Check your cables and connections to make sure they are all clean. Corrosion can travel up the wire (wicking) so if they have been badly corroded they may need replaced. Get your alternator checked to make sure its charging the battery properly.
The brushes in the solenoid are the most common problem with these starters. However they are on the starter and depending on the model you have they can be a real pain to so better off just replacing the whole starter. With 2wd apparently the starter is fairly easy to remove. On 4wd however its a real pain. Either have to remove the exhaust pipe between the manifold and y-pipe (real pain if the bolts are rusted) or unbolt the left engine mount and jack up the engine. The flange bolts at the y-pipe were badly corroded on mine and I ended up having to cut the heads off of them, its just been clamped together since. With the pipe out of the way its still a really tight squeeze fitting the starter between the frame and bell housing.
I replaced mine with an autolite reman
and its been doing well for 2 yrs. There are 2 locating dowels on the starter that dont come with the new one, remember to keep those for the new starter. I didnt know this and had trouble getting it aligned properly.
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