Would I be crazy to try rebuilding my own 5 speed?

[Survivor]

Hello all! I have a 81 Datsun 720 with a bad tranny, I might just try to snag a used one to replace it, but I'm intrigued with the idea of rebuilding it.

 

I'm no master mechanic, and I don't have a well equipped shop, but I learn fast. I found a thread on here awhile back discussing this same topic but can't find it now. As I understand it, other than the massive number of parts that need to be kept in order, the main drawback for a backyard mechanic like me would be the need for presses to install seals and bearings?

 

Anyways, I love a good challenge and the pride that comes with a difficult job done right, any input?

[metalmonkey47]

If you can afford to, and think that you'd be able to do it, I say go for it. But just in case, make sure you have another one or know of another one first.

 

 

If you have questions, we can summon Mike to answer them

[Survivor]

I guess my main question would be if I'll be able to replace the press with some type of improvisation? I've no clue what to expect......

[datzenmike]

If it shifts ok but makes lots of noise it most likely needs bearing(s) replaced. Jumping out of 5th can also be a bearing.

 

You've got nothing to loose by trying.

[jesusno2]

If it shifts ok but makes lots of noise it most likely needs bearing(s) replaced. Jumping out of 5th can also be a bearing.

 

You've got nothing to loose by trying.

 

Popin outta 5th could be a bearing. Hummm mike please elaborate some on this if ya could please. my brother has a ka tranny doing this. He said I could have it and I was gonna rebuild it. I know it growls but the popping outta gear I figured on maybe being a shifter fork problem or a mucked up gear or something.

[datzenmike]

Jumping out of 5th can also be a bearing.

 

 

 

Can be. I pulled a couple apart that had this problem and both had really bad bearings in the adapter plate. The main and counter shafts would wiggle around quite noticeably. The 5th gear and shift fork looked ok, nothing to explain what was wrong.

 

The good thing about 5th is you can get at it easier than the other three gears to the front. Well relatively 'easy'.

[Survivor]

Mine is seized up, kills the engine when you let out the clutch, unless it could be something else?

[DanielC]

Rebuilding a transmission is easier than an engine. But you MUST have a factory service manual to do it.

 

You may also need some special tools, and be able to get them, or improvise a way to make them. these tools could be needed to take things apart,or to reassemble the transmission, or to check some critical clearances, and tolerances.

The factory service manual will tell you what you need for special tools.

 

Inside the transmission, there are three rods that the shifter can move forward and back. One rod typically shifts first and second, the rod next to it shifts third and fourth, and a third rod shifts fifth, and reverse. The arrangement of the rods, and the gears they shift may differ, but it will be similar.

There are a set of spring loaded detent balls that sit in notches in the three shift rods. These balls and notches hold the shift rod in gear, or in neutral, for that rod. There is also a oblong ball between each shift rod, that will not allow two rods next to each other to move at the same time. These oblong balls prevent the transmission from going into two gears at once.

however, it is possible to get the shift rods for gears not adjacent to each to move at the sane time. This would allow the transmission to be in first or second, and fifth or reverse at the same time. This will prevent the transmission from turning the input or the output shaft.

[datzenmike]

I would drain the oil (if there is any) as this is a good indication of tranny maintainance and condition. It should contain about 2 liters of oil, so if very low or it's run dry, throw it away. If full of metallic flecks (aluminum) or the drain plug, which has a magnet, is covered with steel particals of even chunks it may be rebuildable. I've pulled a drain plug with ball bearings stuck it it. Siezed is not good.

 

Do you have any history on this. Do you know what happened? Were you driving it when this happened?

[ggzilla]

Do you want to rebuild it, or repair it?

 

Repairing a problem may be easy...just replace whatever part is bad.

 

Rebuilding involves fitting new bearings, new bushings, new synchros, new seals and all gaskets, and measuring parts with micrometers and replacing any out of specification. Most transmissions don't need this much work.

[Survivor]

I guess I'll just have to drain and drop it as soon as I'm done doing the timing belt on my Accord. I'll also look for a factory shop manual for the thing. Thanks for all the input guys, I'll let you know how it goes if I attempt anything.

[Survivor]

Do you have any history on this. Do you know what happened? Were you driving it when this happened?

 

A month or two before it quit, I started noticing a subtle whining noise on the the freeway, I assumed it was the rearend to be truthfull. The day before the tranny went out it was wanting to push 3rd gear out, the next morning it would just kill the engine when the clutch was released. I checked the fluid in the tranny about a year ago when I pulled her out of the "reserve fleet" after my wifes Tempo blew its headgasket(what a miserable model and make).

 

I'm in love with the simplicity and survivability of this truck, plus its just fun to drive.

[Survivor]

Hmmmm, all the factory shop manuals I'm finding in my price range are a year off, new 81 service manuals are running kinda high, would a 82 or 83 manual be compatible?I'm a poor boy..................

[datzenmike]

The '82 would be the same motor and tranny. '83 would have Z22 and Z24 but the tranny is basically the same for either.

[Survivor]

I found a bargain on a 83 factory service manual, very nice!

[Survivor]

I would drain the oil (if there is any) as this is a good indication of tranny maintainance and condition. It should contain about 2 liters of oil, so if very low or it's run dry, throw it away.

Throw away the oil or the tranny?

[datzenmike]

If the oil is low or empty (and tranny seized) throw the tranny away. Running it low has probably ruined all the bearings and surfaces. By all means take it appart and see how it works and fits together but ecconomically probably better to just buy another.

[Survivor]

Sorry to keep asking questions, but its possible no body could rebuild it if enough damage occurred?

[datzenmike]

Well you might have to replace everything and that's expensive.

[Survivor]

Well, this is why I posted this thread, now I understand the tranny is obviously beyond a basic rebuild kit. I'll be looking for a used tranny. Thanks guys!!

[metalmonkey47]

Make sure to take LOTS of pics during dissasembly. It really does help if you get in a bind during reassembly.

[Survivor]

Don't think I'm gonna bother taking it apart, I might go and drain the oil out of curiosity as to why it died, but I'm pretty sure its beyond what I'm willing to take on. The oil level was good 1 year ago, still have the oil I bought unopened cuz I didn't need it at the time....................

 

 

I just missed picking up a 85 Nissan 4x4 with a smoking engine(my engine would fit it), $500, damn!

[Survivor]

;)

[Javin]

Awe, we (well at least I) were kinda hoping for some oics of the process and you tinkering. Wouldn't YOU like to know why it stopped?:D If you got a replacement, could just be a learning experience!

[oldschool90]

Awe, we (well at least I) were kinda hoping for some oics of the process and you tinkering. Wouldn't YOU like to know why it stopped?:D If you got a replacement, could just be a learning experience!

 

I'm planning on taking my trucks tranny out and trying to figure out why my 5th gear is popping out. I do plan on taking lots of oics, so stay tuned for that. My uncle (who used to be a mechanic back in the day) said it might be as simple as the shaft locknut is loose. I'm definitely gonna check it out. But first, I gotta fix my engine bearing knock (again)