mac t8 grinding

Hi all can anyone tell me what you think this problem is?
Today I went on my bike for the first time in about a month. I don't know what it is but every so often there is a grinding sound from the motor (it sounds a bit like if your in a car and it does not go in gear right)
It does not happen all the time, but when it does happen it's always on acceleration it does not matter if you accelerate fast or very slow, sometimes it will grind.
If the bike is going say 10mph without power and you accelerate nothing no grinding and pulls away like its on steroids.
Do you think this is the clutch or gears?

How many watts are you putting into it?

Jumped off any kerbs recently?

Your clutch (sprag clutch) is slipping. I have the same issue. My clutch would still work on soft accelerations and once I get up to 10+ mph.

You can a replacement clutch from cellman's site, EM3EV.com if it's a MAC motor.

Yes clutch or gears knackered either way change both.

must be the potholes by my work or should I say craters. don't think watts would be a problem as I have only used the bike to go to and back from work and keep the bike to 15mph on the road.
think I will have a go fixing this motor and buy a good direct drive as a backup

is the clutch easy to change?

The clutch is not hard to change if you are mechanically inclined and have the tools needed.

However I assume it would be an intimidating job for a desk jockey who's rarely touched a screwdriver.

You need a circlip removing tool. Possibly a three jaw gear puller.

Problems that arise, screw strips or is stuck in the face plate. Tapout stripped screw remover will fix this.
The clutch is pressed to the shaft so tight it won't budge.
This is remedied with the gear puller, rubber mallet, block of wood, and some creativity.

That being said, I am very mechanically inclined and found it to be a stressful ordeal. Mainly the stripped screw was a huge headache but trying to unsieze the clutch without damaging anything was not fun.

I got a DD after the second clutch and gears. The DD while more powerful actually feels less powerful cause there is very little off the line torque compared to the 10t Mac. Plus its a heavy beast(3540).

So IMHO geared motors are far more practical for performance and efficiency, but the darn gears and clutch will leave you stranded.......

CyberCrime said:

is the clutch easy to change?

Click to expand...

Yep, if you have modest DIY or mechanical skills...

There are threads on ES about this - if you search a bit you can find information about doing the job. Spinningmagnets has a complete teardown thread (lots of pics) that goes further than you need - you can stop right after the gear cluster/clutch comes off.

Here's a YouTube on changing the gear cluster in a BMC- virtually identical.

Not to much to it really. Just don't let the wiring cable flop around...

Use a file to clear burrs/deformities from the edge of the shaft face where it contacts the dropout. This will let the bearing slide off easily instead of jamming during removal and pulling out of the sidecover.


It's easiest to order a new clutch and matching gears - the old gears can be a PITA to remove from the old clutch and the new style clutch needs new thinner gears - so for a few bucks just guarantee everything matches and save the struggle. You will need grease as well. BMC recommends MobileGrease 28, but since you're ordering from EM3EV anyway, ask Paul to add a couple of grease packets to the order and some replacement cover screws and get all the parts at once.