Road Bike, Cycling Forums banner
1 - 13 of 13 Posts

·
Registered
Joined
·
102 Posts
Discussion Starter · #1 ·
I bought a Trek 1400, circa 1989, for a couple of hundred bucks and this bike is pristine, a real garage queen. All components are Shimano 105 and appear to be original, except the shifters. The bike originally had DT shifters that were replaced (by an earlier owner) with Deore SIS shifters. Yeah, I know it sounds goofy but it really works well with my style of riding (95% on the hoods). The problem is that the bike won't shift onto the biggest two gears while on the large chainring. The sucker shifts pefectly thru all gears on the smaller chainring. I'm pretty sure the problem is not with the low gear limit stop screw. I've tried adjusting that and the chain still won't go onto the two lowest gears.

Any thoughts?
 

·
Vintage cyclist
Joined
·
732 Posts
How many cogs in the cassette?
How many clicks on the shifters?
How many teeth on the larger cogs?
Rear derailleur is Shimano 105?
 

·
Registered
Joined
·
102 Posts
Discussion Starter · #4 ·
frpax said:
How many cogs in the cassette?
How many clicks on the shifters?
How many teeth on the larger cogs?
Rear derailleur is Shimano 105?


Seven cogs
Seven clicks
Not sure, have to count
Yes, all components, except shifters, are 105.

I'm think that what JP asked might be critical. When the chain is trying to get onto a larger cog, the RD pulls parallel with the ground. Maybe a longer chain is necessary?
 

·
Registered
Joined
·
102 Posts
Discussion Starter · #5 ·
When the chain is trying to get onto a larger cog, the RD pulls parallel with the ground. Maybe a longer chain is necessary?

Like I said, it works great on the smaller chainring.
 

·
Vintage cyclist
Joined
·
732 Posts
Very possible. Too short of a chain would do it.
I think the tooth limit for 105 derailleurs is like 28. So if the cogs have more teeth than that, then that's a problem also.
 

·
Decrepit Member
Joined
·
1,811 Posts
I'm not sure why you think it's necessary to cross-chain large chainring to large cog anyway. That's pretty rough on the chain and chainring/cog teeth. If you need a lower gear, shift to the small chainring.
 

·
Larry Lackapants
Joined
·
696 Posts
lopresti said:
Seven cogs
Seven clicks
Not sure, have to count
Yes, all components, except shifters, are 105.

I'm think that what JP asked might be critical. When the chain is trying to get onto a larger cog, the RD pulls parallel with the ground. Maybe a longer chain is necessary?
as you said, the rd is pulled paralell to the ground. too much of that and the upper RD pulley won;t be able to clear the larger cogs. The problem doesn;t occur on the small ring as the chain tension is not that great and the upper RD pulley is further away from the cogs.

The spring opposing this forward movement is the one at the RD frame mount bolt. If the chain is long enough , it;s just a matter on putting more tension into that spring.

I think the bolt controlling this is caled the "B" tensioning bolt ? anyway it's placed on the knuckle that also holds the bolt for the frame mount.

You should tighten that bolt a few turns.
If the chain is too short, this will or will not solve your problem, depending on how short the chain is.
If you tighten the B spring too much, then shifting on the smaller cogs will not be accurate any more.

The idea is to set the B spring just tight enough, for the upper RD pulley to keep a minimal clearance(2-3mm) from the largest cog (when the chain is on the largest cog). If that cog is bigger than allowed by your RD, then the above setting for the b spring will cause the RD to shift sloppy on the small cogs.

good luck
brblue
 

·
Registered
Joined
·
16 Posts
Scooper said:
I'm not sure why you think it's necessary to cross-chain large chainring to large cog anyway. That's pretty rough on the chain and chainring/cog teeth. If you need a lower gear, shift to the small chainring.
tis good point

edit: but it would prob annoy me too
 

·
Registered
Joined
·
102 Posts
Discussion Starter · #13 ·
I agree...but if the bike is set up properly, I should have access to all gears on all chainrings, correct? The fact that I have to go to a smaller chainring to pull a hill for me is counter-productive. On my Cannondale, all I have to do is keep in th elargest chainring and downshift to make the hills. I should be able to do that on the Trek as well, agreed?
 
1 - 13 of 13 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top