1975 Mk3 rear Isolastic replacement

Went looking for a video for rear iso replacement, only found one with a guy pounding replacement rubber in the hole with no explanation and mechanic in the way all video.
Reviewed one thread here that ended in disappointment with new rubber being too hard.
Something without pics about bevel to cure.

I have engine out for refresh.

Workshop not helpful.

I got my mk2 iso's out and new mk3 type iso's in tge rear without too much fight. Major pain was all the other work needed to get clearance for rear.
You already have clearance so should be ok from there. Use some silicon grease, like dielectric grease, and things slide in great.

Be sure you have good iso rubber. I had a set that were like hocky pucks new. Ride vibes were awful. Replaced with AN set which were more closer to running shoe sole hardness. Ride vibes now acceptble.

This guy shows a puller setup for removing and installing the mk3 units:

I guess there are still some OEM isolastic rubbers running around that are new but have been siting on a shelf since the 1970s. "Hard as a brick bat" and my grandfather used to say. I still do not know what a brick bat is and why it's so hard?

I ran across a video of a guy replacing some type of rubber bushing in a bus. He was using an all-thread bolt to pull the new rubber into the sleeve and I thought "that's just like an isolastic mount on a Norton!" I have only installed one iso and that was on my old 750 when I installed the MKIIs. It was a horror show. If I ever have to do this again I am making a puller.

Both videos are great, Thank you.
They both have the rear wheel off, no battery tray or wiring,.
I would like to keep mine on , wiring intact, also keep the rear hydraulics intact, oil filter , oil hoses, horn, etc......... so advice or experience or better yet pics of mk3 in this condition.

The item that keeps this Mk3 from collapsing around the rear iso is a long Phillips driver.

I dont have any issues pulling the old iso out or pulling a new iso in , my issue is exposing the rear iso on this Mk3 in this assembled condition .

p400 said:

They both have the rear wheel off, no battery tray or wiring,.
I would like to keep mine on , wiring intact, also keep the rear hydraulics intact, oil filter , oil hoses, horn, etc......... so advice or experience or better yet pics of mk3 in this condition.

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You do need to support the frame so the weight is off the rear wheel. I found there was no need to remove the rear wheel or to remove wiring or hydraulics (left attached to the Z-plate and tied up out of the way) but the lower shock mounts probably need to be detached (or shocks removed) to allow the cradle to be moved far enough forward to gain access to the Iso. I would suggest removing the battery tray.
I dropped the mudguard, resting it on the tyre but didn't disconnect the wiring. I did remove the filter housing as I replaced the oil hoses.
I didn't need any tube or threaded rod. etc. to install the Iso. tube/rubbers.

Electric leg bike might be more complicated, but When I did my mk2, it needed primary covers (both) off. Oil lines and filter stayed. As I lifted the engine/cradles with a scissor jack, found the non stock horn in oem position began to foul and had to be removed. Just needed front end of rear mudguard detached and the horn mounting points released. This was the most difficult task of whole process, including refitting it. Then the iso tube cleared frame sufficiently. Front iso was in place but headsteady off, so assembly could rotate up and forwards.

Tornado said:

Electric leg bike might be more complicated, but When I did my mk2, it needed primary covers (both) off.

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The front Iso. had to be removed (to allow the cradle assembly to slide forward) but both the engine and primary drive remained in position when I changed my Mk3's rear Iso.

Tornado said:

Just needed front end of rear mudguard detached and the horn mounting points released. This was the most difficult task of whole process, including refitting it.

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If the battery tray is removed then the horn goes with it.

I can hang the frame with a strap toward the rear The horn appears very loose.
So I hung the frame with a strap, lifted till weight oiff rear wheel.
Put a scissor jack under gearbox frame, lowered iso till clear, knocked out old iso.
Pretty easy job on Mk3 with engine out.



Did not disconnect any wires, any hoses, fender, wheel , chain, suspension units, chain guard etc.

p400 said:

Did not disconnect any wires, any hoses, fender, wheel , chain, suspension units, chain guard etc.

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Yes, I see that with the primary case removed the cradle can simply be lowered.
With the primary case in position as I did it, then the cradle assembly would have to be slid mostly forward.

Sprayed new rear iso large rubbers with silicone spray, a little in the tube housing. I was able to hand roll and push the new rear iso into place. Kinda tough, but doable. Assembled the iso on both ends then Jacked the gearbox up mate the iso section with the chassis, had to move the rear assembly with large screwdriver, reached thru mounting hole and used a tapered punch to get good alignment. Soft hammered the mounting bolt back thru. Fairly easy job looking back.
When forcing the new rubber in the rear assembly the rear assembly came off the jack, but was stopped by the gearbox housing (at the kick start ) from going very far, only an inch, or maybe less, further down.



You have to turn the rubber iso covers inside out to install, push over small diameter and roll into place.