[Dave Hickey]

The question of Shimano cassette spacing and, in particular, the Dura Ace 74xx series derailleur comes up frequently…

Thanks to Quattro Assi 07 for asking the most recent question and allowing me to screw off at work…


I’ll start with a quick primer on Shimano cog spacing…the below numbers apply regardless of model/year cassette

The amount listed is the distance between cogs( center to center)

7 speed cassettes- 5.0mm
8 speed cassettes- 4.8mm
9 speed cassettes- 4.34mm
10 speed cassettes- 3.95mm

Based on the above, 7 speed shifters need to move the derailleur 5.0mm per click in order to have smooth shifting. 8 speed shifters need to move the derailleur 4.8mm per click, etc….

Now we get to the rear derailleur.

All Shimano road rear derailleurs (except Dura Ace 7400 series) have the same design and parallelogram. That means that any( except Dura Ace 7400 series) Shimano rear derailleur will shift the above listed spacing if attached to the appropriate speed shifter.. Example: the Sora RD has the same Parallelogram as the Dura Ace 7900 RD, etc..One click on 9 speed shifters will move the rear derailleur 4.34mm regardless of the model derailleur( again, except Dura Ace 7400 series)

The Dura Ace 7400 series rear derailleur was a different design and parallelogram than any other Shimano rear derailleur. Because of this different design, one click on the typical Shimano shifter will move the 74xx RD more than all other Shimano rear derailleurs…In order to accommodate the unique geometry , the 74xx RD needed special shifters to move the rear derailleur the proper amount for the above distances between cogs. In the case of 8 speed, Dura Ace 7402 shifters will move Dura Ace 7400 series RD, 4.8mm. However, if you were to connect other Shimano 8 speed shifters to a 7400 series RD, it will move the derailleur more than 4.8mm causing an over shift every click…This is why the Dura Ace 74xx series rear derailleur will only work with certain shifters..

To confuse matters even more, if you connect Shimano 9 speed shifters to a Dura Ace 74xx series derailleur, it will move the derailleur 4.8mm which happens to be the proper distance for an 8 speed cassette…So if you are using a Dura Ace 74xx series RD, you need either Dura Ace 7402 shifters or any Shimano 9 speed shifters to shift for 8 speed.

All of the above information is confirmed by Shimano in their service instructions.

There are also alternate “B” cable attachments that allow 9 speed shifters to shift 8 speed but we can discuss that at another time…

If anyone has similar info on Campy, I would love to see it

 

[Quattro_Assi_07]

The question of Shimano cassette spacing and, in particular, the Dura Ace 74xx series derailleur comes up frequently…

Thanks to Quattro Assi 07 for asking the most recent question and allowing me to screw off at work…


I’ll start with a quick primer on Shimano cog spacing…the below numbers apply regardless of model/year cassette

The amount listed is the distance between cogs( center to center)

7 speed cassettes- 5.0mm
8 speed cassettes- 4.8mm
9 speed cassettes- 4.34mm
10 speed cassettes- 3.95mm

Based on the above, 7 speed shifters need to move the derailleur 5.0mm per click in order to have smooth shifting. 8 speed shifters need to move the derailleur 4.8mm per click, etc….

Now we get to the rear derailleur.

All Shimano road rear derailleurs (except Dura Ace 7400 series) have the same design and parallelogram. That means that any( except Dura Ace 7400 series) Shimano rear derailleur will shift the above listed spacing if attached to the appropriate speed shifter.. Example: the Sora RD has the same Parallelogram as the Dura Ace 7900 RD, etc..One click on 9 speed shifters will move the rear derailleur 4.34mm regardless of the model derailleur( again, except Dura Ace 7400 series)

The Dura Ace 7400 series rear derailleur was a different design and parallelogram than any other Shimano rear derailleur. Because of this different design, one click on the typical Shimano shifter will move the 74xx RD more than all other Shimano rear derailleurs…In order to accommodate the unique geometry , the 74xx RD needed special shifters to move the rear derailleur the proper amount for the above distances between cogs. In the case of 8 speed, Dura Ace 7402 shifters will move Dura Ace 7400 series RD, 4.8mm. However, if you were to connect other Shimano 8 speed shifters to a 7400 series RD, it will move the derailleur more than 4.8mm causing an over shift every click…This is why the Dura Ace 74xx series rear derailleur will only work with certain shifters..

To confuse matters even more, if you connect Shimano 9 speed shifters to a Dura Ace 74xx series derailleur, it will move the derailleur 4.8mm which happens to be the proper distance for an 8 speed cassette…So if you are using a Dura Ace 74xx series RD, you need either Dura Ace 7402 shifters or any Shimano 9 speed shifters to shift for 8 speed.

All of the above information is confirmed by Shimano in their service instructions.

There are also alternate “B” cable attachments that allow 9 speed shifters to shift 8 speed but we can discuss that at another time…

If anyone has similar info on Campy, I would love to see it

Thanks Dave but don't blame me for screwing off at work. I do not put any time limits requests on my questions...

Seriously, thanks for the info, very much appreciated. I was planning on using up the last of my 7400 series parts but am now having a hard time deciding what to use to build up my Zullo. Now leaning towards 9 or 10 speed and using up the last of my 7700 or 7800 series. Decisions, decisions...

 

[Richard]

Speaking of screwing off, I've got to get to work.

A bit on Campy, though. Campy 7 and 8 speed share the 5.0mm spacing - same as Shimano 7. I had great results running Campy 8 on 7 speed shimano freehubs and cassettes as well as Campy 8.

 

[buck-50]

Though I gotta say, I've got DA 9-speed DT shifters hooked up to a DA 74xx rear derailleur and a 9 speed ultegra cassette, and it shifts flawlessly.

As far as I know, I'm not using any special tricks- no funny cable attachments.

 

[Quattro_Assi_07]

Though I gotta say, I've got DA 9-speed DT shifters hooked up to a DA 74xx rear derailleur and a 9 speed ultegra cassette, and it shifts flawlessly.

As far as I know, I'm not using any special tricks- no funny cable attachments.

Very interesting. Originally, when I began my quest, it was just to use 7700 series, 9 speed shifters on an 8 speed group (8 speed cassette) and was told it couldn't be done. I now see that this CAN be done. Your use of the 9 speed DA shifters with a 7400 series RD and getting it to work with a 9 speed cassette is very promising. Is that what you are saying. If so, that would be exactly what I want to do now at this point. What hubs are you using if I may ask? I have the 8 speed 7403 hubs. If I could, I would just try all the different combinations out on my own and see what works but unfortunately, I can't do that right now and need to know what works so when I get home next month, I'll be ready to make it happen. I don't have the luxury of experimenting.

Regarding the "funny cable attachments" how do they affect the shifting ability of the shifters/RD? Does it have an impact on which shifter can be used with which rear derailleur?

Thanks,

James

 

[Bridgestone]

Very interesting. Originally, when I began my quest, it was just to use 7700 series, 9 speed shifters on an 8 speed group (8 speed cassette) and was told it couldn't be done. I now see that this CAN be done. Your use of the 9 speed DA shifters with a 7400 series RD and getting it to work with a 9 speed cassette is very promising. Is that what you are saying. If so, that would be exactly what I want to do now at this point. What hubs are you using if I may ask? I have the 8 speed 7403 hubs. If I could, I would just try all the different combinations out on my own and see what works but unfortunately, I can't do that right now and need to know what works so when I get home next month, I'll be ready to make it happen. I don't have the luxury of experimenting.

Regarding the "funny cable attachments" how do they affect the shifting ability of the shifters/RD? Does it have an impact on which shifter can be used with which rear derailleur?

Thanks,

James

Hubdub or alternate cable attachment;http://www.ctc.org.uk/DesktopDefault.aspx?TabID=3946 http://sheldonbrown.com/derailer-adjustment.html#alternate

 

[Dave Hickey]

Though I gotta say, I've got DA 9-speed DT shifters hooked up to a DA 74xx rear derailleur and a 9 speed ultegra cassette, and it shifts flawlessly.

As far as I know, I'm not using any special tricks- no funny cable attachments.

I'm glad you've gotten it to work,.. I remember you posted this before....I've tried it a couple of times and never had any luck..I fiddled with the barrel adjuster and couldn't get it the shift all cogs......Shimano and Sheldon say it shouldn't work too but as with a lot of things in this sport. experimenting can yield good results... Good for you.....you've inspired me to fiddle this weekend

 

[Quattro_Assi_07]

I'm glad you've gotten it to work,.. I remember you posted this before....I've tried it a couple of times and never had any luck..I fiddled with the barrel adjuster and couldn't get it the shift all cogs......Shimano and Sheldon say it shouldn't work too but as with a lot of things in this sport. experimenting can yield good results... Good for you.....you've inspired me to fiddle this weekend

Dave, a couple of questions...

I have a both a 7402 and 7410 crankset to choose from for my build but only a 7410 bottom bracket. Is there any difference between the required bottom brackets for either of these cranks? Can the 7410 BB be used with the earlier 7402 crank?

Another question, 7700 series chainrings have the pins and ramps that neither of the 74XX series cranks have. Any pros or cons in swapping those over from the 7700 to the 74XX cranks?

Thanks again :thumbsup:

 

[Dave Hickey]

Dave, a couple of questions...

I have a both a 7402 and 7410 crankset to choose from for my build but only a 7410 bottom bracket. Is there any difference between the required bottom brackets for either of these cranks? Can the 7410 BB be used with the earlier 7402 crank?

Another question, 7700 series chainrings have the pins and ramps that neither of the 74XX series cranks have. Any pros or cons in swapping those over from the 7700 to the 74XX cranks?

Thanks again :thumbsup:

BB- With a 7410 BB, you will have to use the 7410 crankset- The 7410 BB is only 103mm long. The 7402 crank requires a 112mm BB.

Rings- I've used both 7700 and 74xx rings on many bikes and really don't notice any difference in shifting..

 

[buck-50]

I'm glad you've gotten it to work,.. I remember you posted this before....I've tried it a couple of times and never had any luck..I fiddled with the barrel adjuster and couldn't get it the shift all cogs......Shimano and Sheldon say it shouldn't work too but as with a lot of things in this sport. experimenting can yield good results... Good for you.....you've inspired me to fiddle this weekend

Could also be that the bike I built this on is freaking magic. Everything I do on that bike just works better, especially riding.

if you ever get a chance to pick up a Serotta NHX with SPX tubing, jump on it.

 

[Dave Hickey]

Could also be that the bike I built this on is freaking magic. Everything I do on that bike just works better, especially riding.

if you ever get a chance to pick up a Serotta NHX with SPX tubing, jump on it.

LOL...I know exactly what you are saying..I have one magic bike..

My red 3Rensho fixed. The bike literally fell together and everything works like a charm....

 

[Richard]

LOL...I know exactly what you are saying..I have one magic bike..

My red 3Rensho fixed. The bike literally fell together and everything works like a charm....

Funny you should mention that. My late '80's Falcon has gone through more changes than Madonna and every time I throw something new/different on it, the sucker performs flawlessly.

 

[MShaw]

Don't forget the Sachs New Success and Ergo shifters working on Shimano cassettes as well as Sachs FWs.

...or is that another day of goofing off at work?



M