Front Mech Replacement - Can I go for a Top Swing Instead ?

[Lard Armstrong]

My ancient but treasured hack bike's front mech has died and I need to replace it.

It's on a 7 speed, 48T-22T triple, with a 28.6mm seat tube. The existing mech is an old bottom swing Shimano Altus.

1) Does the replacement mech have to be for 7sp chainset ? Or will a 9sp work ?

2) Also would a top swing front mech work OK ?

Thanks in advance !

LA.

 

[mrandmrspoves]

The derailleur will be fine so long as it's suited for a triple rather than a double. You could change the routing of the cable to make a top pull work - but if the cable is routed for bottom pull it's much easier to stick with this. A basic model off eBay/Amazon will only cost about £7 or so

 

[Lard Armstrong]

Thanks, I have been looking around, there are a few candidate mechs for not much money, I just needed to check whether a top swing mech would work and whether or not a 9sp would index correctly on a 7sp chainset.

The existing mech is bottom pull (cable) and bottom swing (mech movement). I would like to stick to the existing cabling to make life easier.

 

[Lard Armstrong]

....any suggestions much appreciated.

 

[Rickshaw Phil]

To the best of my knowledge a 9 speed front derailleur will be fine with a 7 speed set up. I'm currently running a 9 speed mech on a 3x8 speed set up and it works very well. Most Shimano front mechs will now accept top or bottom pull cable runs so that shouldn't be a problem either.

I don't think changing from bottom to top swing will be an issue. I can't see the movement of the mech being substantially different between the two types. In my case I had to go for a bottom swing because my frame didn't have sufficient clearance to accept the top swing mech I originally sourced.

48-22 is a big jump between gears. None of the mechs I have looked at will officially take such big difference in chainring sizes. This is the only thing I'd really be concerned about.

Edited to correct my mix up.

 

[Lard Armstrong]

Thanks Phil, that's a big help.

I just realised I made a typo : 48T - 28T (not 22T). Which looks in range for most front mechs according to Shimano TechDocs.

Cheers.

 

[mrandmrspoves]

http://www.ebay.co.uk/itm/SHIMANO-2...sure_cycling_bikeparts_SR&hash=item416674ac17

Yes 48 - 22 should be fine for most Shimano Triple Derailleurs.
Above seller is very good.

 

[Red Light]

I would be very surprised if you had the cable stops on the frame for a top swing and a bottom swing mech and since its cabled for bottom swing that means no top swing stops. You can buy clamp on cable stops but they are not cheap and you would have to either buy several or run a continuous cable run with zip ties to a stop clamped just above the mech for it to work. So unless you want a load of cost and grief, stick with a bottom swing mech. Apart from that any Shimano mech should work.

 

[Red Light]

I don't think changing from bottom to top swing will be an issue.

Errr....cable stops?

 

[Rickshaw Phil]

Errr....cable stops?

Swing and pull are not the same thing and as mentioned in my earlier post:

Most Shimano front mechs will now accept top or bottom pull cable runs so that shouldn't be a problem either.

 

[Rickshaw Phil]

Thanks Phil, that's a big help.

I just realised I made a typo : 48T - 28T (not 22T). Which looks in range for most front mechs according to Shimano TechDocs.

Cheers.

That's fine. I wasn't sure if it was a typo or if you had a really big range custom set up.

Just for further info, the Shimano tech docs state that some of their 9 speed mechs are for a minimum of 22T difference between big and small rings. The one I got works fine with a 20T difference (my set up is 22-32-42) but I had to set it slightly higher than it says in the instructions otherwise it fouled the middle ring. This made no difference to the smooth shifting of the gears.

Edit: I have also made an error. The type I have is bottom swing not top as stated originally(the cage is attached to the bottom of the mechanism). What I said still stands though but you need to check you have enough clearance on the frame (mudguard clearance was the fundamental factor in my case). Looking at the two mechs together, despite the difference in linkages the actual movement of the cage is the same

 

[Red Light]

Swing and pull are not the same thing and as mentioned in my earlier post:

My apologies, you are correct. Teach me to reply before the first cup of coffee to wake me up. I was thinking top and bottom pull.

 

[Rickshaw Phil]

My apologies, you are correct. Teach me to reply before the first cup of coffee to wake me up. I was thinking top and bottom pull.

No problem. I just realised I made a bigger mistake in my post - see correction above.

 

[Lard Armstrong]

I have ordered a replacement top swing, multi pull for eight quid. I will post an update when it gets here.

Watch this space.

Thanks for your insights !