help with 4x4 on 1990 jimmy s-15

[westvilleguy]

my truck wont go into 4 wheel drive but the drive shaft is spinning up to the front when i put it in (i tied a string on it to figure this out lol) when i pull it back to low it sometimes pops into neutral and if i push it back to hi or out of 4x4 it grinds and sometimes i have trouble pulling it into lo or wont even go into lo i checked the vacumn hoses they have suction i dont know how much they are supposed to have but they are sucking and i checked the actuator under the battery and its being pulled in even tried it with vice grips to make sure eveyone thats looked at it says they think its the fork in the front end that lock the hubs in any help would be great cause i cant drive it in the snow or ice cause its useless without 4x4 i also have a parts rig incase i need anything off it and if it is these fork or fork in the front end how big of a job is it to change these could anyone give me the steps

[T Man]

WHen my burb wouldnt kick into 4wd it was an actuator problem. if your driveshaft is spinning, then you know its in the differential somewhere. Coming out of 4 low sounds like a shifter problem, like when you shift from 2wd to 4lo you pass N, sounds to me like it is missing the catch that keeps it in 4 lo

[westvilleguy]

i took the cover of where the actautor cable goes in the frontend and it is still attached not broken or anything i also jacked the front end up and put it in 4wdr and the tires spin freely so it has to be a probalem in the front

[Tink]

You pulled the cable manually to try to engage it and still nothing? The actuator just locks the 2 part RF axle shaft together in the front diff... if pulling the cable manually didn't work, it maybe that the fork has broken, which may be the cause of the grinding noise too... Does your parts rig have the same gears? It may be easier to just swap diffs...

[Tink]

Forgot... here is a write up from posi-lock on diagnosis and repair of S10 Front Axle Engagement Systems... Don't know if it would help or not...

http://www.4x4posi-lok.com/PDFs/TSG_chevyT.pdf

[westvilleguy]

i'm not sure if they have the same gears i dunno even know what the gears are in either of them everything is identical except the parts rig was all power windows,mirrors etc. but my good one is an s-15 jimmy and the other is just a jimmy weather this would make any difference i dunno

[Tink]

Should be able to check the RPO codes in the glove box to find out... I would imagine they both had GU6, which is 3.42s... very commom in the 89 - 91 4wds.

[westvilleguy]

the thing is pretty worn out in my good one but there is a gu6 on it but there is no gu6 in all the #'s on the other one so i'm guessing they are different

[Tink]

So the good one is the one that won't go into 4wd, right?

Does the other one have any of these?

GU2 - 2.73 Rear Axle Gear Ratio
GU4 - 3.08 Rear Axle Gear Ratio
GU5 - 3.23 Rear Axle Gear Ratio
GU6 - 3.42 Rear Axle Gear Ratio
GT4 - 3.73 Rear Axle Gear Ratio
GT5 - 4.10 Rear Axle Gear Ratio
HO4 - 4.11 Rear Axle Gear Ratio

[westvilleguy]

i took a better look they both have the GU6 but they are not in the same spot in both but they both have that # in there