I'm currently tracking down a fixing all of the leaks (3) in my 58 F-100. The engine drips (I think it's the valve covers), the rear differential drips (obvious what that is), BUT, the mystery leak is where the driveshaft connects to the transmission.
From what I can tell, it looks like the driveshaft isn't "pushed in" as far as it should be into the transmission. AND, from the looks of things, the leak has been there for a while...the cab over the leak is wet with about an inch of gunk.
Is there a particular seal there? What's the fix?

Thanks in advance!

TC

 

Sounds like the rear transmission seal. Don't know why the driveshaft wouldn't be pushed in all the way.
Bruce

 

There is a seal in the end of the transmission tail shaft. The drive shaft has to be in past the seal or the out put shaft splines would not be engaged with the driveshaft yoke splines. Thus no driveshaft turning when the transmission is in gear. Replace the transmission shaft seal and check the driveshaft yoke for excessive wear. Also your out put shaft bushing could be worn and allowing the out put shaft to wobble at speeds thus causing excessive seal wear. These are a few things to start looking at.

Michelle
Chelle's 56 Hauler

 

58,

Driveshafts aren't supposed to be "pushed in" as far as it can. There is supposed to be about a 1 to 1.5 inch gap between the transmission seal and the yoke. This is to allow the shaft to move in and out as the rear end travels up and down. If pushed in all the way, it will damage the seal and if not far enough, could create a wobble as Michele referred to and could also damage the seal. If the output shaft bushing is damaged, you should also be feeling a vibration...

Vern

 

I'll post a picture tonight to illustrate what I mean by "not pushed in"...what prompted me to say that is that part of the section of the driveshaft between the transmission and the yoke is really shiny...giving it the appearance that it used to be in, and now it's slipped out.
This is truly my first experience dealing with driveshafts, so I'm clueless to how it should look.

TC

 

Don't know what tranny you have, but I had a rear tranny bushing on my c4. It cost $40 bucks and about an hour at the tranny shop. The cost included a universal joint.

Jet Jock

 

Previous responders have covered the bases: Sounds like you have a worn seal, bushing, or slip yoke. Do not consider altering your driveshaft length yet. You should see some shinning metal on the slip yoke. This is because the yoke is moving in and out of the trans, as it should. If your driveshaft is too short, it may fall out, a disaster. If it is too long, the slip yoke will bump the rear of the transmission and may break the transmission case. It is more likely that you have a wear problem on a 1958 truck than a msimatched part problem. (unless you recently cobblled the vehicle together from a pile of parts.) By the way, since you are leaking trans fluid, be sure to check the level in the trans to make sure it is not too low.

 

how do i check the transmission fluid? It's the original manual 3 speed. There's no dipstick. And furthermore, how do I add more?

thanks!

 

Look for a fill plug on the side of the trans. I am not familiar with the 58 trans, but it should have either a male or female square plug. Remove the plug and stick your finger in the hole. You should feel fluid. If you do not, add fluid until it runs out the hole and replace the plug. Do some research and make sure you add the proper fluid and check the proper fill hole. I looked at your gallery and it seems like you have a relatively undesturbed truck. Since you found a lot of "gunk" sprayed onto the underbody from the rear of the trans, I would think that your driveshaft had been in use for some time and is the proper length. Good luck on stopping the oil leaks. It is very satisfying to eliminate leaks and have a clean driveway. (been there)

 

Forgot to address the actual adding of fluid: You need to get a container with a fill tube of some type that allows you to pour the fluid into the plug hole. This can be tough. Sometimes you have to use a squeeze bottle or whatever works. After you determine what the proper weight fluid is, you may just take the truck to an oil change joint and have them do it. Unless you have a badly worn slip joint that needs to be replaced or need new u joints, having the seal and/or bushing replaced is one of the cheaper repairs. You may want to make a few phone calls to some transmission shops or repair places and see what they would charge. Then at least you know what your saving if you buy your parts and do it yourself.

 

Cool! Thanks!

How tough is it to change that yoke seal myself?
I also have a really leaky differential that has bolts on the driveshaft side, so maybe I can spend an afternoon replacing seals on both ends with the driveshaft out. Never done it, want to learn. Is it worth a shot?

Also, how do I determine what weight oil to use? the stuff that's in there now is thick and clear like Karo syrup, and it STINKS.


TC

 

TC,

Haven't replaced a seal on a transmission just like yours, but I have replaced them on other transmissions and it is a pretty easy job. Pull the driveshaft out and use a large screwdriver of something similar and just pry out the old seal. Place a pan under the transmission because some gear oil will leak out. Clean the area well of dirt and grease and tap the new seal into place with a small hammer or seal driver. Make a mental note of which way the seal goes in because they can be put in backwards. If you have some large sockets they make good seal drivers. Most standard transmissions and rear ends use 90-120 weight gear oil, but you should consult a shop manual to be sure on yours. It's supposed to be thick because it is heavy weight oil. It stinks because it has probably never been changed.

Vern

 

To add to information already provided: Since your original ojective was to eliminate leaks, and no mention of driveline problems was mentioned, I presume you are happy with the drivetrain. (no vibrations). If that is the case, when you remove the driveshaft (d/s) be sure to mark the d/s yoke and the pinion yoke so you replace the d/s in the same orientation as it was removed. If you replace the u joints also mark the front yokes to maintain orientation. Use a punch or a marker. Tightening the u bolts on the rear end yoke is tricky because you can't get a torque wrench on the nuts to obtain an accurate 14 to 17 ft lbs. I have read that the best way to tighten the u bolt nuts is to tighten the nuts until the lock washers (supposed to be new) are flat, then tighten 1/8 additional turn. Too tight and you cause premature wear on the u joint cups. I use a marker to paint a line across the yoke, lock washers and nuts. Then I check to see if the nuts have moved after driving for a while. Changing the seal on the differential is somewhat serious. First, the pinion nut is torqued to about 275 ft lbs. Removing yours may prove to be very difficult with typical home tools. (Then you have to retorque to that spec after putting in the new seal.) Also, there is a "crush tube" inside the rear end that sets the pinion preload. The manual says replace the crush tube if you remove the yoke. However, an experienced person can replace the seal without replacing the crush tube. Bottom line (imo): save some money by replacing the other seals and take the truck in to have the differential seal replaced. Same caution as with the trans: check the fluid level in the rear end!

Good luck, let us know how it all turns out
Mike

 

Thanks for the info and advice. I'll post again to report what I do.

TC

 

TC , my thought processes sometimes are a bit slow, but better than no thought process at all. You mentioned that you had "gunk" on the underbody and both the trans and pinion seals were leaking. You also noted that the trans fluid stinks. This means to me that you were able to touch the fluid level with your finger, meaning the trans fluid was not all that low. It is possible that the leaks you have are merely dripping from overgreased u-joints. I suggest you clean the cab underbody and also the bed underbody. Smell the gunk and see if it smells more like trans fluid or grease. Also, clean the u-joints until you are sure all excess grease is removed. I'll bet your u joints have grease fittings (a lot of replacement fittings do). Drive around for a while with clean u joints and see if your leaks reappear. If they reappear, smell the gunk and if the seals are leaking, you'll know because it smells like rear end/trans dope.