Greetings Forum
Just purchased 1981 ford f-150 custom in july and I've fallen in love with the vehicle. I do not have extensive mechanical experience although i plan on performing extensive work on the vehicle.
half ton, 6 inline cylinder, 4 gear manual trans and I believe it does not have a limited slip diff.
The most pressing issue I'm trying to deal with is a clunking I hear and feel coming from the rear end, driveline clutch or transmission as soon as the clutch engages 2nd and 3rd gear. The clunking is avoidable with very very careful easing of the clutch. At first I assumed the problem was with the clutch linkage. The mechanical linkage is missing an equalizer bar (or z bar) bushing that I cannot find a proper replacement for anywhere. The linkage was slipping out of alignment and therefore pulling the clutch fork out at a different angle. I work in a metal shop so I fabricated a spacer myself and the linkage is functioning smoothly now so I do not believe this is the problem.

This weekend I performed an uneducated inspection of the driveline and a differential fluid change. The driveshaft was not loose and there was no lateral play, the universal joints seem solid. The rear differential housing on my vehicle does not have a drain plug OR an inspection panel (which the haynes manual i work from notes is sometimes the case). I used a hand pump to drain the fluid and noticed metal shards in the fluid. I replaced the fluid with 85w and not the specified 90w because no auto parts stores even had 90w. I need to know how I can properly inspect the ring and pinion gears or whatever might be the problem in the differential housing. And if the ring and pinion gears are the problem how should i go about repair? Is it easier to replace the gears or the entire differential? I was thinking a new limited slip diff might be nice, I could even get one with the luxury of an inspection panel. Does this work require extensive training? Any input on any of these points at all would be a huge help. THANKS! Robby

 

Robby - Welcome to FTE! That is a good looking truck. How 'bout going to the User Control Panel (User CP in the upper left) and telling us where you are located. And, a signature that gives us a bit of info about your truck helps so we don't have to always go back and re-read the whole thread to find out.

Having said that, you said the clunking comes in 2nd and 3rd. But, not 1st or 4th? And, is it a clunk while you shift, or does it continue? If continuous, does it vary with road speed or engine speed?

As for the diff, from your description you have a 9". That is a good diff and usually stand up to most things - with the exception of being run dry. To inspect it you have to pull it, which is done by pulling the axles and then removing the whole diff from the front. But, working on the diff itself is not for the amateur - especially one w/o the appropriate specialty tools. I have a fairly well-equipped shop and I farm diff work out. And, add-on limited slip units are available for the 9", so you could have someone build your 9" into a nice diff.

 

Did you lift the rear wheels off the ground and put the truck in neutral when you checked everything? Make sure you chock the front wheels when you do this. You need to get the strain off everything back there and then start wiggling and twisting stuff.

 

When you change the fluid of the diff the pumpkin needs to come out. This way you can wipe out the metal shavings and adulterants. Also you need to know if you have a LS rear already or not.If you have one and the oil you put back in it isnt the right stuff with a friction modifier added you will ruin it in short order.

Remember what Franklin said, be sure the wheels are chocked on the front before you lift the rear wheels off of the ground.