I was given a 9 inch Ford rear out of a friend's G***er that was in his shop when it burned to the ground. The rear end got hot enough to melt the aluminum wheels and tire off. I pulled the rear end down yesterday and it looks good inside except for the bearings are toast. Pun intended. It has 33 spline axles spool and 4.56 gear. The rear end still had some gear oil in it. Was this just a good heat treat or should I throw all these parts away and buy new ? I have rebuilt engines before that had been in car fire and reused the block crank and rods with no problem. I am on a budget and buying all new would really put me behind. I am only running about 475-500 hp. and low torque small block Ford.
Fire at a buddies used car lot [31 burned], shop burned flat... Inside was the Maine Barrons' bonneville '33 coupe, melted all the alum.... The rule of thumb is if it is hot enough to melt the alum. parts, the steel has crystilized...[might save it with a huge heat treater system...but] Maybe ok on the street but at 200plus MPH ???
High temperatures undo what the original heat treatment did to the parts. For the aluminum to run down into a blob like it did in the pic, the temperature had to go above 1000 degrees. That would be well above the original tempering temp of the original heat treatment, and how hot the internals got during the fire would determine how much softer they are now as opposed to their original hardness. Gears are typically made from 8620 or a similar alloy. Heat treatment consists of holding the part at 1650 to 1700 in a carbon rich atmosphere to increase the carbon content and surface hardenability. Part is then slowly cooled and then reheated to around 1550 and oil quenched. This will leave the surface hardness above Rc 60 and the core around Rc 40. The part is then tempered by heating around 500* and holding for a couple hours to reduce the surface hardness to the mid 50s. Any subsequent heating, like from that fire, that raises the part temperature above the original tempering temp will make the surface softer. The primary reason for the high surface hardness is to prevent pitting on the surface in use due to high point loading. Lose the surface hardness and the gears will pit in use and be gone in no time. My guess would be that the ring and pinion are junk. Only way to know for sure would be a series of hardness tests to compare with the original hardness specs. To re-harden the gears would cost more than buying new. I ***ume the axles are aftermarket. Hard to guess whether the heat damaged them or not since their hardness is typically lower than that of the gears since axles need toughness more than wear resistance. However, most axles are hardened in the spline area for wear resistance and if that's not up to spec then they'd be useless too. Not a clue about the spool since I'm unfamiliar with the materials or heat treatments used to make them. Of course the spool would only be useful if you're building a drag car as they don't function well on the street and can be really dangerous on a wet road. Big difference in a car fire and a building fire, both in temperatures and time of exposure, so engine components being reusable after a car fire don't really tell you much about the condition of parts exposed to a building fire.
I will come over and pick it up.....1220 degrees will warp the housing, let alone draw all the harness from the axle, maybe not the ring and pinion if there was still gear lube.......
metlmunchr: Thanks for that excellent, clear and concise explanation. Metallurgy is a very exciting field to work in.
Buy new. Your parts were annealed. There is more to it than just heating up and cooling down. The method a part is cooled (i.e. Water, oil, etc quenched) is also a determining factor. The easiest way to figure out your property changes is to look at a phase diagram for the respective alloy. My background is metallurgical engineering and in my opinion, replace it. How hot did it get? We know the melting temp of Al but that's much much lower than tempered steel. Sent from my SM-G925V using Tapatalk
It probably warped the housing as well. Door stop material. Sent from my iPad using The H.A.M.B. mobile app
Thank you for the great treatment (pun intended) of some of the basics of the heat treatment/hardening process.
I would think that at some point during the fire, or overhaul of the fire, that the firefighters sprayed everything with the hose, including the rear end, quenching it. I'd keep looking for another rear. Sent from my iPhone using The H.A.M.B. mobile app
Thanks for the explanation . I guess it's another set back. Too bad it was the perfect width for my Morris Minor G***er project. The gear was wrong and I had planned on an aftermarket carrier , but will check the housing straightness . Cheaper to replace parts than having them tested.
whats the pinion seal look like? with oil in the housing still Id like to know if the seal is still threre (also axle seals) are the brake linings burnt off or still stuck on to the metal?
Check with a pipe inspection company,checking weld hardness is a common thing in refineries.I bet some one would do it for next to nothing if you find the right guy.All you need is a few spots buffed up and the tool only takes a few seconds. Sent from my SM-G930W8 using The H.A.M.B. mobile app
Thanks. I know some people at a nuke power plant. Maybe they can help. The pinion seal was intact. The axle bearings are bad, the seals are too. The brakes still had tension on the springs and the shoes on one side didn't look bad . Of course this rear end laid outside on the ground for 3 years uncovered.
ok well in my opinion it hasn't been "that hot" if the seals have not burnt out the center should be fine , same for all the pumpkin, the housing , get it checked for straightness and use it, backing plates will be fine chuck the brakes in the bin , drums may be ok if not out of round but they are cheap enough to replace, (wheel cylinders still have rubbers on them?) Axles, are there any odd heat marks on the axle flange? they are probably fine after all , all this cleaned and rattlebombed black , you'd buy it at a swap and not think twice..... yes I have used burnt stuff............
I spent many years working in a heat treating shop as a operator and inspector. I am very familiar with heat treating processes. Aluminum melts around 1220 degrees. The ring and pinion would probably be tempered at 350-450 degrees depending on the material used following initial quench during heat treatment. Axles often have a dual process, an initial heat treat & quench then temper to 45 Rockwell checked on the C scale this is 600-650 degrees depending on material. This is a good range to allow some twist/spring. Then a second process of induction hardening the splines to provide wear resistance. You will have a difficult time getting the exact process from most companies as its a propriertary process. Racing axles receive a different process, use very high quality steels and aren't even recommended to be used on the street. The heat generated to melt the wheels would exceed the temper range for the axles & gears. The housing if its still straight would be fine to reuse. Don't use the other parts, breaking an axle and having an accident is very real possibility. Mtlmuncher is on point about the problems. Our shop had actually re-heat treated a large lot of hands tool that were in a fire. Chrome was screwed up but the tools were salvaged.
so what your inferring is because the thin alloy rim melted the diff must have been at the same temp? sorry no , what temp will a rubber seal burn at? rubber seals are a good indicator of heat , they are still there therfore the heat at the diff center wasn't a lot (I see your 1220 degrees but some alloys of aluminium melt much lower)
I must admit I have not experimented with what temperature a seal of a particular material type will melt/burn/flash. Neoprene for example will flash at around 570 degress. Part of the wheel visible in the photo that's bolted to the axle flange saw in excess of 1200 degrees as the tire burned completely away and the aluminum formed a puddle. It looks like a centerline so probably a 6061 material and not a cast wheel. I am not saying every surface of the housing and its internal parts rose to the same temperature. I am not a gambler and try not to give poor advice when it comes to my safety and that of my family and others & wouldn't make recommendations that could have a bad result.
If the brake springs still have tension and still have recognizable 'color' on them, it didn't get that hot. The wheels I understand; they had burning tire wrapped around them and the concentration of heat from that would be enough to melt the wheels without getting all the rest as hot. Do check the housing for straightness.
Not all burned vehicles are created equal. While I certainly do not dispute the comments of experts above on the effects of a given temperature on a given part, my experience with a few 'burners' has indicated widely varying temps on the same vehicle. For instance, a particular body on frame vehicle which had the complete interior and tires consumed, and a concentration of heat where the fuel tank was located, still had substantial areas of the frame with unscorched paint clearly visible. The aluminum transmission 'appeared' unaffected. The heat went 'up', as heat is wont to do. This above described vehicle may have been outdoors when on fire. I have seen others that were totally 'burned', not a shred of combustible material left unaffected. Most likely they were in a confined space when exposed to fire. Having said all that, I agree that caution/skepticism be exercised when deciding which parts, if any, of this axle ***embly are usable. Ray
I will call Strange engineering since it is their axles, spool and pinion support, it is a Richmond gear so I will contact them as well. Maybe I can send them the axles to check and if no good then they have the right measurements. Thanks for your concern to all that replied. Will post information after I talk to Strange.
Besides the seals, another visual indicator of temp would be discoloration of the metal. If the gears/axles saw heat much above 350F they will be discolored from light blue to dark. If there is no discoloration that would indicate they didn't get that hot. As someone else mentioned, the hardness can be checked very easily.
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