2126 Posted February 15, 2006 Share Posted February 15, 2006 I have to agree with 2126 abd Zguy36.... There is no more force applied to the engine tranny when mounting the diff solidly... Hence the telescoping AND universal jointed driveshaft... The engine/tranny and the Differential are DIVORCED... There may be a difference in "feel" because the deflection of the soft differential mount is gone... less "windup"... the drivtrain will feel more solid... but this would not add stress to the engine/tranny mounts... JohnC is correct and the solid mustache bar is a great idea... the differential front mount takes force in 2 planes...vertical...and fore and aft... fore and aft does not seem to be that big of a problem... it is the vertical force that tears things up... I am going back to a soft mount and I am adding a "strap" to hold it against the NEW crossmember under accelerating force... Just to clearify my point....I did not say there is less force on the eng/trans/driveshaft.....what I implied was, the force is actually greater at the eng/trans/driveshaft because you no longer have the soft mounts at the diff to absorb some of that energy. That energy has to be going somewhere and it's no longer getting absorbed by the soft diff mounts. Consiquently, that force (torque) is how being placed back on the eng/trans/drieshaft. Remember, for every action there is an equal and opposite reaction! Quote Link to comment Share on other sites More sharing options...
bjhines Posted February 15, 2006 Author Share Posted February 15, 2006 ok... the extra force will come in shock torque loading in the driveshaft...but it is not the kind of binding and twisting that is damaging the crossmember... You cannot convince me that the engine and tranny mounts will degrade or fatigue simply by mounting the differential solidly... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 15, 2006 Share Posted February 15, 2006 On the contrary, I'd say your motor mounts should last longer with the diff solidly mounted. Lets assume that you have a manual trans. The crank is then locked solid to the trans via the clutch, and the trans output shaft is slip yoked to the driveshaft, which is bolted to the diff. The U-joints in the driveshaft might allow the engine to move side to side, but they won't allow the engine to twist, because their function is to not allow loss in a twisting motion. So the engine might still move side to side or up and down, but it will not be able to twist, because when it tries to that torque will travel down the crank to the tranny to the driveshaft to the diff, where it hits something solid and transfers into the crossmember and into the unibody of the car. I still agree with 2126 that the torque does go through the engine, trans, and driveshaft as he says, but the question is where does it END UP? It ends up getting held tightly by the diff crossmember. So the torque either goes through to the wheels, or it starts to tear up the weakest link in the chain, which is the diff mount. Shore that up by rigidly mounting the mustache bar and now it is the driveshaft. Another way of saying it is if you could have the engine in the engine compartment with no motor mounts, the car wouldn't drive, but instead the engine would just spin (in theory). You need to control the torque of the drivetrain before it can transfer its torque to the wheels. The first thing that CAN control the torque WILL control the torque. In our example of the solid front diff mount with soft mounts everywhere else, the first thing that can control the torque is the front diff mount, because it is the only part of the system that is rigidly mounted. And the reason they get tore up is not just because of the lifting of the nose of the diff, but also because it is now controlling the torque of the whole drivetrain. In Cary's case it's a little different. He had everything rigidly mounted and still pulled the washer through the crossmember. Clearly his was isolated from the torque and failed just from the lifting, but the torque AND lifting is really going to do a number on the crossmember. I don't know how to explain myself any better, but I am pretty confident that this is what is happening. Quote Link to comment Share on other sites More sharing options...
2126 Posted February 16, 2006 Share Posted February 16, 2006 Yah Jon, I do believe we are, maybe with different terminology, saying relatively the same thing. Anyway, in Cary's case, the crossmember is failing due to an applied stress that is beyond the limits of the crossmembers design. That thin sheet metal crossmember was just never designed to handle the load a solid front diff mount will impart on it......the thin sheet metal just work hardened and began to fail, as is apparent from the stress cracks. Boy, sometimes providing detailed information from your brain to the keyboard is not always as easy as one might think! But then again, I'm not a university grade professor nor am I willing to spend the time it would take to explain it that finitely. Oh well Cary...just build a beefy crossmember that will last longer. Then, you will likely find the next weakest link in the system as it rears it's ugly head and fails too!!! Quote Link to comment Share on other sites More sharing options...
bjhines Posted February 16, 2006 Author Share Posted February 16, 2006 hey... if this stuff was easy we would all be driving Ferraris.. or our own equivalent... I simply employed a solid mount that was readily available...I used the prerequisit "poly" mustche bar mounts... and it caused a miserable failure of my rear crossmember... I really doubt that ANY mounting method using the original mustache bar would be sufficient.... Hence.... The solid mounts that are commonly sold as "upgrades" are a good way to meet god if you use them for more than just a few years... Quote Link to comment Share on other sites More sharing options...
zguy36 Posted February 16, 2006 Share Posted February 16, 2006 On the contrary' date=' I'd say your motor mounts should last longer with the diff solidly mounted. Lets assume that you have a manual trans. The crank is then locked solid to the trans via the clutch, and the trans output shaft is slip yoked to the driveshaft, which is bolted to the diff. The U-joints in the driveshaft might allow the engine to move side to side, but they won't allow the engine to twist, because their function is to not allow loss in a twisting motion. So the engine might still move side to side or up and down, but it will not be able to twist, because when it tries to that torque will travel down the crank to the tranny to the driveshaft to the diff, where it hits something solid and transfers into the crossmember and into the unibody of the car. I still agree with 2126 that the torque does go through the engine, trans, and driveshaft as he says, but the question is where does it END UP? It ends up getting held tightly by the diff crossmember. So the torque either goes through to the wheels, or it starts to tear up the weakest link in the chain, which is the diff mount. Shore that up by rigidly mounting the mustache bar and now it is the driveshaft. Another way of saying it is if you could have the engine in the engine compartment with no motor mounts, the car wouldn't drive, but instead the engine would just spin (in theory). You need to control the torque of the drivetrain before it can transfer its torque to the wheels. The first thing that CAN control the torque WILL control the torque. In our example of the solid front diff mount with soft mounts everywhere else, the first thing that can control the torque is the front diff mount, because it is the only part of the system that is rigidly mounted. And the reason they get tore up is not just because of the lifting of the nose of the diff, but also because it is now controlling the torque of the whole drivetrain. In Cary's case it's a little different. He had everything rigidly mounted and still pulled the washer through the crossmember. Clearly his was isolated from the torque and failed just from the lifting, but the torque AND lifting is really going to do a number on the crossmember. I don't know how to explain myself any better, but I am pretty confident that this is what is happening.[/quote'] I am really confused as to why you think that a motor that twists or torques over will transfer that motion into the differential. You are forgetting one crucial point here, that the block of the engine is not directly attached to the driveline. It is the crankshaft that is directly attached to the driveline, so when the block of the engine twists, this motion is not directly transfered into the crank. And isn't it the twisting of the driveline that you want? Correct me if I am wrong, but isn't it the twisting motion that is transfered through the driveline that turns the pinion of the differential, that turns the ring gear that makes your wheels go round? To make this simpler, lets analyze all directions of motion, x,y,z. Lets align the y axis with the driveline, the x axis be the other horizontal direction, and the z axis be vertical. Any linear motion of the engine in the y direction is not transfered to the diff because of the splines on the input side of the driveline. Any linear motion of the engine in the x or y direction is not transfered to the diff by the driveline because it mearly changes the angles in the u-joints (but still keeps the centerlines of the crank and pinion aligned). That takes care of any translational movement of the engine, showing no force transfered to the diff. Now for moments. A moment about the y axis transfers torque directly to the diff, now this is good because this is the torque that drives the car. A moment about the x or y axis just causes changes in driveline angles again, but this time the centerlines of the crankshaft and the pinion are not aligned, creating an out of phase u-joint sitiation which can cause vibration. The good thing about this though, is that there are no forces which would cause the engine to twist in that direction, so the forces with would cause moments about the x or y axis are zero, again translating to no transfered force to the diff. If you skimmed all of what I wrote above, in short, you can mount your engine and tranny in rubber with a solid diff mount and have NO problems. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted February 16, 2006 Share Posted February 16, 2006 If you skimmed all of what I wrote above, in short, you can mount your engine and tranny in rubber with a solid diff mount and have NO problems. I agree wholeheartedly. When I saw this idea being floated earlier, I wanted to comment, but couldn't communicate my thoughts on it effectively. The ONLY reason I solid mounted both the diff and the engine/tranny combo was out of convenience. I would have solid mounted the diff regardless of what I was doing to the engine tranny combo. Quote Link to comment Share on other sites More sharing options...
Mikelly Posted February 16, 2006 Share Posted February 16, 2006 Pete Paraska and I were discussing this thread last night and some good points come to mind... These are 30-36 year old shells. The metal is thing to start with and only gets abused and fatigued over the years. Maybe the right answer to all this isn't the mounts, or pickup points, but what they are attaching to. Maybe we need to re-enforce those areas instead of making new subframe carriers, and such? I think the movement of the pinion isn't as much an issue as what it is moving against. Thoughts? Mike Quote Link to comment Share on other sites More sharing options...
Twoeightnine Posted February 16, 2006 Share Posted February 16, 2006 Score! Rubber mount, neoprene, solid. Makes no difference. Look at it this way, exaggerated. Lets say you have a popsickel stick attached to an egg using a rubberband that has a quarter hanging from the far end of the stick. Now you want to hang a shoe from the end of the stick. The stick can handle the weight of the shoe but being concerned about the rubberband, you wrap duct tape around the egg where the rubberband attaches to the stick. Voila! Yes? No! The egg pops!! Break out the welder boys! You need a tougher egg!!! Quote Link to comment Share on other sites More sharing options...
tube80z Posted February 16, 2006 Share Posted February 16, 2006 Oh well Cary...just build a beefy crossmember that will last longer. Then, you will likely find the next weakest link in the system as it rears it's ugly head and fails too!!! I think you're correct. John also provided some good info that I thought was happenning with the rear mustache bar bending. I had a couple of ideas on how to fix this but I never got around to doing them. I was going to use a stock mount (broken) and weld it up solid and have tabs to extended below the crossmember. Then this would be bolted under the crossmember. This was all doable with flat stock, a few pieces of tube, and some bolts. This would spread the load from a sinlge point as well. I do think making a subframe for the back isn't a bad idea as it allows you to keep a lot of bits from flexing and would make the suspension mounting stiffer too. But that's a personal opinion that not everyone shares. The moral of the story is when you start using an old car really hard you need to keep an eye on it and I'm not running a V8. I torqued all bolts before I used the car and replaced them when they started to routinely loosen. Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 16, 2006 Share Posted February 16, 2006 Allright I think I figured out where I was wrong. The pistons and rods can pivot over to allow for the engine block to twist around the crankshaft. So I conceed that point. The engine block should be free to pivot even if the diff is locked down. Still if you run the solid front diff mount and rubber or poly in the back you're asking the narrow front diff mount to handle the lifting and the torque that goes to the diff. So it looks as though solid mounting both the front and the rear of the diff is the answer to making it stronger. Quote Link to comment Share on other sites More sharing options...
zguy36 Posted February 16, 2006 Share Posted February 16, 2006 The problem is that if you solid mount anything, it is going to transfer the vibrations directly, which can lead to fatigue. You are correct in saying that with only half the diff mounted, that this is worse. This concentrates all the vibrations to one spot instead of two. Here is the key for fixing the matter. Steel has an infinite fatigue life. A general rule of thumb is that steel will never break due to fatigue if the stresses that it experiences are less than half of its ultimate strength. (static breaking strength) Figuring out how much stress your parts are experiencing, now that is a different story. Your cracks were starting at bolt holes (I am assuming, I couldn't really see them in the pics) which are giant stress concentrations. The solution, if it breaks, beef it up! Quote Link to comment Share on other sites More sharing options...
bjhines Posted February 17, 2006 Author Share Posted February 17, 2006 Has anyone had a similar problem to date???.... And keep in mind.... Regardless of the mounting methods used for other major components.... The problem occurs because the front of the diff is mounted rigidly and the rear of the SAME unit is mounted in a flexible manner... the differential is ROCK HARD and will not flex... soo the forces are concentrated in the relatively weak and flexible REAR CROSSMEMBER.... destroying it over time. The original mount allowed the differential to move around without stressing the crossmember..... the crossmember was never flexed because the mount did more than enough flexing... To maybe address some confusion....the load limit of the rear crossmember was never exceeded... it was just flexed to death... The reason for stiffening up the mounting locations for the entire driveline is simple.... Less windup means a quicker and more predictable reaction... it keeps the gearshift in your hand under severe loads... and it keeps parts from crashing into the chassis under hard launches and missed shifts... Quote Link to comment Share on other sites More sharing options...
Twoeightnine Posted February 17, 2006 Share Posted February 17, 2006 bjhines Good point. Leaving the rear flex mount, and the front ridged does compound the problem by appllying leverage against the crosmember via fulcrum and leveraged forces. Regardless unless one wants to live with the rear whine that will come from an all "solid" installation, (which by BTW will still be applied to a component designed for less loads), some structural upgrades will still be required. It would be nice to know if we are looking at an isolated verses reoccuring event however. I will do some poking around. Many thanks, Quote Link to comment Share on other sites More sharing options...
blueovalz Posted February 18, 2006 Share Posted February 18, 2006 It's been brought up twice (I think) over the last few years, so it is nothing common, but I believe they were all front solid, rear flex mounting. Quote Link to comment Share on other sites More sharing options...
Twoeightnine Posted February 21, 2006 Share Posted February 21, 2006 Yes Blueoval. I found only a couple of instances as well. I guess if it fails one could beef it or replace it. Im sure you yourself have put some twist on a few. By the way, I really like the Blue oval Z. especially the Ford power aspect!! I might be bais however. many thanks for your hard work!! Quote Link to comment Share on other sites More sharing options...
BlackBeaut Posted February 24, 2006 Share Posted February 24, 2006 Ah, coincidentally I've just got this back from the engineers. A typical OTT Rob design I admit - designed with my short nose diff cradle in mind rather than to deal with the issue raised in this thread, but I'm sure it could cope. Cheers, Rob Quote Link to comment Share on other sites More sharing options...
blueovalz Posted February 24, 2006 Share Posted February 24, 2006 danged firewall Quote Link to comment Share on other sites More sharing options...
BlackBeaut Posted February 24, 2006 Share Posted February 24, 2006 S'up? Can't you see the pics? I can email you them if you want to PM me your address. Cheers, Rob Quote Link to comment Share on other sites More sharing options...
bjhines Posted February 24, 2006 Author Share Posted February 24, 2006 that is stout!!! and light!!! nice work... I dont have access to the machine tools to do anything like that.... But shouldnt the inside corners be radiused to prevent cracking...??? especially if it has to withstand twisting stress... Quote Link to comment Share on other sites More sharing options...
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