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Old 07-20-2015, 03:44 PM   #1
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Default Open diff issues on right hand turns

<p>Hey guys, drove our&nbsp;open diff&nbsp;SC300&nbsp;this weekend. &nbsp;We are getting an awful amount of wheel spin on right hand turns, and absolutely no wheel spin&nbsp;for left hand turns. &nbsp;It doesn't seem like a traciton issue either as maybe once did I get power-on oversteer during a right hand turn and that one required a passenger in the car. &nbsp;The car isn't a miata , but the amount of knowledge from PT racing here is always helpful. &nbsp;We are running rebuilt bilsteins with decently stiff springs all around. &nbsp;Car weight needs some updating, but before some recent changes it was 3200 lbs w/ driver + gas and 52% left, 50% cross weight (LF/RR). &nbsp;So far, adding a passenger helps, but doesn't necessarily fix the issue completely (or move it to the left side for example).</p><p>I am thinking we have a deficiency somewhere in our setup. &nbsp;I was thinking either weight distribution related&nbsp;or possibly spring related.</p><p>-Difference in ride height from RR and RL? or&nbsp;If the RL has more travel (spring/perch are higher)&nbsp;or a softer spring? &nbsp;So in that case, should we limit travel on the left or increase it on the RR?</p><p>-Since our left side is heavier, the ultimate weight transfer under load is not enough break traction on left turns, but for right turns is bad enough? So in that case we need to get to 50/50 static L/R weight?</p><p>-is it possible an issue with the diff or CV joints could be causing something like this?</p><p>&nbsp;</p><p>Any other ideas/suggestions for dealing with an open diff? &nbsp;Since this is mostly planning to be a chumpcar, we can't swap in an&nbsp;LSD.</p>
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Old 07-20-2015, 08:29 PM   #2
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swaybar preload and/or binding?
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Old 07-20-2015, 11:41 PM   #3
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<p>sway bars are oem (including the endlinks). &nbsp;might be right though...since our ride height isn't identical left/right. &nbsp;<br /><br />Other suggestions?</p>
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Old 07-21-2015, 12:37 PM   #4
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It's fine as-is? SC300 is too fast anywayz!


Sorry, I don't have any suggestions. Maybe PM one of the other SC300 teams on the CC forum? Or maybe Google the problem but in regards to Supras (though, I doubt many N/A open diff Supras were used as track cars...

Are you going to be at the 24 hour? I'm driving an e30 with team PBR. Leaving the Prelude home this time...
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Old 07-21-2015, 02:06 PM   #5
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Drag racers have fought this for years (if it is the same issue). Depending upon direction of rotation of the engine and driveshaft, the car will twist when torque applied to the drifeshaft. This will load the rear tires unevenly allowing one to spin more readily.

Another contributing scenario may be that the additional driver's weight on the outside of the turn is rolling the body enough that there isn't enough droop on the inside to maintain traction.
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Old 07-21-2015, 03:05 PM   #6
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<p>
Quote:
Originally Posted by Efini~FC3S View Post
It's fine as-is? SC300 is too fast anywayz! Sorry, I don't have any suggestions. Maybe PM one of the other SC300 teams on the CC forum? Or maybe Google the problem but in regards to Supras (though, I doubt many N/A open diff Supras were used as track cars... Are you going to be at the 24 hour? I'm driving an e30 with team PBR. Leaving the Prelude home this time...
</p><p>I have an offer currently to drive a miata as part of a 5 man team. &nbsp;I am interested and the price is right, but really I am more focused on testing the SC and getting us to the december race. &nbsp;we are close enough, but money is going to be tight as we have another 2-3 test weekends coming up.</p>
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Old 07-21-2015, 04:13 PM   #7
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Less testing...more racing!


24 hour would be like the cheapest two day all you can run testing a person could want...well, maybe not cheapest.
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Old 07-21-2015, 06:49 PM   #8
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It's also the perfect opportunity to be the brakes for someone else 10 minutes into the race. :P
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Old 07-21-2015, 08:15 PM   #9
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Quote:
Originally Posted by Dunning Kruger Affect View Post
It's also the perfect opportunity to be the brakes for someone else 10 minutes into the race. :P
Yea...you take that risk anytime you drive onto a track.


Like when I had car to car contact during my first ever test weekend in my minty fresh ChumpLude...
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Old 07-21-2015, 08:24 PM   #10
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Quote:
Originally Posted by sixshooter View Post
Drag racers have fought this for years (if it is the same issue). Depending upon direction of rotation of the engine and driveshaft, the car will twist when torque applied to the drifeshaft. This will load the rear tires unevenly allowing one to spin more readily.

Another contributing scenario may be that the additional driver's weight on the outside of the turn is rolling the body enough that there isn't enough droop on the inside to maintain traction.
Thats solid axles. Surely an SC300 is irs?
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Old 07-21-2015, 09:45 PM   #11
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Yeah, the rear is fully independent.
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Old 07-21-2015, 10:03 PM   #12
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<p>
Quote:
Originally Posted by sixshooter View Post
Drag racers have fought this for years (if it is the same issue). Depending upon direction of rotation of the engine and driveshaft, the car will twist when torque applied to the drifeshaft. This will load the rear tires unevenly allowing one to spin more readily. Another contributing scenario may be that the additional driver's weight on the outside of the turn is rolling the body enough that there isn't enough droop on the inside to maintain traction.
</p><p>&nbsp;</p><p>I am not sure about the first part. &nbsp;Read some things on hot rod magizine with some google-foo, but I don't think its relevant to this case. &nbsp;But yea, the driver weight seems like a good first guess. &nbsp;Another theory I came out with today is the driver's side rear caliper dragging some. &nbsp;We are getting some noise from it, but the car doesn't seem to pull one direction or another so it seems unlikely. &nbsp;</p><p><br />
Quote:
Originally Posted by Efini~FC3S View Post
Less testing...more racing! 24 hour would be like the cheapest two day all you can run testing a person could want...well, maybe not cheapest.
</p><p>&nbsp;</p><p>Yea, we are trying. &nbsp;Our race options by the end of the year are pretty limited at this point. &nbsp;Dominion is not likely, so WRL is out. &nbsp;That leaves CMP with Lemons and VIR-N with chump. &nbsp;I would prefer North, but I think we are too antsy to wait that long. &nbsp;If we race in October with LeMons, we will only do one more test DE. &nbsp;If we wait till December, might as well get these guys some time in the car. &nbsp;We hashed over the 24 a lot and decided not to go for it at the 60 day deadline. &nbsp;I hope its great, lots of good teams out this year, but I hear Namco is not coming.</p>
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Old 07-21-2015, 10:31 PM   #13
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Try it without the rear sway bar connected. (Just unfasten one end of one link and zip-tie it out of the way).
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Old 07-22-2015, 12:19 AM   #14
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Quote:
Originally Posted by Seefo View Post
<p></p><p>&nbsp;</p><p>I am not sure about the first part. &nbsp;Read some things on hot rod magizine with some google-foo, but I don't think its relevant to this case. &nbsp;But yea, the driver weight seems like a good first guess. &nbsp;Another theory I came out with today is the driver's side rear caliper dragging some. &nbsp;We are getting some noise from it, but the car doesn't seem to pull one direction or another so it seems unlikely. &nbsp;</p><p><br /></p><p>&nbsp;</p><p>Yea, we are trying. &nbsp;Our race options by the end of the year are pretty limited at this point. &nbsp;Dominion is not likely, so WRL is out. &nbsp;That leaves CMP with Lemons and VIR-N with chump. &nbsp;I would prefer North, but I think we are too antsy to wait that long. &nbsp;If we race in October with LeMons, we will only do one more test DE. &nbsp;If we wait till December, might as well get these guys some time in the car. &nbsp;We hashed over the 24 a lot and decided not to go for it at the 60 day deadline. &nbsp;I hope its great, lots of good teams out this year, but I hear Namco is not coming.</p>

What about AMP the end of October? That is probably the next time the 3Bros Prelude will be out.

Sad to hear about NAMCO...
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Old 07-22-2015, 12:28 AM   #15
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<p>
Quote:
Originally Posted by Efini~FC3S View Post
What about AMP the end of October? That is probably the next time the 3Bros Prelude will be out. Sad to hear about NAMCO...
</p><p>&nbsp;</p><p>I can't tell from the schedule, are they opeing the track for testing on friday? &nbsp;AMP would be nice, may not be as crowded...</p>
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Old 07-22-2015, 08:36 AM   #16
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Default Open diff issues on right hand turns

To test the brake dragging, jack the rear and put it in gear while idling. Is there a big difference between sides?

And +1 on disconnecting the sway to test droop effect.
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Old 07-22-2015, 12:48 PM   #17
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So far the list of "free" things to do in order:

1. Check the current corner balance and move the weight by adjusting ride height
2. Swap the springs in the rear to try to put the softer spring on the passenger rear (where the spinning is occuring)
3. Adjust our non-adjustable endlinks (we can throw some 949 heim joints that I have laying around just to check it)
3.5 Disconnect RSB
4. Drill FSB for a stiffer rate (could cause awful understeer)
5. ???
6. Profit

I have access to getting Soarer parts, but we'd eat a bunch of points regardless of what the part was, though.

If anyone has insight for which side in the rear should get the stiffer/shorter spring, we're all ears.
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Old 07-22-2015, 01:29 PM   #18
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Could a control arm be binding and limiting inside droop? Have you compared the left/right droop?
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Old 07-22-2015, 02:02 PM   #19
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Default Open diff issues on right hand turns

Unless it's something flawed (binding or other crap) 50.0% cross might not be ideal on this track/car/driver/conditions.
Just try to see if you can move/reduce/correct the issue by playing with the perches (make a mark and count turns for simplicity).

But moving from garage perfection (eg 50.00 cross) to whatever the feeling/laptime tells you is a step.
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Old 07-22-2015, 09:09 PM   #20
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Adjusting perches?

Lolz
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