jp2012

Recently dragged a 1975 Schwinn Continental out of the shed. Tore it down. Re-cabled, regreased, etc. Rides really quiet and smooth now;

BUT ----

On the small sprocket, chain is "skipping" (kachunk noise) when I put any force into my downstroke pedaling. If I pedal very very lightly, it doesn't happen. Problem doesn't show itself when on the bike stand with no load.

I have searched the forums and sheldonbrown, etc. etc, and thought I found the solution 3 times now, haha. Each time to be disappointed on the following test ride. How deflating. I am out of ideas. I am new to bike repair but not a total idiot (well maybe)

Attempt 1 - Since only smallest sprocket acts up (all others work smooth and quiet), I inspected the teeth of the smallest sprocket. All teeth appear to be in good shape, no rounded corners or chips or saw teeth or bent teeth. Maybe there is some other factor I should look for??? I read sheldon on this topic.

Attempt 2 - Checked the horizontal travel, let the H screw all the way out, even released the rear cable pinch bolt completely just to see. no help. Doesn't seem to be trying to shift back to the next sprocket.

Attempt 3 - Replaced old stretched out chain. Measured it and YES, it was a little more than 1/16" longer that 12". Matched new chain to old (and also verified desired length with the equation)

SIMPLE EQUATION: L = 2 (C) + (F/4 + R/4 + 1)
2(17.625) + (52/4 + 28/4 + 1) = ~56"

NO IMPROVEMENT

Attempt 4
Maybe the derailleur is bent. Yes it appears to be bent inward toward the wheel. Luckily, I have another old Schwinn in the shed with a GT-500 Schwinn Approved Derailleur similar to the other one. It looks to be in good shape. I clean and lube it. Works well. Install on my bike, test ride, and…..

NO IMPROVEMENT

Also checked the frame by running a string from dropout around headset to other dropout and measuring from left and right side, string to seat post tube. dead center.

The chain does seem a little saggy when on little chain ring and smallest sprocket. I have the wheel pulled into the dropout on the drive side as far as it can go until it hits the hanger which i also checked to make sure it was as far back as it could go. This may have helped a tiny bit.

Maybe I am missing something very BASIC, that will tighten up this problem.

Sorry for the longwinded post, but I wanted to show that I had tried most of the things I have found suggested in forums etc.

Any ideas? A totally different derailleur that will pull up the chain slack, maybe???



https://www.bikeforums.net/asset.php?...5&d=1304443071

JanMM

Probably need a new freewheel. Maybe only the smallest cog is worn enough to skip. Don't know if a new cog to match would be available.

Amesja

I bet your worn chain has damaged the favorite cog. It's hard to tell by eye sometimes -especially on the smallest cog (which is often a favorite cog.) A new freewheel might be in order.

relyt

Take the rear wheel from the other Schwinn and install it. Is there still a problem?

jp2012

good idea.
I would try that but the other Schwinn's freewheel is in pretty bad shape including the small cog.

Being no expert at inspecting cogs/teeth, maybe i missed something. I will likely take the advice of getting a new freewheel.

If that doesn't fix the problem, then over the cliff it goes. naw

Thanks, JanMM and Amesja

jp2012

As far as what freewheel to buy, call me insane but I kind of like friction shifting so am going to keep the shifters. Having said that, is there any point to buying a IRD Defiant Freewheel (50 bucks) with the shifting waves and special teeth design (which i understand to be for helping indexed shifting) or should I go with a cheaper sunrace or falcon? I don't really want to fork over the dough for NOS or risk getting a used one that has the same problems both of my old freewheels have. Also, am i correct that going to a 6 spd involves more work than just plug and play? Not really interested in getting into re-dishing or spreading the frame dropouts.

jeepr

Does it skip every time you put force on it, or about every 3rd revolution?

jp2012

more like the latter. Doesn't skip everytime, but is definitely related to when I put force on it.

jimdays

I had the same problem with a mid 70's 10 speed. If the chain were stretched even just a 1/4 inch, a new chain would skip on the small gears. There are three possible solutions. 1) replace the whole freewheel, or just the gears that skip. I've got a whole box of old freewheels that I got years ago from the city recycling station.
2) you can use a grinding wheel and grind each tooth on the gear that skips. I have succeeded doing this, but it takes a lot of time. I don't do it any more because I have so many spare freewheels. Somewhere on the web there is info and drawing just how to grind each tooth. I forget which corner edge (leading or trailing) of each tooth that you have to grind. 3) the newer bikes don't have this problem (skipping due to replacing a stretched chain (up to about 1/4 inch stretch)). The newer freewheels, like on my Huffy have twisted teeth, or some other type of tooth contour that the mid 70s freewheels didn't have. I just replaced the chain on my Huffy- it was stretched more that 1/4 inch. The new chain, did not skip at all. It did make fairly frequent grinding sound for about 500 miles, at that point the new chain probably stretched a tiny bit and now it glides perfectly over the old freewheel. Big improvement, because I don't have to replace the freewheels anymore. I ride a lot in the sand and in 6 months, a new chain is stretched about 1/4 inch- time to replace the chain with another that I get free from abandoned bikes.

jp2012

I bought this to see if it fixes the problem. or did I buy a piece of junk? Any opinions on this freewheel? I will post here after I receive, install, and test it.

Shimano 5 speed SIS Uniglide Freewheel, #MF-Z012


https://cgi.ebay.com/ws/eBayISAPI.dll...K%3AMEWNX%3AIT

hurley81388

Curious to know if this freewheel is good myself.

I also have a chain skipping problem on my 84 Trek 420 on the 2 smallest cogs. I'm waiting for a new chain (supposed to be here on Monday) which I really hope will fix the problem. If not, I'm in the same boat as you and will have to replace the freewheel.

Please be sure to update once you've tested it out! Thanks!

Sixty Fiver

Get a new Shimano freewheel... should solve the skipping issue and the shifting will be greatly improved.

hurley81388

I was just doing some reading and realized that Sheldon says my rear Maillard hub is a "loser" and that it should be replaced...

Looks like if I need a new freewheel I might as well just buy a new rear wheel? Where could I buy a rear 27 inch wheel?

auchencrow

I don't think a new chain will do it for you (it will probably make it worse) and if you have the original hub on your Trek 420 you'll likely have to replace it because FWs for Helicomatics are expensive.

Sixty Fiver

Quite a few folks run Helicomatics without issue but these are a cassette and not a freewheel... they are not as solid as they could be and replacement parts are going to be hard to find.

An issue like this might be a good reason to upgrade to new 700c wheels.

hurley81388

Is it possible to replace just the hub? Sorry I'm a complete newbie to bike repair. From a quick search online this seems extraordinarily difficult to do...

If not, where can I buy a new rear wheel for a reasonable price (<100 for everything)? I'm assuming I would need a 27 inch because that's what's currently on the frame or could I keep the front wheel at 27 inch and have the rear at 700c?

auchencrow

You don't need a new wheel you need a new hub - But if you find a matching high quality rear wheel for a good price that would be easier and possibly cheaper.

The Helicomatic is not a "loser" from the perspective of performance - but it failed more easily when improperly adjusted/maintained, or overloaded. Unfortunately a lot of them found their way onto touring bikes like yours.

hurley81388

OK, I'm a bit confused by all of this... sorry to be annoying.

So it is possible to simply replace the Maillard hub with something different. If so, would this require taking all of the spokes off? I don't think I'm at that level yet... and when you say a rear wheel- do I have to stay at 27 inches or can I switch to something newer like 700c? How will this fit on the bike?

And in terms of parts, is there a good website to find this stuff? Or is ebay my best bet

auchencrow

I have no experience with mixing wheel sizes - typically you change them in pairs. You rear brake caliper MIGHT reach a 700 rim alright but the front has less slot to adjust the shoes the requisite 4mm lower. This is another headache if you have to change out your brakes to accommodate 700s.
Personally I would stick with the 27 inch wheels

hurley81388

Thanks.

It's not worth it then if the new chain doesn't solve the skipping problems...I'll just let the bike go on CL then I guess and save up my money to get a new road bike at my LBS

Sixty Fiver

Many bikes fitted for 27 inch wheels convert very nicely to 700c if the brakes can allow of a small reach adjustment if 4mm... if not new calipers will be required.

auchencrow

You can't put a bike on CL with a skipping problem. Well, you can, but you'll have to warn the buyer because it can cause one to slip off the pedals, and of course you won't get much for it if it is not road worthy that's for sure.

I would find a hub and re- lace the rear wheel. You'll likely have to get new spokes anyway because the dish will likely be different even if the diameter of the hub is the same.
The LBS can do it for you: That won't be cheap - but it certainly will be much less than buying the equivalent of another Trek 420.

Sixty Fiver

The Trek 420 is a nice bike... if it was a good fit I'd keep it and look at new wheels.

jeepr

sorry, I lost track of this thread.

If it skips about every 3rd revolution, I would check your chain for a stiff link.

jp2012

It had the problem before and after replacing the chain. Neither chain appears to have any stiff links, but thanks for the suggestion. I'm hoping the new freewheel will fix the problem.