Just picked up a 99 ranger 4x4 4.0 5 speed.

When its cold, it shifts fine through all the gears. But after a few minutes of driving it grinds when shifting about 60% of the time. It happens in every gear except 5th and reverse, unless i just cant hear it due to road noise when shifting into 5th. Its not a super violent grinding, it doesnt send any vibrations up the shifter, and again its not totally consistent. If i double clutch, it does not happen at all. This leads me to think sychros, but why would almost every gear be doing it. I also find it strange that it doesnt happen at all when its cold.

Dude i bought it from said it had around 500 miles on a new transmission and i foolishly did not ask for the paperwork.

 

Does it look like a "new" to the truck trans? How does the fluid look? When was the slave last replaced? Air might be in the line.

 

Welcome to the forum

Very rare to have a problem with the M5OD-R1(M5R1) manual transmissions
New transmission would be an oddity.

M5R1 was used from 1988 to 2012 in Rangers

Yes, drain the fluid and put in new
M5R1 uses ATF, YES, automatic transmission fluid, Mercon V.
Maybe trans shop used something else, ??, just guessing

Yes, air in clutch hydraulic system is not uncommon if there is a leak, but usual symptom is it is hard to get into 1st when stopped, but double clutch leans towards that or wrong trans fluid