Replacing a RD-7400
 

Ok, maybe it's just too early but I researched and am still confused. I have an old RD-7400 on my sweet Antares. But the resin pulley wheel is cracked and the seal between the pulley cage is gone and the other seals are shot. Do I have to replace this with another RD-7400 or can I used a RD-7401 or RD-7402 SIS derailleur? Seems to be easier to find good condition 7 or 8 speed RDs than the 6 speed and I don't want to buy another RD-7400 just to wind up with bad seals again. And the index shifting was working so nicely before I had problems so I want to keep that sweet shifting going.

Here's a pic of the shifters:

http://www.pbase.com/jhuddle/image/163085505.jpg

thanks!

Why not just buy the jockey wheels themselves? Amazon.com : Shimano Rear Derailleur Pulley Set with Hardware : Sports & Outdoors There are higher quality parts than this as well, if you're feeling spendy.

Because the real problem is the seals and those I cannot find.

Do you have a picture of said seals? Is it one of the parts in this photo? http://biketestreviews.com/wp/wp-con...2014/12/14.png

The one that is now completely gone is this seal.

http://www.pbase.com/jhuddle/image/162841839.jpg

But the seals on the pivot bolts are shot too. This bike sat for most of it's life so although physically looking great all the grease was dried up and these seals appeared to have dry rotted too.

Ah. You could also ask this question over in Bike Mechanics, but I have never personally replaced a seal in that location. Sorry! :( If it's not an oddly shaped seal--maybe a replacement could be found on Grainger's website.

You can use any RD-740x derailleur with those levers. There's also a non-standard cable attachment that makes post 7400 Dura-Ace and other Shimano indexed derailleurs work with those levers.

Ok, cool. That is what I thought but I was confusing myself with the research this morning. Maybe I need more coffee in me. Thanks!

I didn't even know there were seals beyond, ostensibly, the coiled springs.

Yeah and it's binding up because off them.

I can imagine the energy savings by having a sealed arm, not a lot, but maybe just enough for something important.

But with it not working, its way worse than an old fashioned non-sealed movement unit.

Are you the one that wanted me to look in my RD parts bag? If so, I've found the bag, but then I forgot for whom I was looking for it.....
Either way, now that I have the bag out, I'll look in there for that seal.

what are they made of?

what does a pivot bolt seal look like?

i've had derailleurs that had a seal where you have outlined (in red), but they were always metal.

New Dura-Ace (7400 series) had seals on the pulleys, lower pivot stud, upper pivot bolt and the parallelogram pivot pins. This technolgy was also used in 600 Ultegra, 105C and the corresponding ATB derailleurs.

The upper pivot has an inner and outer plastic seal.

The lower pivot has a plastic inner seal.

The pulleys have inner and outer rubber seals.

Each parallelogram pivot pin has an upper and lower rubber seal (not pictured).

^ thanks.

well, if replacement pulleys fit, that's an easy enough fix.

I don't know if they are a plastic, rubber or nylon. Mine was split and finally started "pushing out interfering with the movement of the body. It felt like plastic. Right now there's no seal there. And I took it out for a ride and about 10 miles out the one pulley cracked on a shift and jammed the chain. I was able to free it and ease the bike home. But I ride a lot of miles and need all my bikes in top shape. Walking 10 or 15 miles home in clipless shoes ain't no fun. :-)