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RD-M750 (9S) with 8S Gripshift and 8S cassette??

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RD-M750 (9S) with 8S Gripshift and 8S cassette??

Old 07-30-21, 09:07 AM
  #1  
pstock
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RD-M750 (9S) with 8S Gripshift and 8S cassette??

I am setting up a Bike Friday. which came with an 8S cassette but a 9S RD-M750 Deore XT rear derailleur and barend shifters.
I swapped off the barend shifters (clumsy for the H-Bars on this bike) for SRAM 8S Gripshift twist shifters. And now the rear end is jumping two shifts per click at two points in the small to bigger shifting, up and down.
even though I have tried to setup the rear derailleur carefully

for some reason Bike Fridays often seem to come with what seem mismatched components. I had one with a 9S Campagnolo ergo shifters with a 7S rear cassette and 7S Shimano 600 Rear Derailleur. But Bike Friday said that set up was deliberate, that the 9S Campagnolo shifters best matched the 7S cassette.

my partner for instance also has a Bike Friday, which Also uses an 8S Gripshift and an 8S cassette BUT has an RD-M737 (which is I believe 8 speed.)

so I am not sure if the 9S rear derailleur was a specific choice for this setup.
or if I should be using an 8S derailleur. (I have several on hand that I could try but I thought I would ask advice here before plowing into a day of trial and error.)

Peter

Last edited by pstock; 07-30-21 at 11:32 AM.
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Old 07-30-21, 09:34 AM
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Some SRAM shifters are Shimano compatible and some aren't.
IF you give the model of the shifter, someone can tell you if that's the problem.
I can't remember how their system works. Some have a number and some have a name.
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Old 07-30-21, 09:47 AM
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8 and 9 sp (and 7sp) Shimano deralleurs can be used interchangeably.
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Old 07-30-21, 11:43 AM
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Originally Posted by Bill Kapaun View Post
Some SRAM shifters are Shimano compatible and some aren't.
IF you give the model of the shifter, someone can tell you if that's the problem.
I can't remember how their system works. Some have a number and some have a name.
My BF now has RD-M750 and SRAM 900 ESP gripshift (ESP 900-81) and shifts poorly
Partner Julie's BF has RD-M737 and SRAM MAX Comp 8S gripshift (marked K14Apr16 which I expect is the production date and "240-80") and shifts perfectly.
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Old 07-30-21, 12:08 PM
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Here's a couple examples-
MRX is OK
3.0 is NOT.
https://www.performancebike.com/sram...hcs4hcquqrgqhe
https://www.sram.com/en/sram/models/ts-30-a1

I didn't look past those 2 but there are other models that may/not.
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Old 07-30-21, 12:50 PM
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Interesting.
how though do you determine from the Specs which is compatible and which is not?

the SRAM site lists these specs:

3.0
CABLE PULL RATIO 1:1
COMPAT - DERAILLEUR/HUB (SL) FD: 3s, FD: Micro index, RD: 7s, RD: 8s, Set: FD: 3s/RD: 7s, Set: FD: 3s/RD: 8s

MRX Comp
CABLE PULL RATIO 1:2
COMPAT - DERAILLEUR/HUB (SL) FD: Micro index, RD: 5s, RD: 6s, RD: 7s, RD: 8s, Set: FD: 3s/RD: 6s, Set: FD: 3s/RD: 7s, Set: FD: 3s/RD: 8

the Pull ratios are different but the list of Compatible Derailleurs is prety much the same. reading that list I would have assumed that either would work with an 8S cassette (if I am correct that the 8S vs 9S Deore derailleur difference is not an issue)

no matter how many times I read articles and stare at that colour coded compatability charge, I've never understood pull ratios and shift ratios (I think, but do not actually know, that they are different things? PR relates to shifters, Shift ratios related to derailleurs?)
what does the Cable Pull Ratio of 1:1 versus 1:2 mean in my situation?

Last edited by pstock; 07-30-21 at 12:59 PM.
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Old 07-30-21, 01:05 PM
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Your XT-M750 rear derailleur is excellent. It is on my short list for 7-9 speed systems with a wide range cassette.

Your issue is with the shifters. You need Shimano compatible twist/grip shifters. Back in the 90’s SRAM made excellent Shimano compatible “named” shifters such as Attack and Xray. You just need to find the current Shimano compatible shifters.

I’m not up on the best current ones, you’ll just need to search reviews for SRAM, Shimano, and Microshift.

John
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Old 07-30-21, 02:00 PM
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I am losing my mind with this conversion from Bar End shifters which seemed like a good idea at the time and one that I thought would be fairly straightforward because I have quite a collection of bits and pieces, both road and MTB, to use.
I thought all I would have to do was sort through my parts bins for suitable bits.

I find bar end shifters clumsy on H-bars, so first I tried some 8S MTB trigger shifters I had on hand. the LH trigger shifter I soon discovered was incompatile with the road triple front derailleur.
but a bottom pull tab mount MTB FD is almost impossible to find.

So, I shifted gears (excuse the pun) and tried these twist shifters, because the LH gripshift alllowed some intermediate "trim" click positions which basically worked with the FD.
But, now I find the RH shifter is incompatible with the RD.

so back to the drawing board. I do still have some Deore Thumb shifters. maybe they'll work. though they seem very old for the rest of the bike.
Or, I go back to Square 1 and reinstall the bar end shifters. (but I don't want to go there.)
Or I buy even MORE Parts (someone suggested Claris road trigger shifters or these SRAM Shimano-compatible ones you suggest.) But I really don't want more parts.

I'll keep trying.

Last edited by pstock; 07-30-21 at 02:03 PM.
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Old 07-30-21, 02:12 PM
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Your Deore shifters are compatible.
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Old 07-30-21, 04:21 PM
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Here is the reality of things.

I don’t think SRAM is that keen to supply Shimano compatible lower end shifters anymore. They are competitors and 7/8 speed twist/grip shifters are not their focus anymore. Plus Microshift has stepped in to be the low price Shimano alternative.

Shimano RevoShift have never been that good. If there is one area Shimano has fallen flat it is their twist shifters.

If it were me, I’d buy a set of Microshift twist shifters. All left twist shifters I’m aware of, regardless of mfg, are friction mountain. You can use them with a road FD. It “may” take a bit more effort due to less cable pull (less leverage) with a road FD but should shift fine. The right shifters are Shimano compatible indexed.

John
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Old 07-30-21, 04:41 PM
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Originally Posted by 70sSanO View Post
I donít think SRAM is that keen to supply Shimano compatible lower end shifters anymore.

John
Just curious. Is the SRAM road gear (RIval, Force, Red) lineup Shimano compatible? for some reason (sheer ignorance mostly - I have never used SRAM Road gear) I assumed that if you wanted to sell anything these days and your name was not Campagnolo, then you had to be Shimano compatible.
I can't believe they could survive trying to maintain a 3rd cycling standard.
but then maybe that's the only route for them to not just be a budget shimano alternative as you said.
but thanks for your help with this. it is coming into focus I think.
Peter
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Old 07-30-21, 05:25 PM
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Just the brief research in trying to figure out which SRAM shifters were Shimano compatible, I got the impression SRAM wasn't self compatible in the upper tier.
Look up some of their shifters/der's, and you see a lot of "works with" lingo. Inference being it doesn't "work with" unless mentioned.
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Old 07-30-21, 06:27 PM
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SRAM is trying to become, and may already be, the big dog in mountain. In some circles they are.

I believe that Shimano 11 mountain and SRAM 11 mountain are close enough, but I’m not sure.

Other than that nothing is compatible.

I’m not sure where they are with road. Unless things have changed I didn’t think they have made much of an impact.

John
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Old 08-31-21, 10:08 AM
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I can't win.
just received my Microshift twist shifters. MS29-8
unfortunately it appears that the LH shifter is 3-click indexed.
my error. I should have drilled down and found the base specs. the MS29-8F is friction shift.
I'll try again.
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Old 08-31-21, 03:41 PM
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Are you putting a flat bar on a road bike? In which case you need 'flat bar road shifters', like the Claris SL2400. Road FD's and MTB FD's use different ratios.
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Old 08-31-21, 10:21 PM
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If your Deore thumbshifters are indexed, they will almost certainly work fine with an 8 speed cassette and a 9 speed rear derailleur. I ran this setup for years, because I hate underbar shifters and changing cables on GripShift XRays sucks. 9-speed XTR rear derailleur, 8-speed SRAM cassette, 7-speed Deore XT thumbshifters.

All you need to do is to set the rear derailleur up so that the first click in the shifter is centered on the 2nd cog, with the rear derailleur's limit screw set so that the chain runs smoothly on the 1st cog. This works because 7 and 8-speed Shimano spacing is close enough that the floating upper pulley can compensate for the very small differences, and there is a low-side overtravel built into the 7-speed thumbshifter to allow for high-load low-rpm bailout shifts into low gear. So you set it up so that you have indexed shifting on cogs 2-8 and a friction shift on cog 1 controlled by the lower limit screw.

You do give up that "hammer on the lever and you'll get the gear" overshift capability, and the initial setup is a bit fiddly until the cable is done stretching, but once everything was settled in, that bike shifted great for the 8 or so years I had it.

Might be worth trying, since you've already got the parts.

--Shannon
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Old 08-31-21, 11:04 PM
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Feel like OP has made this unnecessarily difficult and confusing. It would help if we could understand what exactly OP is wanting to accomplish. Victim-blaming aside, there are some cross-compatibility issues between manufacturers, across speeds (8, 9, 10, etc), and across disciplines (road vs mountain), that make this confusing. It's much simpler to just stick to one lineup (eg, I run SRAM GX 10sp RD which is compatible with both SRAM road and MTB 10sp shifters).
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Old 09-01-21, 01:19 AM
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What about:

https://www.paulcomp.com/shop/compon...imanothumbies/
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Old 09-02-21, 09:38 AM
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I (aka Peter Stock, Toronto Canada) am sorry to have belaboured this question, that seems to obvious to more experienced hands. and to have let it go off on tangents.
To reel it back in a bit, here's the recap.
1. The plan was to replace the orignally-mounted Shimano barcon shifters (as I found them clumsy to use)

2. The derailleur setup on this bike (a Bike Friday) is:
RD-M750 Deore XT (MTB) 9S
FD-3304 Sora (Road) triple. Tab mount, bottom pull.. I was stuck with this Road FD because 99.5% of MTB FDs are clampon OR top pull. But not both (as this frame requires).I tried three different shifter setups, but each was incompatible either on the Front (was indexed for MTB but not Road) or on the rear (SRAM 1:1 actuation ratio not compatible with Shimano)
A. Shimano SL-M570 “rapidfire” trigger shifters (FAIL due to Front MTB Indexing incompatible with Road)
B. SRAM ESP 900 3x8 Gripshift. LH Friction, RH Indexed. (FAIL due to RD incompatibility wiht Shimano)
C. Microshift twist shifters. (FAIL due to Front Indexing, which was due to stupid ordering on my part.)

I have though learned a lot about compatability - brand and component - along the way.
the comments on this thread were helpful, as was this:
https://bike.bikegremlin.com/1278/bi...compatibility/
and this SRAM Tech PDF pinpoints (on Page 25) the difference between their 2:1 and their 1:1 model shifters.
https://my-sport.spb.ru/manual_1/2001%20dtm%20mtb.pdf

I now believe that the SRAM MRX Comp (which is 2:1 which is apparently Shimano compatible in the rear and friction shift in the front) SHOULD be the solution. and which I can order new for 20 bucks.
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