Bracket type 8 speed Derailleur

[Kins]

I am going to convert my Falcon to 8 speed, problem I have is the bike the parts are coming off has a screw on derailleur and the bike they are going on has a bracket derailleur.

To confuse matters a bit more, it is currently a 6 speed, the wheel I am putting on is a 7 speed but I want to fit an 8 speed cassette.

If I fit a 7 speed derailleur like the Shimano Tourney will it do 8 speed do you reckon or will my 6 speed even stretch to 8?

Also will an 8 speed cassette fit or will I have to buy a 9 speed an lose a sprocket?

 

[Kins]

Swapped the wheels over and the old derailleur works on all 7, the index shifters even work if you push past the last indexed position which is nice. Not sure how it will fair when I upgrade to 8 and 2300s though.

 

[Rickshaw Phil]

The big question in my mind is whether the cassette will fit the wheel you have:

• If you have started with a 6 speed that suggests the original rear wheel was for a screw on freewheel rather than a cassette.
• 7 speed can be either screw on freewheel or cassette but is most commonly the screw on type.
• If it is an older 7 speed cassette type wheel the 8 speed cassette may not fit as they are different widths

Sheldon Brown has info on this (freewheel or cassette) (cassette types).

The Tourney derailleur may work with 8 speeds but I've not tried so can't be certain. I can confirm that an Acera rear derailleur will work with 8 speed as this is what I used for my 8 speed upgrade.

I hope this helps.

Edit: When you say "bracket type" do you mean attached by one of these? If so they are available seperately and most direct fitment rear derailleurs can be used with one.

 

[Kins]

6 speed was on an old steel wheel and was 6 speed shimano, 7 speed is a Shimano cassette that came off a claude butler that has sora front mech and rear derailleur, with that bracket should fit.

The wheels fit fine but the axel is only just about long enough, with skewers they are both safe. The bike has a large rear stay distance for some reason.

Bracket looks just the job, I'll give it a try. Didn't know you could get these and did have a google for something similar, crap searching obviously, cheers.

Not worried now, with that bracket I will just but an 8 speed derailleur if the Sora mech doesn't work with 8, its just the cassette I need to sort now.

 

[RecordAceFromNew]

It seems to me you might want to read this having read your comment re "The bike has a large rear stay distance for some reason.".

Shimano 6 speed shifters do not pull quite the right amount of cable for 7 and 8 speed sprockets (which have identical spacing themselves). You will find that if the rear mech is lined up perfect and correct at one end (smallest sprocket e.g.) it will be out at the other end. You can minimise (but not eliminate) the problem by adjusting cable tension to center the mech at (one of) the middle sprocket(s).

You can't put an 8 speed cassette on a wheel with 7 sprockets unless it has an 8/9/10 speed freehub. Such a freehub will have an additional 4.5mm spacer in order to take a 7 speed cassette. Depending on the hub you might be able to replace a 7 speed freehub with an 8/9/10 speed freehub.

 

[Christopher]

cheers for that post RAFN! I have on old mech that I am tempted to try on a modern 8-speed setup & from your post above it looks like it won't work very well...

 

[RecordAceFromNew]

cheers for that post RAFN! I have on old mech that I am tempted to try on a modern 8-speed setup & from your post above it looks like it won't work very well...

Er actually for vintage Shimano rear mechs unless it is earlier than 1986/7 (except Dura Ace which changed to the current standard only in 1997) it should index perfectly with all the current Shimano 8 speed shifters. The compatibility issue I mentioned above arises from different cable pull of different speed shifters, not mechs.

But for completeness IME some older mechs can only move across a narrower range than modern, wider 8/9/10 speed cassettes require. Sometimes this can be dealt with by some judicial filing at the clash point.

 

[Kins]

I had already read that sheldon article, but thanks for the link. The bikes original spacing, with the original build steel wheels is 135 mm which according to sheldon makes it a mountain bike! If anything the new (to me) wheels are slightly too narrow if you count axle length but with quick releases they have just enough axle to fit in the stays and clamp up tight.

I think I will try a 9 speed cassette removing one of the rings as sheldon recommends and a narrower chain and see how this works out. The wheel has a HG rear 7 cassette at the moment though and looking at the spacer width on sheldon its smaller than the IG so I don't know if this makes a difference.

Just been out to work and back and the changes with a 7 speed cassette are quick and light all the way through even though the right indexed shifter is only 6 speed. Have to change the tyres though, even though they are pretty new with the furry bits still on, the tyre depth is so low it feels terrible over the crap roads round here.

 

[RecordAceFromNew]

I think I will try a 9 speed cassette removing one of the rings as sheldon recommends and a narrower chain and see how this works out.

While it is 0.5mm out per indexed shift with 7 at the back at the moment it will be out by around 1.15mm per shift with some or all the sprockets and spacers of a 9 speed cassette. See this.

 

[Kins]

Nice article, cheers.

By the time I get a cassette I will have got a pair of STI shifters from CC sale section so with 8 gear sti shifters should only be .45 mm out according to the chart which should be fine. I didn't expect them to work with the 6 speed but I didn't make the fact I was getting new shifters clear. I was more worried about the derailleur situation, which that bracket will sort.

Cheers for help, clarified things nicely in my head!