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Alright, haven't been able to work on my f100 in a while since i adopted a Bike to restore. Here's my issue, i'm tired of hearing my truck make a clunk sound when it goes into reverse, doesn't do it into drive. When im under my truck and i twist the drive shaft it barely moves, and when shaking it, the u joints do not budge, Is my problem in the rear end, tranny, or drive shaft. Is my strength just not enough to twist the drive shaft enough to make the u joints move? I have noticed when i spin tires on the snow, my drivers side tire will grab once in a while, i assume my rear end needs rebuilt.
truck has 169,000 miles
2WD, 300 I6 and a C6
Mostly original or stock.
Have you checked the fluid level back there lately? Any sign of a leak? F100 so 9" rear axle and a fill/ck port is on the front dvrs side edge. Remove it and put your pinky in there to ck the level. That would be the 1st step anyway.
I thought I read that a clunk in reverse could be something with a valve body in the tranny having an issue, especially if you’ve eliminated other drivetrain sources. My Bronco also clunks pretty good going into reverse.
It is NOT unusual to find a u-joint clunking,worn out,completely shot, and finding no play BY HAND.A quicky check by everything in neutral with no tension on the driveshaft ,yes,will a lot of times show worn u-joint(s) by twisting/moving by hand. But,just as often, the only tell tale sign is a bit of rust around a single cup. Once apart you can't believe the missing or ground up needle bearings with no play found by hand ! They get bound up and the torque of the truck is the only thing that will show the wear at times. Don't disregard the u-joints.
Ill have to check fluid in the rear end, never has been checked. The rear end is pretty well caked with grimy oil. Doesn't drip any.
The tranny has had previous problems, when i got the truck, before it would warm up it would slip out of gear, a fluid change and a quart of Lucas oil additive fixed i, at least temporarily. Ill check on the rear end fluid, if its low what weight gear oil should i use in it?
I have also noticed that when im driving, at any speed if i let off the gas it clunks a little then if i hit the gas it clunks a little, my friend claims its just old truck noises.
It would take 1/2 hr. to remove the rear u-joint yokes/little straps,and physically look at front and rear joints. Out in the open you can flop them back and forth,feel grating/grinding,SEE a problem or whatever. But,it is the ONLY way to eliminate a universal joint suspicion 100% if in the truck by hand doesn't show any play etc. At some point you will have to start digging a bit deeper and this would quickly eliminate an obvious thing like worn u-joints.
Another possibility is that the slip yoke needs to be greased. If it becomes dry the result can be a clunk going into gear. If you are lucky you will find a grease zerk on it. If not you will need to drop the driveshaft (which you may be doing if you have a u-joint problem).
I agree with everything everyone else has said. Jacking the rearend up and spinning the wheels will give you more advantage on showing you a U-joint problem. If you are low on fluid in the Pumpkin(rearend gears) you might want to take an afternoon and pull it. Check the lash of the gears before you put it back in. Also, check the gear teeth for wear, you don't know who set it up last time, and if they set the lash too close it will wear. General rule of thumb is that you should be able to pass a piece of newspaper between the ring and pinion gears without a tear in the paper. All in all, you're going to have to do a little digging. Good luck!
1. Fluid ck, add 80/90 as required. If the rear end is caked with grimy oil...you might be empty and there for get a clunk.
2. X2 yes take the pressure off the drive line. Jack up the back of the truck, put in neutral and ck the drive shaft u joints. Some thing is bad, its NOT just old truck noises...
3. Or just park truck on LEVEL ground, chalk wheels. Put in neutral ck drive shaft u joints.
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When one rear axle tire slips (on Ford it is the R/H that is normally the drive tire) and the other passenger side turns that is the sign of a LS (limited slip) rearend. Ck the axle tag for some numbers and a LS stamped on it.
fluid level is good and clearish green. I am hoping to check the u joints this Friday and possibly replace them if need be. I have had previous problems with this tranny slipping when cold. It is a limited slip rear end, it has 2.75 gears, if i went to replace these what would be a better ratio for highway cruising. right now 2000 rpm at 55 2700ish at 70, my tach is jumpy. What is a transmission rebuild like? or where to find a new one in the case i need to.
