Kinda confused what could be leaking from the yoke. Car has been sitting for a couple months while i do some mods. Looked underneath today and on the garage floor was a half dollar sized spot under the driveshaft yoke. I touched it and it was an oily but a clear fluid residue. It smelled like grease too. I touched the yoke and there was no excessive wetness or grease that came off on my fingers. No leaks from the pumpkin either. What could this fluid be and what should i check out?
Leaking fluid from driveshaft yoke
- Thread starter spederman
- Start date
1low03gt
20+ Year Stangneter 
Got any pics?
It could be either a seal at the tail stock of the trans,or sometimes it could be the bushing inside the tail stock,but its most likely the seal.Not uncommon after time.
It could be either a seal at the tail stock of the trans,or sometimes it could be the bushing inside the tail stock,but its most likely the seal.Not uncommon after time.
trinity_gt
10 Year Member
When I had my MGW aftermarket shifter on mine, it leaked at the flange and dripped fluid in that way. I thought I had a yoke-seal leak but it turned out fluid leaking from the top was running down and just appearing like it...
Pearl02
Member
Where was it leaking from? Was it leaking from the top of the shifter or where the shifter bolts onto the tranny? I also had a leak where I thought was the tailshaft. I didn't feel like messing with it so I let Ford repair it. It look's like it's leaking again. It's been less than 2 months. I'm going to take it back to Ford. Pearl02.
dustang50
Member
I had the same problem. Turned out to be a bad differential gasket. Replaced it & no leaks now. Better take care of it now - it's throwing fluid all over the underneath of your car & eventually it'll get onto your brake pads & you won't be able to stop.
stangman11
Member
It sounds to me simply a pinion seal on the diff. In between the drive shaft yoke and the diff pinion gear is a little round seal, they are known to leak over time with normal wear. Not hard to replace but you may have to buy a seal puller to be able to get it out and a seal drive to make sure it goes in straight.
A leak from the rear of the driveshaft is much different from a leak at the front. I think the term yoke is for the front end of the driveshaft, which engauges the transmission. The rear one, I would call a flange.
In any case, a leak there is very possibly differential fluid. Is the fluid very thick? Differential fluid can be lighter colored. If it is thick fluid, then it is most likely the pinion seal. Be aware that it may be leaking because of a bad pinion bearing allowing too much play!
In any case, a leak there is very possibly differential fluid. Is the fluid very thick? Differential fluid can be lighter colored. If it is thick fluid, then it is most likely the pinion seal. Be aware that it may be leaking because of a bad pinion bearing allowing too much play!
stangman11
Member
I agree with bhuff30, it def sounds more like a pinion seal and diff fluid is actually very clean, most of the time though it is never changed and is extemely dirty but when new its a nice light brown color. Another way to tell if its diff fluid is that it smells TERRIBLE, at least to me.
Got underneath and took some pics: This is the rear of the driveshaft, you can see the drops of oil on the u joint, so think its the pinion seal?
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wmburns
SN Certified Technician
how to replace pinion seal
Note, if the goal is to just replace the pinion seal, you can do the job without replacing the crush sleeve. It will require a measurement of the bearing pre-load before the pinion nut is removed. Pre-load is measured with the drive shaft, wheels and breaks removed.
Drain the fluid by removing the rear cover. Remove the pinion nut. It is very tight with thread locker. The Ford special flange holding tool does help a lot. Use a gear puller to remove the flange
Remove the old pinion seal being careful to not scratch the mating surfaces. Install the new seal with a small amount of RTV around the outside. It is vital to install the seal straight. Ford has a special tool to press it into place. I used a thick block of wood with a large hole cut through it. The wood has to be thicker than the pinion shaft is long. Carefully tap the seal into place. If it does not go in straight, it is recommended to get a new seal.
Re-install the flange. Ford has another special tool for this. It is possible to use the OLD pinion nut to press the flange into place (do not use the new nut). Remove the old nut. Put a small amount of RTV between the nut and washer. This will prevent migration through the threads. Torque the new nut to about 70 foot pounds.
Here is where things get interesting. Measure the pinion bearing pre-load. If it is less than the original value, add 5-10 foot pounds to the pinion nut and measure again. Keep doing this until the pre-load is equal or slightly greater than the original value. Do not back off the nut to reduce pre-load. There is a min/max specification for used bearings of 8-14 lb-in.
If you go too far, the service manual states to install a new crush sleeve and start over with the pre-load tests.
Lessons learned: I used an inexpensive beam style inch pound torque wrench. I found it difficult to read the scale as the flange was being turned. A digital wrench with a high value record would have helped. The repeated sequence of installing the holding tool, torque nut, remove tool, measure pre-load is very tedious (especially on your back).
Project results: I stopped the seal from leaking. However, I believe I let the pre-load get too high. 6 months later the rear end started making noise. At the time, I couldn’t find what was wrong. I got p*i*s*s*e*d off and had a pro rebuild the entire rear end. Definitely mixed results.
A close post mortem inspection found the pinion bearing was worn out. Almost surely from excessive pre-load.
Note, if the goal is to just replace the pinion seal, you can do the job without replacing the crush sleeve. It will require a measurement of the bearing pre-load before the pinion nut is removed. Pre-load is measured with the drive shaft, wheels and breaks removed.
Drain the fluid by removing the rear cover. Remove the pinion nut. It is very tight with thread locker. The Ford special flange holding tool does help a lot. Use a gear puller to remove the flange
Remove the old pinion seal being careful to not scratch the mating surfaces. Install the new seal with a small amount of RTV around the outside. It is vital to install the seal straight. Ford has a special tool to press it into place. I used a thick block of wood with a large hole cut through it. The wood has to be thicker than the pinion shaft is long. Carefully tap the seal into place. If it does not go in straight, it is recommended to get a new seal.
Re-install the flange. Ford has another special tool for this. It is possible to use the OLD pinion nut to press the flange into place (do not use the new nut). Remove the old nut. Put a small amount of RTV between the nut and washer. This will prevent migration through the threads. Torque the new nut to about 70 foot pounds.
Here is where things get interesting. Measure the pinion bearing pre-load. If it is less than the original value, add 5-10 foot pounds to the pinion nut and measure again. Keep doing this until the pre-load is equal or slightly greater than the original value. Do not back off the nut to reduce pre-load. There is a min/max specification for used bearings of 8-14 lb-in.
If you go too far, the service manual states to install a new crush sleeve and start over with the pre-load tests.
Lessons learned: I used an inexpensive beam style inch pound torque wrench. I found it difficult to read the scale as the flange was being turned. A digital wrench with a high value record would have helped. The repeated sequence of installing the holding tool, torque nut, remove tool, measure pre-load is very tedious (especially on your back).
Project results: I stopped the seal from leaking. However, I believe I let the pre-load get too high. 6 months later the rear end started making noise. At the time, I couldn’t find what was wrong. I got p*i*s*s*e*d off and had a pro rebuild the entire rear end. Definitely mixed results.
A close post mortem inspection found the pinion bearing was worn out. Almost surely from excessive pre-load.
stangman11
Member
WMburns,
I found this post really interesting and I have a question if you wouldnt mind answering if for me, but I dont have that much experience with differentials, when measuring pinion bearing pre load are you putting a dial indicator on the end of the pinion shaft and simply moving it in and out or measuring how far in the pinion gear is in relation to the crush sleeve? Just a little insight would be appreciated thank you.
I found this post really interesting and I have a question if you wouldnt mind answering if for me, but I dont have that much experience with differentials, when measuring pinion bearing pre load are you putting a dial indicator on the end of the pinion shaft and simply moving it in and out or measuring how far in the pinion gear is in relation to the crush sleeve? Just a little insight would be appreciated thank you.
wmburns
SN Certified Technician
You are measuring the force required to rotate the diff. The force is rather small (inch-pound). Since the pinion nut is rather large and the torque wrench was small, I also needed two adapters to reduce 1/2"s drive to 1/4" drive.
As the pre-load is increase, it pushes the bearings into the race. This increases the force required to turn the pinion. That force is the pre-load.
If there is any in/out play in the pinion bearing, then there is NO pre-load. Hence the reason a dial indicator is not used.
The problem I had getting a good measurement of pre-load was with the diff on the car, it is difficult to rotate the wrench through a large arc and still read the scale. Remember, it will take a slightly higher force to start rotation (break away force). Do not use the break away. Use the steady state force.
trinity_gt
10 Year Member
To measure the preload you mount a large socket on an inch-pound torque wrench, like this:
(really should be a dial-type)
and rotate the pinion in its normal direction of rotation, noting the steady-state torque required to turn it. It might be, say, 15in-lbs. Remember this number.
Take the pinion nut off, remove the drive flange, oil slinger etc and replace the seal. When you re-assemble it, don't just impact the pinion nut in place. Instead, tighten it and measure the torque to turn the pinion again. Keep tightening the pinion nut until you see the same number -- e.g. 15inlbs -- you saw before taking it apart.
You have to sneak up on the torque (preload). If you go too far, you'll crush the sleeve and won't be able to get back to the desired preload without replacing it.
BTW, I didn't read every post in the thread but regarding your oil leak: Have you verified that the differential is not simply over-filled?
Yeah, the differential hasnt been touched since i had gears installed a few years ago. i think i'll take it to a shop & have it looked at, i dont like messing with the rear diff
stangman11
Member
Trinity GT,
Thanks that makes things alot clearer for me. I actually do remember doing that before it has just been a really long time since I have done any diff work what so ever thanks for the info though I appreciate it.
Thanks that makes things alot clearer for me. I actually do remember doing that before it has just been a really long time since I have done any diff work what so ever thanks for the info though I appreciate it.
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