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Old 12-12-2018, 02:13 AM   #1
DrZiplok
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Default [240] Right rear spins turning right, left rear does not spin turning left. Wut?

Subject pretty much says it all. 240 wagon, lowered, spherical everything in the back, no rear sway, 1" front sway, 245s all around, Truetrac. Car sits level left-to-right, no funny business with spring heights, etc.

Left turns are golden, hook up and go. Right turns and it's a one-tire fire. Why?

Haven't moved the chassis-side panhard bar pivot point, so it's probably lower than it 'should' be, but apart from that, nothing seems asymmetrical left vs. right.

Any ideas?

(FWIW: Randy Pobst said his 740 does the same thing, and he weighs next to nothing, so probably not driver weight...)
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Old 12-12-2018, 02:29 AM   #2
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Panhard bar mounts on the right side of the axle.
Maybe that has something to do with it...
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Old 12-12-2018, 03:12 AM   #3
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It has to do with the direction of drive shaft rotation and placement of the ring gear relative to the pinion gear. The transfer of power through the pinion gear is creating a moment acting in the rear axle. Traveling forward is going to load the left rear tire. Going backwards unloads it.
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Old 12-12-2018, 03:36 AM   #4
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Old truetrac without preload?
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Old 12-12-2018, 04:43 AM   #5
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Quote:
Originally Posted by eabras View Post
Old truetrac without preload?
Recent TrueTrac, high preload version.
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Old 12-12-2018, 08:44 AM   #6
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Get the corner weights checked.
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Old 12-12-2018, 12:59 PM   #7
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You can blame the panhard rod for the difference between left turns and right turns.

What spring rate up front? What spring rate in the rear? What is spherical everything, front bushing and rear bushing of the trailing arm? torque rods? panhard bar? Shock mounts?

What kind of corners does it lose grip, tight corners steady state, tight corners with sudden turn-in, fast sweepers steady state, or fast sweepers sudden turn-in?

How much power/torque?

In my experience it's pretty easy to get a 240 to hook up around a road course, as the corners tend to be rather large radius compared with autocross. I had trouble with inside wheel spin during autocross...so I went a bit nuts with lowering the rear even more and adding a tender spring on a main spring to make sure the inside tire wasn't hiking because of short springs unseating. It got better, but I still need to do more. Nice thing about a clutch diff is that I can increase the breakaway torque and hopefully keep the inside tire from spinning. But the closer it gets to a locked diff, the more understeer it will induce, so I don't want to over do it.

With the truetrac, I think you can make some adjustments to help the situation, but it may not be solved without a watts link or perhaps some panhard rod adjustments. Reducing front roll can help keep the rear planted, so roll correction spacers and/or stiffer front springs may help.
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Old 12-12-2018, 02:47 PM   #8
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Its the panhard bar and the fact that its mounted on that side of axle. If you reversed it, it would do the same on the opposite side.

Sphericals and good geometry help prevent that from happening but at some point the jacking effect you get from the panhard bar will be an issue.

Tweaking the height and the angle of the panhard bar mounts can help alleviate this.
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Old 12-12-2018, 03:15 PM   #9
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I really should have a build sheet, so that my lazy descriptions don't force folks to ask all these questions - sorry!

Quote:
Originally Posted by towerymt View Post
What spring rate up front? What spring rate in the rear? What is spherical everything, front bushing and rear bushing of the trailing arm? torque rods? panhard bar? Shock mounts?
Springs are cut IPDs all around (drop is ~2"), shocks are Koni SAs. Trailing arm fronts are still poly, trailing arm rears, torque rods and panhard are all spherical.

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What kind of corners does it lose grip, tight corners steady state, tight corners with sudden turn-in, fast sweepers steady state, or fast sweepers sudden turn-in?
Almost all of them. If you are power on and the wheel is over to the right, the right rear will spin up. You run on the east coast, so examples may not help, but if you are familiar with Sonoma, 2, 4, 5, 7/7a, 10, 11 are all problem areas. If you know Buttonwillow, the car will light up the right rear at 80+ going around Riverside (and most other power-on right handers).

The previous chassis did the same thing, so it's not peculiar to a specific body, but more likely the way we have it set up.

Quote:
How much power/torque?
A generous estimate would be 200-ish on both scales. Possibly less; it's a fairly well-used M52b28.

Quote:
In my experience it's pretty easy to get a 240 to hook up around a road course, as the corners tend to be rather large radius compared with autocross. I had trouble with inside wheel spin during autocross...so I went a bit nuts with lowering the rear even more and adding a tender spring on a main spring to make sure the inside tire wasn't hiking because of short springs unseating. It got better, but I still need to do more. Nice thing about a clutch diff is that I can increase the breakaway torque and hopefully keep the inside tire from spinning. But the closer it gets to a locked diff, the more understeer it will induce, so I don't want to over do it.
I need to go stalk your threads again, it's been a few years. Which clutch diff did you end up with? We've gone through most of the other options at this point, with poor results.

Quote:
Reducing front roll can help keep the rear planted, so roll correction spacers and/or stiffer front springs may help.
More front spring is on the cards, but we didn't like it when it was pushy, so there's probably a limit there...

Thanks for your thoughts.
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Old 12-12-2018, 04:48 PM   #10
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Sounds like power is being applied too quickly with the Truetrac. If you feed it power modestly, it'll hook. If you mash it, you can get it to spin. I'm not saying that's you're problem exclusively, but I bet it'll help.
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Old 12-12-2018, 04:56 PM   #11
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Quote:
Originally Posted by shoestring View Post
Sounds like power is being applied too quickly with the Truetrac. If you feed it power modestly, it'll hook. If you mash it, you can get it to spin. I'm not saying that's you're problem exclusively, but I bet it'll help.
Sorry, no. It doesn't matter how gentle you are, the only way to get it to hook up is to drop the wheel by squaring or segmenting the corner.
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Old 12-12-2018, 04:59 PM   #12
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Roll correction spacers also help keep the rear planted.
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Old 12-12-2018, 05:02 PM   #13
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Quote:
Originally Posted by DrZiplok View Post
Sorry, no. It doesn't matter how gentle you are, the only way to get it to hook up is to drop the wheel by squaring or segmenting the corner.
Have you tried a bit of left foot braking mid-corner to see if you can apply a bit of braking resistance to tire that wants to spin?
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Old 12-12-2018, 05:49 PM   #14
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Is it broken? This just doesn't seem right. I've got experience with these and find they work well.
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Old 12-12-2018, 06:17 PM   #15
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Quote:
Originally Posted by DrZiplok View Post
You run on the east coast, so examples may not help, but if you are familiar with Sonoma, 2, 4, 5, 7/7a, 10, 11 are all problem areas. If you know Buttonwillow, the car will light up the right rear at 80+ going around Riverside (and most other power-on right handers).

A generous estimate would be 200-ish on both scales. Possibly less; it's a fairly well-used M52b28.
Bernal dad?

I don't know Sonoma but did get to run it once in 2011. yeah...you've got a lot of flat right hand corners that aren't really high speed corners. You want to be able to mash the gas and not think too much.

I use a dana powrlok in my autocross car, but it's not known to be a robust diff. I'm not sure I'd want to run one in lemons. If I used a clutch diff, I'd want to add a diff cooler too. Track down some bimmer guys and see what works for them...I've never studied the homemade diff coolers up close. The issue with the powrlok diffs (besides being uncommon) is the cross shafts break. The side gears are small, too. When the cross shaft(s) break, the gears get chewed up. Here are pics of a broken one I bought just for the '87+ case with tone ring.

http://www.pbase.com/towerymt/1030&page=all

In lemons...
We tried a modified G80 from a 940. I cut down the fly weight so it would engage above 20mph. What we didn't do was weld the weight/rod in place, so it must have flung apart somehow and got consumed inside the diff. Only symptom was 1-wheel-drive (obvious change during a race) and it dinged up the ring & pinion. Replaced the axle with...

...a welded diff. I was against it in principle, but I didn't have a better option for a reasonable price. 2-wheel-drive ALL the time with the welded. Pushes a little in steady state, can be especially noticeable in flat/off camber corners. But it makes the car easy to drive for every skill level. We were probably making 200whp at most and with 225s on 9.5", the rear always hooked.

We were using 700lb front springs at one point, but then dropped back to 475lb. I'd aim for somewhere in between. IPD lowering springs are way too soft.

We had revalved bilstein inserts that I had previously had valved for the 475s on my autocross car (as I upgraded the autocross car, the take-offs went on the lemons car). They were just adequate on road courses since they're mostly smooth. I believe the valving was 220/110 on the struts. More specs here: http://www.240turbo.com/specsheet245.html#bilsteins

We had cut wagon overload springs on the rear, so probably not more than ~150lb. R-sport stiff rear shocks (p/n552198, 400/100nm), 25mm front bar, no rear bar. All poly rear bushings, but with the welded diff it doesn't really matter if you hike a wheel a little. Worst case, it can help the car rotate.

The game changer on the front end is the ball joint spacers that moves the bottom of the control arm out about 1-1.5" and got us about -3 to -3.5 deg camber.

http://www.pbase.com/towerymt/image/160231674.jpg
http://www.pbase.com/towerymt/image/160231672.jpg


Triple the front spring rate, confirm (or get) -3 deg camber at least, raise the front an inch, try lowering the rear if you can, and then play with panhard rod mounts & height.
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Old 12-12-2018, 07:34 PM   #16
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Something wrong with that Truetrac if it does that. I've never spun one tire. I suspect mine is a higher preload version but an older model, it's been in use so long.

You might have too soft front springs and it lifts the rear corner. My 245 is way heavier than stock and has 600lbs front coils(had 500lbs) and cut lowering springs rear. Adjustable shocks all round. Rear springs might even be from a sedan because I had them in 242 years ago. Previously had 500lbs front springs but they were a bit soft considering the weight and what I liked it to be. Wasn't an issue really and it's still also a street car.

Had 24mm front and 19mm rear and changed to IPD 25/22mm sways because of too much body roll(and it's "too low"). Later on Kaplhenke Quicksteer Roll correction parts have helped with that too. Front control arms, panhard and rear upper control arms have poly, lower control arm rear bushing is NOS with poly inserts and front bushing is stock.

Lack of grip while accelerating in a corner hasn't been an issue on track with good 225/45/17 street tires. On the other hand Nankang NS-2R semislicks have been lousy :P
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Old 12-12-2018, 07:52 PM   #17
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It also has to do worth the torque reaction of the engine all rear drive cars burned out when turning right the way the engine turns tried to smash the drivers side rear down and pick up the passenger side
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Old 12-13-2018, 12:48 AM   #18
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Quote:
Originally Posted by blkaplan View Post
Its the panhard bar and the fact that its mounted on that side of axle. If you reversed it, it would do the same on the opposite side.

Sphericals and good geometry help prevent that from happening but at some point the jacking effect you get from the panhard bar will be an issue.

Tweaking the height and the angle of the panhard bar mounts can help alleviate this.
I'm all ears on the tweaking side; have not been able to find a lot of guidance that isn't for circle track or R/C cars.

Right now the bar is dead nuts level (12" off the deck on either side) with the car at rest. Obviously if it squats under acceleration, the right side will rise and I could see that jacking the RH end.

I did a lot of searching but haven't found much; it *looks* like we could drill another hole in the body-side mount and shift the pivot up maybe 3/4". Just a little bit wary since there's a ton of load on this when cornering...
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Old 12-13-2018, 01:01 AM   #19
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Quote:
Originally Posted by towerymt View Post
Bernal dad?
Busted. 8)

Quote:
The game changer on the front end is the ball joint spacers that moves the bottom of the control arm out about 1-1.5" and got us about -3 to -3.5 deg camber.
Thanks for the data & suggestions. We have tried the welded rear end, loved the traction, did not like the grenade aspect. Looking for someone to make a spool, but probably not going to be cost-effective.

I fab'ed some LCA extensions (posted pics a while back) and yes, -3 degrees at the front makes a world of difference for turn-in and mid-corner balance. Can't recommend highly enough.


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Old 12-13-2018, 01:10 AM   #20
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Originally Posted by shoestring View Post
Is it broken? This just doesn't seem right. I've got experience with these and find they work well.
The Truetrac? If it is, then we've bought several busted ones, because they all do it.
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Old 12-13-2018, 01:49 AM   #21
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Originally Posted by Lankku View Post
Something wrong with that Truetrac if it does that. I've never spun one tire. I suspect mine is a higher preload version but an older model, it's been in use so long.
I don't want to discredit your experience, but we've had several, and even on the original car with a succession of B230F's we'd lift the RR and it'd spin up.

Quote:
You might have too soft front springs and it lifts the rear corner.
Certainly possible, our setup is currently very soft.

Quote:
Lack of grip while accelerating in a corner hasn't been an issue on track with good 225/45/17 street tires. On the other hand Nankang NS-2R semislicks have been lousy :P
We run 245 Direzza ZIIIs all 'round, traction's not a problem as long as we can get weight on the ground.

Here's some video of someone that knows what they're doing punting the car at Thunderhill last weekend, so you don't think it's just because we're a bunch of scrubs: https://www.youtube.com/watch?v=SvF7IwiQQ2Q
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Old 12-13-2018, 05:32 AM   #22
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Quote:
Originally Posted by DrZiplok View Post
I don't want to discredit your experience, but we've had several, and even on the original car with a succession of B230F's we'd lift the RR and it'd spin up.

Certainly possible, our setup is currently very soft.
I thought it was with all wheels well on the ground. Then it spins just because the wheel doesn't have enough weight on it. Too much weight transfer. And the mentioned torque reaction affects that corner too.
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Old 12-13-2018, 10:23 AM   #23
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It is probably a combination of some/all of the above.

I mentioned corner weights because it's something measurable, not because it's the only answer.
If the panhard is flat, it is less likely to be the big culprit, as compared to the torque of the driveshaft coupled with the soft rear springs (proven over and over again by 16 year-olds everywhere).
But the stiffer the overall set-up, the more corner weight problems matter.

Circle track guys can teach you a lot, but you have to remember they are often TRYING to get an imbalance.

Last edited by mikep; 12-13-2018 at 10:28 AM..
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Old 12-13-2018, 02:34 PM   #24
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Our car is just on cut factory springs with cheap KYB replacement shocks, hardly stiff. Slightly modified B230F. I would say that maybe the additional torque of the M52 is the difference, but you said the B230s you've had did it too. I don't know. Watching the vid you posted I only heard it light the tires in one spot, right crest over hill.

I agree with the rock and a hard place when you add front roll stiffness to keep weight on the inside rear tire.

Maybe rr shocks with more compression and less rebound? Again, I don't know. If you figure it out, I'm interested.
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Old 12-13-2018, 03:20 PM   #25
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Quote:
Originally Posted by shoestring View Post
Watching the vid you posted I only heard it light the tires in one spot, right crest over hill.
It happens in T3 at about 30s into the video, on the downhill coming out of the Cyclone starting at 45s, over on the west side at 1m46, and again at 2m27, over the connector at 2m41, and then a big serve in T14/15 at 3m13 or so.

We'll definitely be trying some of the suggestions folks have made here, and I'll update the thread if we sort anything out.
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