FS5W71B 5-spd won't stay in 5th gear.

[620connor]

Whats up guys. So i found a 1977 280z FS5W71B 5-speed trans that a dude is selling for $80 in my area, but he says when he shifts into 5th gear it pops back out. He says all other gears work fine. My question is- what needs to be repaired in order to make it work properly again? Thanks.

[datzenmike]

Remove the tailstock and tighten the mainshaft nut.

 

 

Over on the middle right side follow the mainshaft to the left and you'll see a large nut. The nut on this model has a collar on it's right side that can be peened over to prevent the nut loosening. Your may not have this on yours. Also your transmission may have the worm gear for the speedometer to the rear of the nut. The torque for the mainshaft nut is 100- 125 ft lbs.

 

Once tightened, if you don't have a way to peen the nut try a small welding tack to hold it in place. Early 5 speeds were prone to this nut coming loose.

[620connor]

Thank you very much mike.

[datzenmike]

This is likely the problem. If it isn't, the tranny has to come out anyway. 5th is a highway gear anyway.

[620connor]

Yeah i hope so, the guy said he can shift through all gears smoothly but as soon as he shifts into 5th gear and lets out the clutch it pops right out of gear. Is there anything else that can cause that to happen besides the loose nut?

[metalmonkey47]

Sorry to hijack, but I don't see a need to start a new thread for this... Mike, I have the same issue with my FS5W71B trans popping out of reverse. Is this likely the same issue?

[ggzilla]

Yes.

[datzenmike]

The loose nut was a common problem on the early 5 speeds. My '78 620 started doing it.

 

Wear or damage to the 5th synchro hub might. The thing is, is 5th gear gets the least use.

 

 

I guess you're hoping there is something you can look at without removing the transmission? Will you settle for a hail Mary?.....

 

This is my FS5W71B from a CA18ET viewed from the passenger side. The front case half is separated from the steel adapter plate that holds all the gears, and the aluminum rear half is still attached, though loose.

 

If you look on the side half way up the steel adapter plate you'll see what looks like two bolt heads. (with oil on them) These are plugs that screw in and beneath is a strong spring pushing a round steel check ball. The bottom one is over the reverse/5th shift rod which has three grooves in it that the ball drops into and holds it in. Reverse... Neutral...Fifth. It provides a slight resistance against slipping out of gear that can easily be overcome by using the shifter. You can remove the bottom one and inspect the ball and spring (in the car) but I have doubts this will be the cause.

[ggzilla]

Syncro hub wear wont cause it. A bent linkage could but not likely with the 71B. Maybe a damaged syncro hub but also not likely

 

Trans doesnt need to come out - its only 5th gear, you could use 4th instead. 5th is always optional. But it is a good idea to.fix it.

[620connor]

Thanks for the help guys, when i buy the trans im gonna see what i can do to fix it.

[datzenmike]

Remove the tailstock and try to tighten the mainshaft nut. This is the most likely solution. (I forgot it's already out)

[620connor]

Okay ill give it a shot! Thanks!