DefenderC5

I was torquing down the M 9.8 Bolt on the rear driver's side which holds the bottom of the shock on the control arm.
The spec I read everywhere for this bolt is 162 ft/lbs

The sucker snapped off at the threads! I never even got past 150 lbs.

The passenger side went on just fine... after a little while.

Its the same thing that happened to this guy, except I only torqued on the nut. Linky Linky

Whats the deal? Two identical bolts, same place same problem, two different cars?
Perhaps the 162 lb spec is for later C5s? Should it be different for 99?

Lastly, what is a good (permanent) replacement for this bolt?

I'm thinking about throwing a grade 8 in there rather than using a GM part which could break again. I'll be replacing both since i dont trust the passenger side where it is now.

FactoryRaceCar

I personally never had the problem with it. Car is a 2000.

vettenuts

I am not too fond of Grade 8 bolts, get the GM replacement. I do remember a glowing error in the C4 service manual I had with regards to bolt torque, and it was for some years that the manual was screwed up. If you used the value in the manual, then the bolts would break. This was on the brakes.

Z28TOZO6

are they torque to yield bolts? If they are you should replace them when you replace the shocks. Typically they are only used in motors but I would verify that.

ErnieN85

Yes that is the problem at the spec they are done (supposedly) after one use.
as was suggested they really don't need to be quite that tight. Just rember when Gm installs them they are stressed to the max!

VFRLuke

so what else would one need to order when replacing shocks??

TopFuelTim

162 ft lbs sounds awfully high for that size of bolt, even though that is what the manual calls out. I'd suspect the manual is not quite correct there.

Tim Glover

vettenuts

I tend to think its none of the above, but rather these bolts are subjected to some bending loads in the course of their installed life such that when re-installed there may have been some over stress in their normal use that ends up with a failed bolt when properly preloaded.

Any photo's of the failed bolt?

quantum

That torque seems way to high for a shock mount, I would be not be suprised if it should read 62 ftlbs.

TEXHAWK0

I have a 2003 service manual and that is what mine says also.

22 ft-lbs for the top bolts
162 ft-lbs for the lower bolt.

04cad

Sounds way too high to me, especially if it uses a nut. Is this a shoulder bolt? If not sounds like you could collapse the mount or at least cause it to bind from being too tight. We need someone with specific knowledge to weigh in here, maybe a GM tech?

Funn One

DefenderC5

These are all the same questions I've been asking myself. I thought the value was high as well. But the manual as well as two writeups stated the same amount: 162 ft/lbs. A similar bolt on the front lower control arms of my truck (which had a coilover front) was a similar size but only needed be torqued to about 85 lbs.

As far as grade 8 replacements, keep in mind that the M9.8 that broke is only slightly stronger than a grade 5. Why would a grade 8 not be a suitable replacement?

I wish the stealership was open on sundays!

gpotski

How did you get the broken bolt out? Drill it out?

Choreo

I am the "other guy" who had the same problem a few weeks ago. As a temporary fix (since it was Saturday when it broke) I went to the local hardware store and purchased a $2.00 Grade 8 bolt and nut until I could get another GM replacement in. I torqued the Grade 8 to 150ftlbs and no problems - so far.

The GM replacement was about $12.00 and just came in. Just like the stock parts, the new bolt is stamped 9.8 and the nut 10. These may have been $10.00 higher, but they came in a throwaway box. One thing I noticed about the replacements is that the nut only threads a few turns onto the bolt by hand before it stops dead (before the bolt threads extend from the other side) - so my guess is these are designed to be used only once? (in contrast, the Grade 8 threaded ALL THE WAY by hand) The forum instructions that I was following said to "save" the old bolt and nut for re-installation - and this "seemed" to work on the rear passenger side.

Unless it is a coincidence, my guess is that these are to be used only once and that apparently the left rear is perhaps exposed to more stress than the right rear. Also because this nut fits so tight on the new set prior to installation, that may explain why this has to be torqued so high to 162 - looks like it would take some serious torque to get this nut to thread? It should also be noted that the stock bolts/nuts I removed threaded fine by hand so I am assuming the clearances open up after the initial use?

Choreo

No problem - the bolt breaks in half and the threaded portion of the bolt is left in the nut and just falls off - what is left of the non-threaded portion of the bolt just slips out from the opposite side.

DefenderC5

This is the same conclusion I came to as well, these are ONE TIME USE BOLTS. They are torqued in to 162 lbs from the factory and they sit that way for years (eight in my case). When the stress is relieved and they come out, then try to torque them down again... its just too much for it.

I replaced both sides with Grade 8 5/8" X 4" with 11 Coarse Thread, Locking nut and washer. Thats stronger than what GM had on there and was nearly identical (had about 1/2" more towards the head).

In contrast, it torqued down VERY EASY this time. We started at 140, then 150, then 162. It clicked down the first time on every rotation. Didn't have to stand on it (driver side) like we did for the GM bolts. Although, i suspect thats maybe why it eventually failed on the drivers side for both of us.

I have a picture of all the bolts in comparison, with the broken one as well. I'll post it up when I get home. My broken bolt just fell out afterwards too, theres no need for any special equipment there.

hotwheels57

Years ago, we used to call that "planned obsolesense"... (I know it's not in the dictionary).

UstaB-GS549

If the nut stops like that, it's probably because it is a Prevailing Torque Lock-Nut. It's all metal and a proper one is difficult to thread on without a wrench.

DefenderC5

I have a similar locking nut on my grade 8s. I used a washer since the stock one had a washer integrated into the nut. Its been working great! Another member told me his F55 suspension upgrade came with NEW bolts. Personally, I'm settling on the determination that these bolts are intended to be used/torqued ONCE. They "can" be reused.... but....

Here's what I used (left) broken bolt (middle) stock bolt (right)