Tascam 38 capstan clacking back and forth like piston in collar

[Bill Dankert]

In 2003, I bought a Tascam 38-8 off ebay, replaced the belt, and it has worked fine ever since. Except, even after replacing the belt, the capstan made a rattling sound whenever the machine was in "Play" mode. This did not audibly (at least to my ears) affect the sound, so I laid the machine on its back, and the problem went away.

Now in 2016, I'm in a space where I would like to use the machine in upright mode, so I'm trying to solve this old problem. When I examine the capstan, there is a small amount of play--a few mm--in a direction parallel with the axis of the capstan post. The capstan (and flywheel) can move slight amount forward (toward front of machine) and backward (toward back of machine). When the capstan is activated (either with pinch roller in "play" mode or by lifting the right tension arm to start the motor) the capstan starts clacking back and forth along its axis like a piston against the metal collar (it's much more pronounced and piston-like with the pinch roller engaged).

Looking at the capstan, it looks like a small amount of distance between the rubber washer at the base of the capstan roller around the post and the collar. So it seems to me like the capstan is set a bit too far out of the fly wheel. I am working on loosening the hex set screws in the back of the fly wheel that hold the capstan post in the fly wheel, and I'm hoping I could set the post a few mm deeper in the fly wheel to fix the problem. I loosened the screws some yesterday, but the post still won't push in, so I will continue and see if this works when I get another opportunity.

But does anyone know--am I on the right track here, trying to reduce this play in the on-axis movement? Or is this problematic? When gravity held the capstan in place all those years, it didn't seem to cause any issues, but just wondering if maybe I'm misapprehending the root cause? (I checked/cleaned the pinch roller solenoid to eliminate pinch-roller tension as the possible problem.)

 

[sweetbeats]

Isn't there a thrust bearing at the base of the capstan shaft? That thrust bearing is supposed to be adjusted so there is a specific amount of play. It sounds as though you may have too much play. There is a procedure in the service manual.

 

[quiberon]

I had this problem with my Tascam 34. What is happening is that the flywheel is scraping on the underside of the base plate the capstan bearing is mounted on.

See my thread over on tapeheads; Tascam 34 Flywheel problem - Tapeheads Tape, Audio and Music Forums

What will have happened is, inside the flywheel at the bottom of the capstan shaft, is a metal washer with rubber bonded to it. This acts as a buffer to keep the flywheel away from the plate. The rubber will probably have turned to goo.

I cured my 34 by using an M6 x 6mm nylon spacer in place of the rubber.

After replacing the flywheel on the capstan in the same position that it was before removal, I did not find in necessary to make any further adjustment to the thrust bearing spacing.

 

[sweetbeats]

A+ to that post ^^^^^^^

I had no idea there was goo-prone rubber in that style capstan shaft. So that would be a potential issue in any 30-series machine, or 20-series machine, and possibly the 388 as well.

Thanks for the helpful post on the issue, but also for including a solution!

 

[Basilharewood]

I have a similar issue going on here. I have two machines that I'm trying to turn into one perfectly running machine. On one of them, the capstan shaft and flywheel can move back and forth (both flywheel and shaft) which likewise to the original poster hadn't caused me an issue previously as I would also record with the machine on its back. When moving back into my studio recently the machine took a fall as the person helping me move in lost grip of their end and it hit the ground from about 2ft. This seriously damaged something as when I loaded it back up and hit play it jammed up and nothing turned. I bought a second machine in better condition but this has quite bad wow/flutter issues when recording. I opened them both up and like I mentioned the original one I had has a lot of slack with the flywheel and capstan shaft, moves back and forth like a piston but the flywheel can spin freely when turned whereas the recent machine I bought with the wow/flutter issues has a very tight flywheel and capstan shaft, I have to really give it some for it to turn and the setup looks different. I can't seem to find any photos anywhere of the perfect setup and wonder if this issue is what would be causing wow/flutter issues whilst recording. I'm yet to disassemble everything to get a proper look inside but any help here would be massively appreciated.

 

[ecc83]

That bearing assembly looks very like the bushings you get on track rod ends and anti-roll bars. The standard fix* is to replace the rubber with urethane which never degrades apparently. A small engineering shop should be able to turn you one up from stock rod.

*I watch a LOT of Wheeler Dealer car proggs!


Dave.

 

[Basilharewood]

Hi @ecc83 thanks for your reply. So I just disassembled the flywheel assembly block, took off the belt and twisted the capstan shaft by hand and the flywheel spins freely and smoothly. Feels like it's all ok in there. I don't want to have to disassemble much more like the actual capstan shaft etc. Would I know if the rubber part inside has gone by the movement of the flywheel? if it spinning ok means it's all good then I'll leave it. This makes me think it was the Capstan belt making it not turn very well and too stiff. I just read another forum saying the belt should be 15" in length, the one that was on there is 16" but wouldn't it being too big not stop it from turning, but be too loose? Makes me think maybe it was just put on incorrectly or unevenly. I have a spare here which is bang on 15" I've put it on but it feels the same, it stops the flywheel from turning freely when I twist it by hand. I guess knowing how the flywheel is meant to spin while the machine is turned off would help me figure out if there's something else going on.

 

[rludlamjr]

Hi, saw this thread and the issue described here is exactly what I’ve been experiencing with a newly acquired 38. Thank you! The internet is amazing. The capstan was working perfectly when I got it, but after a couple of days of use, I noticed it started to come forward when the machine was upright and started rubbing. It also has accumulated a fair amount of horrible black goo around it.

Following the notes in this thread I removed the capstan to access the underside and indeed I see that the black rubber spacer has completely melted. But I’m wondering if there is supposed to be grease here as well? Or is everything on the capstan shaft just goo from the rubber spacer? Going to replace with a more sturdy one as recommended above but wanted to make sure if it needs grease I add that before I put it back together. I just can’t tell because the goo looks like grease and has filled the shaft and area around the bottom of the flywheel.

Should also say the belt in this machine is in good condition, recently replaced and clean so the goo is not coming from there. Attaching photos of the dreaded goo.

Thanks!
Roland

 

[ecc83]

I would say the goo is a mix of grease and ground up rubber. Once cleaned up try the shaft on the bushing and check for 'slap'. I have no idea what the tolerances are but I would expect barely any movement? (the capstan on my A3440 has just a suggestion of movement cold) if it wobbles maybe a local engineer can turn you up a new bushing?

Are the bushings pre-lubricated sintered Bronze? Sweetbeats will know.

Dave.