Rear Alignment Shim and Hub Bolt Torque

As all of you are probably aware, our Prii have a torsion beam rear suspension, which is basically a solid rear axle as it has no factory adjustments for toe or camber. The solution to the lack of adjustments is to install SPC ez-shims in order to obtain the necessary amount of camber or toe change.

In order to install the shims, you need to remove the rear hub assembly and the backing plate. Then, you install the shim, followed by reinstalling the backing plate and hub. Toyota’s factory service manual states that the correct torque for the 4 hub bolts is 66 lb-ft. However, SPC states on the instructions that you should use either 38 lb-ft or 44 lb-ft for this application depending on the model of shim used. There’s also small print on the instructions that the manufacturer’s recommended torque value + 15% is a general guideline.

When I installed these shims, I used 66 lb-ft since 38 or 44 is far below the recommended amount by Toyota. When I reached 66 lb-ft, I went back to check the bolts once more and noticed that the bolts could still move. (Think of a flat tranny pan gasket, sort of.) Basically, each time I tried to turn the bolt to double-check that I had reached the appropriate torque value, the SPC shim would crush a bit more and the bolt would continue to turn. However, after 5-7 tries in a criss-cross pattern, the bolts stopped turning and the torque wrench clicked immediately at 66 ft-lbs.

The values I was trying to target for the rear suspension was 0.14 deg of toe and -1.5 deg of camber, which are the preferred values by Toyota. I have listed below, the before/after alignment readings.

LR, before shim/after shim:

Toe: 0.33/-0.16
Camber: -1.1/-0.7
Shim used: SPC 75600, rec torque value is 44 lb-ft

RR, before shim/after shim:

Toe: 0.24/-0.16
Camber: -1.8/-1.4
Shim used: SPC 75800, rec torque value is 38 lb-ft

Clearly, something is wrong here. I arrived at the same final toe readings on both sides and the same amount of camber change on both sides. However, the values I got are not even close to what I was trying to obtain.

I called SPC’s technical hotline and I went over with them my installation procedure. We are in agreement that my installation procedure was correct, so the only possibility on the cause of these issues is the torquing of the hub bolts. I suspect that following the factory torque specs (and then some) for the hub bolts deformed the shim and caused the readings to change, since the shim does look slightly warped depending on the angle you look at it from. SPC Tech line agreed that this maybe a possibility for my problems, and promised to research a solution.

So, my question is: can I safely use 38 or 44 lb-ft of torque for the hub bolts? Toyota recommends 66, but it is possible that this level of tightness is crushing the SPC shim too much. The hubs did feel fairly tight at 40 ft-lbs, but I also do not want the hubs to fall out.

Also, if anyone has any experience with these things, I would greatly appreciate it.

Thanks!

 

hlunde- the shims are nylon.
xs650- SPC basically said that they are not sure what the problem was, and advised redoing the job.

I did a bit of research online and my understanding is that Toyota is still using a toe correction bushing for the rear torsion beam. I could not find literature stating this in verbatim, but based on this rear suspension used on previous/other models, it is a safe assumption.

When a rear torsion beam has these toe correction bushings, the rear torsion beam is "floating" so the amount of toe-in at any given time (while vehicle is in operation) can vary.

Therefore, Toyota considers the rear alignment to be OK as long as the total rear toe is less than 0.58. In TSB #SU008-06 for the Sienna, which has a similar setup with toe correction bushings, the bulletin says that individual readings on each corner can be out of spec, but if the total rear toe is within spec, all is well. These are the exact words:

"The Sienna rear suspension and axle beam assembly has a toe–correcting feature
built in to the trailing arm bushings. (Refer to the Technical Information System [TIS],
2004 model year Sienna New Car Features, Suspension – Chassis and Drivetrain –
“Suspension”.) For this reason, it is important to focus on the total toe measurement
rather than individual right and left toe measurements. Most 4–wheel alignment
equipment will measure and display individual right and left toe readings and may
indicate that a right or left toe is out of specification. If total toe is within specification,
you may disregard individual right and left readings as the rear suspension and axle
beam assembly will automatically “correct” the individual toe settings while the
vehicle is driven."

Depending on the day and the alignment rack, my total rear toe reading varies between 0.50-0.57. So technically, my rear alignment is OK.

As a compromise, I think I may shim the left-rear side only. The right-rear has always been "in-spec" and only the left-rear has been showing an abnormal amount of toe-in.

If I use a Spicer 0.25 deg shim for the left-rear, I should end up with a LR toe reading of about 0.10. My right-rear toe varies between 0.18 and 0.24. Together, my total toe should then be 0.30-0.35, which is well within spec.

I am considering the Spicer shims this time since they are provide a fixed amount of correction, so perhaps I may have better success.

Thoughts?

 

Just ordered NAPA part#NCP 2643055. This is the reboxed Spicer 0.25 deg shim. This shim provides a fixed 0.25 deg of adjustment of either toe or camber. I have no idea how this works (I'm guessing it depends on the orientation), but we will find out once it arrives. Cost was $10.77.

Once it arrives I will remove the SPC shims from both sides and install the NAPA shim onto the LR side only.

 

Not sure, I'll let you know once I receive them.

MB860 ? 2

 

Just picked up the special-order Spicer shims from NAPA this morning. They are much thinner than the SPC EZ-shim (since it is one piece), and the plastic is very stiff and difficult to bend. I will install them in the near future.

 

I finally got around to fixing the shims. I still cannot believe I drove almost 5,000 miles with the car in this state.

As you can see from the pictures below, the SPC shims I installed basically fell apart. When torqued to the Toyota required torque of 66 ft-lbs, they cracked. And looking back, this is the reason why it took more than seven attempts of torquing the bolts in a star pattern to get them to stop turning - the shims were cracking each time I torqued the bolts:





Although I do not have a picture, the replacement shim from NAPA Chassis (spicer) is much thicker and is nearly impossible to bend, even though it is also nylon. Also, with the NAPA shim I only had to go back and torque the bolts 3 times before they stopped turning - and at no point did the bolts move as much as they did with the SPC shim during the torquing.

I set the NAPA shim to reduce the toe-in on the left-rear corner by 0.19. Before the shim install, I had between 0.33-0.35 deg of toe-in on the left- rear. Here are the post alignment results:



The total rear toe is now well within the Toyota specification, and Toyota puts more emphasis on the total rear toe amount due to the toe correction bushings. Eventually, I will also do the right-rear corner so that both sides can be closer to 0.15, but this is not urgent since the car drives better than it ever has.

 

Yes, and it still does to an extent.


iPhone ?

 

It may not be a problem with the Gen II since the specified bolt torque is much lower for the Gen II application.

I suspect that the 66 lb-ft requirement for the hub bolts on the Gen III is what causes the fracture of the shims.