[punkin]

Hello all,

Some time ago I posted a question regarding putting in a coil over rear in my 68 firebird and some of the responses along with more research has me rethinking it.

One of the appeals to me of a coil over solution is the ride height adjustability. There are other reasons but this one keeps coming to the front. It's been suggested to look into replacement leaf springs but all over the interwebs I'm hearing of camaro and firebird owners who replace them hoping to maintain their existing ride height and then end up trying lowerinig blocks or sending the springs back to have them rearched...just general hassles. I'm sure the existing factory springs have sagged over the years but the stance is exactly where I like it. Is there a devinitive way to measure and order leaf springs to get it right the first time? Apologies if this seems too fundamental but I have no experience in this area at all.

Someone may ask what the plans are for the car...adding a 9" rear this fall. Weekend drag-racing and street use. Motor is over 650 HP/700 torque and 4L80e trans, so upgrading the tired rear suspension is needed to get the most of the motor/trans at the track. The springs are original multi-leaf as are the front perches and rear schackles. I am planning to beef it all up a bit.

Thanks,

[JLMounce]

There's no real way to definitively know what the ride height will be when you're swapping out 50 year old worn out parts for new ones. That said, if you take a look at the galleries that are posted by most aftermarket retailers you can get an idea of how the car is going to sit with certain parts.

The idea that adjustable ride-height is worth the cost of a coil-over conversion really depends on if you're actually going to use that adjustability. The vast majority of people will set it where they want it, and never touch it again. This is usually billed as an "ease of installation" idea, but forget that it's much more time consuming to actually install the coil-over conversion in the first place vs installing new leafs.

So you kind of have to decide if you want to spend your time installing the coil-over system, then setting the ride height, or installing new leafs and playing with various lowering blocks to achieve desired ride height. At the end of the day you're probably going to spend about the same amount of time under the car. You're going to spend about double for the coil-over conversion though.

That said, it sounds like you're trying to convince everyone else of something you just want for you car, which is the coil-over conversion. If the money isn't an issue and you want it for the cool factor, get it. I'd recommend this one.

http://www.cachassisworks.com/p-1285...uspension.aspx

The reason I like the chassis works offering over the similar ride-tech system is because it has a better motion ratio and Chassis Works is smart enough to use a double sheer coil-over mount instead of a single sheer mount that ridetech uses.

At your power level on a first gen, I'd be less concerned about beefing up the rear suspension and more concerned about not tearing the subframe out of the car. You absolutely need a set of solid body mounts and subframe connector from the front sub-frame, tied into the back of the car. With the amount of power you have, sticky tires will rip body away from the subframe.

[vertigto]

FWIW...after a bit of research/numerous reviews, I ended up going front/rear Viking coilovers for my 70 GTO restomod.

The price point wasn't crazy expensive for the quality, and adjustability with a spanner wrench should be pretty easy. I like to tinker/adjust and stance/ride height is important to me...sounds like weekend drag racing might give you another reason.

[65madgoat]

Ditch the leaf springs, and get a speedtech or ridetech coil over kit for the rear. Both are easy to install, and work great. Then do as you wish on the front. Speedtech is really at the top of their game right now.

[punkin]

Thanks everyone,

The rear is coming out of it and a new one going in. With the recent power increases, I really don't think the original hardware and springs are going to live long and some additional improvements do need to be made.

I'm actually quite in favor of the leaf springs for the simplicty of the installation and cost. I seriously haven't ruled that out. I'm hoping for some wisdom on how to order replacements and get it right the first time.

I do understand that most people (and my self included most likely) will set ride height once and leave it...that's really what I'm hoping for and this really is a selling point for the leaf springs and certainly they work very well at the drag strip.

As for all the work...well...I'm in pretty deep already. Too deep...I need to put it back together and get back to driving and enjoying it. So far, new motor, 4l80e, efi, new fuel system and lines, 4-wheel disc conversion, solid body bushings (in a box in the front seat), sub-frame connectors, cross-member...the list is longer I'm sure...just ask the wife.

I digress. Thank you all for the input and suggestions. I'm notorious for my analysis paralysis.

[JLMounce]

I really like my hotchkis leafs, with one exception, they are de-arched too much in their 3" lowering package, and will hyper-extend on occasion. What I would suggest is a 1.5" drop leaf from a place like hotchkis or global west. The 1.5" drop spring is probably going to set the car close to where it's probable sitting right now.

Grab a couple 1" and .5" lowering blocks as well to make final adjustments to ride height. Going that route you still have a leaf with plenty of arc in it and if it doesn't sit low enough you've got a few blocks to get it the rest of the way.

[punkin]

I thank you Jason. Giving them a call today!

[389]

Go on Pro Touring and look up David Pozzi... He knows the F body cars really well...

http://www.pozziracing.com/

[punkin]

I'll look him up. I have spent a bit of time lurking over there. Lots of supporters for the 4-link and torque and IRS. I thank you for the reference.

[Paul E]

Best suspension modification I have done on my cars. I used on on my leaf spring 73 Cougar and was extremely nice in corning and no harsh ride effects. I installed on in my 70 Lemans when restoring and it handles extremely well and will hold the rear end stable in hard acceleration or turning. True race quality not a toy.

http://www.fays2.net/

Paul

[JLMounce]

A watts combined with leafs actually works really well and is the setup you would have seen predominantly on the Trans Am series cars from the late 60's through early 70's.

I don't necessarily know if it's needed for the OP's intended purpose, but if he's going to be trying to fill up the wheel wells, the positive location of the watts helps with that for sure. Only thing with leafs you've got to watch out for is getting the watts link's roll center even with the roll center that the leaf springs create. You end up with competing roll centers otherwise.

[punkin]

Thanks Paul, thanks Jason,

Definitely wanting to fill the wheel well. It just looks right. Part of the reason for my postings on the subject is to keep me focused on the original plan and that is to get a great ride for street driving and go out and be reasonably competetive at the track (drag racing). When I do remind myself of these two things the leaf spring solution can't be ignored. I've made a couple calls and sent some emails.

I've had some bad experiences with wheel hop and when you apply the cheap/inexperienced solutions like slapper bars/helper springs/clamps etc to band-aide the problem the ride quality goes to heck. I really want to put that behind me. With the new motor I'm just going to tear things up if I don't do it right.

I thank you all for the great suggestions!

[JLMounce]

The Watts link does help with axle wrap, which can contribute to wheel hop. Another contributor to wheel hop is deflection from bushings.

This is a weak spot for both converging 4 link and leaf spring suspensions because to an extent they require bushings in several areas to avoid hard binding.

If this wasn’t a street car I’d say run a cat 5 spherical bearing package in the leaf springs. But this is going to have a pretty negative effect on ride quality. Not only does the stiffer shackle add rate, the spherical bearing will transmit a decent amount of NVH to an area of the car that directly intersects the passenger cabin.

What I would recommend first is to get into a quality set of leafs like a hotchkis or global west product. With those lowering blocks you may want to try out some shims as well to truly dial in your pinion angle beyond what’s built into the system. With a quality shock and sticky tire to control traction, you may find that wheel hop isn’t an issue.

If it does start coming up I’d look at chassis rigidity first, then possibly other remedies like a watts link, cal-tracks etc.

[rohrt]

650 HP? You need a 4 link setup.

[JLMounce]

Originally Posted by rohrt

650 HP? You need a 4 link setup.

The issue here is that majority of 4 link kits available for the first gen F-body aren't actually going to be any stronger than the leaf package the car came with.

They all utilize the front eye pocket in it's standard location and some variation of the factory shock mounting plate. The support structure is cross-bolted through the frame at a place that the rear sub-frame is not designed with a lot of torsional rigidity.

The only 4 link kit that truly addresses these issues is the DSE kit which requires heavy modification and fabrication to the rear section of the car.

As I already mentioned, at his power level I'd be far more concerned with tearing the car off the front sub-frame than anything going on in the back.

[punkin]

After soliciting input from a number of different sources and considering the large number of changes I've already made to the car I've decided to keep it simple. Get it runnning, work out all the bugs and then reevaluate. For the time being I've decided to go with a split mono leaf spring and caltracs.

I thank everyone for their input and suggestions.

[JLMounce]

a proven combination. I don't think you can go wrong there.

[Paul E]

Originally Posted by punkin

After soliciting input from a number of different sources and considering the large number of changes I've already made to the car I've decided to keep it simple. Get it runnning, work out all the bugs and then reevaluate. For the time being I've decided to go with a split mono leaf spring and caltracs.

I thank everyone for their input and suggestions.

It is always good on this board when people post helpful options so the owner can look at different options and opinions and make a decision on what would work for him. Sounds like you did with good feedback and options. Always a bunch of good ways to do something but also a few wrong ones.

Good luck with your project!
Paul

[punkin]

Originally Posted by Paul E

It is always good on this board when people post helpful options so the owner can look at different options and opinions and make a decision on what would work for him. Sounds like you did with good feedback and options. Always a bunch of good ways to do something but also a few wrong ones.

Good luck with your project!
Paul

I forgot to mention, I did also contact Fay's and left a message. I'm interested in learning more about ther Watt's link as well. I'll update here if I jump into that as well.

Thanks for the tip!