Broken Frame on R686ST

[LoggerGary]

I have a 80 model R686ST. The frame is broken on both sides in front of the tandems. The previous owner was pulling dump trailers with it. I used it to spot log and chip trailers on a logging site. The other issue we had it was geared to high for our application. Really would like to fix frame.

 

[Mark T]

Lots of work to address both those issues.  Maybe a bigger tractor that needs an engine like in your truck ??? 

[70mackMB]

Gary, Welcome to BMT!  What was the angle iron, bolted thru the top flange, used for? Was it meant to be a temporary repair or for something else?    .....Hippy 

[Joey Mack]

since its a site truck, can you get 2 peices of inner frame from double frame truck, and overlap the cracks?  then weld the crack shut after the overlay is in?  A full frame replacement is a lot of work, even on a short truck like yours..  I know JoeH can atest to that...  

[tjc transport]

proper way would be to strip that section of frame, v notch both sides of the crack, then weld it on both sides. 

once welded find an inner frame section to bolt over the weld with plenty of extra on each side of the weld. then fish plate the outer side of the frame. 

[Mark T]

For what he's talking about, he'd be better off splice'n a bigger lower geared cut off to it (like out of a CL) . Some of those Rs  (like that one) had tiny frames and some don't even have a shim between the crossmembers. I've done repairs on those and had a local guy bend some flat plate like a liner for the frame. Crossmembers had to be shortened. Lots of work. He's not content with the axle either , aside from the broken frame. 

[Mark T]

1 hour ago, 70mackMB said:

Gary, Welcome to BMT!  What was the angle iron, bolted thru the top flange, used for? Was it meant to be a temporary repair or for something else?    .....Hippy 

😂 that bolt through the top flange is exactly what it needed

[Joey Mack]

good point about the gearing.  

[Joseph Cummings]

Are you going to ever use it on the highway? Here in the anthracite region if it wasn't going to see the road it would just get welded up and even the fishplates welded on 😄. Burn it in with 6011, and cap it with some 7018 passes.

I'm guessing you have 3.87 ratios. What do you expect to do with this truck. How fast does it have to run. you can find some really low ratios out of something with an overdrive trans, and end up with a truck that tops out at like 35mph but will pull anything

[LoggerGary]

I am getting used to this site so bear with me. If it only ran 35 mph it would be great for my application. I understand from the guy I purchased it from it would only run 55mph now. There is a local guy advertising a Mack/Hendrickson 44K suspension with 3.9 ratios for $3500. He advises the frame is bent at the fuel tank on that truck. Doesn't provide pictures of the truck. He was planning to cut the frame and sell with suspension attached is my understanding.

 

[Joey Mack]

just curious,,,  what ratio rears are in it now? 

[LoggerGary]

We may just use it as a shop truck to move empties.

 

[LoggerGary]

I am not sure why the angle Iron except my machine mechanic may have put it there trying to not let it fall apart in the yard.

 

[Joseph Cummings]

23 minutes ago, LoggerGary said:

I am getting used to this site so bear with me. If it only ran 35 mph it would be great for my application. I understand from the guy I purchased it from it would only run 55mph now. There is a local guy advertising a Mack/Hendrickson 44K suspension with 3.9 ratios for $3500. He advises the frame is bent at the fuel tank on that truck. Doesn't provide pictures of the truck. He was planning to cut the frame and sell with suspension attached is my understanding.

 

You need ratios considerably lower than that. Is it a 5 speed truck? A set out of a truck with a big overdrive like a Mack 2050 trans or a 2090. Probably where you want to be is around something in the 5s or more

[mrsmackpaul]

If it is 55 MPH it must 5.73 or similar

35 MPH would need to be in the 7 or 8 ratio 

I am think a cut splice and ass end and rails is the 

Interesting that we plate both inside and side in Australia 

Years ago people would cut 'V's or Z shapes in the join, the thoughts were the longer the weld the less chance of breaking it

However as technology has improved a straight cut is normal, this means lesd heat in the rail

Anyway I am thinking shopping around for donor ass end with the desired ratio is go 

 

Paul

[Mark T]

R models are not as wide as most anything else. If it's not going to see on road service, should be easy to splice something else on it. Like from a packer or a mixer. (something geared lower for it's application. Just couldn't be another R 

[Joseph Cummings]

30 minutes ago, Mark T said:

R models are not as wide as most anything else. If it's not going to see on road service, should be easy to splice something else on it. Like from a packer or a mixer. (something geared lower for it's application. Just couldn't be another R 

Years ago I had a single axle IH wrecker with the cab burned off of it. I got an R model with a broken trunnion. The R model frame slid right inside the IH frame. Spme minor shimming and it bolted together so nice with lots of overlap. I was tempted to not even weld it, but I did weld it some. That saved me so much work. If that hadn't worked out I would have had to change all the mounts for the crane and the body to make it fit the R Model Frame. Not to mention putting all the single axle suspension under it. I think I probably saved a weeks worth of work

[Mark T]

I'm thinking that might be the way for this guy to accomplish what he's hoping for.

[JoeH]

If you're deadset on keeping that truck then look for a donor parts truck with good rails.  For what it's worth, U models use the same frame rails.  We've welded the rails on our R686ST.  Ours are sleeved on the outside, just with a bolt on section.  You're supposed to use 110,000 lb welding rods according to the Mack frame repair book, not 60/70k's as referenced by others.

[Joseph Cummings]

10 hours ago, JoeH said:

You're supposed to use 110,000 lb welding rods according to the Mack frame repair book, not 60/70k's as referenced by others.

Yeah I read the book, but I'm talking real world where truck is broken and it's got to be running and under load in the morning. You can't use what you haven't got and downtime is expensive