C3 conversion for CSX style chassis

[my427cobra]

A question for Robert (moore_rb):

Isn't the pinion shaft bearing diameter 1.625"?

Cheers
Greg

[Tjd]

Greg
it’s 3/8 plate
Tom

[my427cobra]

That should be plenty strong!

Cheers
Greg

[Tjd]

This different conversion is meant for highway cruisers with 400 horse and street tires if you’re going to build a monster motor then go 9 inch
Tom

[eschaider]

With no intention to rain on Tom's parade here, you might want to look into the Ford Aluminum 8.8 IRS center from an 03/04 Cobra or an '06 - '10 Ford Explorer as an alternative to a 9" Ford. Below is a link to a post I did a while back sharing some information on that particular solution. While not as strong as a 9" they still easily handle 900+ hp in 3400 lb SVT Cobra's. Click here => Ford 8.8 IRS

There is also a very nice HD rear cover available for them from right from FRPP, click here =>Ford Racing IRS Cobra Axle Girdle

When you get done with the conversion the 8.8 IRS center and associated toys will be less expensive than the 9" option. and very likely more than adequate for the application.


Ed

[Tjd]

Ed
you’re not raining on my parade you have a perfectly good point I was originally looking for a 8.8 to do this conversion but they are different designs on the 8.9 as far as the front pinion mount. And you have the issue of space it’s kind a close quarters where the Diff goes in the original CSX chassis and looking around when I was trying to find out 8.8 it seems to be easier to find a C3 diff than an 8.8. I just wanted to make something that would bolt directly in without any modifications to the CSX chassis. And if I do find a 8.8 case that will work I will make Kit for that too
And remember I talk to my phone so anything is spelled wrong or doesn’t seem right is the phones fault not mine.
Tom

Tom

[eschaider]

Thanks, Tom it was not my intention to. I am flat impressed with what you have done with the C3 hardware.

The 8.8 as you accurately pointed out is physically larger and in the CSX chassis I can easily see where the size will be problematic. If the builder used a less original construction model in the rear of the chassis, like some of the Replica Manufacturers, the 8.8 fit is easier but still requires some fabrication.

Ford's 8.8 IRS is really an alternative to a 9" that requires considerable fitment and fab work. Your approach is a bolt in and I still think a way cool approach.

Ed

[Tjd]

Robert
All I’m trying to do trying to build something as close to the original and as economical as possible. I’m doing a 427 Chassis ( to help finance my leaf spring car) right now so I set it up so that differential would fit in that of somebody so desires or original Shelby differential . I’m doing one more then I’m switching to 289 Leaf spring. When I put the 9 inch in a 289 chassis I had to modify the chassis to get it in that’s why am using the Corvette All the chassis I’m doing will come with complete original style suspension that would fit a CSX, Kirkam,hi-tech or any chassis that takes original suspension. Except for the first couple of chassis that I did everything else is been as close to original as possible do not know how many I have built Probably more than a bakers dozen
And thank you to everyone that’s posted on this thread I’ve learned more about the C3 Diff since this thread is been posted.
Thank you again to everyone
Tom

[my427cobra]

Well Tom. I really like your concept and I'm seriously considering it as an upgrade to my car.

But as I look at all the components I have to ask:

What the heck makes the Spicer splined yoke shafts (3-82-268x at $346.00 each) so EXPENSIVE?

The Cobra name, strength low volume?

There are so many Spicer splined yokes available at a third the price.

Just wondering.

Cheers
Greg

[Three Peaks]

I put an 8.8 in my original style chassis from Roger Bollick. It needed a bit of modification to do the install but it fit in fine. I also used the 91 T-bird IRS uprights in the rear and that also needed a bit of modification but I was able to make it fit without too much messing around. Also had to design and build my own control arms to use the Tbird uprights and add new pick up points for the lower arms....

The 8.8 requires a different mount for the front pinion, depending on the year you use. I used a cast iron case, but the aluminum cased units from the year I used were the same for mounting purposes. I welded in a piece of 2 x 3 tubing between the frame tubes, which strengthened the chassis significantly. I had to be sure to weld it eccentric to the frame center so the pinion mounts would line up close to my required pinion angle. Then I cut a half round where the nose would project through. The rear of the differential also needed a modified mounting point, but it wasn't a big deal to fabricate a mount...

Anyway, if anyone is interested I could probably get some pictures. I have found the 8.8 to be plenty strong for my 525 hp 393 engine.

Bob

[my427cobra]

So I'm still following along on Tom's vision of using a Corvette C3 diff.

But I had to learn more about the Cobra/Spicer half/axle shafts and how they would mate up with the C3 diff.

I found a neat Spicer Parts Catalog on ebay which arrived today and I'm pouring through it learning what I can.

And I think I have a few ideas to work on and suggest to Tom.

Later.

Cheers
Greg

[Three Peaks]

It would be interesting to see a pic of the C3 differential to see if a guy could adapt the Porsche 930 axles to it and the uprights in the same manner that Kirkham does with their diffs now.
I have a couple original style uprights with Corvette spindles in them that would probably work in this situation that I won't be using if anyone would be interested in taking them off my hands for a very reasonable price...

Bob

[my427cobra]

Bob,PM me.

Cheers
Greg

[Three Peaks]

Originally Posted by my427cobra

Bob,PM me.

Cheers
Greg

PM Sent

[my427cobra]

This concept of using a C3 diff has really got me thinking and also has left me with some questions.

Can any of the experts answer this question for me:

Why did the original 427 Cobra rear suspension use a Spicer splined half shaft?

I would have thought with fixed length upper and lower a-arms the half shaft would be a fixed length also.

Or was it because the original rear suspension used rubber bushings which allowed for a lot of suspension "movement" and therefore required some "slip" action in the half shaft?

Can anyone give a simple explanation?

And if one used fixed a-arm joints (hiems or poly), would a fixed length half shaft like a Corvette C3 half shaft work?

So many questions!

Cheers
Greg

[eschaider]

All IRS suspensions used fixed length upper and lower a-arms, Greg. In addition all half shafts are fixed length but usually with a sliding coupling like a drive shaft yolk on the output shaft of a transmission. That I am aware of no IRS has ever been manufactured, for production, with variable length a-arms or half shafts.

As the IRS suspension moves up and down through its range of motion the wheel spindle traces out a modified arc defined by the length and location of the upper and lower a-arms in conjunction with the design engineer's chosen pivot points on the spindle.

As the spindle moves through its range of motion there will be increases and decreases required in the length of the fixed length half shaft to make the connection between the side gears and the axle flange. The changes in required half shaft length are absorbed by either a splined coupling (like used on a drive shaft), usually near the center section, or travel built into the CV joints if the design uses CV joints.

Get yourself one of the free or cheap 3D Cad programs out there, draw up the basic geometry and move it through its range of motion. If you have difficulty visualizing spatial relationships in motion the 3D CAD software will help you see what is going on.


Ed

[Mongoose930]

The original style Cobras use variable length 2 piece half shafts to allow for a change in length as the wheel travels in an arc through the travel of the suspension. These are the Spicer part numbers that I have on my car. Bought them through Amazon:

Spicer 3-3-118KX Slip Yoke
Spicer 3-82-268X Yoke Shaft Assembly
Spicer 3-2-159 Flange Yoke

[my427cobra]

Hi Ed and Mongoose. Thanks for your responses and info.

How much spline "slip" do you think there is in the Spicer half shaft during the up and down suspension movement?

1/4 to 1/2 and inch?

Cheers
Greg

[eschaider]

I never really measured it but if you go by CV joints there is not a lot of movement but there is some. I would expect less than or equal to the slip yoke on a drive shaft. The shorter you make the control arms the greater the impact on the movement.

If you are worried about separation pull out your coil over and move the drive spindle through it's full range of motion measuring the movement of the half shaft. Try to shoot for a similar engagement length as your slip yoke on the transmission tail shaft when you are fully extended and you should be more than safe.


Ed

[my427cobra]

Hi Tom. I just PM'd you.

Look forward to talking with you.

Cheers
Greg