Adjust dual-cable rear derailleur, women’s CCM Targa road bike, circa mid-70s

Submitted by Ken Riddell on Sun, 11/15/2020 - 13:35

Hi I'm wondering if anyone can point me towards either a video or printed instructions on how to do the above adjustment. Women's 10 speed Targa road bike circa mid-70s I believe. Rear derailleur has two control cables; one for upshifts and one for downshifts. I do a fair bit of bike maintenance but have never seen this before. I overhaul/and or donate, bikes for some low-income families, as a hobby. Thanks

5 Comments

Submitted by william rudolph on Thu, 11/19/2020 - 18:49.

adjusting 2 cable derailleur                      you deraileur is called a positron    internet has a few instructions and video use the word positron in your search  hope this helps  william rudolph

Submitted by T-Mar on Sat, 11/21/2020 - 15:21.

1. Shift the derailleur into the 3rd/centre cog.

2. Loosen the cable set screw on the shift lever.

3. Use the CENTER ADJUST on the outerside parellogram arm to cntre the jockey pulley under the 3rd cog.

4. Position the shift lever so that the cable fixing bolt is alignd with the '3' on the fiction plate.

5. Use the barel adjuster to take any slack out of the cable. If it is insufficient, turn the barrel 3/4 in and loosen the cable fixing bolt on the derailleur. Pull the slack out of the cable and tighten the cable fixing bolt on the derailleur and use the barrle adjuster to remove any remaining slack.

6. Tighten the cable fixing bolt on the shift lever.

7,. If the jockey pulley (upper pulley wheel on the derailleur) is misaligned with a particular cog, use the CENTER ADJUST screw to correct.

8. If the chain is having difficulty moving to a larger cog turn the CENTER ADJUST screw counter-clockwise.

9. If the chain is overshjifting whn moving to alarger cog, turn the CENTER ADJUST screw clockwise. 

If this doe not solve the issure, then are the other issues, the most common being a bent derailleur (cage or mounting claw,, a replacement freewheel with non-compatible cog spacing, ot just a worn chain or freewheel. 

 

Sustituting a modern Shimano Centeron jockey pulley and compressionless cable housing also make the Positron indexing system more reliable. The Centeron pulley has a small amount of lateal play for self-centring, while compressionless housing alleviates changes in cable tension due to the long housing runs.

 

Submitted by Ken Riddell on Thu, 02/11/2021 - 11:04.

Thanks so much. I haven't checked this site for a long time. Thanks again 

Submitted by Ken Riddell on Sun, 02/14/2021 - 20:42.

Thanks William Rudolph and T-Mar for your help.

T-Mar, whoever you are, you are a rock star. Those instructions worked perfectly! Took me a few times to get it right, but this beast now shifts correctly. There was a time that I doubted that could happen.

thanks again

Submitted by T-Mar on Thu, 02/18/2021 - 08:43.

Ken,

I'm glad to hear that things worked out well. Positron is not that difficult to set-up but most people give up too easily because of the poor reputation that it has within the cycling fraternity. I've never had much difficulty with it but then I was the manager and head mechanic at a bicycle shop when Shimano originally released it for the 1975 model year.

In case you're interested, it is very easy to determine the model year of a Targa with Positron. CCM didn't spec Positron on the Targa until it's penulimate model year and there was a slight difference in the model names between the last two years. The 1976 version had a decal that simply said 'Targa', while the 1977 version stated 'Targa 10'.