truthseeker14

I found a SRAM rear derailleur in a spare parts bin and wanted to know what its capacity is. The only markings i saw where 8E 0 on the back of the body. It has a long cage. I have not been able to find anything else on it. It looks like it came from a cheap bike. I can't find any information on this. Biggest question is whether it would work on a seven speed cassette.

FBinNY 

I'm not, and never hope to be a fount of spec data, however I may be able to help.

SRAM RRs of the era had the jockey wheel mounted on the swing arm pivot. So estimating the take up capacity is fairly easy. Measure the on center distance between pulleys, then add the radius of the idler pulley. Multiply the sum by Pi, to get the circumference of the circle the arm sweeps. Finally, estimate the amount of swing as a fraction of the circle, and that's the take up capacity in inches (or cm). knowing the sweep, and that chains have half inch pitch gives you the info you need.

If, in fact, your RD has the idler cage mounted someplace along it's length, the calculation is similar, but requires a bit more work because both pulleys move. Total takeup is the sum of the sweeps of both pulleys.

One added thought, RD capacity isn't only a function of cage length and sweep. The pulley radius also factors, so ANY derailleur can have it's capacity increased or reduced by using a larger or smaller idler pulley.


LASTLY - Just about ANY RD can be used on a 7s cassette. The RD itself doesn't care. If indexing, the final answer depends on having the correct matching 7s shifter lever.

alcjphil

Another question is what shifter you will use with that derailleur

cxwrench

A photo might help...

Andrew R Stewart 

I suspect that the "8E 0" is a manufacturing date code. One could search for a matching image (via on line photos or catalogs) then search for that match's specs. Andy

truthseeker14

I'm not clear on this. Freewheels and cassettes have different widths (i.e., distance between the largest and smallest sprocket). It's hard to imagine that a RD from the 70s for a 5 gear freewheel could be used for a freewheel or cassette that's noticeably wider. I've seen RDs described as compatible with clusters with a certain number of speeds.

A little more background on my question. My church accepts donated bikes and gets them in working condition to give to people who need them. I was working on a cheap Huffy that looked like it came right from a department store but was missing the RD. I found the old SRAM RD and thought it would be straightforward to look up whether it was compatible with a seven speed rear cluster. I did try another older RD from the 70s, and it did not have the range. I can get a picture when I'm there again.

oldbobcat

The short-cage version of these, 10- and 11-speed, is rated to 28t, which I have used with no trouble. You might be able to push them to 30. I believe the long-cage version goes to 32. When 10-speed Red was race issue, some teams used long-cage Rival RDs to get up some of the passes in the Giro d'Italia. And, of course Force FDs, because the titanium cages on the early Red ones wore out.

SRAM rear derailleurs take 3.1 mm of cable per click, 10- or 11-speed. Shimano 7-speed indexing uses 2.9 mm per click. Make of it what you want.

alcjphil

The Raleigh Professional that I bought new in 1973 had a 6 speed freewheel, fairly rare at the time. The Campagnolo Nuovo Record derailleur handled the extra cog with no trouble. Later on I upgraded to a 7 speed freewheel and that derailleur worked fine with that as well. 6 speed and 7 speed freewheels are basically the same overall width

FBinNY 

You missed the "just about" lead to my statement. Freewheels come in 3 common width ranges. 5s, 6s/7s (7s is narrower and overall f/w width is the same as 6s) & 8s. So yes, an older 5s derailleur will likely have less trvel raange, but they allow for a degree of over travel, and it MAY work if you're lucky.

OTOH - SRAM as a company didn't exist in the 5s era, so any SRAM RD will have travel distance for at least 7s, and more likely 8s. If using a friction lever (not index), that compatibility won't be an issue, except that it's barely possible that the inner (low gear) limit may not be restrictive enough, but that can be worked around if/when it arises.

Indexing makes things more complicated, because the lever, derailleur and freewheel spacing MUST be compatible with each other. FYI 5s and 6s f/w spacing is the same, so if you want index look for a 6s system.

FWIW - sounds like you're working on a sow's ear, so don't waste money trying to make it more that it is. Find a derailleur with adequate capacity, and set it up to work with the friction lever that's there.

alcjphil

Agree. As usual a very good explanation of those times. Indexing introduces all kinds of compatibility issues if parts are not designed to work together. Friction shifting is much more forgiving if the user is willing to learn how to use it. The one thing omitted was the Ultra 6 freewheels that had 7 speed spacing and could be used on a bike frame with the 120 mm dropout spacing of bikes that had 5 speed freewheels

Bill Kapaun

I doubt if that Huffy ever had an indexed system or compatible to anything RDER's.
The ones I dealt with had a twist grip shifter with an indeterminate number of coarse clicks.
In both cases, the shifters were near or impossible to turn.

Do your shifters actually function?

oldbobcat

OK, now I get it. An old SRAM rear derailleur, probably the really cheap one. Yes, it will work with a 7-speed cassette if the big cog is 28t or less. 7-speed SRAM rear shifters are hard to find now, but here's a 3x7 3.0 Comp set on Amazon. https://www.amazon.com/SRAM-Mountain.../dp/B000X9WDZS

You don't want the MRX-Comp shifter. That is for Shimano rear derailleurs.

truthseeker14

Yes, the grip shifter was nearly impossible to turn. "indeterminate number of coarse clicks" is a good description. A lot of the bikes in our inventory are cheap department store bikes. They can be quite unpleasant to work on.

Thanks everybody for the education. I'll the SRAM a try and hope for the best.

Bill Kapaun

Trying to fix up that pair to a safe enough condition to sell w/ good conscience, got me into wheel truing.
The brake calipers had so much flex, the wheel had to be near perfectly true so the pads could be very close to the rim to keep from running out of lever travel
Found some SAE? threaded fasteners where you would expect Metric. (Lowest bid for "some screws")
I was able to use some cheapo friction shifters off a slightly better bike from the used parts bin.
They were still an overweight sow's ear. They aren't worth the time/effort if you have other bikes to fix.
I simply wouldn't touch them after that, I wouldn't even strip one for parts. Why bother putting crappy parts on something you're trying to make dependable, safe & functional?
I think I'd rather have a can of Kroger coffee than a Huffy.

oldbobcat

You could try replacing the cable and housing, but threading cable through grip shifters is a pain in the ass. I do it, but I know some pro mechanics who just say, "You're shifter's busted. Buy a new one."

truthseeker14

I know what you mean. But the unknown SRAM RD worked. Shifts well. Thanks for all the help.