How to choose a derailleur?

zcacogp

Chaps,

I have an old bike which I am using for commuting. It's about a '91 Peugeot Premiere. I know it's an antique, but I like it!

It has been pressed into (gentle) service recently after having sat outside for about 10 years, and pretty much everything on it has been replaced in the last couple of months. Which has proved quite expensive and very annoying - both because cycling every day was meant to be cheaper than the bus (which it has failed to be, by some margin!) and because of the time taken to do the maintenance.

Last night, the front derailleur broke. It was the original shimano thing, and fitted via a clamp around the upright tube in the middle of the bike. A bit of plastic in the middle of it broke, and it's not repairable.

So, I need a new derailleur. How do I choose one? It needs to attach to the bike by means of a clamp on the frame, as there is no lug on the frame for it to screw onto (whcih there seems to be on most modern bikes.) The gears are changed via levers on the downtube (which I am told is so dated as to be untrue, but then it's an old bike and I like it!) Looking online, I can spend between £5 and about £300 on a new derailleur; which one should I choose?

This one (Shimano 6500) looks good.

http://www.chainreactioncycles.com/Mode ... elID=13616

For a fiver - heavily reduced. It seems to be made of cast alloy, rather than pressed-out tin-steel, which I am guessing is a good thing. Or would I do better to buy something a bit more expensive? (Remember, it's an old bike so anything very flash would be wasted on it.)

While I'm at it, the rear derailleur is also pretty worn, and drags a little (and isn't in-line with the chain, hence the drag!) So, same question again - how do you choose a replacement? Something like this looks good (Shimano Nexave C600):

http://www.chainreactioncycles.com/Mode ... elID=36451

... for the grand total of a tenner (again, quite reduced.) A good buy? Or would I do better spending the cash on something else?

Probably should add that the bike has two chainrings on the front and five on the back, so a total of 10 gears. And the gear change cable for the front derailleur comes up from the bottom of the bike, having passed underneath the bottom bracket.

And, while I'm at it, another question. How is the rear derailleur fitted onto the bike? I have never actually removed one! Is there a bolt, or a rivet, or something else? Will I need a special tool to change it over?

Thanks, in advance, for any help.


Oli.

supersonic

Many bikes use a seat tube clamp for the front derailer. Ensure that the swing and pull are the same as what you have.

The one you link to is for frames with braze on mounts, and is discontinued anyway.

Look at the specs closely and match to what you have ie max teeth, capacity. You will have no probs with your shifters as they are friction.

Rear mech: how does this mount to your bike? Does it use a claw clamp over the dropout?

Pisc of both mechs would be good if you are unsure.

zcacogp

Supersonic,

Hello, and thanks again. You helped me with the bottom bracket bearing as well.

You've asked questions that I don't even understand, let alone know how to answer. Seat tube clamp - great. What is the swing and pull?

Thanks for pointing out my mistake about the one (front derailleur) that I had posted ... stupid mistake, what! I guess that means I'm either looking at one of the other £5 ones, or to spend a huge double the price on a £10 one. So, for £5, this:

http://www.chainreactioncycles.com/Mode ... elID=42328

Or (splashing out) £10 for this:

http://www.chainreactioncycles.com/Mode ... delID=8284

... or this, for £12:

http://www.chainreactioncycles.com/Mode ... elID=39508

That last one is by campagnolo, the other by shimano. Which would you choose? (Is the "Double" and "Triple" in the title referring to the number of chainrings at the front? If so, I guess I ought to be looking at a double - non?)

Or is this whole exercise a false economy, and I should be looking at spending nearer £20 or £30 on one?

Back to your points, max teeth is presumably the number of teeth on the chainring (and I can just count them? That's a stupid question probably.)

Rear: I don't know what a clamp claw over a dropout is, but photos of the bike are here. BE WARNED, it looks particularly ugly in these photos. (I guess it is probably quite ugly in real life too!) Yes, it's dirty. And I'm ashamed how much the rust shows up on the chain and the rear sprockets. But hopefully it shows the current arrangement. Oh, and it's probably so old-fashioned you'll have difficulty remaining in your chair from laughing ...



Rear 3/4 angle:



Rear view:



View looking down on the front chainring (the old derailleur broke so isn't on the bike. It rides fine without it but you can't change gear - funnily enough! I have the bits of the old one if a photo of that would help - I can dig them out of the dustbin.)



Side view of the front:



And, for a final laugh, a picture of the whole of the bike:



Do those help?

Oh, one final point. The old rear derailleur isn't shimano, as I thought it was, it was sachs-huret. I suspect the front one was as well.


Oli.

supersonic

The Swing refers to the position of the clamp of the mech in relation to the cage, but is going to make no difference to a road bike (and pretty much all road mechs are the same type). The pull is the direction of cable (from the top, or from under the bottom bracket) and will be an important factor

What size is your seat tube though? You will need to match that. At a guess is 28.6mm diameter.


As for the rear mech, that looks like a standard bolt on type. But you may need to check the the thread - 10mm x 1.0mm is standard.

zcacogp

Supersonic,

Thanks. The front derailleur cable pulled from underneath - it looped underneath the bottom bracket, as you said. I guess that makes it a bottom-pull?

Seat tube, measured with a pair of callipers comes up about 27.9mm. If 28.6mm is a standard size, will a clamp designed for that size of tubing fit my bike?

Rear - I guess the answer is to take it off and have a look at the bolt. Will it unscrew from just beside the rear wheel? If it is, as you say, a standard bolt-on type, will the one I linked to (here: http://www.chainreactioncycles.com/Mode ... elID=36451 ) fit?

Thanks again for your help.


Oli.

supersonic

The 28.6mm is what you need, bottom pull for a twin chainring.

I can't see from your pics how you mech attaches - most use a 5mm allen key. The mech you link to should work nicely.

davis

How's the rear shifting feel? That outer looping round to the rear derailleur looks like it's a bit cracked, which I suspect means it's pretty old and corroded inside, making changing gears hard work. (I stand ready to be corrected here)

zcacogp

Supersonic - thanks again. I still can't tell from the advert whether it is a bottom-pull ot top-pull mechanism. I guess the answer is to call the shop and ask. Thanks for the advice about the size of the tubing.

Davis, Erm, it's probably rubbish. I don't have anything to benchmark it against, so I don't really know! Putting it simply, it works ... but, like everything else on the bike, if I was to replace it then I would notice a HUGE difference! Thus far, since I dragged the bike out of the garden and washed the grot off it I have replaced both tyres, the bottom bracket bearing (there is a separate thread about that on here), the brake blocks, the pedals and pedal toe clips and a crank, and the innertubes. Each one has made a noticable difference for the better (apart from fitting a Schwalbe Marathon Plus tyre, which is so heavy and hard work I wish I had bought two gator skins instead!) I guess that leaves me with two sets of brakes, two brake levers, a chain and a couple of sprockets to go and I'll have a pretty-much-new bike. Oh, and the saddle. And the mudguards have broken and come off as well, and I need to get some new ones of those too. The list just gets longer, eh?

This thread is about derailleurs, and I guess I'd do well to replace the cables when I replace the mechanisms. Thanks for the suggestion.


Oli.