FS5W71B transmission troubles need some input

[PAwelder]

so here is the story i own an 85 720 4x4 kc z24 with the fs5w71b transmission and a month or two ago i began noticing some noise coming from my transmission, from what i assume is the main shaft. it would make a low pitched race noise when in neutral with the clutch out, well being the procrastinator i am, i ignored it till now. on my drive home from work today cruising on the highway in 5th gear the engine revved up while in gear. i shifted to 4th and continued driving seeing as i was almost home. when i got on the off ramp i realized i had no other gears except 4th. i managed to get her home with alot of lugging, a few blown stop signs and 4x4 low to get her up the driveway. now my next question is where do i go from here, it didnt make any loud cracks, snaps, pops, or grinds, so do you guys think the transmission is rebuildable? i am going to call all the junk yards in my area to see if i can find a replacement, since that would be easier, however i havent found anything yet. 

 

my two main questions at this point would be what is the difference between the fs5w71b and the fs5w71c and are they interchangeable? and do you think my exsisting transmission is rebuildable assuming i cannot find a salvage one?

 

i really love my 720 and i would hate to see it go over something stupid

 

any other input, tips, hints, or knowledge would also be greatly appreciated

 

 

 

[datsunaholic]

When mine did that, it destroyed the transmission front case along with the broken bearings and damaged shafts.  So I would say it's unlikely rebuildable.  However, mine lost the input shaft bearings, whereas it sounds like you lost the countershaft bearings.  Only way to know is to take it apart.

 

The "C" type trans is longer and uses a different shifter, in a 2WD that just means a shorter driveshaft and a couple other mods due to length and making the starter work, but in a 4x4 that makes things much more complicated due to transfer case.

[wayno]

Your going to have to pull it apart anyway, so you might as well check it out, maybe it didn't destroy the front case.

Find a place to park it and pull it apart, drop the transmission, then look in the bell to see if the front cover is busted, then remove the front cover to take a look at the two bearings.

If the front case is shot/tore up, I can likely send you another front case if the rest of the transmission is alright.

[datzenmike]

 

The top is the mainshaft, driven by the engine. The bottom in the counter shaft driven by the mainshaft. The first gear on the main and the counter shaft are meshed and transmitting power at all times.

 

 

Counter shaft without the driven gear or the bearing on it (left side).

 

 

Mainshaft above and the counter shaft driven gear beside it. The counter shaft gear is held onto the counter shaft by two Woodruff keys and fits on the left side of the counter shaft above..

 

 

 

The destruction of either top or the counter bearing would not stop the counter shaft from turning. Those two gears would still be in mesh. So either the woodruff keys have sheared or the top gear on the mainshaft has sheared.

[PAwelder]

so let me get this straight, your saying that either the woodruff key sheared on the counter shaft or the gear on the main shaft sheared. That makes sense because the gears feel exactly the same as they did before on the shift knob. and it didnt make any weird noises. i do have a few questions though; Does the gear on the main have woodruff keys as well? what would cause them to shear?, and lastly are they special woodruff keys or can i go to the hardware store to get new ones ? sorry for all the questions im just trying to figure it out to get her back on the road. 

[datzenmike]

The top input shaft and gear may be cut from the same piece of metal and the bearing just pressed on. I haven't taken one apart, or know even it it will come apart.

 

Whoa.... they don't shear off for no reason. Something probably seized to cause this. In the picture below the counter shaft snapped off on the far right from a bad counter bearing.

 

[datsunaholic]

What I was thinking, Mike, was if the countershaft bearings went bad, it could cause the counter shaft to deflect enough that the gears are no longer in contact with the mainshaft.  Since all the synchos are on the mainshaft, it would feel as if it shifted normally, but no power was being transmitted.  Either way. only way to know is a teardown.

 

And I was mistaken on mine- it WAS the countershaft bearing that siezed and tore up the bearing retainer (and the front of the trans case as the countershaft bounced around).  It still moved under its own power but would sometimes jam or skip, which only happened when I moved it from the backyard to the driveway to swap transmissions.

[datzenmike]

That last picture was a z22 720 in good shape but had obviously been sitting for a long time in someoone's yard. It was scrapped and I pulled the transmission and drained it. Ball bearings fell out along with oil that looked like silver paint. The counter had wobbled so much the metal fatigued and snapped off.

[PAwelder]

that is alot of metal fatigue right there. hmm i hope mine isnt that bad. i think i am gonna still look for a replacement tranny on friday because there are no salvage yards open on thanksgiving and if that turns dry then ill rip into it, plus if i do find one and mine is fixable then a get a speedy repair and a backup tranny

[PAwelder]

well it's that bad... identical to the last pic posted by datzenmike the front counter shaft bearing failed leading to extreme fatigue on the shaft which led to the shaft shearing just outside the rear counter shaft bearing. so here is my next issue, and i think i have it solved, but i need to make sure im on the right track before i proceed.

[PAwelder]

so here is my problem all my local junk yards dont have any short tail shaft transmissions and only a few long shafts. i was looking at another transmission thread ( http://community.ratsun.net/topic/42934-my-transmission-finally-exploded/) and i learned so much from it and the one thing i read is that you can swap parts between the long tail shaft transmission and the short shaft. so my plan at this point is to buy a long tail transmission and swap the parts from mine into it to convert it to a short tail. my question would be did i read the thread right and is this possible, and also is there anything i should be aware of before i jump into this head first. i tried posting pics of my trans but i couldnt figure it out. however i couldnt find any damage on the main shaft cluster i plan to fully disassemble the tail of mine and clean each part and replace the bearings. any other advice would be appreciated

[wayno]

No you cannot make a shortshaft out of a longshaft.

Your best avenue is to have someone/a business ship you a shortshaft transmission, you might be able to buy a clustergear or remove the cluster gear out of a longtail if it is compatible, and rebuild yours if only the clustergear was damaged, but you can likely buy and ship a used one for cheaper.

You also can just use the longshaft and use the short driveline instead of the long one that you have between the transmission and the transfer case, but they discontinued the short driveline for a reason.

You would also have to change your console if you have one to a longtail console.

[datzenmike]

After '84? or starting '85 the front counter bearing was increased from 56mm to 62mm and a modified front cover used to house it.

 

Unfortunately there are different counter gear sets and they have to match the gears they drive above them.

[wayno]

One can always use the smaller bearing, but having the correct cluster gear shaft is very important, that is why I said, "if it is compatible", he is on the wrong coast for this type of issue.

How could I tell if I have a transmission with the proper cluster gear shaft, I have one out back that needs rebuilt, it pops out of first under compression, and second gear synchros are shot, but that likely would not be a cluster gear issue, and I don't think I will ever rebuild it now.

After '84? or starting '85 the front counter bearing was increased from 56mm to 62mm and a modified front cover used to house it.

 

Unfortunately there are different counter gear sets and they have to match the gears they drive above them.

[PAwelder]

ok so the cluster gears are different between the short and long shafts, which in turn makes all the gears different, would it be possible to put the long shaft main gears on the short shaft main shaft? or are the shafts slightly different too? sorry for all the questions im just trying to figure out all my options

[datzenmike]

No, only that there are differences and you may get a different one. Yes all the gears should swap to the shorty transmission.

[PAwelder]

Ok cool im gonna start tearing down my transmission after work today and cleaning every piece extremely well, the best deal i found was a 2wd long shaft, if i buy that i should be able to take the counter shaft and the main shaft gears and put them into my short shaft case and tail, the only difference should be first gear which is taller, am i on the right track, also is the taller first gear going to be noticably taller or just a little bit

[wayno]

You have a Z24, you likely won't even notice a difference if there is one.

Is your front case alright?

Didn't you notice a noise at intersections coming from the back of the engine when idling in neutral waiting for the light to change?

[PAwelder]

I did hear a noise but it was a low growling noise, it matched the description of the front counter bearing failing exactly, when the bearing failed and the shaft snapped it chewed into the aluminum in one spot at the very front right next to the lowest of the three shift rod holes it stayed out side by 2 mm or so. I think the damage is cosmetic and will not affect anything, the main shaft was fine because it was not run for long after it failed, and honestly finishing the drive home when it went in fourth gear sounded completely normal. However when i completely disassemble to clean i will scrutinize the case and the shaft heavily for defects and damage, are there any spots in particular i should check extra heavily

And it is a z24 so thats good

[wayno]

I just read the first post again, you had noise/a warning but didn't do anything about it, now the damage is much worse, it likely could have been repaired with a new bearing, now it's a much bigger issue, and way more time/money will be needed to fix it.

It's not easy to do what you are planning, removing one set of gears to transfer them to another shaft, it might require special tools to succeed, I am not even sure I could remove the used cluster gear out of that shortshaft transmission I have in the back yard, if we were sure that what I have is the same as yours, I could try to remove it and send it to you.

I removed that transmission because it was getting hard to shift it into 2nd without grinding, and it popped out of first under compression, I don't believe that either of these issues were caused by the clustergear shaft, but I would like to know if all the shortshaft transmissions were the same before I tried pulling it apart.

[84720FourWheel]

Try Car-part.com

They might have a tranny somewhere nearby, or somewhere willing to ship.

[PAwelder]

847204wheel you may have saved the day! That website is awesome! I called a place about 2 hours or so away that said they had a 2 wheel drive trans, called a little too late though so i wont know for sure till tomorrow (crossing multiple fingers) its an 86 2 wheel trans with supposedly less than 60,000 miles, im gonna have the guy count the splines on the output shaft just incase.

as for my original plan i got about half way through the transmission, and given enough diligence and patience i think i could have seen it through, but there was so much potential for one thing to be wrong and i would have wasted money and time, some things are better left to the experts i guess. however i now can visualize the inside of my transmission in my mind and understand what each part does which i couldnt do before! hands on learning is the best learning.

[wayno]

As long as it is a out of a regular cab short box  86 720, you should be fine, all the tailshaft splines are the same, you just need a shortshaft.

[PAwelder]

got my tranny!!! the original guy i wrote about ended up not having it, so i used that website again and found one 100 miles in a different direction, right on the other side of philly. but anyway i attempted to get the rear main off and between the rain, cold, and frustration i gave up. do i need to drop the oil pan to get the rear main seal out, there are no bolts or flange plate but i can see there is an insert that is half of the circle then decends down the block to where i forms a seal with the oil pan gasket i cant see any bolts for it or anything. 

[PAwelder]

my bad i should clarify i am talking about the z24 engine rear main not the transmission rear main, i figured while i was down there i might as well do everything

got my tranny!!! the original guy i wrote about ended up not having it, so i used that website again and found one 100 miles in a different direction, right on the other side of philly. but anyway i attempted to get the rear main off and between the rain, cold, and frustration i gave up. do i need to drop the oil pan to get the rear main seal out, there are no bolts or flange plate but i can see there is an insert that is half of the circle then decends down the block to where i forms a seal with the oil pan gasket i cant see any bolts for it or anything.