Cracks in rear cross members

[93Canter]

I was giving my 1993 FG439 chassis some paint prior to starting on a new camper body and I noticed cracks that start between the lower rivets in the cross members at the rear of the truck.

Cracking issues were discussed in the FG fleet mechanic interview thread.

The concerning bit is that these cracks are only visible from above and are easily missed. Here are some pics:

Front Right

Rear Right

Rear Left

Front Left

My FG has done about 38,000 km, it had a tough time as an overloaded fire truck for the first 9000 km.

I am now pondering how I "plate the cutouts at the end and weld it all together so that it becomes 1 piece."

 

[engineer]

I cut mine right out and replaced one with a Volvo X member, the other i just ground out & welded. both are still fine.

 

[gait]

I'm not much help with the repair but I've joined all those inspecting their chassis this morning and have a question about the pics. I think I can see something at the start of each crack, looks to me like a small weld. Am I seeing it correctly? Not present in mine (later model?) but could help explain why your cracks have occured in those places.
Don't forget its high tensile steel when welding. A trip to the wreckers may help.

 

[93Canter]

Yes 2 small spot welds on each one.

I will post a close up of the worst crack later.

 

[kerry]

For those of us who don't have the luxury of looking down on our crossmembers from above, can you tell us if you can feel those cracks by reaching up from below and running a finger or finger nail across that area?

 

[gait]

For those of us who don't have the luxury of looking down on our crossmembers from above, can you tell us if you can feel those cracks by reaching up from below and running a finger or finger nail across that area?

have you tried a mirror and a bright light?

 

[engineer]

I'm not much help with the repair but I've joined all those inspecting their chassis this morning and have a question about the pics. I think I can see something at the start of each crack, looks to me like a small weld. Am I seeing it correctly? Not present in mine (later model?) but could help explain why your cracks have occured in those places.
Don't forget its high tensile steel when welding. A trip to the wreckers may help.

They seem more like mild steel to me.... Nothing like the chassis of yore.

 

[kerry]

Looks like it's cracking right thru the center of the rivet holes. Have you look from below at the crossmember where the two top rivets go thru it?

 

[93Canter]

Here is a close up, it will give you some idea of where you might feel the crack with your fingernail if the crack is bad.

Thanks for the comments on Volvo bits Engineer, do you have any tips on which Volvo model I should be looking for.

I should point out that the cracks only became apparent after I had attacked the area with a wire brush attached to an angle grinder.

If you don't have access from above to inspect your rivets it might be possible to take a photo of the area with a small digital camera that has a flash.

 

[engineer]

I'll have to dig for the receipt, let you know tomorrow. I'll take some pics at work.

 

[whatcharterboat]

Yep, looks familiar. Some of the beach bus operators plate this whole area now as soon as they buy a new chassis rather than wait for it to happen down the track and then be faced with the difficulty of trying to repair it with a body on top.

 

[gait]

They seem more like mild steel to me.... Nothing like the chassis of yore.

they seem like that to me also, might have been in 1993 (I really don't know) but recent spec for chassis tensile strength is 450Mpa
http://www.thetruckcentre.com.au/range/spec/Spec_fg649.htm
Its a long time since I looked at steel in a lab but steel with yield strength between 340 and 690Mpa is possibly low alloy high tensile, known for cracking in heat affected zone of welds if appropriate practice isn't followed. Possibly why these cracks seem to start at the edge of the welds (probably just outside the weld bead but I can't quite see).

 

[93Canter]

I'll have to dig for the receipt, let you know tomorrow. I'll take some pics at work.

Thanks those pics of plating will make a big difference.

 

[kdgreene]

Thanks those pics of plating will make a big difference.

I have a 2004 FG that I'll have to crawl under to check out. This sounds like it could be a major job if we have a problem - we have a box on our truck and now have over 150,000 km on the truck.

If you wouldn't mind posting your photos for the rest of us to see, it would be a great help. Thanks.

Don Greene
Adventure Learning Foundation
Americas Overland
www.questconnect.org
www.americasoverland.net

 

[93Canter]

If you wouldn't mind posting your photos

Sorry Don, No photos yet, my comment was in anticipation of photos being posted.