Replacing 7 speed shimano deraileur

[Dr pepper]

I have a trek 6000 vintage Mtb from the 90's, it has exage 400 lx shifters.
The rear is worn to the point its falling apart and is starting to phantom shift, new pulleys fixed it last year but now I think its done its time.
Rather than buy another worn out one on ebay I want to fit something newer.
I see sjs sell a shimano acera Rd-M360, seeing as my original is a Rd-M300 is sounds close.
The direct mounts on these look the same, is the pull going to be similar on a 8 speed to that of a 7 speed, and is the smart cage on the acera similarish to the lx 400 (its stamped sgs), I deleted the smallest chainring on the front so I dont spose I need the same distance between pulleys.

[Brucey]

the 'shift ratio' determines whether or not given mech will be index-compatible, so any shimano 7s, 8s, 9s and some (not all) 'road' 10s mechs will work OK in this respect.

[Dr pepper]

Ok I'm learning.
So I'm assuming this is correct, 7,8,& 9 speed cassette's & freewheels have the same spacing between sprockets, and shimano deraileurs have the same cable pull distance to cage movement ratio's, thats cool to know if its correct.
I did some research on smart cages, it doesnt specify cage length it sjust a means of pulling the chain without splitting the cage.
I found a cool website that shows you how to calc cage length, looks like loosing my likkle sprocket on the front will take me from a long cage to a medium or short, its also interesting to know shortening the cage increases the tension on the slack side of the chain.

[nirakaro]

7,8,& 9 speed cassette's & freewheels have the same spacing between sprockets

No. AIUI, the indexing is between the shifter and the cassette. The shifter pulls a different length of cable for 7,8 or 9 speed, which tells the derailleur how far to move to engage the next sprocket. So the shifter needs to know how many sprockets there are, but the mech doesn't.

[Brucey]

-so 7s,8s,9s shifters all pull different amounts of cable, so that the net result matches the (different) sprocket spacing, even if they use the same shift ratio in the mech.

[Dr pepper]

I got it, but messed up explaining it.
7, 8 & 9 shifters pull differently, but work with the same deraileur.
Theres only one spacing for shimano 7, 8 & 9 speeds, ie there isnt different spacing versions for 7's for example.

[Brucey]

....Theres only one spacing for shimano 7, 8 & 9 speeds, ie there isnt different spacing versions for 7's for example.

just to clarify; shimano 7s,8s,9s all use different sprocket spacing (pitch) from one another, but the same shift ratio in the mechs.

[peetee]

I got it, but messed up explaining it.
7, 8 & 9 shifters pull differently, but work with the same deraileur.
Theres only one spacing for shimano 7, 8 & 9 speeds, ie there isnt different spacing versions for 7's for example.

Shimano, SRAM and Microshift, yes.
Campagnolo stand alone in their compatibility - although some ‘fringe’ suppliers such as Miche did some cassettes to suite.

[Dr pepper]

For my commuter I stay away from exotic stuff, for various reasons including theft.
I sorted it out yorkshire style, for nothing.
My junk box had a shimano deraileur marked SIS, its a Rd-r552, and had a hanger mount.
I managed to disassemble my 400Lx and this one and came up with a suitable unit thats in very good condition, and works like it meant to, no more messing around shifting.
I'm still going to get myself a spare tho.

[Brucey]

good work!

you were lucky that you had that mech, IIRC it is about the same vintage, so the chances of swapping bits about is greatly improved.

[cycleruk]

For a spare you can use MTB or Road rear derailleurs up to and including 9 speed.
So you can use Tourney, Claris, Acera, Deore, 105, Ultegra, etc.
The main thing is to get one that suits whether you have a double or triple chainset.
I've used STX and LX on both my MTB and road bikes on 8 speed.

[SprokenBroke]

I'm pretty sure that 7s and 8s are the same spacing. When you put a 7 cassette on a freehub that will take an 8 you have to use a spacer behind the 7.

[cycleruk]

I'm pretty sure that 7s and 8s are the same spacing. When you put a 7 cassette on a freehub that will take an 8 you have to use a spacer behind the 7.

Not exactly:-
7 speed = 5mm pitch, 31.9 stack.
8 speed = 4.8mm pitch, 35.4 stack.

An 8 speed cassette won't fit on a genuine 7 speed hub.
But yes a 7 speed on an 8 hub requires an extra spacer.

[SprokenBroke]

I'm pretty sure that 7s and 8s are the same spacing. When you put a 7 cassette on a freehub that will take an 8 you have to use a spacer behind the 7.

Not exactly:-
7 speed = 5mm pitch, 31.9 stack.
8 speed = 4.8mm pitch, 35.4 stack.

An 8 speed cassette won't fit on a genuine 7 speed hub.
But yes a 7 speed on an 8 hub requires an extra spacer.

Wow so close and yet so far.

I'm sure that I used a 7 shifter with an 8 cassette one time (or it might have been the other way around) and it worked ok.

[Brucey]

.....I'm sure that I used a 7 shifter with an 8 cassette one time (or it might have been the other way around) and it worked ok.

when everything is matched, you can go 2 clicks on the SIS cable, in either direction, and it'll still work.

When you are using a mixture of 7s and 8s it'll probably work but there will rarely be much tolerance.