There are two adjustments in an 8 track's tape head. There is the azimuth, or tilt angle of the head, and the height. The two will sometimes affect each other as you make adjustments. An out of adjustment azimuth will make the deck loose high frequency response. The adjustment is beside the head on a set screw. The height adjustment is usually behind the head, but it varies from deck to deck where it actually is. You've experienced what a bad height adjustment does. Frequently, it is on the track changing mechanism, which moves the head up and down to align it with the different tracks. One of the things to also look at is the lubrication on the track changing mechanism. Your problem could be related to gummy lubrication keeping the head from moving up and down freely when the track is supposed to be changed. There could also be worn/loose parts in the mechanism too (go figure, the decks haven't been made in 20 years!). Take care of this before aligning the head!
Proper alignment usually requires an alignment tape, which would be practically impossible to find nowadays, so I just use a pre-recorded tape with good high frequency response. Play track 1 to start with. First, align the head for the loudest response by moving the height adjustment while listening to the music playing. If the audio sounds muffled, tweak the azimuth until it sounds clear and bright again, then go back to the height adjustment and give it another slight tweak to see if you can get it any louder. Usually doing this procedure 2X to 3X will get it dialed in pretty darned good. Run the tape till the song ends and listen to the break between the tracks. Make sure the crosstalk between the tracks is not objectionable (some cheap 8-track decks have wide head tracks, and it is hard to work it all out!) Lastly, cycle the deck to the other tracks on your tape and see if it sounds good on the other tracks. A few decks also have what I call a "jump" adjustment, and it adjusts how far the head moves when a track change occurs. Go down to track 4 and listen to it and then back to track 1, if 4 has lots of crosstalk and 1 still sounds good, you need to tweak this adjustment until track 4 has minimal crosstalk, and sounds the loudest. Once you are happy with the sound, put a little dab of locktite on all the screws you adjusted.
If it slowly works it's way back out of alignment as you changed tracks, you need to perform some mechanical work on the track changing mechanism (cleaning, lubing, etc). I cannot tell you exactly where all these adjustments are because they vary from deck to deck, even within same makes. The track changing mechanism is the archilles heel behind the 8-track format. Some higher end decks used a stationary head with 8 gaps in the head and only switched electronically. This is the ultimate way to do the 8-track. This is a rare feature and did not come about until the late 70's due to the cost factor involved in making heads like this, usually only found on Japanese made decks .
Lastly, before placing any tape into the deck, check the pinch roller and the pressure pad behind the tape. Some of the early tapes have issues with the pinch rollers getting gummy and tarry. This was because of a bad rubber formulation, and heat from being left in cars, and in attics. You stick one of these tapes in your deck, you will get black grime all over EVERYTHING, and it's next to impossible to remove! Look behind the tape at the pressure pad. The best tapes to align with are the ones with the felt pad on a metal tab. Usually the foam pad types deteriorate and don't hold enough pressure on the tape. Part of your alignment problems can also be related to this pressure pad letting the tape "drift" across the head and loose it's proper alignment...check this before even touching the deck with a screwdriver!!! Lastly, I recommend getting some splicing tape and "walking" the tape to the loop splice manually and reinforcing the splice. In many tapes, the adheasive will fail in the original splicing tape and cause the tape to fail. I like to put some on the back side of the tape loop too, and leave the metal piece on the front for the tapes that sense this to operate the changer mechanism properly.
