Mazda Repair: popping out of 5th gear, manual, mazda tribute, 5th gear

Question
2001 mazda tribute, 5 speed manual trans.

driving down the highway anywhere between 70-80  mph. the car pops out of 5th gear. problem getting worse. was informed by a mechanic that i might need a new transmission something related to a synchronizer. does this sound accurate? any input?

just had clutch replaced, flywheel resurfaced, slave cylinder and serpentine belt replaced. i spent $2600 on repairs from march - may not including this.

thanks so much for your help!  

Answer
  A synchronizer is defiantly the culprit. The synchronizer is a bronze helitical cut gear that is positioned in front of a drive gear. Every gear except reverse has one and its primary purpose is to line up the teeth of the gear you are in with the next gear up or down. The gears are cut at an angle so when they are aligned at different speeds of rotation they will be able to mesh. This is where the term double clutching comes from. When a car with no synchronizers is driven "or one with broken ones" it will grind going into gears if you try to shift it in between gears without matching the speed of the gear you are trying to go into with the one you are shifting out of. Double clutching is when you push the clutch in once, pop the car out of its present gear, then release the clutch, which allows the transmission to match speed on all the components in the transmission, and then clutch again to engage the new gear. Now, the second function of the synchronizer is to keep the car in its selected gear. Because the gears are helitical "teeth cut at an angle" the direction the angle faces can have a dramatic effect on how the gear reacts. The gear is designed to act in a way that when you engage it the rotation of the gear and the direction of the teeth force it to disengage. If it were the other way around the disengagement of gears would be next to impossible at any speed. This is where the second function of the synchronizer comes into play.
It prevents the gear from backing out of gear unless the clutch is engaged and there is no load on that gear.
So, your synchronizer is internally worn and is no longer tight enough to prevent the gear from slipping out at or above a certain load or RPM. You can probably find a new transmission in a salvage yard or better yet... Stop driving 70-80 as you get the best fuel economy at 60-65 which is a scientific fact. Many methods from strategically placed bungee cords and of course holding it in gear are all options for this in the short term. But you will eventually need to install a transmission in this car. Try to get one out of a salvage yard. And one last note on this, I see 90% of my broken synchro at the shop belonging to people who cowboy the shifter and stuff it through every gear, and then use the shifter as a hand rest. This practice sucks Swedish fish and if you do this you should stop immediately. It is a real problem with today’s driver and it makes all of use who drove race cars wonder why they call it race shifting, we never broke a thing!

Regards,


John