Grinding In Reverse

‘75 304 3 spd. Shifts like butter, until I’ve driven several miles, then, reverse is nearly impossible to get into, and 1st as a bit rough. 2nd and 3rd are unaffected. Fluid is correct weight, and only several months old. I don’t recall the brand. Is there a certain brand/weight that these like better that others ?

 

Could be a clutch issue. Checked the fluid/adjustment?

 

I agree, it sounds like the clutch isn't fully releasing.

 

What they said. Also make sure you are using true GL-4 gear oil and not the GL-5 that says it is GL-4 compatible. It isn’t. It can cause shifting problems when warmed up.

 

Found the container Does this say anything

 

Yes, that is GL-5. You need GL-4. Check clutch adjustment first though. You might search about this as it has been discussed a lot.

 

In regards to gear lube I've had good results with this in manual transmissions.

 

Ditto.

In brief, GL-5 is incompatible (corrosive) with bronze or brass components, such as synchonizer rings.

Not your immediate problem however.

 

Depends. If the clutch adjustment is not the issue the incorrect lubricant might be contributing to the issue. Seen it many, many times, as I’ve posted many, many times. And have experienced, many, many times. Hopefully a simple clutch adjustment will solve the issue. Regardless, the OP needs to change the lubricant.
Very long term corrosion of the blocking rings is only one issue, and is a very long term issue. Short term and more damaging is grinding of gears and physical damage to the blocking rings and engagement teeth of the synchronizer teeth on the synchronizer sleeve and gear because the wrong lubricant won’t allow the blocking ring to grab the cone on the gear properly. Basically the lubricant is too “slippery” and won’t allow the blocking ring to grab the cone on the gear to bring the synchronizer sleeve and and gear to the same speed so they can do engage each other. Hence the sleeve and gear grind against each each other. Not only causing hard or impossible shifts but also introduces metal particles into the transmissions n which goes through the bearings, etc.

 

But, in this particular case, do first and reverse have synchronizers? He reports no problem with second and third.

 

He should have a T-15 so yes, first is synchronized. Reverse is not. As I said, the clutch adjustment and linkage should be checked first but I have seen the wrong lubricant cause similar issues so is something to eliminate if the clutch adjustment is not the issue. We know he has the wrong lubricant so by simple process of elimination that would be the next thing to fix. And yes, I’ve seen the wrong fluid cause issues with non-synchronized gears like reverse.

 

Lube is on the way