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R75/5 SWB front fork rebuild

maddrobh
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R75/5 SWB front fork rebuild

Post by maddrobh »

Hello
I just drained the oil from the front forks of my recently acquired R75/5. The bike has an indicated 30k miles on the speedo. The forks dived and appeared to have little damping. The fork oil was black and had rubber and other particles suspended in it. I could only drain about 150 cc from the right fork leg. I plan to strip and refurbish the sliders & dampers, and replace the springs. Two questions: 1) am I correct in thinking that I can drop the sliders and dampers off without removing the stanchions from the yokes? 2) I weigh about 150 lbs and will ride mostly solo with minimal luggage; is it worth fitting progressive springs or stick with standard?
Robert
‘71 R75/5, ‘21 R1250RS, & a couple of brits

cwf
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Re: R75/5 SWB front fork rebuild

Post by cwf »

Sounds like the oil hasn't been changed in a while, it's often overlooked. I'm familiar with the /6 and later forks but there might be an Allan bolt at the bottom of the slider that holds the damping rod and releases the slider. You might be able to release both at the same time, which avoids disturbing the fork brace. Take the spring out the top first. There might be a rubber bump stop, which has failed and might be the cause of the bits.

You can mark the stanchions and twist them 90 degrees, which means the wear, which mostly occurs during braking at the top rear and bottom front, gets spread more evenly. I used to do it every 50,000 miles.

Charlie.
75/7+ offroad sidecar; 50/2; R 35; XR125V; XR200A; Solex; 1939 Hillman Minx DHC.

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schrader7032
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Re: R75/5 SWB front fork rebuild

Post by schrader7032 »

Be careful removing both sliders at the same time. It's possible the fork springs will over stretch or rip the gaiters. Don't ask me how I know.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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drpetemurray
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Re: R75/5 SWB front fork rebuild

Post by drpetemurray »

I would fully disassemble the forks and drop the triple trees to service or replace the steering head bearings and races.
PeteM
Stroudsburg,Pa
73 R75/5 , 1014 RTW, IBA 359

Tinkertimejeff
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Re: R75/5 SWB front fork rebuild

Post by Tinkertimejeff »

Stick with the standard springs if you replace them. The progressive's might give a harsh and very stiff front suspension, you can adjust stiffness of the front suspension with the viscosity of the oil. I stuck progressive's in a bike once and it was a terrible ride, it felt like the front suspension was frozen. I would also agree with the suggestion to service the steering head bearings while your at it. Mark the stanchions and twist and twist 180 degrees as well as replacing the fork gators if they are old or show signs of cracking or dry rot.

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srankin
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Re: R75/5 SWB front fork rebuild

Post by srankin »

Depending on past maintenance, at this point I would at least determine if the steering head bearings need changed. At the very least, not knowing when they were last lubricated, I would pull them apart and re grease them.

IF they have high mileage on them, it would be best to bite the bullet and replace them regardless. High mileage, say 100,000. If they are notchy acting, forget the miles and change them.

Steering head bearing maintenance along with the transmission input shaft are two things a LOT of airhead owners seem to forget about or don't do on a regular basis. St.
Owner of a 84, R80RT and 79 R100RT being stripped naked for summer, turned Into a frame up restoration,

maddrobh
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Re: R75/5 SWB front fork rebuild

Post by maddrobh »

Thanks all for your suggestions. I particularly like the idea of turning the stanchions by 90 deg, that I had not thought of. I shifted one gaiter up and the chrome stanchion looks good. I will update once I do the job, likely next week (when my wife will be away ;) )
‘71 R75/5, ‘21 R1250RS, & a couple of brits

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schrader7032
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Re: R75/5 SWB front fork rebuild

Post by schrader7032 »

About the stanchions. I believe they have a small hole drilled into the side of them. From a structural stress standpoint, the hole should be either pointed directly at the other one or directly away. Bending stress is minimized in these orientations along the centerline...it is maximum at the most forward or most rearward surfaces during operations.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

Tinkertimejeff
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Re: R75/5 SWB front fork rebuild

Post by Tinkertimejeff »

180 degree spin does the job.

maddrobh
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Re: R75/5 SWB front fork rebuild

Post by maddrobh »

Fork legs stripped and I found both the lower, large black 'buffer' in the slider cap and the white (silicone?) upper buffer on the damper, had disintegrated / dissolved. Both springs in the damper have lost 'strength' when compressed compared to the new ones, and the damper piston rings are weak compared to the new ones.
The dampers are the older type with no extra plate in the base of the stanchion - the parts lists in the knowledge base on this site and https://brook.reams.me/bmw-motorcycle-r ... k-rebuild/ have been invaluable. Some pictures attached FYI.
Suffice to say I have bought top quality fork oil to put in the forks!

I have three questions:
1) Should the white upper buffer be a fairly loose fit on the damper (i.e. buffer ID > damper OD) ? The OD is a snug fit into the stanchion.
2) What are the red plastic washers (see attached picture) that came with my rebuild kit for? (I will ask the supplier, but stupidly the bags for the individual items are labelled with something other than the BMW part number.)
3) I think I read that the extra plate in the base of the stanchion was to reduce noise. I'm guessing it would also prolong the life of the white buffer. Can the parts be retro-fitted or would I need to get new stanchions with longer internal threads at the base (or get mine threaded).
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‘71 R75/5, ‘21 R1250RS, & a couple of brits

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