Grinding when shifting to h4

[Spencerfj6289]

Hi I have a 1990 fj62 and when I push the h4 button on the dash, the second the light comes on I hear a very loud gear grinding noise until the vehicle comes to a full stop. It sounds like gears trying to mesh together while spinning. Similarly, when I shift back into 2wd I hear the same sound. It also does it while in 2wd under regular on road driving conditions, but randomly, and it will stop when I bring the vehicle to a stop. I can then continue driving normally down the road. I've already replaced the h4 solenoid, rebuilt the vacuum actuator, and replaced the t case fluid. No difference. I did re-use the diaphragm in the actuator, which seemed to seal Well, but I'm not sure if it is supposed to lock into position in either direction, or just one. In other words, when I move the diaphragm to the un-resting position inside the aluminum casting, it doesn't want to stay in position. Is this how it should function? Any other ideas or info would be greatly appreciated.

 

[3_puppies]

the slide collar could be very worn or the fork that moves the slide collar is worn.
Most likely need a rebuild with some "new" parts. collar, fork and maybe the gear on the front output

originally I was thinking your hubs weren't locked until you said it does it sometimes in 2wd.

 

[Spencerfj6289]

the slide collar could be very worn or the fork that moves the slide collar is worn.
Most likely need a rebuild with some "new" parts. collar, fork and maybe the gear on the front output

originally I was thinking your hubs weren't locked until you said it does it sometimes in 2wd.

I was not locking the hubs while doing the test. I just shifted it to 4h and 4lo and 2wd. Do I need to lock the hubs before I test this?

 

[3_puppies]

Yes if you are moving, the hubs need to be locked so both driveshafts are turning at the same RPM. the slide collar connects both driveshafts.

if the hubs aren't locked, you will be trying to force a rotating assembly onto an assembly that isn't turning. thus grinding trying to engage.

 

[Spencerfj6289]

Yes if you are moving, the hubs need to be locked so both driveshafts are turning at the same RPM. the slide collar connects both driveshafts.

if the hubs aren't locked, you will be trying to force a rotating assembly onto an assembly that isn't turning. thus grinding trying to engage.

When shifting to h4 I was in a full stop with the t case and tranny in neutral. Could this still be the cause?

 

[OSS]

When the transmission & transfer case are in neutral, the transmission can still spin the gears slowly in the transfer case Then it would grind -a little bit- when shifting to 4wd.

Try testing it normally:
Shift from 2H to 4H directly while the car is stopped. It won't chatter.

 

[Spencerfj6289]

When the transmission & transfer case are in neutral, the transmission can still spin the gears slowly in the transfer case Then it would grind -a little bit- when shifting to 4wd.

Try testing it normally:
Shift from 2H to 4H directly while the car is stopped. It won't chatter.

Thanks I'll try that too