Help with SPC shim and Hub Bolt Torque

[The Critic]

My Prius had 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. 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!

 

[Trav]

What kind of material is the shim made from?
Are you using Loctite or never seize on the bolts?

 

[The Critic]

Originally Posted By: Trav
What kind of material is the shim made from?
Are you using Loctite or never seize on the bolts?


The SPC shim is nylon plastic, fairly flexible too. They can definitely crush/deform easily.

As far as the bolts, I installed them dry. I talked to the techs at my local dealer and they told me they always reuse the bolts and install them dry. However, the service manual says they are a non-reusable part, so I ordered a new set of bolts but did not use them. The new bolts I ordered do have some red stuff on the threads, which I presume is red loctite.

 

[Trav]

My first thoughts..
Are there any metal shims available?
These are critical fasteners and while 44lb may hold them though i wouldn't come right out and say hey no problem.
IMO this is sketchy as heck, reducing manufacturers specified torque for a critical part because of a plastic shim.

On the other hand the red Loctite will probably hold them just fine at 44lbs but if these things compress any at all in use they will be play. I don't like this at all.
If no metal ones are available i would talk to a machinist and maybe get some ground from metal stock using the plastic ones as a template.

 

[mechtech2]

NYLON SHIMS?

I think you have found the real problem!
More probable than our accumulated proofs of Einstein's field equations!

Maybe steel shims from another car make are obtainable, with a bit of filing/grinding.

 

[Trav]

After looking into this a little more the shims appear to be the same thickness all around. Could you use the plastic ones as a pattern to cut some out of copper or metal sheet of the correct thickness?

Shim Stock

 

[PandaBear]

I've done something foolish when I was replacing an ATF pan gasket in the past, and learned that torquing an elastic material is very different than torquing a metal / metal contact.

When I misread the torque on the gasket, and keep torquing away, eventually the gasket would deform so much that it is squeezed out on the side. I'd imagine if you torque 66 lb-ft but the material is only design to handle 38-44, it will not be good. I would try 38-44 as that may be designed with the shim in mind.

If you do not feel safe with the torque, maybe you should try to find something that is metal like mechtech2 said.

The reason it is the same final value that is off from what the shim originally tries to get you is most likely due to the shim being compressed and deformed.

 

[chrome]

There is a mismatch in the torque value recommended by Toyota with that of SPC's due to the shim material. Toyota never allowed for nylon shims in their design when they specified the torque value for the hub bolts. SPC should have followed Toyota's torque value and specified a correct material to suit, obviously nylon will deform way before the correct torque is reached.

 

[The Critic]

Originally Posted By: Trav
My first thoughts..
Are there any metal shims available?
These are critical fasteners and while 44lb may hold them though i wouldn't come right out and say hey no problem.
IMO this is sketchy as heck, reducing manufacturers specified torque for a critical part because of a plastic shim.

On the other hand the red Loctite will probably hold them just fine at 44lbs but if these things compress any at all in use they will be play. I don't like this at all.
If no metal ones are available i would talk to a machinist and maybe get some ground from metal stock using the plastic ones as a template.

Thanks, do you know of a source for metal shims?

Another thought is that I had originally torqued to 66 lb-ft, then went back to double check and then found the bolts to still move when I tried to "check" with a torque wrench.

I wonder if I torque to 66 lb-ft ONCE, and leave them that way, if that would be adequate.

 

[The_Eric]

Originally Posted By: The Critic
Originally Posted By: Trav
My first thoughts..
Are there any metal shims available?
These are critical fasteners and while 44lb may hold them though i wouldn't come right out and say hey no problem.
IMO this is sketchy as heck, reducing manufacturers specified torque for a critical part because of a plastic shim.

On the other hand the red Loctite will probably hold them just fine at 44lbs but if these things compress any at all in use they will be play. I don't like this at all.
If no metal ones are available i would talk to a machinist and maybe get some ground from metal stock using the plastic ones as a template.

Thanks, do you know of a source for metal shims?

Another thought is that I had originally torqued to 66 lb-ft, then went back to double check and then found the bolts to still move when I tried to "check" with a torque wrench.

I wonder if I torque to 66 lb-ft ONCE, and leave them that way, if that would be adequate.


Doubtful.

As you torque the remainder of the bolts to spec, the clamping load will increase, crushing the shim and effectively loosening the other bolts... You've already gone down that path, no need to do it again.

I'm mostly with Trav on this. 40 odd pounds would likely be fine, but I too am not a big fan of nylon as a shim. The truth is that the rear doesn't see huge loads and those shims would likely be fine, due to their relatively thin design (I'm assuming) and shouldn't flex much, if at all. Still, that being said, I'd prefer aluminum or steel.

 

[Trav]

Grainger has metal slotted shims but you would need to know the exact thickness of the ones you need.
This might be best to left with a pro on the alignment rack so the changes can be seen and shims changed on the spot.

Did you go by their chart and cut the the shims out in the right places? What numbers did you get e.g. 35/17 ?

You can try this..
Torque it up to 66lb in 3 steps criss cross.
First 20lb
Second 45lb
Third 66lb and leave it, don't go back over them.

 

[mechtech2]

Also note that shims SHOULD be tapered, not flat.
I guess flat could work OK, but tapered would fit better .

 

[The Critic]

Originally Posted By: Trav
Grainger has metal slotted shims but you would need to know the exact thickness of the ones you need.
This might be best to left with a pro on the alignment rack so the changes can be seen and shims changed on the spot.

Did you go by their chart and cut the the shims out in the right places? What numbers did you get e.g. 35/17 ?

You can try this..
Torque it up to 66lb in 3 steps criss cross.
First 20lb
Second 45lb
Third 66lb and leave it, don't go back over them.



25/9 was the left one, I cannot remember the combo for the one on the right.

SPC's tech line was not able to offer a conclusive answer or idea as to what may have went wrong. Their only advice was to try again.

I will probably do the job over again in about 2 weeks. If this still does not work, I will just run without shims and align the car as best as possible.

 

[The Critic]

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?

 

[The Critic]

So I finally got off my bottom and fixed the shim issue. 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, the reason why it took more than 7 criss-cross torque sequences to get the bolts to stop turning was because the shims kept cracking.

Although I do not have a picture, the replacement shim from NAPA Chassis (spicer) is much thicker and is near impossible to bend, even though it is also nylon. Also, this new shim from NAPA only required 3 criss-cross torque sequences to fully tighten, and at no point did the bolts turn as much as the SPC shims.

My local Firestone has not been able to get me in for an alignment, but I had Sears do an alignment check and my LR toe (which has the shim) is now at 0.22, and this side was previously in the mid 0.30 range. So, the shim is working.

I am just glad I got it done, as driving around with cracked shims was probably not a good idea. Also, the car now drives 10000x better, lol.

 

[eljefino]

wow those SPC are junk!

 

[Trav]

That's terrible. I feel your pain, garbage parts are getting all too common today.

 

[The Critic]

Got an alignment, the NAPA shims worked well. Toe is within spec for rear total toe, which is what's important per Toyota. However, I will eventually put a shim on the RR corner as well. As of now, it drives straighter than it ever has.