Leaky and Slipping 5-speed transmission

[AmishRoadster]

Hello All!
First time writing in but I have been researching the site for the last year or so to get my roadster finally up and running. I was able to get my 68 2000 on the road last summer and noticed a few leaking issues and the clutch started slipping once the motor was warmed up for a while. I just pulled the motor/trans recently and noticed oil on the flywheel/clutch, where the speedometer cable attaches, and where the shifter rod connects to the transmission. The speedometer cable looks like it was a bit beat up and leaking, but I believe I can get a new one of those. The clutch being oily looked like the oil pan gasket was leaking and seeped up into the clutch area. The leaking on the top of the transmission by the shifter I am a little foggy on how to fix. It doesn’t look like it was from the vent, but where I marked on the photo. Any help would be appreciated!

[Habitat.pat]

There is an O-ring in a cup on the right hand x on your shifter drawing. I don’t think you can replace it without pulling the tail housing off the trans. If it doesn’t leak much, just put it on the list for when you need to tear the trans down.

As for the clutch, check carefully for oil leaking @ the rear of the engine, between the head & block. This is a common issue. If not, I would think that the rear crank seal could be bad. Pull the flywheel & find the leak.

The fitting where the speedo cable attaches contains a seal.

All needed parts are available from our vendors.

Peace, Pat

[unklpat]

The plungers leak when they get old and worn. There is an o-ring solution that was used in some transmissions. Pricey to duplicate.
There is also an o-ring sandwiched between the bellhousing and center section of the trans. Oil comes out the end of the tube the throwout bearing rides on, and gets flung around the inside of the bellhousing. Pat

[Habitat.pat]

How could I forget about the trans input seal, I just replaced mine on a new transmission! Tip the trans up& see if fluid leaks out. I tipped mine up & left it overnight after replacing the seal.

Peace, Pat

[david premo]

There is also an O-ring in the bell housing between the steel sleeve that the throw out bearing rides on and the aluminum bell housing. You need to have the bell housing off the main case and drive it out to expose the O-ring on the sleeve. DO NOT use an O-ring from the hardware store, it needs to be buna or nitrile rubber or it will desinigrate. Also the speedometer seal is still available and it’s the same one on the tach drive. Both should be replaced so you don’t end up with oil in your tach or speedometer. FYI there are no O-rings on the plungers on the tail housing. Most likely the O-rings on the selector is the problem.
Dave

[redroadster]

Check the vent is clear & open too, tiny spiders luv to build in the tube then it will build pressure and leak past seals

[unklpat]

There were o-ring grooved plungers, I have seen them, and duplicated them. Very expensive to groove those plungers, but worth it if yours are worn. Pat

[AmishRoadster]

Thanks everyone for the responses, I’ll try to answer what I can! As a heads up I am a novice when it comes to working on cars, so I might have a bunch of stupid questions/responses.
I removed flywheel and plate and did not see oil leaking between head/block. It seemed like the area around the crank was dry(ish) but all along the oil pan gasket was wet. Could it be that a bad oil pan leak could cause oil to get into clutch area? The plate was only wet where the oil pan touched it. I added in some more photos that might help explain what I found while removing.
Sounds like the leak around the shifter is a pain to fix. I am hoping the speedometer cable leak is the main culprit. The underside of the car and the rear of the transmission were completed covered in gear oil, and when I wiggled the speedometer cable it would drip.
I will check to see if the vent is clear and no bugs are living in there!

[jrusso07]

Based on photo #3, I would suspect the leak is on the transmission side, the O-ring that seals the tube that the throw out bearing rides on. DO you have a pic of the inside of the bell housing? On the shift/control. There are two seals, a o-ring and a rubberized metal cap that holds the -o-ring in place. As said, You have to remove the tail piece and drive them out from the inside. See #9 and 10 in this diagram https://www.carpartsmanual.com/datsun/s ... -control#2. Also note that this diagram shows the plunger o-rings (#83). I guess not all transmissions had them.

Here's a pic of a rebuild kit from DatsunParts.com. The black circle shows the control o-ring and cap seal (shiney one). The yellow circle shows the seal on the shaft in the bell housing.

[AmishRoadster]

Thanks for the info! I have a few pictures of inside the bell housing. I plan on putting the trans upright this weekend and see if it leaks and I can take a better picture if needed. This is probably a stupid question but with this rebuild kit is it something that can easily be done or best bet to send out to a shop.

[jrusso07]

Bell housing doesn't look too bad relative to leaking. Do the shaft side down test like you plan. I set the bell housing on 2 2x4"s so that the shaft doesn't hit the ground. Put a pan under the shaft to collect anything. The rebuild kit I pictured is just the seals. They are more important things inside that you would want to check/replace liek bearings, synchros and shift forks.

[Gregs672000]

OK AmishR, I think you're getting to a point where you're going to need to consider a few things here as I see some rabbit holes opening up... namely what's your intention for this Car? Do you have a budget in mind? A Timeline? For a novice, you have quickly yanked out the motor and pulled the flywheel off no problem, so we'll done! I also read elsewhere you did carb work and ignition timing. You are now discovering some things that may require a more significant investment of time, money and tools, so understanding your general intentions and desires will help us advise you (having been there, done that with these cars!). Hope that makes sense and helps us help you.

[AmishRoadster]

Gregs672000 good questions. I intend to just drive the car for weekend rides , nothing too far away. Not making a show car, something fun to drive. I am just looking to get the car mechanically sound and drive it without much worry. (plan to work on body, and rust later!!) As far as timeline, I am hoping to get back on the road soon so I can enjoy the nice weather then, if need be, take motor back out in winter time. The main reason I took the motor out was because the clutch was slipping.

[theunz]

I agree with others that it’s likely the trans input seal leaking. The main cap looks dry and the only oil I see is on the bottom of the bell housing. The little bit of oil on the flywheel probably dribbled onto it when you pulled the engine and separated the trans. If it had been on the flywheel while the engine was running centrifugal force would have spread it out all over the flywheel.
I would check the trans input seal for leaks and replace that if necessary. At this time I wouldn’t worry about the leakage from the top of your trans. I would replace the clutch disc, pressure plate, and throw out bearing. Have the flywheel surfaced if there is enough thickness left or replace if necessary. If you’re looking for a little increase in performance you could have it lightened or replaced with an aluminum one. Probably a waste of money if you just want to tool around.
Good idea on your part to enjoy it for awhile before tackling major repairs. Good luck!

[Gregs672000]

Agree with Mike on all above and plan. Understanding what you want to do short and long term is very important. We tried to fix the same leak at the plungers the last time the trans was out without success... it can wait. If the header is bad that's an easy replacement and you'll need one anyway. Shim the upper timing chain tensioner and make sure the gasket is replaced. Make sure the tach cable isn't leaking at the distributor mount and repair as needed. Put it back together, install and enjoy the summer. Come winter you'll know more about what's needed and what it may cost, and be (hopefully) even more in love with the car. These cars are rewarding to work on and well within your ability. We can help you with all of it and save you a lot of headache.
Enjoy!