'80 Datsun 720 - 5 speed manual transmission popping out of 5th gear

[zwebslinger]

I've scoured the 720 forum for this exact issue for this year, but haven't seen anything that matches yet.

 

I have an '80 720, 2wd that I grew up around.  My uncle just have her to me after sitting in a garage for 10 years.

I put a 32/36 Weber on her and did a ton of restoring/replacing.

Luckily the engine purrs like a well oiled sewing machine and the oil was like honey (obviously I replaced it due to age).

 

My only issue at this point is that the transmission is very picky about the RPM being exact before it will allow you to smoothly put it into the next gear.

Same with the downshifting.  It just won't let you put it in a lower gear until the RPM is right.

This is no big deal, but what is a big deal is that it pops out of 5th gear.

 

I hadn't replaced the gl4 gear oil yet, and it did lose a good amount when I replaced the output seal on the transmission when I had the driveshaft out to replace the u-joints.

I still haven't replaced the gear oil since I can't get the drain plug loose.  Looks like some sort of specialty socket is required. 

Instead I felt with my finger in the fill hole and I could feel plenty of oil in there, but topped it off till it ran out nonetheless. 

 

After topping off, it will stay in 5th for a little while but pops out once you go over 50mph or so.

Reverse works just fine.

4th gear sounds way too stressful (high rpm) at speeds over about 55 (Truck came with no tach but intend to install one soon). 

I certainly wouldn't want to drive on the interstate like that.

 

Ideas? 

Thanks in advance!

[datzenmike]

Use a 1/2" ratchet or breaker bar without a socket on them to fit the drain or fill bung. I place a 8" length of pipe over the handle to increase the length and leverage.

 

Don't let the 4th gear sound bother you. It's only sound and in no way is the engine at any risk at that speed. At 80 MPH in 4th your engine is only turning 4,100 RPM... it's nothing. All 5th does is lower the RPMs to 3,600 at 80 MPH.

 

 The transmission should not be difficult to up shift. As a test idle in neutral with the clutch pedal up. Depress the pedal and slowly shift into reverse.... is there any grinding of gears????

[zwebslinger]

I shall try that when I'm out of work in a few hours. 

I did try the breaker bar with no socket, however it is such a shallow hole that it just can't get the bite needed to put torque on it.

Also, either it's really boogered up or it seems to be some sort of squareish star pattern as opposed to being a nice and square 1/2 inch hole.

 

I REALLY miss 5th.   When I put it in 5th and hold it there, the engine is just so much quieter when doing 50+mph.

[zwebslinger]

https://photos.app.goo.gl/Ba8YajJ9qMhdqkWD7

 

Goes into every gear very smoothly when idling.

[datzenmike]

Only need to know about reverse. If grinding, the clutch, for what ever reason, is not releasing and that will make up shifting when driving very difficult.

 

So when up shifting the shifter is hard to push into gear??

[bottomwatcher]

Classic bad countershaft bearing symptoms. Others are all gears are noisy except 4th. You can feel it in the stick if 4th feels smoother and shifts easier classic counterbearing issue.

[datzenmike]

There was no mention of noise.

 

The mainshaft nut used to come loose on earlier 71Bs. This holds 5th and reverse in place on the mainshaft. Newer ones had a skirt around the nut that could be staked to the groove cut into the threads. Years ago I had a 5 speed that started jumping out of gear, got worse and worse and in 2 weeks 2nd went away also. Should have taken it apart.

[bottomwatcher]

I have had 3 blow countershaft bearings, on 1 5th gear walked off the shaft. It was just suddenly gone. I drove from California to Florida like that and a while longer as a 4 speed. The countershaft issues started with 5th jumping out. Anyways don't drive it like this because there is hope if the carnage hasn't started and countershaft bearings at least the front and rears are easy to change. Clean the inside of the plug with a pick and you need a 1/2 inch breaker bar and a propane torch. You need to be able to get fully under the truck so you can press the bar "home" in the plug while loosening it to avoid stripping. Practice first because you want to work quick and not screw up. Once in position heat the aluminum housing around the plug, you want the plug to stay cold. Just slowly circle for a minute, set the torch out of the way and get to loosening. The faster you start after heating the better the chance of success. There is a magnet on the plug small metal good. Bearing cages, balls and gear teeth bad.

[datzenmike]

Usually it's the front counter shaft bearing that does all or most of the work and gets growley. There's a smaller one in the adapter plate and one more in the rear case. Between these two is the counter reverse and counter 5th drive gear. Fifth gear is on the main shaft above this.

[zwebslinger]

1 hour ago, datzenmike said:

Only need to know about reverse. If grinding, the clutch, for what ever reason, is not releasing and that will make up shifting when driving very difficult.

 

So when up shifting the shifter is hard to push into gear??

If I wanted to do a low speed shift through all of my gears, it is not at all possible.  Matter of fact, 2nd gear is not possible without being at the top of first.

You could probably force it in there, but it's like it isn't lined up with the gate and it just sounds like a grind.

However if you are at the top of each gear, it slides right in nice and smooth.  If a bit early, it'll grind just a smidge but will go in.

So basically the more you drive it, you could pretty much get it to shift perfectly by learning exactly when to shift to avoid that grind.

Downshifting will NOT let you put it into a lower gear till you are going a certain speed for each one. 

First gear you've practically gotta be stopped, barely rolling.  But it goes in like butter once you're almost stopped.

Very weird.

[datzenmike]

How much oil did you have to put in it????? to top it up?

[zwebslinger]

3 minutes ago, datzenmike said:

How much oil did you have to put in it????? to top it up?

Bout a pint and a half.  More came out of that rear seal void than I expected.  However I only drove it about a mile, not jamming through gears or racing it and no faster than 50 when it was low.

[datzenmike]

So 1.25 liters left, more than enough. When did the stiff shifting happen then???

[zwebslinger]

4 minutes ago, datzenmike said:

So 1.25 liters left, more than enough. When did the stiff shifting happen then???

Upon receipt of Betsy.  She was parked in a garage in Florida for the last 10 years. 

I paid to have her brought to Virginia in an enclosed trailer rather than drag her up.

 

Took a while to discover the shifting as I had to rebuild the brake system and replace tires, bearings, etc.

Got lucky to find the gas tank was squeaky clean inside.

 

He said she was shifting fine when parked, and I know first hand he was extremely gentle with her since 1980.

Could something be sticking from sitting so long?

[zwebslinger]

Oh, and at first I thought it was popping out of 5th because once I got going about 45mph, the entire truck was shaking like a washing machine full of quarters.

Discovered that the front u-joint was demolished.  I was very hopeful that it was the horrible vibration that was popping it out.

However after replacing the u-joints, the vibration is gone but it's still spitting out 5th. 

[bottomwatcher]

Ok I am still thinking countershaft bearing and yes it is the front one that takes a dump. Also you are shifting kind of soon. These 4 cylinder Japanese motors are happiest reving a bit. Like don't shift before 3k otherwise they will kind of lug on the next gear. I never put it in 5th before 55. I am sure others will chime in but if you are used to driving a jeep 4.2 6 cylinder it will sound like you are over reving the datsun but the L20 is happy to go at 4k all day long.

 

[zwebslinger]

What's involved in replacing that bearing?   I'm assuming the tranny has to be removed/dropped to do that?

I don't typically shift soon, just giving the example of it's inability to.  I've driven stick my whole life and know that altho not optimal, you can shift into whatever gear you want whenever you want and it shouldn't clunk into the gear.  Should just lug on to the next gear as you said.

 

Is it this?;

TIMKEN 304WB {Click Info Button for Alternate/OEM Part Numbers} Info

Front; Base Model

 

[zwebslinger]

Looks like it would open a whole can of worms to open up the tranny.  Can't even find rebuild kits for them, and not sure I'd be able to handle it.

Replaced an engine in my Subaru but pulling a transmission apart scares me.

 

From my service manual;

https://photos.app.goo.gl/z9KA2KhNvaBDyGMx9

[datzenmike]

Does it make any noise? If no noise the bearings are likely ok. The one I had made no noise what ever and 5th just refused to stay in gear. It's odd that at the same time it is difficult to up and down shift. Could be related.

 

Before tearing into it try to replace the gear oil first. Not saying there is any water in there buti f there is it's below the oil. Old oil will usually display fine metallic grit and even pieces of bearings on the magnet.

 

 

I drained a 720 once and ball bearings dropped out, another the oil looked like silver paint in yogurt. If there are chunks on the magnet, best to just rebuild or replace it.

 

If oil is 'normal' fill to the level of the fill hole with GL-4, 80 or 90w. 2 liters. Oil quality affects how well the synchronizers work. Go from there.

 

[zwebslinger]

Ok.  Sounds like a plan. 

No noise while engaging or driving. 

The oil that came out when seal was replaced looked good.  I caught most of it in a plastic jar.

I'll try the torch/breaker method to get that plug out.

How did you get a picture to show up on your post?  🙂

[datzenmike]

Lower left of posts says Drag files here to attach, or choose files... but size limited. I use a free picture hosting sit called imgur, but there are others. Take and store a picture there, when needed copy it and bring here and paste into your post.

[zwebslinger]

Well, got the plug out and was pleased to find only tiny shavings.  No chunks of any kind.

Drained it all and put all new GL4.

Shifting seems about the same, maybe a tiny bit smoother.  Using all of each gear is still required to shift.

Downshifting seems a tiny bit more forgiving.  5th still kicked me out 1 mile down the road, but after about 5 miles it seemed to stay in but just going 50.

Didn't get to test over that today since I didn't go near any speed limits over 45.

 

Hoping that with a little more use on the new oil, it'll free some things up?

 

Imagur wants my phone number.  No thanks.

Here's my google photos link;

https://photos.app.goo.gl/7ftULgR65B575te88

 

My plug was pretty boogered up.  Had to order a socket that worked perfectly. 

Reinstalled with anti-sieze after cleaning well with brake parts cleaner and a wire brush.

 

[datzenmike]

What did the old oil look like?

 

You should be able to up shift effortlessly at any speed. What's "Using all of each gear is still required to shift." mean?

 

 

Idle in neutral with the clutch pedal up. Now using the clutch, shift into reverse slowly. Is there any grinding????

[zwebslinger]

On 3/14/2021 at 6:14 PM, zwebslinger said:

If I wanted to do a low speed shift through all of my gears, it is not at all possible.  Matter of fact, 2nd gear is not possible without being at the top of first.

You could probably force it in there, but it's like it isn't lined up with the gate and it just sounds like a grind.

However if you are at the top of each gear, it slides right in nice and smooth.  If a bit early, it'll grind just a smidge but will go in.

So basically the more you drive it, you could pretty much get it to shift perfectly by learning exactly when to shift to avoid that grind.

Downshifting will NOT let you put it into a lower gear till you are going a certain speed for each one. 

First gear you've practically gotta be stopped, barely rolling.  But it goes in like butter once you're almost stopped.

Very weird.

This is what I'm referring to by saying that using all of each gear is required. 

 

Still zero grinding when shifting into reverse.  

 

Oil looks darkish, but not dirty and no sludge.  Wiped my finger around inside around drain hole and pulled out nothing but decent looking oil.  

[zwebslinger]

Well, I've been driving her around a bit and it's still definitely popping out of 5th no matter what.😔

No grinding or sounds at idle when shifting into reverse.

 

Not sure what to do.

 

I do have a spare 4 speed that I took out of my 76 280Z.  It shifted fine when pulled, but I wanted the OD so I got a 5 speed installed.

I've heard that I can just use the bellhousing from my 720's 5 speed and bolt it right up to my spare 280z 4 speed.

Is that the case and will it be plug and play after that?

 

I'd be hesitant to do that if my current 5 speed shifted smoothly in all 4 of the first gears, but it is not fun to drive when you must shift only when it lets you put it into the next gear.

Does the dedicated 280z 4 speed have longer gears than the 5 speed's first 4?  Or are they essentially the same thing, with the 5 speed just having an extra OD gear?

Not sure what the ratios are.