MGB My '80 B used to shift fine

[The Green Hawk]

I just topped off the gearbox with 90w and it still has a problem shifting, especially into 1st and 2nd but in all gears occasionally.
The master and slave cylinder were recently replaced by the previous owner.
The question I am looking for help with is this....Is it possible to determine if it is the clutch/throw-out bearing or say a prayer, the gearbox itself?

Everything is original including the 84K miles. I believe these gearboxes are generally bullet proof but anything is possible!

Any thoughts ??

Peace

 

[Bob Claffie]

Not sure on late model MGB's but all I've dealt with take 20/50 ENGINE OIL in the transmission.

 

[Mickey Richaud]

I'm a bit confused, though. Your title says it used to shift fine, but then you said it still is difficult going into first and second. Do you know what kind of oil was in it?

At any rate, I'd drain whatever is there, being as sure as possible that it's all out, and then put in 20/50 and see what happens.