Ford IRS retro fit

pcf_mark

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Aug 22, 2008
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Has anyone attempted or considered converting their C3 to the variety of Ford IRS available? I have seen T-Brids and Mark VIII for $2,500 for the WHOLE car!

I had an '04 Cobra with a few aftermarket parts that made almost 400 RWHP and the rear end was bullet proof with sticky 285 wide tires and the handling was incredible.

I like the CTS-V rear too but that is a more fragile..

Factory Five puts these in Cobra kit cars too. The 92-97 Mark VIII is all aluminum also. Wide vareity of 8.8 gears can be fitted too I think.

Photo of how Factory Five retro fits it into a Cobra attached for opinions. The coil overs won't fit but the upper link, plunging axles and triangulated lower link look to solve some problems our set up has now.

http://parts.factoryfive.com/newcatalog/chassis/pictures/irs.jpg
 
I put down 432 at the wheels at 5lbs of boost through a stock rear end and 275 tires. Now I'm at 13lbs of boost, hp? ...more. Rearend is still spinning along.

PS, I can outhandle a Cobra. Easy.

So can you? Sure, but why would you? Are you simply trying to avoid the toe problem? If so, I think it would be easier to find a different way to setup the stock rear than figure out a new one.
 
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I am looking at options that have a more durable CV axle and stub axle design. Improving the toe change, stupid trailing arm design, fit larger tires etc are bonuses. I have a very good, all new rear in the car with the big 4:11 case, shot peened HD carrier and actual L88/ZL1 carrier gears. It has held up well to ~580 HP coming down the driveshaft with street tires. I have owned this car a long time and can spit out a half shaft u-joint almost at will with 275 wides on the car. I have also twisted off stub axle clean with the bearings on a power shift. I started using u-joints with grease fittings so the u-joint breaks and not the diff case.

Back of the envelope math says you are around 550 hp. If you are not breaking things you either have an automatic with a converter absorbing the shock or are gentle on launches and shifts.

Nothing for nothing but a Cobra will clobber your car in the handling department unless you have some race set up. My '68 has every bit of Vette Suspension upgrades, a bag of tricks from GM and it is still a go-kart compared to my '03-'04 Cobra.
 
The real nice thing about the 8.8 IRS (especially the cobra since it has aluminum lower arms & diff, the stuff from the thunderbirds and all is steel/cast iron) is that it bolts in like a complete package. Too bad I can't find one here.
 
Ford 8.8

The real nice thing about the 8.8 IRS (especially the cobra since it has aluminum lower arms & diff, the stuff from the thunderbirds and all is steel/cast iron) is that it bolts in like a complete package. Too bad I can't find one here.

The aluminum 8.8 has one issue, the carrier caps are flimsy aluminum. I have a 8.8 aluminum housing and sent it to Strange Engineering and had them install billet HD 2024 T-3 caps. I have since decided to go with a Viper Dana 44 and have no need for my 8.8, Mark Williams billet yoke and HD "Control Freak" rear cover and other parts. If you want a double wishbone or upper and lower links with slip axle, the 8.8 or Viper is the way to go.
 
CV joints

Has anyone attempted or considered converting their C3 to the variety of Ford IRS available? I have seen T-Brids and Mark VIII for $2,500 for the WHOLE car!

I had an '04 Cobra with a few aftermarket parts that made almost 400 RWHP and the rear end was bullet proof with sticky 285 wide tires and the handling was incredible.

I like the CTS-V rear too but that is a more fragile..

Factory Five puts these in Cobra kit cars too. The 92-97 Mark VIII is all aluminum also. Wide variety of 8.8 gears can be fitted too I think.

Photo of how Factory Five retro fits it into a Cobra attached for opinions. The coil overs won't fit but the upper link, plunging axles and triangulated lower link look to solve some problems our set up has now.

http://parts.factoryfive.com/newcatalog/chassis/pictures/irs.jpg

PCF Mark,
Another issue (for me) is the factory Tri-pod style CV joints, As shown in your attached pic. They are not as strong as 930 or 934 CV joints, and you should convert to the stronger CV set up if you are running high HP or driving it hard.
 
TT all the Mark VIII are aluminum. I tried to convince my wife to let me buy a used one for the DOHC V-8 and IRS. The look was priceless!

VooDoo - do you have any photos of the set up you have based on the 8.8 IRS?
 
The real nice thing about the 8.8 IRS (especially the cobra since it has aluminum lower arms & diff, the stuff from the thunderbirds and all is steel/cast iron) is that it bolts in like a complete package. Too bad I can't find one here.

The aluminum 8.8 has one issue, the carrier caps are flimsy aluminum. I have a 8.8 aluminum housing and sent it to Strange Engineering and had them install billet HD 2024 T-3 caps. I have since decided to go with a Viper Dana 44 and have no need for my 8.8, Mark Williams billet yoke and HD "Control Freak" rear cover and other parts. If you want a double wishbone or upper and lower links with slip axle, the 8.8 or Viper is the way to go.

The viper dana 44 has a forged aluminium cap, like the C4 Super Dana 44. The 80-82 C3 ones have a cast aluminum cap with a non machined cap to case register
 
8.8 Irs

TT all the Mark VIII are aluminum. I tried to convince my wife to let me buy a used one for the DOHC V-8 and IRS. The look was priceless!

VooDoo - do you have any photos of the set up you have based on the 8.8 IRS?

PCF MARK,
The only pics I have are of the differential itself, did not install. Went with the Viper Dana 44 that I am in the process of fabricating the rear frame structure. My set up will be very similar to http://streetshopinc.com/c5andc6for53-82.html. This shows the Dana 44 with a C5 rear cradle and narrowed frame rails on the lower section of the page. This is what I am building, but there are several "less radical" possibilities depending on how much you drink.:mobeer:
 
Another issue (for me) is the factory Tri-pod style CV joints, As shown in your attached pic. They are not as strong as 930 or 934 CV joints, and you should convert to the stronger CV set up if you are running high HP or driving it hard.

voodoovette,

Who is making your halfshafts.
Thanks
Jim
 
Half shafts

Another issue (for me) is the factory Tri-pod style CV joints, As shown in your attached pic. They are not as strong as 930 or 934 CV joints, and you should convert to the stronger CV set up if you are running high HP or driving it hard.

voodoovette,

Who is making your halfshafts.
Thanks
Jim

JJTOMA,
If you want to go with the 8.8 or the Viper and to get away from the tri-pod CV, I know "The Drive shaft shop" will sell just the inboard splined drive flange for the Viper and the 31 spline stub shaft for the 8.8. This is not the complete axle, just the more difficult part to find. This will allow you to use a 930 CV joint or if you want to use the larger 934 CV, as I did, you need to MFG an 1/2" thick adapter to adapt the 930 drive flange to a 934 pattern. I could not find anyone who sells the I/B flanges for a 934 CV. If you are rich, you could have The Drive Shaft Shop make a complete custom length pair of axles for you, with 930 CV joints only,934 not avail. From this point you need a pair of axle shafts splined at both ends to match your CV, I used Dutchman, but most axle MFG can make them to your required length. On the O/B end I used a micro stub for the 934 (or 930 is also avail) that is avail at most off road shops, then a C5 corvette hub that was drilled and re-splinded to match the larger 33 spline micro stub. If you do not want to go through all of the BS:bullshit: and want to retain your U-joint and trailing arms, then I suggest you contact STINGXRAY, he posted a pic of a nice set, and ask him where he had them made. Either system will require an upper link of some type. If you want an aluminum differential but keep the U-joints, a second generation Viper Dana 44 would be a good choice, but for CV go with a third generation Viper Dana 44 or the 8.8. I hope all the rambling helps.:D
 
voodoovette,

Thanks for your reply. I have spoken to the Driveshaft Shop already(was wondering if you had another source) looking for more options. I will be starting a C2 project with a SRIII frame soon. Found a good ebay deal on a Viper GIV diff. w/ 3.73 gear. Best wishes on your project.

Jim
:bestwishes:
 
voodoovette,

Thanks for your reply. I have spoken to the Driveshaft Shop already(was wondering if you had another source) looking for more options. I will be starting a C2 project with a SRIII frame soon. Found a good ebay deal on a Viper GIV diff. w/ 3.73 gear. Best wishes on your project.

Jim
:bestwishes:

JJTOMA,
Are you going with CV or U-joints?
 
voodoovette,

Thanks for your reply. I have spoken to the Driveshaft Shop already(was wondering if you had another source) looking for more options. I will be starting a C2 project with a SRIII frame soon. Found a good ebay deal on a Viper GIV diff. w/ 3.73 gear. Best wishes on your project.

Jim
:bestwishes:

Jim, What is a "Viper GIV" differential?
 
Jim, What is a "Viper GIV" differential?

Viper Gen IV are 2008-2010. Same housing as GIII, but they replaced the posi unit with a new improved part. ( GKN Visco Lok). Mine is a GIII housing rebuilt with a new Visco Lok and new 3.73 ring & pinion. Found it on ebay, Buy Now price was $1210.00 (to good to pass up!)

Jim
 
Now I get it. I didn't even know there was a 4th gen.

I have a 3rd gen without stub axles and would like to find stub flanges or stub w/u-joints. Not having much success. I can't even find if 2nd gen u-joint stubs will fit.

You guys got any info?
 
What is the spline count on the Viper units? Also what are you guys using for the outer shafts if using CVs? The C3 version is a pencil!
 
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