1960s Campag Gran Sport - Sprocket size limits

[Pumpman]

I was not sure if I should post this as “Maintenance and repairs” but as it involves a bike of about 50 years old, “Classic and vintage” seems to be the right place.

A while ago, I refurbished an old Carlton, with some help from this site. This inspired my brother-in-law to dig out a 1960s Pennine from the garage, to join me on some runs. He had repeated problems with the gears jumping/slipping, either when changing or even when just riding along in gear. I thought it would be a simple matter to correct it and I offered to do it. I have no direct experience with Campag gears, but I have worked on other makes, so I assumed I could do it.

I feel sure that wear/stretch of the old chain is a factor, but I believe there are other issues and that simply fitting a new chain may not solve the problem.

I suspect that the rear block/cassette is not the original one and that it is beyond the range of the derailleur. The teeth numbers are 14-17-20-24-28 at the rear and 46-50 at the front. Is there anyone with the knowledge or experience of Campag gears who knows whether the 1960s Gran Sport was suitable for a 28 tooth low gear and/or an 18 tooth total difference? If not, what is the maximum range?

Any information, help or guidance would be greatly appreciated.

 

[classic33]

I was not sure if I should post this as “Maintenance and repairs” but as it involves a bike of about 50 years old, “Classic and vintage” seems to be the right place.

A while ago, I refurbished an old Carlton, with some help from this site. This inspired my brother-in-law to dig out a 1960s Pennine from the garage, to join me on some runs. He had repeated problems with the gears jumping/slipping, either when changing or even when just riding along in gear. I thought it would be a simple matter to correct it and I offered to do it. I have no direct experience with Campag gears, but I have worked on other makes, so I assumed I could do it.

I feel sure that wear/stretch of the old chain is a factor, but I believe there are other issues and that simply fitting a new chain may not solve the problem.

I suspect that the rear block/cassette is not the original one and that it is beyond the range of the derailleur. The teeth numbers are 14-17-20-24-28 at the rear and 46-50 at the front. Is there anyone with the knowledge or experience of Campag gears who knows whether the 1960s Gran Sport was suitable for a 28 tooth low gear and/or an 18 tooth total difference? If not, what is the maximum range?

Any information, help or guidance would be greatly appreciated.

One like this?
Years: 1953 - ?
Max Cog Size 26

http://velobase.com/ViewComponent.aspx?ID=96c406b5-3ec5-4875-bf84-4f706b8749ca
or this
Years: 1952
Max Cog Size 26

http://velobase.com/ViewComponent.aspx?ID=c9705308-3bc1-4bcd-aedf-8f22d18bf3ec

 

[Pumpman]

One like this?
Years: 1953 - ?
Max Cog Size 26
.

Thank you.
It is the 1953 one (but with less chrome), so it looks like it is 2 teeth over the maximum. So it looks like I should look for a smaller sprocket or a new block/cassette.
Thanks again for your help

 

[stevevw]

26 is the max 24 is better. Having said that I have a friend that has 46-36 on the front and a 26 on the back.

Good luck finding a 14-26 block

 

[raleighnut]

http://www.ebay.co.uk/itm/Vintage-S...195867?hash=item41ac931a1b:g:bLAAAOSwGIRXYDW2

As long as you don't mind the Bay of evil.

 

[classic33]

Thank you.
It is the 1953 one (but with less chrome), so it looks like it is 2 teeth over the maximum. So it looks like I should look for a smaller sprocket or a new block/cassette.
Thanks again for your help

Link under the picture gives another two, slight cage variations.

 

[mikeymustard]

Is this campag's specs? I have no knowledge of campag but when say shimano states max teeth they're normally quite conservative and a couple of teeth extra doesn't present a problem.
Being an older style they may not have any leeway but someone has fitted and hopefully ridden it with 28t freewheel

 

[classic33]

Is this campag's specs? I have no knowledge of campag but when say shimano states max teeth they're normally quite conservative and a couple of teeth extra doesn't present a problem.
Being an older style they may not have any leeway but someone has fitted and hopefully ridden it with 28t freewheel

Campag spec as far as I can find out.

 

[Pumpman]

Is this campag's specs? I have no knowledge of campag but when say shimano states max teeth they're normally quite conservative and a couple of teeth extra doesn't present a problem.
Being an older style they may not have any leeway but someone has fitted and hopefully ridden it with 28t freewheel

I have now fitted a new chain, still with the original 14-28 range. It is far better and no longer jumps off the teeth. It is possible to use the low gear, but it is less smooth than the changes between the other gears - so it does look like the extra teeth are eating into the margin. I have passed the decision about changing it back to my brother-in-law, who will need to decide between the rough change or harder hill climbs. I suspect he will leave it as 28.

My remaining minor concern is the chain tension on the higher gears. It seems quite slack, compared to my Simplex derailleur of the same age. This may be partly due to sizing the chain for the large low gear. I will try to take a close look at some other Campag gears to compare.

Thanks to you all for your inputs.

 

[Illaveago]

Do you have another wheel with the correct size sprocket that you could just pop in to see if it makes any difference. I have had a few problems on another bike with chain jumping issues and I think it may be due to the chain being too long.

 

[mikeymustard]

I have now fitted a new chain, still with the original 14-28 range. It is far better and no longer jumps off the teeth. It is possible to use the low gear, but it is less smooth than the changes between the other gears - so it does look like the extra teeth are eating into the margin. I have passed the decision about changing it back to my brother-in-law, who will need to decide between the rough change or harder hill climbs. I suspect he will leave it as 28.

My remaining minor concern is the chain tension on the higher gears. It seems quite slack, compared to my Simplex derailleur of the same age. This may be partly due to sizing the chain for the large low gear. I will try to take a close look at some other Campag gears to compare.

Thanks to you all for your inputs.

I suspect you're right in thinking your bro-i-l will be able to live with this compromise if the chain doesn't fall off in higher gears - I changed to a 28t rear when I first got my mercian and found that, while it would go largest to largest, it wasn't good. Older derailleurs weren't recommended to be cross-chained anyhow.

 

[raleighnut]

I suspect you're right in thinking your bro-i-l will be able to live with this compromise if the chain doesn't fall off in higher gears - I changed to a 28t rear when I first got my mercian and found that, while it would go largest to largest, it wasn't good. Older derailleurs weren't recommended to be cross-chained anyhow.

Plus they were only designed to cope with 5 gears, they cope OK with 6 but with 7 (and a larger range) they're pushing it.

 

[Pumpman]

Do you have another wheel with the correct size sprocket that you could just pop in to see if it makes any difference. I have had a few problems on another bike with chain jumping issues and I think it may be due to the chain being too long.

I have sized the new chain to suit the 28t sprocket, so it is loose on the smaller ones. Changing to a smaller size would not tell me anything unless I shortened the chain, which I am reluctant to do. I think I will just leave well enough alone.

 

[Pumpman]

Plus they were only designed to cope with 5 gears, they cope OK with 6 but with 7 (and a larger range) they're pushing it.

I'm having enough problems with 5 gears - I daren't even think about 6 or 7.