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Transmission grinding

I have a 1998 Pontiac Sunfire 2.2l 5 speed. 3rd and 5th gears are grinding as i enter the gear. It happens when i am up shifting sometimes, but more often happens when down shifting. im not sure if i have a clutch issue or if i need to replace the transmission. I recently replace the clutch slave cylinder/throw out bearing. at the same time i flushed the fluid. How do i start to diagnose the problem?

When you replaced the slave cylinder…did you also replace the clutch master cylinder? They should be replaced in pairs. Never replace one without the other.

Grinding entering a gear usually means the synchronizer is shot. I’m assuming all other gears shift normally.

It could be a clutch problem since it seemed to occur after the clutch work you had done. Maybe all the air wasn’t bled out of the slave cylinder, or the clutch MC is bad too. Or a clutch linkage problem. But I don’t think so, because you have no complaints about the clutch in other gears. If you can easily shift into and out of first and reverse at idle or with the engine off, then I’d discount this as being a clutch problem.

My first guess is what @insightful suggests, worn out synchronizers. Now be honest, do you sometimes drive this car a wee-bit aggressively? Rapid shifting sometimes at fairly high rpms? I’m guessing the answer is “yes”. But even if you don’t, a car of that vintage can develop synchronizer problems.

My early 90’s Corolla – mildly driven for the most part – has a 3rd gear synchronizer symptom sort of, on the margin shall we say, of being on the fritz. The problem is manifested when down shifting, never on upshifting. It doesn’t happen if I double clutch when downshifting. That can often be an effective work-around to this problem. In the early era of cars, synchronizers hadn’t yet been invented, and everybody had to double clutch to avoid gear grinding on down shifting.

Its pretty rare to wear out a 3rd and 5th gear syncro. Usually 1st and 2nd, especially 2nd take the biggest wear.

I’d go along with @missileman on this one.

Try re-bleeding the clutch first on the off chance there is a little air in there. If that doesn’t get it, clutch master is in order.

It could be a problem in the trans, but that is an outside chance.

It would be a good idea to check the transmission fluid level too. If the fluid has never been replaced, now would be a good time to replace it with a fresh batch. And it would give you a chance to sieve what you remove to look for slivers of metal.

Some more info might help. You mentioned replacing the clutch slave cylinder but did not mention the clutch kit. I would hope the kit would have been changed also; just asking.

Any surfacing of the flywheel?

How much free play in the clutch pedal before you feel any tension while depressing it?

Once depressed, how far does the pedal have to come up before you feel the car creeping?

Offhand, I tend to think the problem may be in the synchronizer assemblies internal to the transmission as a clutch issue should show up even more in 1/2 gears and reverse.

You replaced the throw out bearing and reinstalled the old disk and pressure plate? Why would anyone do that? Unless there is now some way to replace the bearing without removing the clutch assembly. I’m old school and ignorant.