Finding the instant center on a leaf spring car

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John_Heard
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Re: Finding the instant center on a leaf spring car

#31 Post by John_Heard » Mon Apr 21, 2014 10:31 am

I don't think it's possible for a leaf spring car to squat at launch, as you said what they are seeing is the sidewalls crush which sucks the rear down.

When's the last time you put some fresh slicks on it?

grandville455
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Re: Finding the instant center on a leaf spring car

#32 Post by grandville455 » Mon Apr 21, 2014 10:43 am

These were just put on in Aug..actually won the race lol.. then next race it was right back to spinning. I think I was dead hooking n too much comp in shock n not enough air n running over the folds.
74 Pontiac Grandville
7.33- 1/8th @ 94.55/ 11.501 @117.74- 4550 pds
1.60 60 ft....all bests

74 Firebird 3580#
2016 1.377 60ft, 6.33@106.87- 10.02@ 132 mph

grandville455
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Re: Finding the instant center on a leaf spring car

#33 Post by grandville455 » Sat Apr 26, 2014 9:33 pm

Started out a tad rough lol xmas tree is still up! After the second pass of spinning , I went two tighter in front, and 4 tighter in back, 15.5 in tires n went 1.50 carrying the front up and out! Then tightened two more in back and went 1.50 again then a 49.then a 48. last pass tightened two more in back n went 1.47. Best ET 10.605@124.49 into headwind, Leaving right from idle, went to 92 jets , started with 90.. was running low 60's,then I sat for a hour and it went to shit! Dunno if it was part track n for some reason I lost the pre load in my cal tracs... but it was picking the front up like never before! I was pleased up til whatever happened. Anyone seen that with cal tracs before? I had them tight with 1 flat when I left home. When I got home the passenger side was loose, like a full turn before it was tight again, half turn on drivers side. And the car is loaded down even with everything I take to the track, they should've been really tight yet. The rear end didn't shift etc, Ideas??
74 Pontiac Grandville
7.33- 1/8th @ 94.55/ 11.501 @117.74- 4550 pds
1.60 60 ft....all bests

74 Firebird 3580#
2016 1.377 60ft, 6.33@106.87- 10.02@ 132 mph

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Re: Finding the instant center on a leaf spring car

#34 Post by John_Heard » Sun Apr 27, 2014 6:34 am

Good to hear you made progress!

Not sure on why your bars loosened up, yaeh that's a bit odd. I'm wondering if something is binding up in the rear like shackles or spring bolts too tight, etc. Try unhooking the shocks, unhook the caltracs and see if it moves freely up and down. Also check driveshaft unbolt u-joints and see if it's moving in and out freely.

Also, remember the front end effects the rear as well, if something is binding up there it can change the weight on the rear.

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Re: Finding the instant center on a leaf spring car

#35 Post by Craig W. » Sun Apr 27, 2014 7:03 am

Also, be sure the car is level and sitting at ride height when you set the bars. At the track, the surface in the pits may not be nearly as level as your garage so that can through off the preload you find there.
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grandville455
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Re: Finding the instant center on a leaf spring car

#36 Post by grandville455 » Sun Apr 27, 2014 8:47 am

Thanks guys, as far as stuff too tight the front I have nylocks on the bolts on bottom, and the top I have them backed off too so they move, the back the front spring eye bolt is loose, where the cal trac goes thru, with no pre load those wiggle easily, and the back shackles I took off last year and ground the frame bushings down some as travis told me and greased up well, and the bottom shackle bolts are loose too. I will unbolt tho and try and see if I get a lot of movement. I se the bars in the garage at ride height with full cell and weight to mimic me in drivers seat. I rechecked that in the same garage last night, that's when I seen they were loose. Here's two videos, one reg speed the other slowed to 1/8th...

http://smg.photobucket.com/user/Grandvi ... c.mp4.html

http://smg.photobucket.com/user/Grandvi ... d.mp4.html
74 Pontiac Grandville
7.33- 1/8th @ 94.55/ 11.501 @117.74- 4550 pds
1.60 60 ft....all bests

74 Firebird 3580#
2016 1.377 60ft, 6.33@106.87- 10.02@ 132 mph

grandville455
Posts: 176
Joined: Sat Sep 13, 2008 9:11 am

Re: Finding the instant center on a leaf spring car

#37 Post by grandville455 » Sun Apr 27, 2014 11:46 am

So I went out and lifted the car, it definitely is not running out of shock travel as u can see in the pic and where the fender lip looks in video. A couple of things , 1 when I jacked it up like u see in the pic, should the cal trac pin still be on the leaf? I thought the whole idea of the cal trac was to put pressure on that spring to keep it from wrapping up when ext shocks and pushing tire into ground, 2. I removed shocks and bars and I can only push up on the trunk frame rail a 1" , that doesn't seem right to me? I would think the shackles would move freely wouldn't they? Here's the pic's of full ext and ride height of shackle.

Image

Image

Image
74 Pontiac Grandville
7.33- 1/8th @ 94.55/ 11.501 @117.74- 4550 pds
1.60 60 ft....all bests

74 Firebird 3580#
2016 1.377 60ft, 6.33@106.87- 10.02@ 132 mph

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Re: Finding the instant center on a leaf spring car

#38 Post by John_Heard » Sun Apr 27, 2014 12:21 pm

Yeah when the spring arches with the weight off the cross pin is gonna hit the leaf.

Looks like it's got miles of travel in extension which is good. When you set it on the ground without the shocks can you bounce it easily?

grandville455
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Re: Finding the instant center on a leaf spring car

#39 Post by grandville455 » Sun Apr 27, 2014 1:03 pm

Yes, that's just it, with the weight off like u say the pin is a 1" from the spring, also yes it bounces but just from the flex in the spring, but I tried to lift it up and it only lifts a 1" and it doesn't push down much either, in the pics are those shackles maxed out? I would think it should move a lot more than what it shows?
Last edited by grandville455 on Sun Apr 27, 2014 3:08 pm, edited 1 time in total.
74 Pontiac Grandville
7.33- 1/8th @ 94.55/ 11.501 @117.74- 4550 pds
1.60 60 ft....all bests

74 Firebird 3580#
2016 1.377 60ft, 6.33@106.87- 10.02@ 132 mph

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John_Heard
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Re: Finding the instant center on a leaf spring car

#40 Post by John_Heard » Sun Apr 27, 2014 1:13 pm

Shackle shouldn't be maxed out unless the spring eye is hitting the frame.

Are you saying with the shocks hooked up you can only pick it up off the ground extension 1" ?

grandville455
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Re: Finding the instant center on a leaf spring car

#41 Post by grandville455 » Sun Apr 27, 2014 1:25 pm

No with shocks and bars off I can only pick up the car a 1" or so.Its really stiff to me . I read on yellow bullets cal trac thread Jeff c said with that stuff disconnected the car should move like 4-5 inches ?
74 Pontiac Grandville
7.33- 1/8th @ 94.55/ 11.501 @117.74- 4550 pds
1.60 60 ft....all bests

74 Firebird 3580#
2016 1.377 60ft, 6.33@106.87- 10.02@ 132 mph

grandville455
Posts: 176
Joined: Sat Sep 13, 2008 9:11 am

Re: Finding the instant center on a leaf spring car

#42 Post by grandville455 » Tue Apr 29, 2014 9:59 am

Ok here's a update, I found that my Bottom shock plate had moved a tad, and after talking to travis he said they usually retorque after i hit or two, so that makes sense y i lost my preload, I also removed my shackles and drilled out the hole's larger so the bushing is able to freely rotate around the bolt, still have the stock style shackles. Everything is free now, those upper frame bolts were really tight in the bushings. Here is a video of how they look now..The plates are retorqued and these will be back on tonight.

http://smg.photobucket.com/user/Grandvi ... 9.mp4.html
74 Pontiac Grandville
7.33- 1/8th @ 94.55/ 11.501 @117.74- 4550 pds
1.60 60 ft....all bests

74 Firebird 3580#
2016 1.377 60ft, 6.33@106.87- 10.02@ 132 mph

User avatar
John_Heard
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Re: Finding the instant center on a leaf spring car

#43 Post by John_Heard » Tue Apr 29, 2014 2:03 pm

That should help things move more freely. Good investigative work!

grandville455
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Re: Finding the instant center on a leaf spring car

#44 Post by grandville455 » Tue Apr 29, 2014 4:32 pm

Thanks John!!! I will put STP oil on bolts n bushings and put back together tomorrow. Then fill cell sat n put weight n drivers seat n set bars. Should have a camera mounted under car too for Sunday!
74 Pontiac Grandville
7.33- 1/8th @ 94.55/ 11.501 @117.74- 4550 pds
1.60 60 ft....all bests

74 Firebird 3580#
2016 1.377 60ft, 6.33@106.87- 10.02@ 132 mph

grandville455
Posts: 176
Joined: Sat Sep 13, 2008 9:11 am

Re: Finding the instant center on a leaf spring car

#45 Post by grandville455 » Wed Apr 30, 2014 4:17 pm

Its all back together and their moving now easily, put jack stands under frame n jacked up rear and dropped rear and it falls right down. No more squeaky sounds either from the shackle area when jacking it up. I hope to have camera mounted for Sunday under there too! Just got to fuel it n set preload with weight in seat.
74 Pontiac Grandville
7.33- 1/8th @ 94.55/ 11.501 @117.74- 4550 pds
1.60 60 ft....all bests

74 Firebird 3580#
2016 1.377 60ft, 6.33@106.87- 10.02@ 132 mph

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