Fellow geniuses,

my '15 E350 RWD has been aligned, new tires and balance, every tire tried on a different location, and varying air pressure, and I still can't dial out a slight right drift. Not a pull, just a drift regardless of road crown, Certainly it does it more when there is more crown.

The alignment is perfect.

The caster is +6.9 both sides, and of course is not adjustable. Using the axiom of positive caster pulls, I would love to either increase the left side about .3, or reduce the right side .3 using a single caster adjustment bolt like the #28815 from SPC products.
The part is practically free, and I have a lift, handbook of cusswords, and holy water.

Any feedback or practical advice?

 

Have you considered that American roads have pitch to the right for water drainage? Maybe it’s not the car but the road? Sounds like you you have detailed info on your alignment so maybe it’s worth considering.

 

Find empty road..

Drive one way in a lane..
Then reverse direction and drive back in same lane..

Hence make sure empty...

 

I think OP is well aware of road crown effects, and has experimented with several roads. I think he simply wants to know how to adjust a supposedly unadjustable caster.

As I understand standard practice, RWD cars should have a miniscule amount of right drift (on American roads) to protect from drifting into oncoming traffic. My car has this, meaning I can take my hands off the wheel on a flat road and it will start to drift right in 8-10 seconds (but not before). Works fine for me.

I've owned FWD cars that would track within a lane for 1/2 mile or more. I sometimes miss my FWD cars... but only sometimes.

 

mine goes straight as arrow on pretty much all good roads..

 

It must be a significant pull to be annoying. I’ve never owned a car that had a significant right pull ever.

 

I have owned at least 100 cars. Certainly enough to know what is normal, and what could be better.

I am wondering if I install the caster bolt, which is $15 shipped, 20 minutes to install, and it corrects .3 of a degree, should I add caster to the left side, to pull it left in a miniscule fashion, or subtract from the right, which still makes the left side .3 proud of the right and would seemingly add a tick of left correction?

I have been driving down many a road lately on the wrong side of the road, trying the opposite crown, and it still likes to go right.

 

Believe me, I stay up at night wondering if it is my imagination or just road crown.

 

Do you have any autocross or SCCA race drivers nearby? They may know which makes more sense, and/or they may know alignment shops that could possibly help.

Many years ago I took my autocross car to a highly-regarded local alignment shop. I gave the tech my car, and my written alignment specs, which were far from stock. He looked at the specs, asked basically "Are you nuts?" I politely asked him to simply dial it in, then take a test drive. A short while later I heard my car leave the shop (open headers are hard to miss) and take a tour of the local downtown area. I heard his speeds increase and I heard some aggressive downshifting and cornering. He came back with a mammoth smile on his face, and his immediate comments were "NOW I see what you want! Let's make a little tweak here, and here, and. . . " My point is that a really good alignment tech can make all the difference in the world.

Maybe the road racer guys know him. . .

 

I worked for a Nascar team until we sold it last November. We have alignment methods that shops have never even thought of, because we had to dial in for short track, super speedway, 1.5 mile, triangle tracks at Pocono. The shop is still there with most of the machines. My issue is much more simple, thankfully

So, having never looked at another E350 to see what their caster is, I have 6.9. Feel free to chime in with yours, I would love to see the comparison.

Should I install a bolt that gives me .3 degrees on the left, to have 7.2 positive left, 6.9 right, or install one corrective bolt on the right in the minus position, to give me 6.6 right, 6.9 left? I want positive caster on the left, just don't know how middle of the road the current 6.9 for both sides is.

 

Here is my final solution, he says as a response to his own post.

I had the proper staggered caster backwards in my head. The car always pulls towards the side with the lowest positive caster. I had +6.9 on both sides, US car, so crown sloping downward towards the right. car drifting to the right.

You want about .5 degrees less positive caster to the uphill or road center direction.

I ordered 2 Mercedes part number 000 333 1071 for my 2015 W212 car (or SPC #28815), older cars may use 000 333 0018. These can be used to change camber if used in the rear holes of the lower control arm, or caster if used in the forward most lower control arm.

This was super easy. I have a lift, and I know that is cheating, but you don't need one. You can change camber or caster up to .3 either direction, depending on which way you move the attachment arm, in or out for camber, backwards or forwards for caster.

Once the tire was off, and you don't have to but it makes visualizing better, remove the lower plastic front cover to change caster, no need to remove for only changing camber.

Installing the adjustment bolts took 10 minutes or less per side. There was no grunting or knuckle busting. Mark the direction you want the adjuster bolt with a sharpie, because it is dark and scary under there, and they move when you are tightening them. Lower your jack onto some wood blocks under the tire to put weight on the bolts when tightening, because you want them at ride height.
You need a 21 mm combo wrench, and a big female torx, a 60, I think, but you could survive with vice grips if you had to, because you are just holding it in place. I know, blasphemous.

You can just change one side to tweak things, not an absolute requirement to put bolts on each side, only if needed.

The car drove like a dream on the way to the alignment shop, and it confirmed my installation was accurate. Now 7.2 caster right, 6.6 left. The right camber went more vertical an exact amount of the caster change from installing caster adjustment bolts, from -.5 to -.2.

The alignment guy just has to adjust the left tie rod about 1/16 of a degree, and he didn't charge me.

This has been keeping me up nights with this alignment drift, and for the parts price of $17 total for both bolts shipped to the house, I feel victorious.

 

Good result. I'm sure others will now do what you have, so kudos on the instructions. Now get some sleep.

BTW, they make pills for OCD....