Author Topic: Vette Diff  (Read 7499 times)

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Offline aussievetteracer

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Vette Diff
« on: April 15, 2011, 09:29:55 PM »
G'day from Oz,
                  I am preparing A C4 vette for saltracing here in Oz. As the car will be used in other motorsport events, I would prefer to retain the IRS and Dana diff. Can any of you vette salties or scruits advise if it is possible to convert the stock diff to an "approved hub" (SCTA 2.E) If so can you advise where I could locate the necessary parts? Thanks in advance,
                                                                                  Denis
Denis

Offline kiwi belly tank

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Re: Vette Diff
« Reply #1 on: June 19, 2011, 12:48:25 PM »
Hey mate, I'm wondering if you might have struck on something that the tech guys hadn't thought about. The idea of the rule is to retain the wheel on the vehicle in the event of an axle failure. The fact that axle assembly on a Vette also doubles as the upper link for the suspension might not be common knowledge. If you were to break an inner axle, the wheel probably wouldn't leave the vehicle but the bitch sure wouldn't be pointing in the right direction & if the axle came out of the diff, it'd eat up some crap!.
About the only thing I can think of doing is to fab a safety link with pivot centers the same as u joint centers on the same plane.
You might want to look into the road race stuff & see if they are doing anything.
  Sid.

Offline Nexxussian

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Re: Vette Diff
« Reply #2 on: June 19, 2011, 09:53:46 PM »
I don't recall which 'Vette generation it was exactly, but I thought the C4 already had an upper link on the rear suspension.

Like an upper A arm, but I don't recall the shape.

 If you don't have an upper link, check with the guys that work on the Sundowner Corvette ('68 I believe) as they must have done something.
Just happy to be here. :-D

Erik

Offline manta22

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Re: Vette Diff
« Reply #3 on: June 19, 2011, 10:39:18 PM »
The late Corvair and early (sort of) Corvettes had very similar rear suspensions-- the rear axle formed the top lateral suspension link. Not a confidence- inspiring setup if one thinks about a broked u-joint. :-P

Regards, Neil   Tucson, AZ
Regards, Neil  Tucson, AZ

Offline vette#128

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Re: Vette Diff
« Reply #4 on: June 19, 2011, 11:37:22 PM »
If the C4 generation is in question;  The car has a 4-link (2 on each side from the frame)  that holds the hub in place. The cover of the diff is actually a "bat-wing" that bolts to a bracket on each side of the frame. There is also a strut rod from the diff to the rear hub on each side.  This ties everything together - the rear end and hubs all form one structural unit. There are no axles, in the traditional sense. There is a stub axle on each side of the diff, held in place with a special C-clip and a short half-shaft to the hub (u-joints on each end) . A picture is worth a 1000 words here..... Point is, the stub axle can't come out of the diff as it is held in place by the half shafts. If the u-joint fails, the stub will be captured by the C-clip.... but who cares, the damage is done with a half-shaft flopping around! In practice, at high speed, the half-shaft will tear itself loose. (by the your chute is out and brakes on!). The wheel will not fall off as it bolts directly to the hub, and the hub is secured at the top by the 2 links, and at the bottom by the strut rod. The hub is capable of standing alone. I've broken a lot of U-joints in other forms of racing, and aside from damage to the bottom of the car from the brief (about the second rotation of the loose halfshaft breaks it free) flopping of the half-shaft, I have been able to safely bring the car to a stop. I emphasise that this example is for a C4 only, because not all IRS set-ups have the hubs secured if the half-shaft. 
Ed Van Scoy
Four Deuces
(Salt,Dirt & Pavement)

Offline kiwi belly tank

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Re: Vette Diff
« Reply #5 on: June 19, 2011, 11:54:35 PM »
With that said by someone who really knows, sounds like Ozzy Denis is good to go mate!
  Sid.

Offline maguromic

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Re: Vette Diff
« Reply #6 on: June 20, 2011, 02:15:54 AM »
The Dana 36 IRS from the early C4 suffered from jacking effect due to high roll center (not good in a spin or if you plan on road racing you car, during a spin or cornering the outboard wheel jacks up the diff like a pole vaulter giving a severely reduced contact patch and a sudden loss of grip/reduced slip angle). The later model Dana 36 from the C4 have a better roll center than the early C4s.  The other issue you will have with the stock suspension the toe control is not 100% accurate. Even though this involves some fabrication work, my friend designed a double “A” arm suspension for his corvette.  Tony




“If you haven’t seen the future, you are not going fast enough”

Offline salt27

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Re: Vette Diff
« Reply #7 on: June 20, 2011, 02:30:50 AM »
If you don't have an upper link, check with the guys that work on the Sundowner Corvette ('68 I believe) as they must have done something.
If my memory is correct I believe that they removed the I.R.S. and installed a early Olds differential in the Sundowner.

Don

Offline manta22

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Re: Vette Diff
« Reply #8 on: June 20, 2011, 06:35:14 PM »
The Dana 36 IRS from the early C4 suffered from jacking effect due to high roll center (not good in a spin or if you plan on road racing you car, during a spin or cornering the outboard wheel jacks up the diff like a pole vaulter giving a severely reduced contact patch and a sudden loss of grip/reduced slip angle). The later model Dana 36 from the C4 have a better roll center than the early C4s.  The other issue you will have with the stock suspension the toe control is not 100% accurate. Even though this involves some fabrication work, my friend designed a double “A” arm suspension for his corvette.  Tony






Tony;

How does he solve the problem of axle plunge as the wheels move up & down; I don't see any splines or Rzeppa joints?

Regards, Neil  Tucson, AZ
Regards, Neil  Tucson, AZ

Offline vette#128

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Re: Vette Diff
« Reply #9 on: June 21, 2011, 12:21:24 AM »
There is an easier way to overcome the IRS "jacking effect". When I first started out, my vette (1985 with a Dana 44) handled well with only minor alignment adjustments. As it got faster, the looser it would get.... so I would just dial in more negative camber in the rear to adjust for the lift due to low pressure over the rear of the car. When it got to the point that I needed 3 degrees of negative camber to go straight at 220 mph, I figgered there had to be a better way to keep the camber from going from negative to positive as the speed increases. There is..... Simply re-locate the bottom strut rod about 1 1/2 inches directly below the stock mounting point (in other words, fab a bracket that lowers the inboard strut rod) The result is, the strut rod is now parallel to the half-shafts (I use heim-joint rod ends to make the fine adjustments). So, you know how the tires fold under when you jack up a stock Vette? Won't happen now, the wheels now stay in place.

But, if I ever got the car to the 250 mph range, I would put a solid rear end in it just to make me feel better.  The Vette IRS is like a 27-piece screwdriver.... It works well, but it doesn't need to be that complicated.

 And you guys are right about the Sundowner, it has a 10-bolt under it.... last I looked.
Ed
Ed Van Scoy
Four Deuces
(Salt,Dirt & Pavement)

Offline maguromic

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Re: Vette Diff
« Reply #10 on: June 21, 2011, 01:34:02 AM »
Neil, I am in Asia for the next month.  I will send an email and ask how he did it, but I believe it was done with the half shafts.  Tony
“If you haven’t seen the future, you are not going fast enough”

Offline hotschue

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Re: Vette Diff
« Reply #11 on: June 21, 2011, 09:25:23 AM »
Hello Neil/Mag.....To allow for axle plunge just remove inner stub axle retainer clips.  With upper and lower A arms there is minimal lateral movement.

Udo
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Offline manta22

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Re: Vette Diff
« Reply #12 on: June 21, 2011, 12:56:35 PM »
Hello Neil/Mag.....To allow for axle plunge just remove inner stub axle retainer clips.  With upper and lower A arms there is minimal lateral movement.

Udo

Thanks, Udo.

Regards, Neil  Tucson, AZ
Regards, Neil  Tucson, AZ

Offline Nexxussian

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Re: Vette Diff
« Reply #13 on: June 24, 2011, 11:43:25 PM »
Don, Ed, thank you.

I figured it would be something robust. :)
Just happy to be here. :-D

Erik