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Author Topic:   left side 4bar spring behind question
Dirt Roller

Total posts: 6
posted November 18, 2005 11:18 PM  
whith sping behind on birdcage it seems coil over eliminator will max out on extension when birdcage rotates back Can someone explain proper way to run this set up I have always ran my lr in front on a perch but would like try something new Thanks for any info given Mod 75x

Dirt Freak

Total posts: 240
posted November 19, 2005 06:52 AM  
i'm not too familiar with a coil over eliminator, but, it is common (on our and most) latemodels to run a shock extension on the shaft of the front mounted shock when running a shock/spring behind setup.
some cars will run a a dropped upper shock mount as an alternative while others will run a chain.
all these are basically just travel (extension) limiting devices to avoid having the rear mounted shock extended to maximum which in extreme cases can pull the shaft/piston out the bottom of the shock body, though i have never seen it.
at the moment we (on our rocket late model) are not running any front mounted limiter or control shock on the front of the birdcage and are just running the coilover (control shock) and sping behind, which seems to really let the car jump on the bars fast, but i think we will put a chain limiter on the front side to avoid shock damage.

Dirt Roller

Total posts: 22
posted November 19, 2005 09:04 PM  
with the spring behind on birdcage the bottom of the eliminator will go up when on the gas from the cage indexing. I run coilovers on mine with this setup and I have had no problems with the shock. unless you have excess body lift the eliminator should not come apart. the spring will actually compress sometimes with indexing of the cage. if rules let you, you can run a chain from frame to rearend to limit the travel but make sure you have enough room for the rear suspension to travel front to back for steer.

Dirt Roller

Total posts: 24
posted November 20, 2005 08:34 AM  
I was told by a latemodel guy that the chain was used to keep the lr bird cage from going over center. I only saw that happen one and the car was stuck up on the bars, and would not come back down, made the car terrible.

Dirt Full Roller

Total posts: 58
posted November 20, 2005 06:46 PM  
mod57x if i am thinking correctly you mean with the spring in the back and shock in front the shock is over extending. you will have to drop down the upper shock mount to where you have most of the shock travel out and very little in,or i moved the shock to the back beside the slider.had to add a mount to the birdcage and chassis. hope this helps

Dirt Roller

Total posts: 6
posted November 23, 2005 12:02 PM  
If you mount spring behind shock in front does it matter if you have the bottom of the shock mounted to a clamp bracket or to the birdcage?

Dirt Freak

Total posts: 240
posted November 23, 2005 02:41 PM  
i've never really thought about mounting the front side shock to a seperate clamp bracket as our car uses the multi-piece birdcages, but i guess it would still work the same.
when the front mounted shock is on the birdcage running left rear spring behind, and the associated "hike", the indexing of the birdcage makes the shock's shaft speed increase because the shock is extending faster than the chassis is rising.
it is also quite common for a spring behind setup, to have the spring come completely off of its seat and the chassis to be riding entirely on the bars, this is when the shock can be pulled apart.

Dirt Maniac

Total posts: 171
posted November 23, 2005 03:33 PM  
We have run the shock on a clamp bracket in the front and run the spring behind on a b/c on a slider on lr and seemed to help with forward bite. We were told it would help with forward bite and it did help us.

Dirt Roller

Total posts: 6
posted December 12, 2005 07:30 AM  
Wouldn't running a coilover bolted where your shock goes on your birdcage behind the rearend on the LR, be alot easier than risking pulling your shock apart and worrying with contrary eliminatiors?? Thats what I am going to try this year. Just my two cents!!

Dirt Roller

Total posts: 6
posted December 15, 2005 03:35 PM  
what are the pros/cons of the spring on bc behind with shock on clamp up front vs. the coilover assembly on bc behind? I've been told that the slider is the way to go. Maybe someone can explain the difference.

Dirt Freak

Total posts: 276
posted December 16, 2005 08:50 AM  
The way I understand, the placement of the shock is about controlling the motion- both body roll and indexing. If you think about it, when the shock is in the front, as the chassis rolls and you get on the gas, the shock will be extending because of the chassis roll and the birdcage will be indexing, also causing the shock to extend. As the chassis drops, the shock will compress and the indexing will work the other way also causing the shock to compress.

If you run the shock in the rear, when the chassis rolls the shock tries to extend, but the indexing will be trying to compress the shock, vice versa for chassis drop. So, the shock in front better controls the motions of the chassis and indexing.

Dirt Forum Champ
Total posts: 846
posted December 16, 2005 10:25 AM  
You can run the shock in front, on the birdcage, or you can run it on a clamp bracket in front.

Your shaft speed on a clamp bracket in front may be better, and it will add some degree of leverage to the LR tire as the rear end rotates back under acceleration, i think.

At our outlaw track we run at, i am gonna try a 4/4 valved shock with a coilover kit behind, on the birdcage of course. Then on the front going to run a 7 or 8 comp and 0 rebound or maybe even a 90/10 on a clamp bracket on the front side. Should be the best of both worlds, i hope.


Dirt Freak

Total posts: 240
posted December 16, 2005 03:36 PM  
krom, that kind of set up is regular on late models (not on the clamp bracket though). you will find with that shock in front, even though it has a 0 rebound (no valve) it will still provide some resistance and slow down extension against not running one at all. we ran a 0 valve (c & r) on the front side of our left rear (on the birdcage though) with an extension and ran back to back races with it on and then removed. despite that shock basically having nothing inside it, it still provided resistance.
most of you would have the latest grt book by now, they run a 9/1 on the back side of the birdcage with the spring regularly. i'm led to believe that some of the top end lm guys can and have run 14c/1r rates with these fancy gas charged mono tube shocks.

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