Solid axle vs. IRS

[Samckitt]

I have thought of doing that. Might be the way I end up going.

I quickly made some half shafts. I don't know if they are the correct OD or length yet. I did not measure what I have. The ends are probably nto correct either. So yeah if you don't mind, it will save me a little work, send what you have to me please.



Thanks.

[Twin_Turbo]

my models are for 3" OD shafts w/ 1350 yoke ends. I'll send them your way.

[J68Bird]

Scot,
I was able to fab up my own "Batwing" using the files that you sent me. I found a local Corvette place that would have sold me one, but it was about 6" too wide. I'm using a C3 rear. I've got all the parts made and as soon as I get the center section powder coated I'll be putting it all together.

J. Clear
68 Firebird 455/4spd Conv.

[Twin_Turbo]

That looks like an eaton diff, I sent scot the models for that one. The late C3 (80-82) uses a batwing similar to the C4 one. Like your mounting systen. How are you mounting the pinion? I'd advise you to use a heavy duty lid, the non HD ones have significantly thinner ears (original leaf spring mounts) and they crack quite easily.

Looks like you are building a trailing arm IRS? Nice, please keep us updated on it, I for one would love to see it.

[Samckitt]

J68bird - Looks good.

I was reading some yesterday & found that the D36 batwing can be used on the D44, looks like there is an adapter plate of some sort between them. What is different between them besides the extra bolt hole on the D36 cover?

[J68Bird]

TT
The rear I have is an early style, '68 I believe. This is the first I've heard about the "lid" being weaker, but this is all pretty new to me. Not sure if mine is the HD style or not. I've got a pinion mount made and will try and get a few pics. (didn't model that one yet)

Scot,
When I talked to the Corvette guy he mentioned something was different about how the newer style bolted up. I remember looking at the piece and thinking that it wouldn't be problem to drill new holes to make it work. Unfortunately, now I can't remember exactly what the difference was.

J. Clear

[Samckitt]

Maybe the internal cast bosses for the bearing cap supports are in the wrong place.

Scot

[Twin_Turbo]

TT
The rear I have is an early style, '68 I believe. This is the first I've heard about the "lid" being weaker, but this is all pretty new to me. Not sure if mine is the HD style or not. I've got a pinion mount made and will try and get a few pics. (didn't model that one yet)

If you have an original diff you always have the weaker lid, ther HD is stricty aftermarket. Also, if you have a 68 or other early year (pre 72 I think it was) you also have the weak posi case with the small square window and the weaker 18-10 spider gears, the later large teardrop window case and the 17-10 gears are much stronger. You can easily see if it's HD or not, the moutning flange is much thicker on the HD one and the reinforcement rib that runs to the yop shaped like a ) is less deep there also.

The later differentials use a batwing like the C4 corvette, the pre 80 eaton unit (cast iron, what you have) uses a bolt on crossmember on the top of the lid. That's the difference, there's also a difference in the camber bracket and how that's setup (earon bolts to main case on the bottom, dana alu C3 80-82 and C4 bolts over the lid to case mating flange)

[pdq67]

Anybody ever think about playing w/ the old Pontiac Tempest transaxle swing-arm rearends??

I think that they were only in the '63 and '64 Tempest cars back then.

I don't know if a 4-speed was ever offered, but do know that they were auto and 3-speed stick back then.

pdq67

[Atrain]

I put a 90 vette IRS and 6-speed in my '70 Camaro. I am still a long from being done with the car though...

[jeffandre]

I put a 90 vette IRS and 6-speed in my '70 Camaro. I am still a long from being done with the car though...

Cool, get more pics and use it. Looks like a sway bar mount attached to the underside of the trunk? Might need some sort of rigid support for that one, the trunk floor will flex more than you think, even though it is welded to the gas tank support metal. Have you beefed up the trunk pan from inside?

[Atrain]

I had to pin a few things together in a hurry before our move...but thanks for pointing that out. No meaningful bracing for the rear sway bar yet, it will probably come off the cage inside the trunk. I need to buy my fuel cell first and get that sorted out. With two small kids, and tons of body work to be done (which I can't stand), my project is moving pretty slow so I don't see a test drive in the near future, but I will snap a few more pics of the rear end for you. I'm learning as I go with this so I'm definitely interested in people's feedback. Drivetrain is the vette D44 with 4:10's, ZF 6 speed (the black tag one), and a 500 HP 383 with a cheater system. It's going to be a retro-ish trans-am racer kind of thing.

[Norm Peterson]

What you'll want for reinforcement is something that runs laterally from frame rail to frame rail. Fairly rigid, too, as any flexibility of this supplemental framing detracts from the effectiveness of the bar (making it behave like a smaller bar) The way the rear sta-bar works requires that it resist the roll of the chassis as a whole, so you need to tie back to major chassis structure.


Norm

[Texas Hotrod]

I finished my all-custom sub frame and have the Crown Vic (police car) aluminum (almost all aluminum) front suspension unit bolted in. It's finally all mounted to the Camaro. The Ford suspension is roughly 4" wider than what the 68 Camaro had, so now my Z06 wheels should fit nicely. Now on to the next phase.

I had a blazer 12 bolt (w/machined and redrilled axles) mocked in with 10.5X18" wheels and tires installed. The truck axle is 6" wider than the stock Camaro 10 bolt, making the Vette wheels fit perfectly inside the rear fenders.
All the hard work that went into the front frame and I just couldn't stand not having an IRS in the back. I did some measuring and figured out that the 12 bolt truck axle is the exact same width as the Vette unit. I dropped the axle, pulled the mono-leafs and took more measurements. I'm surprised that the mounting points of the bat wing line up with the boxed sections under the car. It looks like I can make this work as well.

I purchased a stick of 3X3 thin wall tubing and started fabbing the mounting for the BW. I need to hang the center unit first and then I'll verify if I can retain the Vette torque arm. I have the engine mounted (w/custom motor mounts) and the tranny is jacked up into position, I just wasn't quite sure about the crossmamber. The strange thing about Corvettes, they don't have crossmsmbers. If I can tie the torque arm into the back of the tranny, then the Camaro won't need a crossmember either. Running 3" duals will then be a lot easier to install.

I own an '88 C4, so I have the luxury of easily getting measurements first hand. For what it is, the C4 is a fine car. Anti-squat????? I have never noticed mine squat in a hard launch, I guess I'll have to pay more attention next time I drive it. Even hard on the gas/hard o the brakes it tracks stable and true.
My friend's C3 has totally different issues. His has major squat under power/shifts. Then again, C3 is a crappier system. It's mostly made of steel (the C4 is all aluminum) and the torque point is directly above the pinion yoke. The C4 ties the torque arm to the transmission tail shaft, which transferres all the lifting forces from the rear end up to the motor mounts.
The Corvette rides nice and handling is crisp and precise. Taking the same car and adding a straight stick in the rear would be detrimental, it would be a totally different car (more of a Camaro????). The same goes for adding the IRS to a Camaro, It'll make it more of a Corvette. In all reality, it does need to be engineered correctly. Will it out perform a 3-linked (or a 4-link) properly set up 9" in a hole-shot? Maybe not, but that doesn't mean it can't be raced either w/o good results. Then again it's a pro-tourer, not a pro-streeter. Each one has its place.

I've heard all the sad stories from many different people about my IRS install. Each of them had owned a Camaro (or a Mustang) at one time, but none had ever owned (or even driven) a Corvette.
So coming from a Vette owner/driver, if it's IRS that you want, then go for it and don't let others second-guess your decision. Just make sure it's done correctly.
Post pics as you progress.

Good luck,
Gene

[Atrain]

Here are some additional pics of my C4 IRS install into my 70 Camaro. I'm embarrassed that I let things get so rusty. Like I said before, it was a rush to make it a roller before we moved, and of course we hit a storm on the way...likely because I neglected to paint things. Anyway, in the interest of knowledge, here you go. Please feel free to make constructive suggestions as I am new to this...

[Texas Hotrod]

Does the spring rate seem stiff for that car? I'll retain my spring too, I just wondered if it was too stiff. Might be hard to tell w/a gutted interrior as I'm working w/a bare shell also.

[Atrain]

It seems pretty stiff but so did the vette I took it out of. Really too hard to tell until the car is put together and driven...

[hossdoc]

[quote=RobM] Id go with truck arm or a good three or even four link with a solid axle.

With regard to the Four link; Do you have to worry about significant binding under hard lateral acceleration. I can forsee that a streetcar might never experience this, however if I intended to autocross or open track the car might it be detectable?

[68sixspeed]

With regard to the Four link; Do you have to worry about significant binding under hard lateral acceleration. I can forsee that a streetcar might never experience this, however if I intended to autocross or open track the car might it be detectable?

I can shed a little light and almost 20K miles of experience on a 4 link - If you leave it set for optimal drag settings, you have little to no roll ability in the rear, but, 15 minutes, move the lower link closer to parralell with the ground and if need be level out the upper link some, it behaves closer to a 4 bar setup and I can get 2.5"+ free roll; add some upper links with birdcages and urethane springs and it rolls even more and takes the tire shock out of it exitting the corner. Even on street/cornering settings the 4 link works well and has zero wheel hop. Yes, it does weight transfer a lot better on the drag settings, but it does good on the cornering settings too. (it just won't hang the front end unless it is on drag settings.)

Back on topic, IRS is cool, but unless you have a bumpy track I'm not sure if you would notice it. Ever drive a newer vette with the traction control off? They are all over the road in 1st and 2nd gear-- no weight transfer. A good 3 or 4 link on a fixed axel can weight transfer a lot better.

-Dan

[Norm Peterson]

[quote=hossdoc]

With regard to the Four link; Do you have to worry about significant binding under hard lateral acceleration. I can forsee that a streetcar might never experience this, however if I intended to autocross or open track the car might it be detectable?

If you're talking about triangulated 4-links a la A/B/G body, you do. But the 'bind' issue there is a function of what you've got in the ends of the links for bushings rather than the fact that you've got four links. It is a case of the stiffer you make the bushing material the worse it gets, and could amount to 50 lb/in or more at the wheels. Since this effect more or less works in parallel with your springs and sta-bar, stiffening those components will reduce the bushing effect.

If you know what you're looking for, or even if you don't and make immediately-before and immediately-after drives over certain types of pavement unevenness at low speed, you can clearly feel the difference in ride with only four of the eight rear bushings swapped from OE rubber to poly (as most such bushings are sold).

Four links is kinematically the correct number for a stick axle, so there isn't any inherent bind as long as the links can only carry axial loads (i.e. no bending, torsion, or shear). However, that doesn't address other issues even if the links are all rod-ended and the amount of 'bind' really is negligible - for example, I'm not at all sure what path the axle follows in roll (it may not be pure rotation).


Norm