I have a 1999 f250 SuperDuty with a nasty vibration That begins at about 70mph. The truck is an extended cab 5.4l Manual trans 4X4 with a one piece driveshaft (No mid bearing). The Vibration appears to me to be a driveline vibration that is speed dependent. It is the same in gear, out of gear clutch in or out. I have replaced the wheel bearings/hub assemblies on all four corners, completely rebuilt and balanced the driveshaft the driveshaft, removed the front driveshaft, put brand new tires mounted and balanced on all four corners, new clutch, had the flywheel turned and balanced, and replaced the transfer case output bearings. Pinion bearing feels tight and does not leak. Also the Input in the trans felt tight when i had the trans out. The truck had the vibration when i bought the truck and still vibrates after i have done all of this work. i did not change the motor mounts because they looked fine. when i bought the truck the tabs on the extension housing holding the trans-mount to the trans were broken so i make a huge "exhaust clamp" to straddle the trans and bolt to the trans mount. After driving the truck up north last weekend the truck seems to shake going taking of at lower rpm as if the motor mounts and trans mounts are bad. I guess my questions is can a bad trans mount, motor mounts cause this Vibration at highway speed. if so is there a way to fasten the trans-mount to the extension housing without replacing the extension housing. If not what else can cause this issue?
I would bet it is the trans mount and I would be replacing that as it sounds like you spent the time on money on ruling out pretty much everything else. When you take off you are putting a lot of torque on the engine and trans. If it is not mounted correctly you can get a bump, noise and etc. At highway speeds the driveshaft is spinning fast which can cause a vibration if the trans is not mounted correctly. Poor trans mounts will just put more stress on the engine mounts and possible wear them prematurely.
It has a new mount just the tabs it bolts to on the extension housing are busted off. i made a big exhaust clamp from a threaded rod and chunk of angle iron to mount the trans to the trans mount. is there a better way i can secure the trans to the mount without replacing the extension housing? I have to pull the transfer case and i Have not been able to find one for a 4x4 5speed trans anywhere(including junkyards, Ford dealer and online). i only found some for the automatic trans.
I did some searching it it looks like Ford discontinued the extension housing you need. So you are stuck with repairing what you got, finding one in a junk yard or coming across one on Ebay or similar place. You may be surprised what you can find on Ebay. If you would pull the extension and find a GOOD welder/fabricator I am confident he could weld new "ears" on and add some reinforcement to prevent future breakage. I do/have done a decent amount of aluminum casting repairs with both MIG and TIG and it can be done with the know how and experience. The 5 speed was also used in HD trucks made prior to 99' so you MAY be able to find a serviceable replacement from them. The 6.8l used the 5 speed for 99' also.
It looks like a break at the trans extension on the 5 and 6 speed is fairly common which leads me to believe it can see quite a bit of load at times. Your repair may be allowing just enough movement in the wrong directions that are causing vibration.
If the mounting tabs are busted off I would make some new ones out of some 6061 bar stock and fit them to the case. I would also add some gussets with some thinner 6061 bar stock for extra strength. You have to chamfer both the new tabs and the case to make sure you get weld penetration. After cleaning the area and chamfering, bolt the tabs down to a piece of steel with holes that match the mount to ensure the tabs stay flat and the holes align. The entire extension and tabs are going to have to be preheated prior to welding to both burn off any impurities and help with weld quality. Aluminum takes a lot of heat to get a puddle and a cold casting can make things much worse. You can use an aluminum MIG with a spool gun or push pull gun but I would TIG it to held ensure penetration and to control the bead better.
ok so ill have to remove the extension housing from the truck if im going to pre-heat it correct? too much heat will be bad for seals and gaskets i would assume. i only have access to a MIG gun. I could wait till college starts up to borrow a tig machine but my skills are limited with TIG so i will Probly just stick to MIG.
Im going to replace motor mounts next week and tighten up my half *** trans mount and see if that makes a difference. i need the truck Labor day to Haul my boat but after that I will Take the insurance off of the truck and back onto my focus so i will be able to work on the truck and fix it right. Thanks for the advice dkf hopefully this helps.
Yeah the housing will have to be removed. You will need to get it to properly clean, prep, preheat and weld. This is not a repair job for a beginner. A standard MIG welder will not feed aluminum wire fast enough. You need a spool gun or a push pull gun with a fast enough feed rate. I have a MIG spool gun and TIG and I would use the TIG for this repair.
If you have a weld shop at college you might be able to get the instructor to weld your part for you.(assuming he is proficient with TIG aluminum.