okfoz

WHo here has done it.

I kind of understand the physics behind the idea of IRS. Lower unsprung weight means that your tires are more likely to stay on the road when turning/bumps. It should also eliminate some of the "bump steer".

The Mustang has a conversion kit to go to IRS, what does it look like, could something similar be made for our F-bodies with a "bolt up application." (Remember removing the gas tank is a must just in case if you have a fuel pump problem.)

I read in the archives about this and lots of folks said full tube frame stuff. I do not believe it so don't say it. I know it should be possible to take what is in existance and make something to bolt up. The car WILL gain wight, but I think it might be worth it in the end.

John

Jza

I think the biggest problem is that you need a solid place to mount the center portion of the IRS assembly, and there's not really a way to do that easily. (there's probably a way, just can't see it being what you call "easy" in the fabrication world).

We don't really get bump steer from our rear end. The only measurable difference between the solid and the IRS rears is ride comfort. That and the fact that if one wheel goes over a bump or dip it doesn't effect the other in any way. I don't know that that makes it "worth" it, but I am curious about the whole concept. It's certainly something worth investigating, but for now it's way up in the lofty category of "custom work".

I think I'll do a little investigating of my own in fact. I've designed and built a suspension before (even though nobody here appreciated it.. ), so I might want to see what I can do with what's out there.

okfoz

What I was thinking is make a cage that would support all the pieces, it would be all inclusive, shocks, springs everything. I would mount it with the existing holes in the car.

There are 5 mounting places currently in the rear. The Panhard bar, both of the control arms and the shock mounts. If I welded an extra piece on the oppisite side of where the pan hard par mounting point was I think I could get away with it.

its a cool idea, and as long as I keep the rear end from beating me to the finish line it would be a good idea.

John

soulbounder

No one on the board has done the conversion. But it has been done a couple of times. Once on the firefox, the other in Florida.
www.rareautodesign.com
He was going to make a kit for it but got a bad reputation for dealing with potential buyers, so the whole thing was cancelled. Don't know if he ever plans on doing it again.

okfoz

thanks,

John

BretD 88GTA

Well, I'd have to disagree with that. Try cooking down a twisty road and hit a small pothole or bump. The rear end will tend to "jump" out on you. With IRS that won't happen. IRS provides much better handling capabilities. That's why hi perf cars like Corvettes, Porsches, Audis, etc... use it.

IRS is doable in our cars, but it's probably not an "easy" conversion.

okfoz

Bump steer will occur with any car with a solid rear axel. The reason why is the way everything works.

As seen in the sketch, because we are working with a system that uses a "pan hard" bar the one end is in a fixed spot on the chasis, the other is on the axel. As the bar pivots and the higher the axel is, the more to the right the axel will go.

I forget which side our bar attaches to, but its all the same, it happens to be the nature of the beast...

okfoz

it did not want to post pic, lets try again.

Irhal

I heard about 1st gen F-bodies hooking IRS' corvette on their rear, you think it is doable on our generation? If so I believe it would be the simpler way, which is why I wanted to do for a while... but then again, for your informations the F-Bodies have better handling than Mustangs because we are lower and larger :P

89 Iroc Z

The pic doesn't work

REZN8R

A note on 1st gen cars. Correct me if I'm wrong, but I think the 1st & 2nd gen F-body's had a body and a frame. The 3rd & 4th gen have a unibody. Therefore it would be easier to put a IRS setup on a 1st or 2nd gen. Right?

okfoz

I'm pretty sure all F-bodies have been unitized. A larger problem with the Gen 1 & 2 is they used Leaf Springs, The up side is more trunk area, the down side is less room for the IRS.

properly designed IRS I believe could be a driect bolt in, with possibly one weld spot. I would even venture to say that a stock exaust system might be able to be utilized if properly designed.

John

soulbounder

All F-body since the 67 Firebird have been unibody. The biggest problem on our cars when trying to retrofit an IRS is trying to mount the center section of the differential housing. On our cars, the gas tank is above that area or at least close to it. But there is still a way to do it.

soulbounder

I know Comp. Engr. used to make rear frame rails that would extend off of our existing rails simulating a full frame in the rear. You could weld a crossmember between them to give the IRS a mounting place.

Here's a pic for those who need something visual.

REZN8R

Sorry, I was under the impression the early F-body's had frames because Energy Suspension makes Poly Body mounts for them.

okfoz

Gen1 & 2 if I am not mistaken have like a sub frame, unlike our cars that is welded directly to the body, was bolted. It was for the Engine cradle, and possibly for the rear axel. They were not a full frmae car to my understanding.

John

iroc22

Ding Ding Ding we have a winner.

soulbounder

Yea, what okfoz said.

TVP

OK ... I got the welder , tubing bender , notcher and the experience ... so who's got the money ?? let's hack up a car and put an IRS under it .. I even have a mule to hack on .. anyone ?? anyone ??

Tom84L69

yeah the c4 vette rear suspension is nice and all but how bout doing a c5 rear? that would be the shiznit for sure!

in fact, the whole c5 rear suspension comes down in an aluminum cradle held up by 4 bolts, it maight make it easier to install in a thirdgen (?) or maybe harder? hell, i think either one is too much work for a street car but everyone needs a hobby.

REZN8R

I thought the C5 and C4 rear suspension was the same?

Then again for a second I thought Tom84's sig said Geo Prizm LS1 That would be fun.

AFrikinGoodTime

Sorry to burst your bubble but this example is not BUMPSTEER, It is simply LOSS OF TRACTION. Panhard bars do not create bump steer either. In their range of motion they only cause tranfer of weight.
Bumpsteer is only caused by a bump in the road changing the angle of attack of a front wheel by shorting or lenghtening the geomety of the tierod causing the tire to change the path intended by the steering wheel.The car is steered differently than intended by the dip or bump in the road and should not be interpeted that by hitting a bump with a tire and skipping off is bumpsteer, merely loss of traction.
The reason why IRS works better on uneven surfaces is beause the bump is only absorbed by one rear tire causing only one tire to lose traction. On a solid axle, both tires are affected by the bump. Solid axles work better on smooth surfaces than IRS because of less deflection of working components ( less moving parts or pivot points) and camber can not be flexed or changed by cornering forces. That is why we don't need a rear spreader bar (a.k.a. strut brace, etc.)

Tas

I'm not sure on the 2ndgen but the 1stgen has a bolt on subframe in front (its removable with bolts) and a welded on subframe in back (sort of unibody but not really). In back it can be removed and welded back on unlike 3rd and 4thgens.

Tom84L69

no, c5 rear suspension is totally different than the c4. it's different and much better.

too bad my prizm isn't an LS1, in fact i included the LSI just to get second looks at my sig.

TVP

doesn't a C5 have the transmission in back ???

TVP

Tom84L69

yes it does, it's a t56 bolted directly to the differential. the suspension would probably be one huge pain in the *** to put in a thirdgen, just starting more conversation.

soulbounder

I think the C5 rear would be nice but it might be too wide for our cars.

okfoz

THat would help on our balance by getting more weight in the rear.

ON A SIDE NOTE:, interesting fact, the Vette was not the original car to have a front engine, rear trans from GM. Back in the 60's there was a little Pontiac, that was built on the same platform I think as the Skylark (cant remember the name). It used that setup and the rear suspension of the Corvair...

John

Tom84L69

that's true, i have heard of that pontiac also. porsche used the rear trans setup on 928s and 968s, possibly all their front engine cars. we'd have a helluva time fiting a trans back there in our cars though.

REZN8R

How's that work anyway? Don't you need the clutch up on the flywheel? Isn't the clutch attatched to the transmission?

okfoz

Basically I think its the same trans, the only difference is the location of the transmission. What they do is put the "driveshaft" between the Engine and transmission. You could easily run hydrolics for the clutch, and with a little bit of work run some linkage for the shifter.

Putting one in our car I would not suspect to be impossible, but you would have to run an IRS, and your back seat would become null.

John

REZN8R

So the clutch is in front mounted to the engine or in back with the trans?

TVP

so what you guys are saying is ... GM switched to the T-56 .. from the ZF ... and now uses the T-56 in the back ????? I think not ..
the way motor trend put it .. GM designed a WHOLE transaxle
for the rear of the vette ...

TVP

okfoz

The clutch is probably back with the trans.

John

Tom84L69

the clutch is still directly behind the motor along with a flyeheel, and they use the SAME t56 tthat goes into a 4th gen f body but without the bellhousing(except Z06 which uses a t56 with different ratios). They do not use the ZF 6 speed used in the C4.
Gm used the T56 to save money because they used it in the fbody and it's also a great tranny(used in the viper).

the engine and trans are linked with a torque tube(driveshaft) with plastic or nylon rings to compensate for angles. a bigger tube that does not rotate goes around the whole assembly from the rear of the motor to the front of the trans. the differential is bolted directly to the back of the trans.

I've taken these apart before so I'm sure of it. here are the cars I've worked on.

www.djrace.com

Tom84L69

also, the t56 in a corvette does not have the mounting pad for a torque arm like the fbod's trannies do.

REZN8R

You've worked on racing C5's? How'd you get to be that lucky? Hmmm.. maybe I could be the first one to give a 3rd gen perfect 50/50 weight distribution.

iroc22

Tempest Lemans

Built on the same platform as Buick Special and Oldsmobile F-85, though those cars didn't get the transaxle.

Porsche 924 and 928 adopted the concept from Pontiac.

Tom84L69

i've known the guy for 20 years, which also is how long I've been alive. My dad is an old college friend of the guy, so yeah, I got lucky!

JAY4SPEED

Tempest Lemans....... I think Iroc22's right.

Dunno I'm going to have to check the movie "My Cousin Vinnie" to refresh my memory. Isn't that the car she was talking about with the independant rear suspension?

okfoz

It was the Tempest, I am real sure, thats the same car that my dad and me came up with last night...

John

lonsal

iTrader: (2)

Yep the tranny in the rear originated with the 1961- 63 Pontiac Tempest (also the Buick Special and Olds F44 I think). It didn't get the "Le Mans" moniker until 62. My first car was a 61 Pontiac Tempest station wagon. Slant four engine, manual brakes and steering, 2-speed auto tranny with a shift paddle on the dash. Tranny in the rear connected with a torque tube to the engine. Back in the days when restoring the dash meant sanding it, taping it off and repainting it with a rattle can. Lon

okfoz

The Buick and Olds did not get the rear trans tho like the Tempest.

I was looking at a Buick Rondevouz today, and am wondeing if the IRS would work from one of those. They can be Fwd or AWD, I wonder if even the Aztec might be a good doner...

The only thing I worry about is the geometry of the rear suspension with our wheels. A suspension is designed for a certain offset wheel, if you go outside of that you get a softer ride, but the loads are in the wrong place. Seen too many cars with the ugly "reversed" wheels that the suspension is permenanty bent because of it. We might have to go with a Vette wheel, or a 4th gen wheel to make it right or even a FWD wheel...

John

Tom84L69

interesting you bring up the aztek. the pontiac solstice show car uses that cradle and suspension. the drive unit is not strong enough for a dedicated rear drive car. engineers countered this by using an S10 differential (weird huh?). the goal for this car was to make it easy to produce with existing parts.

that would be a very interesting proposition putting one in a thirdgen, you can bet it would bve one of a kind and a lot of work.

iroc22

The Special was built on the same platform but didn't recieve the transaxle (or a bunch of other parts) and the it was the Olds F85. Didn't anyone read my post??

JAY4SPEED..yeah it was the tempest in that movie...one of the skid marks went over the curb without effecting the other one in the picture.

lonsal

iTrader: (2)

Sorry I missed that part. I did a web search and discovered it was the F85. I wasn't aware that my Pontiac model was the only one of the 3 that had the rear transmission. What can I say? Even some at GM forgot they had made it. Lon

GTA-SPD

Hello all. I just registered yesterday and I believe that I can help with this I.R.S. question. My brother has sucessfully pulled off the conversion in his 87 IROC using a rear set-up out of an 89 Vette. Two thing that I'd have to say are paramount, once you do this conversion you CAN'T go back (lots of smoke wrench work under there) and make sure that you have a GOOD shop do the work. If they get it just a little out of whack, you'll have nothing but problems. I'll post pictures on Monday of his car and if you have any specific questions I'll do my best to anser them or I'll ask them to my brofus.

soulbounder

Sounds like a winner. Thanks. Welcome to the board by the way.

okfoz

KEWL! I would like to know all the specifics, but I imagine we will get to them like:
did he move the gas tank?
Can you still remove the gas tank?

the little things...

John

Black Knight

Count me in too.

www.rareautodesign.com never did anything for us, nor do they respond to emails and the compamy that built the Firefox is no longer in Business