Rear wheel alignment?

toyota will replace the rear axle beam, and that's about it. i have yet to hear of a case where that solved the problem ultimately.

prior to that one guy coming in and demanding a free shim job from PC, i believe DH was the only tech who shimmed prius rear wheels. afterward, he was expressly forbidden from doing so.

we have intended to find a good material for quantity production and set up a shim shop, but things have been kinda hectic here lately.

 

Apparently most of you must have good alignment specialist. I purchased the Firestone lifetime alignment and at the time it seemed like a great idea. Unfortunately the firestone dealer here hasn’t anyone that can use the machine properly. Oh they call themselves specialist but over the last year I have had my Prius aligned 10 times, and the readouts very so much that it makes them useless. I may have better luck if, when traveling, I use another Firestone dealer. I ended up paying someone else to have the job done correctly.

Bob Wilson, this is why I never got back to you on the difference a .005 shim made.

 

<div class='quotetop'>QUOTE(grasshopper @ Sep 17 2007, 05:08 AM) [snapback]513610[/snapback]</div>

One of my complaints in the other thread is that I can't find a good alignment shop in my area. Most of the shops are Tire Shops that just happen to have alignment equipment on site. The dealer was worst of all; they actually made the front camber worse when they worked on it.

The biggest problem that I have had is that all the shops in my area are setup to give toe-in in fractional units (i.e. 1/16 inch) while the specification is stated in degrees (preferred) or decimal inches. Out of five shops that I visited, only one was able to give me the toe measurement in decimal inches. The techs don't seem to be able to change the software settings. Most of them said "Our machine only gives inches".

 

I just recently bought some AA-size shims from Aloma - I haven't actually installed them yet, but they seem to be of very good quality and look promising, although a tad expensive.

Perhaps someone can verify my math. Given that the distance between the bolts on the mounting plate is roughly 3 inches, and treating this side as the "adjacent" side of a right triangle and the shims (mounted on the leading two or trailing two bolts) to be the "opposite" side, my ancient trigonometry skills tell me that shim size = 3 tan x, where x is the angle of correction on the alignment. If this is correct, then here are some angles and their corresponding shim sizes, in inches:

angle shim size
0.05 0.0026
0.10 0.0052
0.15 0.0078
0.20 0.01047
0.25 0.0131
0.30 0.157



<div class='quotetop'>QUOTE(galaxee @ Sep 16 2007, 08:04 PM) [snapback]513431[/snapback]</div>

 

<div class='quotetop'>QUOTE(mini2prius @ Sep 17 2007, 03:44 PM) [snapback]513952[/snapback]</div>

Are your angles in radians or degrees?

You are in the ballpark based on the thickness that I used. I needed to correct from .40° to ~ .15°and used a shim thickness of .016.

Shape of the shim may affect the angle somewhat, so I don't know if your formula can be exact unless you look at exactly where the backing plate contacts the axle mounting flange.

 

Heh. You can't measure an *angle* in *inches* without some
surrounding context. Is that delta inches between front and back
of the wheels, or away from absolute? Is the measurement taken at
the edge of the rim, the tire sidewall, the wheel centerline, what?
Anyone who went to tell me I was out of alignment by so many
sixteenths of an inch would immediately be asked "between where
and where" ...
.
_H*

 

<div class='quotetop'>QUOTE(hobbit @ Sep 17 2007, 06:24 PM) [snapback]514031[/snapback]</div>

One guy at a local shop (recommended to me by an auto body shop) said to me: "I've been a mechanic for 27 years and I have never heard of toe-in measured in anything but inches". I just thanked him for his time and left.

The service manual gives the preferred measurement in degrees, but also gives an alternate spec which is the difference between the front tread of the tire and rear tread of the tire.

[attachmentid=11511]

However, the actual measurement is made by attaching (4) targets to the wheel rims and then the data is calculated by the computer. So, what the computer is calculating is the relative angle between the targets and then converting that to inches for the printout.

I wish I had their equipment so I could measure myself and leave them out of it.

 

Okay, at some consistent feature of the tread. You might be able
to sleaze this with a tape measure and a couple of people at home...
.
_H*

 

Angles are shown in degrees, which is also the units shown on my alignment readout.

I'm sure you're right about the shim shape - just trying to get close with the math. With the shims I bought, I should be able to do just about any adjustment in 0.001 on an inch increments.

<div class='quotetop'>QUOTE(dogfriend @ Sep 17 2007, 07:08 PM) [snapback]513965[/snapback]</div>

 

<div class='quotetop'>QUOTE(hobbit @ Sep 17 2007, 10:19 PM) [snapback]514062[/snapback]</div>

there's also a home-version of the alignment, but the accuracy leaves much to be desired. DH did a quick attempt at minimizing differences in the LH and RH front tires when replacing the rack in the es250, and there were still some major adjustments required. because you can't get more precise than with good equipment.

 

The practical problem in doing a home measurement of the toe-in is that there is a bunch of stuff (like the car body) in the way where you need to do the measurements.

Camber, on the other hand, can actually be measured at home because the reference is vertical. In fact, I am going to measure the front camber one more time at home with a digital level (and a jig that I need to fab) and then take it in one more time to get the front toe checked and/or adjusted.

 

I think that last number should have been 0.0157, correct?

- Dean

...
angle shim size
0.05 0.0026
0.10 0.0052
0.15 0.0078
0.20 0.01047
0.25 0.0131
0.30 0.157

 

I have not visited this site in awhile and came in search of the latest in alignment "thinking" for the Prius. I was one of the original "critics" of the Prius road manners, especially on the deep road grooves we have here in SoCal. Twitchy doesn't really do it justice. I invested many hrs in seeking out alignments that would help but never really solved or found "the problem" that Toyota deemed "normal". It's probably the most "unloved" car I've even owned when it comes to this characteristic. I recently managed to make it worse with the Falkon 912 tires I put on it to replace the Hydroedge tires I had. I even managed to screw up the gas mileage by about 10% with the 195x60 size and these tires so I'm looking for some fixes.

This thread about rear alignment has me interested in what I can do, besides tires, to improve my unloved Prius. I'm currently running maximum toe-in on the front of 0.10 and 0.09 deg left and right. The back is 0.16 and 0.21 deg left and right, which probably isn't all that bad. I have read where tramlining is affect also by too much neg camber. Mine is about -0.7 deg on the left and right front. So maybe something lower might help

I did some experimenting with adding the rubber wedges to my suspension and that reduced the tendency for the car to sway or roll at speed. That did help as did tire pressures closer to what Toyota recommends (36,34). Sure it hurt gas mileage but the constant corrections on the freeway were sometimes (and are once again) very scary. Since then taken the rubber wedges out and that combined with these new tires has me looking for the cure again. I know not all Prius handle like this because back in 2004 I tried to drive as many others as I could and I didn't find one this bad. But I could not convince Toyota that there was an issue.

I would probably be in the market for a 2010 except for the fear that I'd get another ill handling car that I would hate. I'm going to Vegas next month and I'm going to have to take a big loss on these tires before I go, they're that bad. Any suggested fixes or tires would be appreciated. Thanks.

 

I had great success with a product called E-Z Shim from Specialty Products Co. (800 525-6505 or spcalignment.com).

This product is a pair of segmented plastic wheels, joined in the center. The numbered triangular segments vary in thickness. An accompanying chart lets you select the amount of camber and toe to be corrected, in the range of plus or minus 1.5 degrees (also listed in inches). You simply rotate one wheel to select the pair of numbers shown on the chart, cut out 4 segments with a box knife or similar tool to match the bolt holes in the rear hub, and insert the shim between the hub and the axle.

All you need is the computer printout from the alignment shop (showing the specified range for each adjustment and the “as is†condition for your Prius.

Like many others, my Gen 2 suffered from poor tracking on the highway, especially in crosswinds. My alignment printout showed one rear wheel out of spec. for camber and toe. When I mentioned the out-of-spec values to Toyota customer service, they accused me of having collision damage and said replacement of the axle was the only remedy.

I installed the E-Z Shim (# 75800) myself and noticed an immediate improvement in tracking stability – no more wandering and constant correction. I had previously told the alignment shop to set both front wheels to .05 degrees of toe-in (as recommended in other posts here) which helped some, but with this rear wheel correction, the Prius tracks (almost) like all the other cars I’ve owned.

The amazing thing is that the E-Z Shim cost less than $9.00 at a local tire supply store. It’s about double that directly from Specialty Products. Imagine the cost of a new axle and installation at a dealer!!!

Indy John

 

Thank you for providing that information. The price is right, but how is the durability? You mentioned plastic parts?

http://spcalignment.com/PROD_DIR/SPC_PROD_SEARCH_DYN.cfm?cmd=Cam&cmd2=75800(1)&cmd3=

I guess for the price, one can throw it away every 2-3 years if need be

 

DH is not a fan of EZ shim. having one of those and an alignment machine to play around with, he was not pleased with the accuracy (more to point: lack thereof) of the correction, and the fact that it's really damn thick.

 

So not that great of a fix. Too bad a company can't offer high quality metal shim kits for the Prius. I know the impossible to align "Twin I Beam" Ford Truck front end (Another better idea from Ford!) has a wide assortment of weird little eccentrics, half moons, and other shimmies

 

I've been shimming rear solid beam axles for over twenty years. Currently I have been using MOOG plastic shims. They seem durable enough in that I have regular customers that I have shimmed in the past and their alignments have held.
Be aware, if you are installing a shim at home using the printout from the alignment shop you will be changing the thrust angle and your steering wheel may not be centered when you are done. Be sure to use a torque wrench when you tighten the axle stub bolts. The plastic shims will distort with too much torque.

Rod