Rear end slid forward on leaf spring, tire hit wheel well, how can i fix this? 68bird

[Shawn MacAnanny]

I got to do my first launch in my 68 firebrid today in 70 degree weather. Spun the tires a little to heat them up and did a 3500 rpm launch and a solid 6000rpm shift i had no wheel spin and when i got back i noticed the tire was sligtly rubbing where the rocker pannel wheel well meet. It barely rubbed the tire. Tire is fine. I had 5/8" clearence befor the launch though. This never happened when i was running the 28x10.5 Et drag even in 90 degree weather but i couldnt get them to stick even in 2nd.

Anyway i know i can just unbolt it and slide the rear back. There rear end is from a 74 nova, 8.5", 4.56 gears. I have summit adjustable shocks, set soft. I removed a half leaf from the leave springs but cut them and left a pieace in there as a spacer. I also doubled up the spring rubbers if i remember right. I installed competition enginnering traction bars with it and i have a mini-tub on it was well as a competition inner shock relocation kit but not a relocation spring kit. I do have lift shackles. The car has NO wheel hop, it dead hooks, and im putting about 420 to the wheels right now through a 6 speed.

How can i keep this from happening? I thought about welding a metal block in front of the traction bar plate on the leaf spring to keep it from sliding forward but it think this would weaken the spring. Any thoughts? It slid forward on the driverside.

Here's a pic

[b-man]

Shawn,

Don't even consider welding anything to your springs, this is a no-no. Your springs will weaken and eventually fail there.

You say you've doubled-up on the rubber spring isolators, why did you need to do that?

It sounds like the extra spring rubber pieces are not allowing the spring pin that locates the axle housing is not fully engaged, allowing the housing to slip off location.

Bart

[Shawn MacAnanny]

They were used perches and i couldnt get the regular spring pads at the time in installed the rear so i installed them doubled up. I dont quite remember my reasoning behind it or even if i did it. It just happened tonight i havent really looked at it that well i just hopped in my other car and went to the bar since i saw the tire rubbing. Yeah i remember the locking pins. I guess i should order a set of new rubber pads, make sure they tighten into the locking pins, and see if it happens again, right?

[b-man]

Definitely put what the factory intended in the spring to axle interface.

Or better yet completely eliminate any rubber in there by changing the perches on the axle to a set of aftermarket universal perches. I've seen some made by Mopar Performance that would do the trick.

Then you reinforce the new perches by welding in some plates on the front and back from the perch to the axle tube, to keep from breaking the perch to axle tube welds under hard use.

Heavy-duty U-bolts too.

[Shawn MacAnanny]

Here's a pic of the rear suspension. What would happen if say i didnt run any rubber? Just wondering incase i didnt use two pads. I'll be taking it off in the next couple days to see what i did. It was like a year ago. I really didnt think i would see any problems with it since id thoroughly testest it with ET drags. these 30x14 Et street radials are just alot stickier i guess.

[b-man]

As long as everything is held in place properly and bolted down firmly with no rubber in there, I'd say you're much better off without it.

The rubber bushings on the rear eye of your springs look like they've seen better days, replace them with something new as soon as you can. Solid aluminum or urethane bushings wouldn't be a bad idea in all 4 spring eye locations.

[CarlC]

I have not run the rubber pads for many years with no ill effects.

The interlocking pin system is a must to keep the differential housing centered on the spring. Many lowering/angle blocks cause the spring pin to not mate with the differential housing. For lowering blocks I'll use a short Allen cap screw that mimics the spring pin. It requires machining to make this type of block but it is very secure.

[camrat68]

CarlC-do you have any pics of your cap screw setup? I can't quite follow what you did with the cap screw to make that work. I ask because I used to have really stiff lowering springs with aluminum lowering blocks and the rear end felt solidly attached. I had to raise the car with stock rate springs and poly pads and now the rear end just doesn't feel as securely attached as it did before.

[Shawn MacAnanny]

Yeah that was my next step. The rear end got bolted in semi-temporarily so that i could get a driveshaft measurement for Dennys then i went to my mount my Et drags and realized the new 8.5" rear end was 7/8" narrower than my stock 8.2 rear so i started mini-tubbing it and one theng after another it all got overlooked. I have a brand new set of nova springs but they are like 5 leafs instead of the 3 i made. Honestly the spring/sock setup i have is SOLID for hooking up. I cant believe the traction i have with no wheel hop now.

I'll try boling them together with no rubber pads. I'll eventually get some spring bushings too. The front ones are a paint to get to it looked like. I had the castle nut break loose when i installed my subframe connectors so im sure the other bolts arent in much better condition. thanks for the replies!

[sporter]

Definitely put what the factory intended in the spring to axle interface.

Or better yet completely eliminate any rubber in there by changing the perches on the axle to a set of aftermarket universal perches. I've seen some made by Mopar Performance that would do the trick.

Then you reinforce the new perches by welding in some plates on the front and back from the perch to the axle tube, to keep from breaking the perch to axle tube welds under hard use.

Heavy-duty U-bolts too.

I run Mopar perches with no rubber and solid bushings in the front of my leaf springs, the ride is really not any rougher. Be sure to follow B-man's advice and box your perches. Moser told me it was not necessary at my power level. Not! The result was ugly and $$$.


Only took about 500 hp, a manual trans and slicks to rip these perches up.
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When the rear rotates on the starting line, it gets ugly. This was my floorboards above the pumpkin. Also drove my Denny's nitrous ready driveshaft into my TKO, bending the mainshaft.
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Properly boxed perches.
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[Shawn MacAnanny]

Hmm i dont think my spring perches look like yours. Here is a pic of my setup installed. It looks like i used a rubber pad for above and below the leaf spring. I'll take them both and and use some 1/4" aluminum spacer mater or something. The bottom of my springs is a 1/4" thick plate on my traction bars. Above them are heavy duty u bolts that go all the way around the axel, not like the stock bolting plates on one side.

[camrat68]

Don't the Firebird's use staggered shocks with one in front of(PS) and one behind(DS) the axle tubes like the Camaro's?
Jim

[Shawn MacAnanny]

Well when i got under there and actually saw what i did i see why it happened haha. I put the rubber plates on the top and double up the rubber plates on the bottom. This held up to dozens of ET drag radial launches but i could never get them to hook until 2nd gear. I guess the quick 1-2 power shift at 6000rpm is what finally jerked it enough to come out.

So heres all the pics of what i did. Let me know if you think it will hold or see something i should change.

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Here's the old set of springs i had on it. I had an extra set of springs that were very nice from a 74 nova i decided to stick on instead since i needed new bushings anywah. Notice the missing leafs and no bolt to hold them

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I decided to use a piece of 3/8" steel for my shim. I had to drill a hole in it to clear the new springs bolt.

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I tightened them all down and they just about tightened all the way up to touching the traction bar plates. Couldnt have gotten a better fitting piece of steel IMO.

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When in installed the new springs they car sat ALOT higher. I had my shakles installed at the 3rd hole to begin with and now i had to go up the 1st hole and it still about a half in higher than it used to be. I also noticed getting my traction bars to fit was not a big problem. They were 2" further drop from me getting my pre-loading u bolt on. I jacked the front of each traction bar up to where i could get the nut started and tighten them down until they just had enough threads to go through the nut.

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I actually have about 3/4" clearence now as opposed to the 5/8" i had before

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It's all done here now.

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So heres the question, do you guys think this will hold it? I REALLY dont want it to jump forward again like it did. I dont see how it could but it still makes me nervous. Also when i mounted the rear on the leaf it had about a 1/4" of play frontward to rearward (like the hole was oval in the spring perch) on both sides. Do you guys forsee any problems with this? Do you guys see anything i should fix or do differently?

I really didnt want to remove my old springs but i mean they DEAD HOOKED. Now the springs seem much stiffer and have ALOT more preload on them with the traction bars. I'm just hoping they will wear down a little since they havent been in a car for like 5 years. The softer springs are what made my car hook so good IMO.

Opinions? Thoughts?

[CarlC]

Does the pin on the top of the spring go into a matching hole in the pad, and then a matching hole in the differential?

The new steel pad you made that goes on the bottom of the spring also should also have a matching pin on the bottom to interlock it to the shock plate. Without that it does not provide fore/aft positioning placement beyond the clamping/friction force generated by the U-bolts.

Both the top and bottom need to interlock into their respective mounting components. The top is the most important.

[Shawn MacAnanny]

Don't the Firebird's use staggered shocks with one in front of(PS) and one behind(DS) the axle tubes like the Camaro's?
Jim

Yeah they do but i have an after market shock system that bolts on a crosmember inward of the frame rails. I had to relocate them to minitub my car.

[Shawn MacAnanny]

Does the pin on the top of the spring go into a matching hole in the pad, and then a matching hole in the differential?

The new steel pad you made that goes on the bottom of the spring also should also have a matching pin on the bottom to interlock it to the shock plate. Without that it does not provide fore/aft positioning placement beyond the clamping/friction force generated by the U-bolts.

Both the top and bottom need to interlock into their respective mounting components. The top is the most important.

The pads did go into a hole matching in the differntial but i am not running any rubber in there now so the pin goes directly into the hole in the differential.

Yeah i was wondering about the matching pin. Cant i just weld my 3/8" thick steel plate directly to my 1/4/" thick traction bar plate? This will still make the rear end easily removable and i dont think that the 1/2" bolt and nut that are inside of the hole i made ate going to move anywhere.

I am asking because it's a pain for me to take it all back apart and weld a tab on there which may not even hold. Id trust a weld of the plate directly to the traction bar much more. I am doing all of this by myself in my grass so it's hard to remove and reinstall a rear end and all of it's suspension by myself.

[Shawn MacAnanny]

Well I didnt get to weld the plate today but i'm gonna try to do it tomorrow and hopefully it'll be in the 50s so i can try a launch on the new springs and see if it holds.

[protour_chevelle]

are you going to weld that 3/8" plate to the traction bar? If not you are going to have the same issue again.

[Shawn MacAnanny]

Yes i am going to weld it hopefully today. I have to pick up some more 6011 rods.

[CarlC]

Yes. I welded mine to the shock plate.

Was the pin on the top of the spring too tall for the differential hole? Often they are and the spring does not fully seat.

[protour_chevelle]

Yes i am going to weld it hopefully today. I have to pick up some more 6011 rods.
why 6011? Because its easier to store? I'd personally weld it with 7018. Just buy a small box. If you go to use it again, toss however many rods you need on a cookie sheet and place in the oven at 350 for an hour or so. For shop use we re-cook for 4-6 hours but it will not hinder the strength in ways that you will notice.

[Shawn MacAnanny]

Yes. I welded mine to the shock plate.

Was the pin on the top of the spring too tall for the differential hole? Often they are and the spring does not fully seat.



Yeah it looked like maybe a 1/32 too long when it wasnt tightened down on one side, the other side was fine. I figered that will tighten in a 1/32.

I used 6011s alot around here they are great for burning through rust and paint. To be honest i dont really know a whole lot about welding when it comes to the rods and such. I've never used 7018 other than in a highschool shop when i went there but ive used 6011 and 6013 on my projects as well as flux wire welding. Working on buying a MIG possibly TIG welded next so i can plasma cut too.