MrHubyUK

I have a 1992 Trek 750 Multi-Track that I would love to keep going, but teeth on the smallest gear have worn off to result in a slipping chain. I'm interested in sticking with all other shifters and ders and continue with 7 speeds in the back wheel.

Any advice on replacement (or repair)?

Iride01 

Is this the freewheel that actually had splined sprockets that could be easily replaced? Don't know myself, but might be some interesting history if anyone here knows about it and responds.

Still, I think it's a freewheel that probably can be replaced with any freewheel with 7 speeds and the tooth counts you want. But if it's functioning still and is the type freewheel that the cogs can easily be replaced, then you might want to wait till you can get to an LBS that has been around forever. They might still have some cogs for it laying in a bin.

MrHubyUK

I understand that this is a "Freehub"...I have pictures that I can post once I get to 10 (newbie). Since I have two of these bikes, there is a chance I can use one to save the other. The cassette in better condition but started to come loose (and then ball bearings came out when I removed it - i still have them ;-)

In the meantime, I can't find a new 12-30T 7 speed freewheel for replacement. Must be rare. Do I need to worry about Hub and wheel compatibility?

noobinsf 

You can still find Suntour cassettes on eBay, but many are very expensive. You can start by searching eBay for "Suntour cassette 12" to find cassettes for sale with 12-tooth cogs. Unfortunately, the Suntour cassette system is not compatible with Shimano, SRAM, Campy, or Sunrace (which is based on Shimano specs) cassettes, so you cannot use any of those to rebuild a Suntour.

You said the "smallest gear," which I assume means the smallest cog, the 12. If so, then you would need to replace that cog it to keep it going, since it is threaded, and it cannot be reversed. If you mean the lowest, or the 30-tooth, then I have read that you can reverse the cog to keep using it. When you have 10 posts on the forums, you can post pictures, which would be helpful.

I looked at a vintage Trek catalog online, and the 1992 750 definitely has the Suntour APII cassette, not a freewheel.

Looking forward, if you eventually build a wheel with a different hub, I have read that a Shimano 7-speed cassette should work with Suntour 7-speed shifters, but I cannot vouch for that myself, as I've never done it.

MrHubyUK

It's indeed the smallest cog (newbie speak)...so that means I can probably remove it. For which I think I'd need a chain wrench?

Since I have two bikes, I might be able to rebuild....

(waiting for post 10)

MrHubyUK

I've read that it might be referred to as a "Freehub"...But no YouTube videos I can find with this experience.

noobinsf 

Yes, the freehub is the splined section of the hub where the cassette cogs are mounted.

I recently did a deep clean on a Suntour cassette, so I have been reading about them lately, too.

https://www.bikeforums.net/21358216-post23.html
https://www.bikeforums.net/21358223-post24.html

noobinsf 

Yes, to disassemble a Suntour cassette, you need two chain whips. Or, rather, you need to immobilize the larger 6 cogs and be able to rotate the smallest cog in the opposite direction to unscrew, and using two chain whips is the easiest way.

Bill Kapaun

IF you have a 7 speed Shimano type rear wheel you can borrow, give it a try.
That might be your simplest option.
I think the hub dimensions are similar enough to Shimano, that you could do a "hub swap", keeping the existing spokes & rim.

Jeff Wills

If you were in the US I would point you at Yellow Jersey in Wisconsin. Sadly it appears they are sold out of their cache of SunTour cassettes: Suntour Cassettes at Yellow Jersey Suntour Accushift and PowerFlow Cassettes at Yellow Jersey

As others said: your only choice is to install a Shimano or Shimano-compatible cassette hub and cassette. This might or might not work... it's not something I've tried personally.

Andrew R Stewart 

We've done some 1990s SunTour replacements over the years. I ask the customer if they need to retain the shifters. If so then I am the bearing of bad news. As mentioned above ST used a different cog to cog spacing and thus the compatibility with current Shimano (and their clones) stuff isn't what we will suggest as it's not meant to work. If the customer can handle a different shifter (as in friction, thumb being the most common) then a shift lever and cog set replacement works. If the customer wants to retain indexing then a complete system swap to current stuff is needed. Then the cost is quoted and most fall back to the friction thumb lever option. Andy

MrHubyUK

Thanks Jeff for the link. I am in the US (Maryland) and will update my profile. I will post pics here soon - when I can get to 10....

If you or others have links/pointers to Shimano for Suntour replacements, I could use a hand. I don't know where to look.

MrHubyUK

You wouldn't be surprised to hear that I replaced the stripped and broken grip shifters with at Shimano SL-RS45 3x7 Twist Shifter set. They worked great - only to help me discover cassette problems. Since I have 2 Trek 750s, my hope is to salvage parts from at least one. And then take the thumb shifter with a different cog spacing alternative.

Still waiting to get to 10 post to show pictures. Didn't expect to see bearings.

MrHubyUK

Any other sources in the US for Suntour parts (besides eBay) based on experiences would be helpful.

Andrew R Stewart 

If your area has a bike recycler, sometimes called a bike kitchen (which I dislike as a reference term), they might have some 20+ year old parts on their shelves. Our local non profit (R Community Bikes, mission is to get bikes into the hands of needy people) doesn't intend to sell just parts but if one befriends them (maybe volunteer, certainly donate) they have been known to help out some of us.

There's not really enough potential customers to pay for a retail based used bike shop in most communities. Craig's List, Facebook Marketplace are two more on line potentials. Andy

MrHubyUK

There are indeed some of these in the DC area and should be very helpful. Thanks Andy. Shame about the timing - meeting these folks for tips and parts will have to wait a few months.

masi61

Be sure to post a photo of the AP II 12-30 cassette when you get to 10 posts. I'd personally like to see a photo of that worn small cog. Did you say part of one cog tooth broke off?

And while I agree with what others have said about having difficulty finding a replacement for this cassette, if you know precisely what you need and you keep checking eBay, you are more likely to find a suitable replacement at a reasonable cost.

The smallest (outer) cassette cog is threaded onto the freehub body. It requires a chain whip to loosen the cog, then the whole cassette will slide right off. There was a "Microdrive" variant that permitted the use of an 11 tooth cog. These have a stepped freehub body. For this particular iteration, the outer 2 cogs thread together in a subassembly, then thread onto the freehub body.

To me, these SunTour Accushift cassettes work well and should last a long time. The spacing is unique for this so to get it to index correctly with the SunTour Accushift 7 shifters, you need to stick with a SunTour cassette. I have bought them for less than 35$ new but that was in a 12-24 or 12-28 combo.

Not to confuse you further but any SunTour 7 speed freewheel with a 4 prong freewheel body such as the Winner, Winner Pro or AP (black cogs) in a 7 speed will share the same spacing. So with the SunTour freewheel you could sub in a different rear wheel that uses a more standard threaded freewheel. SunTour 7 speed freewheels that are NOS (new old stock) have also become expensive, unfortunately. But again, they are out there and clean used examples pop up on eBay pretty regularly.
Am looking forward to seeing that picture of the 12 tooth cog!

Iride01 

Are you sure the chain isn't the culprit? Perhaps it's stretched and simply slipping on that cog. I've never worn out a cog.

MrHubyUK

This is Bike #1 , Cassette still in place and showing the teeth broken on the 12T cog.

MrHubyUK

Here are pictures from the cassette dis-assembled from Bike #2 . Hopefully I can clean this and reassemble with some reading and supplies assessment (my preference) or bring to an LBS (to potentially save the bike).


Bike #2 Cassette - In good shape but hub was loose.


Bike #2 Cassette - Wheel Side

Bike #2 - Freehub

Bike #2 - Wheel backside

Bike #2 - Pins and nuts

Iride01 

Well yeah, I guess it's not the chain................... <grin>

MrHubyUK

Here are some better pictures of the cassette from Bike #1 showing 12T cog damage. They look (and feel) broken...so I would not be surprised if the chain was this issue. Poorly maintained in the past....

Jean_TX

In addition to the damage to the smallest cog, the next smallest cog appears to be badly (ie, fatally) worn.

masi61

Here is a replacement cassette that will work. It has a 28 large cog, not a 32 though.

https://www.ebay.com/itm/233486475123

And, for a bit more money - here is a nice silver nickel plated one that does have the same 32 tooth biggest cog:

https://www.ebay.com/itm/383487367840

MrHubyUK

Thanks masi61. My biggest cog is 30 (I counted 3 times)...but it looks like I have options and could browse for a little to get lucky.


Will get a couple of chain whips, some supplies to clean and repack some bearings, more research, and some confidence. I will post a new thread if I get stuck....