Please help; Car darts to the right when the throttle is closed?

[10 10 Flyin]

Guys - Just got my mark 3.1 together and on the road (still need to register). Here is some information on a driveability issue I am facing.

Setup:
mark 3.1,
Rear - 3 link with koni coil overs
front - FFR tubular upper and lower control arms with koni coil over
Power steering with rack extenders and offset bushings
275/40 17 front and 315/35 17 rear
Aligbnment specs: .5 caster, 4.4 camber, .07 toe in (approximately 1/16")

Symptom: when you close the throttle (let off the gas) the car darts to the right slightly. If your cruising along steady state and let off the gas you notice it slightly. When running through the gears on a full throttle run you notice it pretty significantly every time you let off the gas to shift.

Any suggestions? Could it be pinion angle or just maybe the positioning of panhard bar on the rear?

Thanks,
Jeff

[Jeff Kleiner]

Aligbnment specs: .5 caster, 4.4 camber, .07 toe in (approximately 1/16")



I think you have your caster and camber numbers transposed.

Assuming you have checked tire pressures and have assured that the rear end is centered the first thing that comes to mind is that your corner weights are off. I doubt you have the ability to actually weigh the corners but if your ride height is set take a look at the spring adjusters; they should show virtually the same amount of threads side to side (not necessarily front to rear). What you don't want to see is diagonal corners differing greatly from the other side---for example the LF and RR are cranked tighter than their partner on the other side of the car. This indicates that the car is "cross jacked" and will cause unstable behavior, particularly under braking.

With power steering you can go up even further with caster which will help with straight line stability. If you do please read THIS (http://www.ffcars.com/forums/17-factory-five-roadsters/244160-lots-caster-warning.html) as you will probably need to use a longer link on the forward leg of the UCA.

Good luck,
Jeff

[seagull81]

Double check your tierod ends and make sure they have seated and are tight. Just because the nut got tight doesn't always mean it bottomed out first. Also the ball joints on the A-frames, as well. Some of those have been know to come thru too far and the nut bottoms out on the shaft before contacting the spindle. Make sure all the A-frame mount bolts on the A-arms are tight.

[Bob Cowan]

Something like that is usually caused by a problem with the rear end. Make sure everything is tight, and make sure the differential is centered and squared.

[10 10 Flyin]

Thanks guy. Jeff your are correct. My castor/camber #'s are transposed. The reason I stopped at 4.4 on the castor was because that was as far as I was comfortable with the current front links.

Are there any tips to center the rear end - I.e. Good points to measure against?

I did verify tire pressures. Will double check balljoints/a arms joints and try to get some rough corner weights to make sure nothing is way out of whack. Thanks for the help!

[Bob Cowan]

Are there any tips to center the rear end - I.e. Good points to measure against?



This is where high school geomtry comes in hand. You'll need a plumb bob, some masking tape, a pencil, a tape measure, and an extra person.

Hang the plumb bob off the ends of the axles at their centers. Put some masking tape on the floor, and make a pencil mark. Hang the plumb bob over the round frame rails, in the center of the A-arm tabs. Put masking tap ion the floor, and make pencil marks there, too.

Now measure from axle point to the front frame point on the opposite side. Make an X. Those two measurements should be very close to the same. In theory, they should be exactly the same; in practice they should be very close. If they're not, the axle is not straight.

[CraigS]

I have that problem about twice a year.Cause is that the FFR adapters that bolt to bottom of the rear axle ( for the LCA's to attach to) get a little loose.So the axle moves forward on accel and rearward on decel. For whatever reason one side always gets a little looser than the other so the rear axle steers the car. I tighten them w/ a 2.5 foot bar. I keep meaning to get better bolts so the solid shank is doing the locating.I think my current bolts have thread the full length so they are sloppy in the holes. HTH

[AC Bill]

I have that problem about twice a year.Cause is that the FFR adapters that bolt to bottom of the rear axle ( for the LCA's to attach to) get a little loose.

Huh? Never heard of that happening before..Did you use the FFR provide bolts and nuts on them? I thought FFR provided nylok nuts? If they are backing off, perhaps just change to new nuts, as those kind of nuts can't be tightened/untightend, over and over again. As well, I would think torquing on them hard with a lever bar, could render them useless.

Perhaps stover nuts would be the best, along with a little locktite..

I measured my 3 link set up simply using a tape measure, from off a point on the frame, over to the inside wheel rim. Adjusted the panhard bar till both sides were the same. I had it checked at the alignment shop, and it was almost dead on, with only a fractional adjustment required.

[Roy Hewson]

I had the exact same problem on my coupe after we had messed with the alignment. I went back to my old number ----all is well in coupdom
Roy

[CraigS]

Bill-agreed that I need better bolts/nuts and they are on the list. I think the main cause is all the autocross starts on R compound tires.Not quite drag radials but much better than street tires.