on my 89 s10 blazer 4.3L v6 i get a terrible grinding noise when i engage and disengage 4hi or 4low. once engaged they work and sound fine but getting to and from sounds horrible. i think the Tcase needs to be replaced. any ideas would be greatly appreciated.
Is the sound coming from under you or from in front of you?
If it is from in front of you, it likely is a problem with the front axle engagement. Either the vacuum actuator is not properly pulling on the cable (bad actuator, bad vacuum line or poor vacuum source), the cable could be froze up somewhat - just needing some WD40 or other suitable lubricant to free it up, or the shift fork and/or collar inside the front axle is somehow messed up.