Fitting Hyperglide sprockets on a six-speed Uniglide freehub
NB since I created this post I have seen that 7 speed Uniglide cassettes are availabe from SJS Cycles – not sure how I missed them. However, their cost including postage is almost £30 and that doesn't include a compatible chain. I will leave the following post unchanged in case SJS – or any other supplier – runs out of stock.
One of my oldest bikes has a Shimano Uniglide freehub. It is a Shimano 600 model with enough space for six Uniglide sprockets. Or five Hyperglide sprockets and one – the smallest – Uniglide sprocket. (See an earlier post for the difference between the two systems and Sheldon Brown's very detailed explanation.) I am thinking of fitting larger (Uniglide) sprockets on the freehub to help me get up hills, but supplies of these are scarce (fortunately I have a little stockpile from the early 90s). Here's why you might want to use a Hyperglide cassette:
Older Shimano freehubs are 126mm OLN. This will normally mean the rear triangle (ie the distance between the two rear dropouts) will have to be spread to fit a more modern – 130mm or 135mm – freehub, either on your existing hub or on a new one, maybe on a new wheel. This spreading can be done by a competent bicycle mechanic and is called cold setting. So to upgrade you might factor in the cost of a new rear wheel, the cold setting, a cassette, and a suitable chain. (But be careful if you want to go up to nine speed as the gap between the chainrings on an old chainset may be so great that the chain could fall between the two rings.) Do also bear in mind that a new freehub could mean that your old wheel will have to be re-dished to avoid other problems I won't go in to here.
So if you stick with your old wheel and freehub you can lower your gearing for around £20 if buying online (excluding the price of specialist tools such as chainwhips). Here's how:
You can easily choose from a range of Hyperglide cassettes in seven, eight, nine and ten speed versions. For the purpose of this post I will use the example of a typical Uniglide cassette with original sprockets of 13/14/15/17/19/21. You might want to lower the gearing to 13/15/18/21/24/28 – assuming your rear derailleur can cope with such a large sprocket as 28T. To do this I suggest buying an eight speed Shimano HG41 11-32 cassette and using the sprockets highlighted above. You will also need a Hyperglide chain, such as HG50. (Six, seven and eight-speed chains are interchangeable. Nine-speed are narrower, 10-speed narrower still.)
Uniglide freehubs have nine equally spaced splines around the freehub body. Hyperglide freehubs have one narrow spline to align with the one wide tab on each of the sprockets of the cassette. This tab will need to be filed down if the selected sprockets are to fit on the Uniglide
cassette freehub body. Once you have your donor cassette you will need to remove the three rivets that hold the largest sprockets together. In the past I have drilled out the rivets from the large sprocket side (see another post), but lately I have simply tapped through the rivets from the small sprocket side (required: hammer, centre punch, safety goggles and somewhere for the rivets to go when you try to drift out each one). NB sprockets on a Uniglide cassette were typically held together with small threaded bolts with either hexagonal or allen key heads.
You will then need to file down that tab. I found this surprisingly easy to do with a set of warding files; the metal is alarmingly soft. Don't take too much off the tab as a snug fit is desirable. You don't need to reuse the rivets, but some people claim you should.
If you are unlucky you may shatter the eight speed spacers, but it is the original six speed spacers that you will need when you re-assemble the cassette (do bear in mind that there may be a little plastic lip underneath each hole on the six speed spacer – see the stack of spacers in the top left of the photograph at the top of this post. These may need to be got rid of).
Slot your five new HG sprockets on to the freehub and separate them with the original six speed spacers. You should be presented with a similar image to that below. NB for this photograph I used the eight-speed spacers, simply because I didn't want to take the lips off my six-speed spacers as I am still using them with a Uniglide cassette. There shouldn't be so much thread visible on the freehub body. If your original cassette came with a 1mm spacer (next to the 13T sprocket on the first photograph of this post) you should put that on the freehub next. Then hand-tighten the smallest sprocket on to the freehub body. Tighten by putting your wheel in to the rear dropouts, slipping the chain over the smallest sprocket and pressing down on the pedals. You are ready to ride your bike, maybe up a few tougher hills...