reel to reel tape thickness problem.help?

My sony reel to reel records real well on tape that is 1 mil polyester but does a poor job of recording on 1.5 mil durol. both are kodak.I must put pessure on the feed reel in order for it to sound good.it makes poor contact on the record head.is this a problem or do some decks not like thick tape.I use a mint sony tc-640 and made a bunch of adjustments and nothing works

 

Kodak? That's the problem right there. That tape is almost 40 years old. Probably dried up and inflexible.

 

That is what I belive is the problem.its reel stiff. Ive always used 1800 foot 1 mil tape with no problems. I record test tones(1.5 khz 3.5 khz and 9.5 khz)At 0 VU without a wiggle on the meters. I will try other 1.5 mill tapes to see if they work but I dont have but the one kodak tape that has the problem.

 

A lot of half-mil (.05) manufacturers put on a thinner layer of oxide, which is why you can't get the sound volume the other thicknesses have. With so much reel tape hitting the thrift stores these days, I would concentrate on the better stuff -- it's all priced the same.