steering and suspension Broke A Front Subframe Bolt...aarrgghh!

[jmiller]

So I was installing my newly powder-coated front subframe with zinc-chromate re-plated bolts.  With a touch of antiseize on each bolt.  The front bolts have a lot of friction; is this normal?  I tighten them with the normal ratchet wrench.  The Haynes manual says torque to 55 ft.-lbs., so I start with the front bolt.  It doesn't seem to want to tighten up.  I'm worried, so I stop and move to the next bolt back.  It doesn't seen to want to tighten up either, but as I'm pulling...BAM!  Bolt has sheared off!  These are 8.8 hard bolts!  So I have some questions:

 

1)  Did the replating of the bolts somehow weaken them?  Or did I just have one weak bolt?

2)  Is it normal for the front bolts to have so much friction, as if they were self lockers?  Or are the frame threads messed up?  I should mention this is most likely the first time the subframe has been off since the car was built in 1970.  Certainly it hasn't been off since I've owned the car since 1980.

3)  Did I over-torque, given that I was using antiseize?

 

Right now my plan is to buy new bolts; not going to mess around. I'll drop the subframe and try to get the broken bolt out using a back-off drill bit.  I assume I'll need to use my Dremel so the bit has a good surface to stay centered.  Any other suggestions? 

 

Thanks,

 

Jeff

 

[AceAndrew]

1) Not unless there was some pretty intense voodoo going on.

 

2) Should feel like soft molasses.  Threads might have gotten messed up.

 

3) Do not fully torque one bolt at a time,  get all the bolts up and snug before full torque spec is applied (think of it like a headstud procedure).
 

I'm guessing you somehow cross-threaded them or you didn't chase out the bolt holes, but its anyone's guess at this point.  Was the subframe supported as you bolted it up or was there quite a bit off load on the bolt?   There should not be much friction (just a consistent snug feel).

Edited June 14, 2013 by AceAndrew

[BillWilliams]

With the Ace on a few points, use a thread chaser for the threads and support the sub-frame and sneak up a little with each bolt before putting the monkey on them

[jmiller]

Thanks guys. Got the broken bolt out with a back out bit kit. Easier than I thought it was going to be. From the looks of the threads in the frame for the front bolts, a thread chaser is definitely in order. Still not sure why the bolt in the middle broke, so I'll just start over with new ones. And I'll work up more slowly with the torque. Thanks again; advice is spot-on.

[Honolulu]

I think the plating _could_ have had something to do with it, but I'm not well versed in plating chemistry except to note there are some pretty strong chemicals used.  A conversation with the plating outfit could be revealing, and may shed some light on the expected strength of other bolts treated by them.  Although it's a done deal you ought to check that out for peace of mind.

 

New bolts should be okay.

[oldskoolvws]

All fasteners are designed with minimal and maximum tolerances to their mating surfaces with regards to application and torque, especially in the automotive and airplane industies. Plating absolutely could have an effect on the fastener especially if it was a close tolerance fastener to begin with.

[Luis]

I bet you the powder coating got into the threads and that stuff is hard. Chasing them is definitely called for.

[jgerock]

Agree with the other responses - especially Luis.  Even if the powdercoater put plugs in the openings, the paint can seep into the threads.

 

Another crazy thing that happened to me while installing an old subframe:

 

Could get one side lined up and bolts started on the frame rail, but the other side would not line up at all.  Thought the frame rail was bent NOPE.  Turns out the steering linkage (tie rods) were installed wrong so they put everything in a bind, even at the steering box.  Reversed the tie rods and the subframe fit perfectly into the rails.

 

Look at the linkage in this picture.  The assembly closest to the car is the temporary one slapped together. The one near the wall is the original one from the 69.  The outer tie rods are installed toward the front of the car. I had accidently put them behind the center linkage.

Edited June 16, 2013 by jgerock

[jmiller]

Thanks, everybody. I should have mentioned those bolts were difficult to remove when I first pulled the subframe. That's why I thought maybe there was something different about those threads. Didn't look like any powder coat got in there. I started to chase the threads with clean bolt, but there was so much friction I assumed that was normal. I feel silly now. I should have looked more closely, and used a proper thread chaser. As far as the broken middle bolt, those threads are fine. I can twist a bolt in with my fingers. Not sure what else to do there except get new bolts and start with the torque wrench at a lower setting before cranking it all the way up. There's something reassuring about hearing that click as you go up stepwise.

Wish me luck...

Jeff

Edited June 17, 2013 by jmiller

[gfairchild]

I realize this is an old topic but I am getting ready to reinstall the front subframe on a 73 2002 and can't seem to locate the original bolts. Does anyone know the correct size bolts to use?

[jgerock]

I realize this is an old topic but I am getting ready to reinstall the front subframe on a 73 2002 and can't seem to locate the original bolts. Does anyone know the correct size bolts to use?

Just looked at penskeparts website...

 

You will need (4) M10 x 30  and (2) M10 x 50 hex bolts.

[nbcbird]

I am confused. Aren't the threads for the subframe in the interior of the bodyframe rails (and not subject to powder coating)? Bolts simply pass thru the subframe for attachment.

[gfairchild]

Thanks jgerock.

[Hans]

Check Amazon for thread chaser kits. I got 

Kastar 971 - Master Thread Chase Kit.

Seems fine.

[Beck180]

Years ago when I rebuilt the front subframe I snapped a subframe bolt (because I misread the torque spec). However, I highly suggest to always chase all threads when ever possible. I bought a Craftsman metric die and thread set. Makes everything come together faster, easier and better.

 

Totally worth it.

http://www.sears.com/craftsman-19-pc-tap-and-die-set-metric/p-00952348000P