Tailshaft Leak?

[MikeyB]

I am getting trans fluid under the bed of my truck. The fluid collects on the bottom of the bed and drips onto my driveway. It appears to be flinging off the first u-joint at the transmission tailshaft. No fluid is visible on the u-joint or tailshaft but you can see the pattern of spray on the bottom of the bed. The transfer case shows no leakage or the trans itself. Anyone experience this?

Mike

[madmatt]

sure you've not got the "pump rub" hole????

[MikeyB]

sure you've not got the "pump rub" hole????

Pretty sure. There is no fluid visible anywhere except for the spray pattern that is dripping from the bottom of the bed. If the transfer case was leaking, wouldn't it puddle below the tc while it was sitting? The only small puddle and drips I have are from the bed bottom at the first u-joint from the trans. Where does the clip wear through on the tc? I have looked at the transfer case and front differential(?) and case and found no fluid leaks at all.

Thanks,
Mike

[madmatt]

Since it only leaks while in gear, it usually goes everywhere and puddles in random places. I've got a housing out in my shop that has the hole in it. I'll try to remember to get a pic of it tomorrow to show you where to look. It is on the right side right, back half, above the fluid level.

[cowboywildbill]

Had the same problem on our 07 classic. Dealer replaced the tailshaft seal. It didn't stop the leak. He then replaced the seal again along with a new yoke. Problem solved. Also when looking at the old seals and yoke, we couldn't see any visible reason for it to leak, but they did. The dealer said he had seen this on a couple of trucks before.

[DmaxMaverick]

If you have no sign of leakage anywhere on/under the transfer case, then the leak is likely at the shaft seal. But, that doesn't mean the seal is bad. It doesn't take much fluid to make a big mess.

Have you replaced the U-joints (either one). Is it a one piece or 2 piece shaft? Balance is very important. If a shaft is not balanced, not only can it cause a vibration (but not always), it can cause seal distortion when at higher speeds. Cause or effect, it usually indicates a failed or failing output shaft yoke and/or output shaft bearing. A failed carrier bearing (2 piece shaft) can also do the same. The same effect can be seen from a bad rear-most U-joint, but it usually causes pinion seal issues. If you have replaced your U-joints, perhaps you reinstalled the yoke 180° off? The shafts are factory balanced fully assembled, and yoke/shaft orientation is important, as well as a caution in the service manual.

[MikeyB]

I must admit I am stumped. Spent hours under the truck today looking for the dreaded pinhole case leak but couldn't find it. I have a two piece driveshaft which has never been apart. Original u-joints are installed. The only seepage I can find is out the tailshaft itself. it looks like the output shaft has a metal cap or such at the yoke. If I let it sit I can see seepage, nothing else. Cleaned the underside of the truck and checked the case in the usual spots for the pinhole leak and found nothing. Would the dextron leak out while sitting so I could atleast see it? Or must the truck be driven for leakage to occur? Again, I am stumped any info would be much appreciated.

Thanks,
Mike




If you have no sign of leakage anywhere on/under the transfer case, then the leak is likely at the shaft seal. But, that doesn't mean the seal is bad. It doesn't take much fluid to make a big mess.

Have you replaced the U-joints (either one). Is it a one piece or 2 piece shaft? Balance is very important. If a shaft is not balanced, not only can it cause a vibration (but not always), it can cause seal distortion when at higher speeds. Cause or effect, it usually indicates a failed or failing output shaft yoke and/or output shaft bearing. A failed carrier bearing (2 piece shaft) can also do the same. The same effect can be seen from a bad rear-most U-joint, but it usually causes pinion seal issues. If you have replaced your U-joints, perhaps you reinstalled the yoke 180° off? The shafts are factory balanced fully assembled, and yoke/shaft orientation is important, as well as a caution in the service manual.

[DmaxMaverick]

There are several things to check/confirm. If your carrier bearing and isolator has never been changed, it is probably due, considering the time/mileage. Many chassis configurations had the 2 piece shaft replaced with a one piece for another reason, but it could just as easily cause a leak at the output seal. Harmonic vibrations can cause a seal to "dance" on the yoke sealing surface, at certain speeds. If the yoke sealing surface is pitted, or damaged in any way, it can leak. If the tension spring in the seal pops off, the seal can leak. If the TC is overfilled, it can leak (thermal expansion forcing fluid out the vent). If the vent is plugged, it can leak (thermal expansion, causing the fluid to take the path of least resistance, the seal).

Check the output shaft and yoke for play. Chock the wheels and place the tranny out of P or gear. If the shaft has any play, it's either the yoke, output shaft bearing, or a U-joint. Also a good time to inspect the carrier bearing and isolator. Any of which can cause a leak under specific conditions. If this is the case, it will only get worse, to a point it leaks while not moving, or worse.

[MikeyB]

There are several things to check/confirm. If your carrier bearing and isolator has never been changed, it is probably due, considering the time/mileage. Many chassis configurations had the 2 piece shaft replaced with a one piece for another reason, but it could just as easily cause a leak at the output seal. Harmonic vibrations can cause a seal to "dance" on the yoke sealing surface, at certain speeds. If the yoke sealing surface is pitted, or damaged in any way, it can leak. If the tension spring in the seal pops off, the seal can leak. If the TC is overfilled, it can leak (thermal expansion forcing fluid out the vent). If the vent is plugged, it can leak (thermal expansion, causing the fluid to take the path of least resistance, the seal).

Check the output shaft and yoke for play. Chock the wheels and place the tranny out of P or gear. If the shaft has any play, it's either the yoke, output shaft bearing, or a U-joint. Also a good time to inspect the carrier bearing and isolator. Any of which can cause a leak under specific conditions. If this is the case, it will only get worse, to a point it leaks while not moving, or worse.


I have not found the vent, where is it located? I found the rubber plug that allows the snap ring access and checked it but did not find a vent. On another topic, I remember reading that the transmission had a service bulletin for the dipstick not being vented. This allowed pressurized fluid to coat the bottom of the truck and an improved dip stick was available. Wondering if I am chasing the wrong problem....

Thanks for all your help,
Mike

[DmaxMaverick]

The dipstick update is a valid TSB. Most do not see this problem. If this were your problem, you'd have fluid in more places than what you are seeing. I don't think this is your problem, or the "spray" above the U-joint would be the lesser evidence.

The vent is located above the encoder motor, in front of the chaincase, , about mid way between the main barrel (planetary drum) and the front output shaft. If it is leaking from the vent, follow the vent tube. If it has a hose attached, find its termination. If no hose, it should have a vent cap in place (don't know why, but some have this).

[CoyleJR]

I have a 2006, Chevy, D/A, CC, DRW, LBZ, 4X4, with 123,860 miles. Recently it was spraying transfer case fluid on the bottom of the cab. It took some time to locate the precise cause of the leak. It turned out to be the front driveshaft yoke leakng behind the U-joint. On the back of the yoke there is a cap much like a freezeplug and it was seeping fluid around this cap. I did not need to replace any parts. I cleaned the area around the cap and the yoke and sealed the seam with J B Weld. It has not leaked a drop since and it is towing a 38 foot, 16k, 5th wheel full time.