Transmission makes grinding noise when under load in 3rd, 4th, and 5th

[curtis52285]

I have a 91 Ranger with a 2.3L and the manual Mazda M5OD/M5R1 transmission. Ever since I had the clutch replaced the truck has made grinding noise in 3rd, 4th, and 5th gears when torque is applied. If the truck is pulling hard the grinding noise is louder and the grinding noise is also quite loud when the engine is coasting (the momentum of the truck spins the engine). The grinding speed is related to engine speed and if the engine speed is increased to above 2500 rpm the sound disappears. I have driven it like that for several thousand miles and the sound has remained consistant. Also the truck has all new universal joints. I also replaced the clutch again but that had no effect on the sound. I don't understand where the grinding noise is coming from because 4th gear is a direct drive and is thus not relyant on the gears in the transmission. Why should 4th gear make noise?

Any help to get rid of this noise or similar stories would be helpful.
Thanks Curtis

 

[rurouni20xx]

all gears will make noise especially when they are synchronized as your transmission is. how is the tranny fluid? when was it last changed? has it ever been changed? what kind of fluid in the tranny? hope you dont go to drain it and find metal shavings to say the least...if im not mistake they also had a problem w/ the plugs on the top of the tranny getting hard and letting the fluid out, causing low tranny fluid. id check it out, and your tranny calls for mercon atf when you go to change it/check it.

 

[locovaca]

My tranny does what I think your describing when the engine is lugging, but for me it stops at about 1500 rpm. The key isn't to drive it that low in the rpm range, at least for me. Since I'm lugging the engine I don't think anything of it, I just downshift or else keep it in the same gear and keep the throttle largely closed until it accelerates enough to get into non-lugging range.

 

[curtis52285]

Transmission

The plugs on top have been replaced with metal plugs and the oil was changed. However, the oil might have been changed after the noise started and yes I used ATF. locovaca, does your truck make that sound when coasting (the engine is slowing the vehical down)?

If the oil were to have run low or been in the transmission for an extended period of time would the bearings go out or would the gears be shot, or both. If the bearings are the problem I can replace them but if I have to go in and replace the gears I might as well get a new transmission. What would wear out first?

By the way, I am actually not sure that the transmission is causing this noise. I don't have a way to put a load on it while crawling under it so I simply hear this grinding noise while driving.

 

[locovaca]

Don't know about the slowing down because I hardly ever engine brake, I just coast in neutral.