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1970 R75/5 Clutch problem?

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schrader7032
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1970 R75/5 Clutch problem?

Post by schrader7032 »

If it were me with unknown history, I'd replace the entire clutch pack - spring, fiber disk, pressure plate. You could probably get away with reusing the throwout bearing once you inspect it. You'll need a seal or two at the rear end of the tranny where the throwout bearing goes. You should be able to take out the clutch without removing the engine. It might require removal of the battery and/or tilting the rear of the engine up so you can remove the transmission. Clean and grease the input splines to the transmission. Also, you should replace the four bolts that connect the tranny output shaft to the drive shaft. The updated bolts are short (with no split washers) installed clean and dry...I'd recommend some blue loctite for good measure.

Removal of the clutch pack is a puzzle...basically, it's installed under pressure of the spring plate. There should be six screws holding the clutch pack together. Remove three of the screws and install longer bolts with nuts/washers...about 70mm long. Run the nut/washer down to hold the clutch pack togther then remove the remaining three screws. Finally, evenly back off the three nuts/washers to relieve the tension on the pack.

Make note if there's any oil on the front face of the tranny bell housing...could be the front tranny seal needs replacing...that oil could be getting on the fiber disk. Also, if you see fresh oil running down behind the flywheel and onto the shelf below the transmission, then you are looking at replacing the rear main seal as well as the oil pump seal. Taking the flywheel off can be a bit of a problem and there's the possibility that the crankshaft can move forward and come off the locating pins inside the case...not a good thing. The crankshaft has to be blocked to prevent forward movement...not a difficult thing to do to block it.

Just be ready to repair everything you find...you don't want to go in this far only to have to do it again in a few thousand miles. Fix it now and it's good for 50-70K miles.

As for the front end, I'd first suggest a complete refurb and cleaning. It's not too difficult to remove the lower sliders and clean the dampers. Remove the springs out the top of the tubes and install new wiper rings. There are also probably some rubber bumpers at the bottom that have turned to mush...replace them. Put in the proper amount of fork oil and see how it works then. You can always put in new springs later. Also be sure that the sliders work together and there's no binding. Check how the sliders move together without the fork springs in place...there should be no stiction otherwise the front end will feel harsh over bumps.

It's all doable...just be prepared to fix what you see...

Kurt in S.A.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

magnetic
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1970 R75/5 Clutch problem?

Post by magnetic »

Thanks a bunch, I think I can do it, as soon as my manual gets here, and the tips on parts that I should replace is most appreciated.

magnetic
Posts: 11
Joined: Mon Apr 02, 2007 9:24 pm

1970 R75/5 Clutch problem?

Post by magnetic »

Finally got the job done, the friction disk was burnt black and the compartment covered in "soot", the disk was worn to the rivets.

All in all this was a very simple job, as a super novice mechanic I found it rather simple and straight forward. Certainly not something I would pay someone $800+ to do. At the time I did this I replaced all the drive oils, air filter and gave the engine a thorough cleaning/polishing. I also replaced the 30 year old fuel line, and the rubber couplers from the carb to the head. This really took the bike up to the next level, in looks, and the new airfilter made a dramatic difference in the performance.


Now to figure out the front suspension issue...

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schrader7032
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1970 R75/5 Clutch problem?

Post by schrader7032 »

It's good to find something that you can point to as the problem...sounds like things are improving...

I've only been into my /7 forks once...not sure of the similarities with the early /5. I'd certainly change fluid and see how that goes. You could consider heavier fork fluid, like 10 or 15wt, or change the amount of fluid. Some like to increase the level above stock to reduce the air volume above the oil. I suppose to little air and you might blow the fork seals out at the top of the sliders.

If that doesn't help, then probably taking the sliders off as well as the fork internals would be the next step. You might have some gunk in there clogging the damper holes. It's possible that the springs have sacked. My Haynes manual says the free length of the early /5 springs should be 530-542mm.

Kurt in S.A.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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VBMWMO
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1970 R75/5 Clutch problem?

Post by VBMWMO »

RE: 1970 R75/5

In my haste the bike I picked up (bought it in a lowlit parking garage) needed a serious cleaning, including significant rust(I love you Navel Jelly), now after its looking sweet I take it for a ride I lay into the throttle and as I go from(after a 50 mile ride) 3rd->4th gear that clutch totally slips and stinks up the road, I had to lay off the throttle and let the flywheel wind down before it would re-engage. This is pretty obviously a clutch problem, my question is this, what part is the most likely culpret? Stuck throwout? worn spring/piston, or worn clutch plate pads?

Also how difficult is it to replace clutch parts, and can it be done without removing the engine.


On an unrelated note, the front suspension "feels" terrible, its mushy and makes noise on pots holes and bumps. Will new springs revitalize this, or are there other components that may be bad?
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