bad 4th gear syncro

[SMGST]

My buddy has a bad 4th gear syncro. He did have regular gear lube or what ever it calls for in a manual trans and during the colder months (winter) it would shift into 4th right after he started it in the morning and started moving (when the fluid was cold and thicker) but once the fluid warmed up and got thinner it wouldn't shift into 4th. He now has Pennzoil Syncromesh in it and it didn't change a thing. The fluid is actually thinner. What is the thickest lube we can put in our transmissions safely? Do you think it would help?
He doesn't have the money to replace a syncro right now.

 

[viprez586]

The synchro will eventually start getting worse, and you wont be able to go into 5th. grinding into 4th your going to start tearing up the teeth on 4th gear anyway.
fix a little problem now, or fix a costly problem later, just something to keep in mind.

 

[SMGST]

why wouldn't I be able to go into 5th? do they share the same blocker ring?

 

[viprez586]

4+5th share the same synchro, your creating wear on the 4th side of the synchro so its possible it could lock in 4th and cause some very serious problems. Theres a good chance you'll be able to still shift into 5th but wear can cause things that werent intended.

For instance lets say your 4th gear sync is so bad that you try shifting into 4th and tears the teeth up so bad your sync wont engage. it could get stuck in the "neutral" state so you wont be able to go into 4th or 5th. However it is very likely you'll have a 5th but it just wont be as smooth as 2nd and 3rd. It all depends on how much wear has taken place and you really wont know without taking it apart.

Im pretty sure this is what would happen but im going from a 5-speed medium duty trans.(what class im taking right now) but i still think they'd be similar to a car trans.

I wouldnt reccomend driving for too long with a bad synchro, but since its 4th gear you wont really be too much in the red. 2nd or 3rd however would suck!

 

[talondsmawd]

my car is doesn't like to downshift into 4th...how much are syncro's

 

[donniekak]

4+5th share the same synchro, your creating wear on the 4th side of the synchro so its possible it could lock in 4th and cause some very serious problems. Theres a good chance you'll be able to still shift into 5th but wear can cause things that werent intended.

For instance lets say your 4th gear sync is so bad that you try shifting into 4th and tears the teeth up so bad your sync wont engage. it could get stuck in the "neutral" state so you wont be able to go into 4th or 5th. However it is very likely you'll have a 5th but it just wont be as smooth as 2nd and 3rd. It all depends on how much wear has taken place and you really wont know without taking it apart.

Im pretty sure this is what would happen but im going from a 5-speed medium duty trans.(what class im taking right now) but i still think they'd be similar to a car trans.

I wouldnt reccomend driving for too long with a bad synchro, but since its 4th gear you wont really be too much in the red. 2nd or 3rd however would suck!

4th and 5th have nothing to do with each other. Every gear has it's own synchronizer ring in between it and the sleeve, except reverse. The reverse synchro is actually on the end of the input shaft and engauges with the case to stop the shaft so reverse can engauge. 4th gear is on the other side of the sleeve from 3rd anyway not 5th.

 

[luv2rallye]

^^^ Donniekak is correct here (not viprez586 - ignore his comments).

talondsmawd: syncros don't cost much but putting them in sure will (as well as very time consuming). Also once the tranny is apart most people wisely do a rebuild or complete overhaul.