Engine/Transmission (1994 - 1998) transmission noises, strange!

[Matthug]

I've been having this whining/grinding noise on deceleration (when I use a gear for the engine braking power) and it's the worst in the lower gears. Well I read about not using regular old gear oil and having to use synthetic only in the NV4500, so in an effort to try anything other than a rebuild I went to the local autozone and picked up mobil 1 synthetic 75W90. I heard castrol syntorq was the best but no one had it. The more I drive the truck now the more the noise goes away, I almost have to try the make the noise now, but it's not completely gone. So I'm pretty happy about that. My question is does anybody know whats causing this noise? I find it strange for it to be the synchro's because it makes the noise decelerating in forward gears but accelerating in reverse. My other question, is mobil 1 good enough? I figure I'm gonna change the gear oil again in about a few hundred miles because obviously I couldn't get all of the old gear oil out. Also will it be OK to go from mobil 1 to castrol without any bad things happening? Will they mix OK? Or should I stick with mobil 1? Thanks in advance.

 

[firemanmarc]

I have been having the same strange noises upon deceleration. I have changed oil to Amsoil and it's a little better as well. I will be pulling the transmission here soon since my rear seal on the engine is leaking. At that time I will tearing into the NV4500 and see what is going on, it does have 283k miles on the original 5th gear and nut..... I will let you know what I find... Marc

 

[Matthug]

255K here on completely untouched transmission, let me know cuz thats quite interesting you have the same thing. Does yours also have the noise accelerating in reverse? Seems to be the worst in reverse for me.