1.4's was the best it would do before catracks and the front end work. What kind of front springs are you running??
 
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