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I had my 1988 RD686sx fitted with new rails from the back of cab. Donovan Spring Manchester NH did the work in winter of 2012. They 45 angled in back of cab and about 30 inches back for inner rail. Also had them sandblast entire frame, axles and everything else under there and the painted it with a black epoxy paint. Also had cab painted and a new dump body put on. Put a lot of money and time into it but for me it was well worth it.

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I'm looking at the same problem on a smaller scale on a '98 Ford Ranger- only 90k miles, never uses any oil, cab and box have at worst surface rust on the bottom, but frame is rusting badly in back. This is a common problem on Rangers, just google it and you'll see 10 year old Rangers with collapsing frames, bumpers falling off, etc.. Mine ain't that bad, it passes the Toyota "hit the frame with a ball peen hammer and see if it goes through test" and the "jump on the back bumper" test... But in a couple years, it probably won't. I've got a leaking rear brake line to find and fix and the fuel system seems to lose prime if I park it for a while anyways, so I'm probably gonna pull the box off, fix those problems, and further inspect. Don't want to put much money in it, since the 12 year old tires need replacing too... But I looked it up on KBB and it's worth $4-5k, so maybe worth cleaning and repainting the frame behind the cab where it's rusted the worst. That rust behind the cab is it due to rust from road salt?

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Yup, probably due to salt. Body looks great, a little surface rust on the bottom and that's it. But all the paints rusted off the rear of the frame. I've got the box off now, replacing a leaking brake line and may go ahead and do all the rear brake lines. Checking the fuel system too- Takes a lot of cranking to start if it's been parked a few weeks, sort of like the system is losing prime.

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Truck is super clean-285,000 miles. He has 35 g into it. As I see it, too much invested to walk away. Plus I'd take this old simple dog over a new one any day.

This is a nice truck. I would spend the money maybe not 20 grand but come up with something. That truck will last forever.

Rob

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Yup, probably due to salt. Body looks great, a little surface rust on the bottom and that's it. But all the paints rusted off the rear of the frame. I've got the box off now, replacing a leaking brake line and may go ahead and do all the rear brake lines. Checking the fuel system too- Takes a lot of cranking to start if it's been parked a few weeks, sort of like the system is losing prime.

I have a ranger that came from the north reason I ask but have not yet found any rust.

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Typical any 80-90's Ford truck the paint bubbles on the frame and then rots bad from under the paint(just like the oil pans back then). No matter how clean you try to keep it.

My '89 came from S. Carolina and I oil spray it heavily once a year and it is still clean underneath. Messy, but no rust. Did the doors, under bed, tailgate, hood, fenders. It has oil slime coming out everywhere..............but it will NEVER rust. It is likely the cleanest looking '89 running around Ohio right now that sees weather all year.

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My '97 F350 is still all there except for a aftermarket cab corner that rotted. The truck had a 200gal. tank in the back that was over filled a few times and got the truck covered in diesel. Truck has 277,000 and no rot. And it plows too.

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Ford did a great job of rustproofing the 2nd generation Ranger cabs and boxes with galvanized steel, but their supplier for the frames, AO Smith (now Tower Automotive) really dropped the ball on the frames. Typically the frames rust through first behind the rear wheels and the bumper starts to sag, and in some cases frame mounted hitches with trailers attached have pulled the frame apart, spare tires have fallen on the road, etc.. This frame rust through is so common that I've heard of only 10 year old Rangers being scrapped because of it, and a whole cottage industry has sprung up to make frame repair pars for Rangers. Suffice to say, doesn't exactly motivate me to buy another Ford product!

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KInda like the Chevy malibu back in the early 80's. Use it up before the rear frame falls off(along with the bummper). It was common to see bungie cords holding up the bumpers to the deck lid.

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 I have an 85 or model 686 ST my frame is pretty good till the cab so I need to replace from the cab back I spoke with the people in Vermont and they are currently getting me numbers on new frame rails I'm going to try to do this job myself 

I would love any input from you guys that I've done this before

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First, update on the Ranger- Now almost 20 years old, the  frame is OK but the front brakes lines rusted out and had to be replaced. No original fit or pattern parts available, had to use generic lines which of course don't fit worth a darn. Bleeded screws rusted up so I can't do a good brake bleed and with a bunch of other stuff ready to fall off, the Ranger has been retired to round the homestead duties.

As for your old Mack's frame, if the frame is beyond hope from the cab back, repair it right and get complete new frame rails.

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                                             I don't know about Macks guide lines for frame repair but I will throw in PacCar's approach and by their book of guide lines.

 

                                              The cut should only be vertical, the insert rail should extend no less than three feet from welded frame joint and no less than six 5/8" flange bolts

                                              spaced equally apart vertically and no more than 2" from splice or weld. I have always done them this way, 70 plus of them. And I always preheat

                                              the rail and stick weld with 7018 DC. The weld is usually 5/8" wide.  It's always worked well for me.

 

                                               Truck Shop

                                                

                                               

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As always guys and gals, I'm stunned by the diversified level of knowledge you all possess! I was in the mobile welding business full and part time for 12 years. I have done a lot of heavy equip.repairs, but have.never stretched,repaired or replaced a.big truck frame! However, I have welded dozens of rusted car frames. I agree with Red Horse in general on fishplating( by itself as a repair!) I like the idea of the 45 degree cut when splicing a frame (more weld,and less chance of the splice  separating!) In the old days fishplating was common on new trucks as a reinforcement in the critical area under the cab and directly behind it,often done by the body company if the truck was expected to see heavy service! This was almost always done using the existing holes in the rails to avoid heat! I've been told,and this is purely heresay that you NEVER do a vertical weld on a truck frame if it can be avoided! I also like David's step cut even MORE inches of weld and less chance of separation! I see the dying art of flame cutting with a hand torch is still practiced! Kudos David! Of course all these repairs must be step welded to avoid warpage and heat damage to the frames alloys! Gearhead Grrrl, depending on the overall condition of the truck you could clean the frame as well as you can and use a combo of rattle can rust oleum for the tight places and canned R O with a brush for the other areas (cheaper) or if you have a  sprayer do the whole deal with that! Eastwood and  a couple of other companies sell some paint Por- something that is supposed to combine with the rust chemically and end it forever! I've never used it but you can be sure it ain't cheap! If you're losing prime in the fuel system the hose connections and or the hoses themselves are the first place I'd look! If you have the truck jacked up and are laying under the fuel connections, stay off to the side so if the hose comes loose you don't get sprayed! I got an earful of gas a couple of years ago! The pain was excruciating! A lot worse than getting gas in your eye! Plus the obvious fire implications! Red Horse I agree on.repairing a simple.old truck(especially a clean one like that dump!) Rather than buying a new complicated unit with all that potential for problems!

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On all my heavy equipment repairs I've used 7018 Lh except on thin rusty metal 1/8 or less then 6010 or 6011 if using a.c.. Low hydrogen used to be available in 10018 but I only used that once. I'm amazed that the step splice is considered to be unacceptable, but I'm not an engineer so can only go by General knowledge of mechanics! However I'd like to hear from David a year or two in the future about the longevity of the splice! I won't be welding  commercially again,but strictly for academic reasons this stuff interests me! I respect Steelmans input and Paccars recommendations are surely backed by their engineers! If any of you are unfortunate enough to go to jail in Monongalia county WV I welded some of their remodeled cell blocks those welds aren't gonna break! But there isn't much strain on a cell block😁

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The truck body guys around here all do vertical straight cuts and weld with migs ER90S B3 or a ER110S.  

They typically don't fishplate as the older truck frames were diffrent type of steel.   But if the frame is double at least 12" stagger and they will try to place a cross member or suspension bracket on the splice to reinforce it.

I spoke to a lot of folks about this as I was going to have one of my trucks streached a couple feet to make it into a tri axle, but found an end dump I could afford 

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On 3/24/2017 at 11:05 AM, BillyT said:

I've been told,and this is purely heresay that you NEVER do a vertical weld on a truck frame if it can be avoided!

No, you are never supposed to weld horizontal on a frame. That's why I don't like the step cut.  Another reason I don't like the step cut is the angle changes, that can lead to cracks developing. I will probably be ok, but like with all frame repairs, you need to keep a eye on it for cracks starting. 

Frames flex a lot. You make a frame where it can't flex in a particular spot, it will break every time.

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Stopped by P.G. Adams today on my lunch break and got a quote on 20 feet of 3/8 x 10 1/2 with no holes drilled $860

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