Broken Rear Frame

Just wondered if anyone else had come across this. I bought my ST1100 last August and the tail has always been a bit rattly - I put it down to a loose Givi top box mounting. However, last weekend I was doing a bit of fiddling and discovered the rear frame extension was broken. This supports the tail piece and grab handles. Difficult to imagine the weight that must have been on the rear rack, and the size of road bump that would have caused that shear. And no other part of the bike damaged?

Common problem with ST1100s that have some age and miles on them. The leverage of the top box usually does it over time.

TomASmith said:

Just wondered if anyone else had come across this. I bought my ST1100 last August and the tail has always been a bit rattly - I put it down to a loose Givi top box mounting. However, last weekend I was doing a bit of fiddling and discovered the rear frame extension was broken. This supports the tail piece and grab handles. Difficult to imagine the weight that must have been on the rear rack, and the size of road bump that would have caused that shear. And no other part of the bike damaged?

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Mine broke in the same spot. My Givi 52 liter topcase definitely had a lot to do with the metal failure. I have just installed a new one, but am switching from the Givi mounting plate to an alternative rack that will move some of the topcase load off of the new plate.

STraymond said:

Mine broke in the same spot. My Givi 52 liter topcase definitely had a lot to do with the metal failure. I have just installed a new one, but am switching from the Givi mounting plate to an alternative rack that will move some of the topcase load off of the new plate.

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!!! I just discovered the same problem a few weeks ago. I also have a big Givi case installed. I removed the bracket and welded it back to gether with my MIG welder.

The question I have is : Why does it seem to break on the same side of the bracket ?

Maybe it has to do with the side stand being on that side. The force of the weighted top box leaning towards that side over and over again. Although, my uneducated brain could argue that the other side is stressed equally yet opposite, so I really have no clue if this theory has any merit or not...

The OEM topbox that was available for the 1100 in early years had a maximum load capacity of about 20 pounds. Might have been a bit less than that, but can't remember the correct number. Putting more than that in a Givi or otherwise, which would be heavier than the OEM box to begin with, is the reason these things break. One thing that could possibly be done to strengthen that part would be to weld a couple pieces of thin steel plate onto the outsides of the arms over the large hole area.

Seems like a guy handy with a welder could reinforce the brackets easily enough as Jim did. But really who never exceeds the load recommendations for bags and boxes.

Has anybody preemptively reinforced the brackets?

ST Gui said:

Seems like a guy handy with a welder could reinforce the brackets easily enough as Jim did. But really who never exceeds the load recommendations for bags and boxes.

Has anybody preemptively reinforced the brackets?

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I was going to preemptively get my new bracket reinforced, until I saw this:
http://www.mmotoracks.com/product/rear-rack-for-honda-st1100-pan-european

I have ordered and waiting for delivery.

OK, But that rack still mounts to the bracket under the plastic that is the problem child.

ST Gui said:

Seems like a guy handy with a welder could reinforce the brackets easily enough as Jim did. But really who never exceeds the load recommendations for bags and boxes.

Has anybody preemptively reinforced the brackets?

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Well, I didn't really reinforce it, I just repaired it. I had an IBA SS1K Ride to do the next day and didn't have much time to spend on the job. But in the spring, I will remove the bracket and reinforce it with a few small steel plates welded across the holes where the cracks developed. And I'll do both sides, to be on the safe side.

Jim Van said:

OK, But that rack still mounts to the bracket under the plastic that is the problem child.

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But, it also mounts to the forward frame bolts used by the OEM grab handles.

I've been concerned that my Givi box mount doesn't seem that sturdy for a while. What do I have to remove to see if I have this issue?

RobbieAG said:

I've been concerned that my Givi box mount doesn't seem that sturdy for a while. What do I have to remove to see if I have this issue?

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The saddle.

RobbieAG said:

I've been concerned that my Givi box mount doesn't seem that sturdy for a while. What do I have to remove to see if I have this issue?

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The saddle.

John OoSTerhuis said:

The saddle.

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To inspect.

To remove & repair, then additionally the saddlebags, side covers, top box mount, and the plastic cover over the tail light. Doesn't take long at all.

If one side of the top box seems a bit looser than the other side, you probably have a cracked bracket - easy to inspect.

John OoSTerhuis said:

The saddle.

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Well, that was easy! Thankfully no sign of cracking. It does seem that it would be best to not put a lot of weight in the top box. On camping trips, I put all the light stuff in there. When I commute to work, I need to put my laptop in it - it won't fit in the saddle bags. That might be pushing it.

Check the 4 8mm bolts that fasten the Center Plate to the frame (see the Seat Cowling schematic, p.2-3 in the manual). Following my friend Bill on one of our WeSTOC trips I noticed his Givi sagging on one side... missing bolt. Trip to a local hardware store fixed him right up. Hell of a mess in the motel lot getting to the bolt hole.

John

Mine says DON'T PANIC! But I do.

Excessive lateral forces would weaken the rack over time especially with something heavy sliding around in the trunk. But unless you have a 70s-80s "portable" computer (Osborne anyone?) a 5-6lb laptop strapped in place shouldn't push any limits. But if it breaks your bracket I don't know you and we've never met.

John OoSTerhuis said:

The saddle.

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+1...
And I'd regularly inspect all 4 bolts holding the subframe to the backbones for proper torque, as their known to come loose over years and years of (too heavy) topcase-rattle...
A torque wrench and a drop of thread-lock deals with the issue ;-)

The easiest (and FOC!) countermeasure seems to keep your topcase payload at bay and within the MFG recommendations of 6.5kg/14.3lbs nett or 10.0kg/22.0lbs gross weight...
(brief observation of driving physics should prohibit one from placing weight that high and that far aft on a motorcycle anyway; heavy stuff is to be packed as low and forward as possible...always...)

And IMHO is ST Gui on the right track with his remark about lateral movement (shape and kind of material fracture enforces that argument):
cracked subframes seem to occur almost exclusively due use of unsuspended after-market topcases/racks, whilst I've never seen one coming apart in such matter when an OEM carrier plate with lateral damping is installed; food for thoughts...

Last but not least my very own experience in this issue:
- I'm using the OEM carrier plate with lateral suspension
- I never leave the topcase on the motorcycle when not needed/riding solo/commuting...
- On tour I only pack the very lightweight items there: his/hers thermal liners/fleece-jacket, spare gloves, balaclavas, a hand full of road-maps, mandatory roll of toilet-tissue/wet-wipes...
never suffered a broken subframe ever... go figure...

John OoSTerhuis said:

Check the 4 8mm bolts that fasten the Center Plate to the frame

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ST1100Y said:

And I'd regularly inspect all 4 bolts holding the subframe to the backbones for proper torque, as their known to come loose over years and years of (too heavy) topcase-rattle...
A torque wrench and a drop of thread-lock deals with the issue

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Everything seems snug but it flexes more than I'd expect. Both sides flex equally. I do think it's worth having a look to make sure all the bolts are there and torqued properly. When I put the same box on my 1300 it seems more solid (less flex).