I think my tranny broke down

[gunsmith]

MY truck is a 1984 720 extended cab 4x4  2.4L gas engine and FS5W71B transmission. A couple of weeks ago a new noise started it sounded like a tapping sound ONLY when I shifted into 5th gear.  Gears 1-4 were smooth and quite.  The engine runs smoothly no issues, normal amount of power, normal throttle response nothing wrong that I can fine.  Since I 've own the truck (2yrs) I've never changed or checked the tranny fluid, I removed the filler plug and could not feel any fluid, I decided then to drain it and put in new fluid.  The only fluid I could find the specifically stated would hurt the "yellow metal" was Royal Purple gear oil, everything else on the shelf was GL5 fluid.  I put it in everything ran better, shifting was smoother and it felt like engine wasn't working as hard through and the gears. The noise in 5th gear was still present but significantly less. I used the truck for a day and half approx. 80 miles of driving and suddenly I'm getting terrible vibrations through the drivetrain and it sounds and feel like a hard knocking  in all gears from low RPMs through 2000, then it smooth's out a little.   While in neutral sitting on my driveway I can see the engine moving like something is out of balance.  When a hold the clutch in and let it idle the engine movement is reduced,  engine timing a correct, no back firing, motor seems to fine.  Suggestions on how to isolate this issue?

 

How difficult is it to rebuild this transmission? 

[Draker]

Just depends on what's broken. 

 

You might jack up the rear wheels leave it neutral and see if you can easily move the driveshaft. It should rotate fairly easy. Then have someone push the clutch pedal and do this for all gears. Again should move pretty easy.

 

If there is any binding, or its hard to rotate you might have some issues with the transmission. 

 

 

As far as rebuilding, it just depends on what's broken. If bearings, should be easy for a shop to fix. If hard parts, gears or shafts, then it goes in the scrap bin. Hard to find those parts anymore.

 

[Crashtd420]

21 minutes ago, Draker said:

Just depends on what's broken. 

 

You might jack up the rear wheels leave it neutral and see if you can easily move the driveshaft. It should rotate fairly easy. Then have someone push the clutch pedal and do this for all gears. Again should move pretty easy.

 

If there is any binding, or its hard to rotate you might have some issues with the transmission. 

 

 

As far as rebuilding, it just depends on what's broken. If bearings, should be easy for a shop to fix. If hard parts, gears or shafts, then it goes in the scrap bin. Hard to find those parts anymore.

 

I'm rebuilding a stumpy 71b right now, center bearing on the 5th/ rev shaft was junk.. im replacing 4 bearings in it myself, but i actually found a company that rebuilds them, and has the gears and shafts and other parts available....

https://www.midwesttrans.com/FS5W71_Manual_Transmission.html

 

 

[datzenmike]

Oil should be checked every 15K but I check mine once a year without fail. If nothing else you should, at the least, inspect the outside for oil leak wetness. Usually the rear seal around the driveshaft.

 

So how much oil came out? Should be 2 liters or about 2 US qts in there. Was there any metal parts on the drain bung magnet? Like a part of a bearing cage...

 

 

I'll assume that running it out of oil is the cause of the noise and the most likely bearing to fail is the front countershaft. Can't see how this would affect the balance enough to cause vibration of the engine. At this point something has disintegrated so drain the oil (you can always put it back in) and see if any additional metal parts fall out or are clinging to the magnet on the drain bung. The oil may also now have ground up aluminum flakes in it.

 

If the oil is normal perhaps the clutch disc has come apart. This would easily explain the vibration that stops when the clutch is disengaged.

 

 

[gunsmith]

There was less than a quart drained out and there was a small piece of metal it looks like a small curve piece that had small rivet on each end like what's sticking to the left side of the magnet in the photo above.  I do have a small leak at the top of the tranny where the cylinder looking thing that the shifter is attached to goes into the transmission body..  

[datzenmike]

7 minutes ago, gunsmith said:

There was less than a quart drained out and there was a small piece of metal it looks like a small curve piece that had small rivet on each end like what's sticking to the left side of the magnet in the photo above.  I do have a small leak at the top of the tranny where the cylinder looking thing that the shifter is attached to goes into the transmission body..  

 

Yeah that was the bearing cage from the front counter bearing, although there are others inside very similar. Balls fell out with the oil.

 

 

Here's another where the front bearing disintegrated leaving only the inner bearing race. The front was no longer supported and the counter gear flexed and snapped at the adapter plate. It's not even collected to the transmission anymore.

[weldingrod]

Never checked the oil................

I am at a loss for words.

[bottomwatcher]

This is the classic bad countershaft bearing. 4th gear should be fine because that is 1 to 1 and doesn't go through the countershaft. Need new trans and go to c series much better with bigger countershaft bearing.

 

[datzenmike]

It's the only gear that power is not transmitted through but it's still being forced to turn by the mainshaft. It may still make noise and it may still destroy other parts including the case.

 

The C is a nice upgrade but needs the driveshaft shortened if from a 240sx or lengthened slightly if from the KA D21 Hardbody. The Z and the KA are virtually the same bolt up alignment.

[gunsmith]

When I drained the oil I did not find any ball bearing in the oil, so if they haven't falling out of the cage yet, they will I'm assuming.  My truck is a 4x4 will a non 4x4 tranny work?  I know the transfer box is separate from the tranny, but what about the cross members and clutch hydraulic assist and all that external stuff?

 

[bottomwatcher]

You will want to get the 2 wheel drive version because the later 4x4 trans were married to the transfer case. The good news is your speedometer cable is in the transfer case so that remains the same. There is a small adapter you have to make from plate to bolt trans to crossmember and have the intermediate driveshaft lengthened but everything else works the same.

[gunsmith]

Would the same modifications apply if I find another  84' FS5W71B non 4x4 transmission?

[datzenmike]

20 hours ago, gunsmith said:

MY truck is a 1984 720 extended cab 4x4  2.4L gas engine and FS5W71B transmission.

 

All 720s (built to October '85 or 4 months into the '86 model year when it was replaced by the D21 Hardbody, November '85 and on... ) had the divorced transfer case and 71B transmissions. Yes a 2 or 4 wd transmission will work equally well. You will have to seal up the 2wd speedometer so it doesn't leak. I left the speedometer pinion sleeve in and cut the threaded collar from a spare cable. RTV'd the opening closed and when set just screwed this on to seal it. 

 

 

Measure the length of your 5 speed. There were two lengths used during the 720 run, 26" and 31.5". Get the match to yours, OR if shorter or longer get the primary driveshaft so it will fit. A shorter transmission will use a longer driveshaft, a longer transmission will use a shorter driveshaft...

[datzenmike]

 

This is the driveshaft for a 31.5" transmission that fits to the transfer case. A short 26" transmission driveshaft will be 5.5" longer

[wayno]

No Mike, that is the driveline for the short transmission, the long shaft has a much shorter driveline.

[bottomwatcher]

Find another b series and it bolts right in. If you keep the truck you will get to do it again and again. You will get good at trans changes. I did it 4 times before putting in a c series 13 years ago. No issues so far.

[datzenmike]

3 hours ago, wayno said:

No Mike, that is the driveline for the short transmission, the long shaft has a much shorter driveline.

 

 

Right you are wayno, grabbed the wrong picture...

 

[Madkaw]

So if you tried installing a C transmission , it would likely be 33” , so the short shaft would have to shortened anothe 1.5” - correct? 

Would that be too short to even work? Really would like to find a heavier duty trans for my 4WD , but at 33” it seems like a squeeze 

[datzenmike]

The spline could be cut down and the trans/transfer case don't move back and forth much. This would be the S13/14 transmission? The D21 Hardbody is shorter I think, I don't have a good length on one yet.

 

 

 

D21