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Jim Smolka's Avatar
 
Join Date: Aug 1999
Location: Hickory NC USA
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Question Welding the rear Diff instead of Limited Slip

Is it possible to weld the rear differential on a 901 gear box so to make the tranny positive traction?

If so, how would it effect the handling (mostly for the track)?

I have read that the 917s had a locked diff.

Thanks
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'75 914-6 3.2 (Track Car)
'81 SC 3.6 (Beast)
'993 Cab (Almost Done Restoring)
Old 04-05-2002, 11:29 AM
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Jim, this can be done. The owner of the shop that I work part-time at has a 914-6 race car with a 2.8L. He welded the 901's diff last season. This car sees alot of PCA Club Racing and Drivers Ed's. So far no mechanical problems. It does not slip at all, so slow and tight turns are probably interesting, but it works on the track.

Ed
Old 04-05-2002, 11:55 AM
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Join Date: Mar 1999
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Sure.....weld up the spider gears.

Let's talk understeer.........but you've got the power to overcome
it......ala WOO (world of outlaws) sprinters Not so shiney for the street.

For some reason, my car spins both tires (stock trans, no LSD) under hard acceleration in a straight line. Dunno why, but I ain't complaining.
I can kick the rear out at will, when cornering....... I love playing with the waa waa pedal. Just wish I was better at controling it.
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Old 04-05-2002, 11:56 AM
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Welded spiders are okay until you have low speed corners such as the top of the hill at Willow Springs and then the car will push terribly since the inside wheel will do it's best to go exactly the same speed as the outside wheel! A second but little know factor is, if one of the axles breaks, the car will do a violent 90 degree turn with little or not chance of recovery and a violent crash usually results. Because of these factors, I have a Quaiff limited slip in my close ratio gear box and I am using a GT limited slip in the long gear box. Either will work well although they are both in the $1200 range. There is also one made by Chris Fisher at PowerHaus II in the midwest which is like the GT model I.E. a torque-bias type which is much better than the factory clutch type of limited slip. These limited slips are one of the few things that you can put on any race car and probably get you money back if you decide to get out of racing though! Good luck.
Old 04-05-2002, 01:47 PM
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I've been running a solid rear diff for 2 years and various people (through my local race shop) have done so for a much longer period......

The low speed push can be a) tuned out and b) counteracted with driving style.....

It works.... and some believe that in certain situations and corners it works better than the torque biasing..... however in other situations and corners it does not work as well........
Alot of pro - race set ups will use a clutch pack, limited slip set to 90% or more

bad= on a wet or sandy track......

Of course if I had the money I'd build a 2nd box with a gt diff.... but on my budget its not a bad way to go.
brant
Old 04-05-2002, 02:49 PM
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Jim if you do decide to weld it make sure you fill in the gaps between the teeth with grade 5 or 8 bar stock (or cut off bolt shoulders) so that the weld isn't trying to fill in the entire space. Seems to be more reliable this way. On the tracks in the Southeast (very open except for Carolina) a locked diff has worked well and the car can be tuned to work with it. Don't even think of driving on the street as it will drag the inside wheel all the time (characterized by a chirp, chirp, chirp... as you go around the corner).
Old 04-05-2002, 05:47 PM
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We run a welded rear diff and intermediate torsion (front diff is open) on our Audi S4. This setup has been run for the last 2 seasons in Grand-Am Cup and going on its third with no problems. The only real complaint is pushing the car, don't even think about trying make a turn unless you have at least 4 people helping you.

AV WINANS
Old 04-06-2002, 07:06 AM
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Try This

Jim a old Circle track Racers trick was to melt down some old tire weights. (remove the steel clips that mount them when its hot) seal up the diff with some roof flashing and hose clamps. Leave a hole at the top. And pour the molten lead inside. After it cools remove the flashing and You have a locked diff that can be returned to stock anytime with a little heat. This method has the advantage of giving if a real shock load is applied. And if the lead gets loose in the diff it won't really hurt anything.
Old 04-06-2002, 08:02 PM
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