21 BMW 1973 R75/5 Remove and Inspect Clutch

This page covers the removal of the clutch and inspection after the transmission has been removed.  Refer to following page and sections for details on how I removed the transmission:

02 BMW R75/5 General Tear Down
– Remove Rear Wheel, Fender and Sub-frame
– Remove Rear Drive
– Remove Swing Arm
– Remove Transmission

When I measured the clutch parts (see below), I decided that they were worn enough to replace the entire clutch.  The clutch replacement with new parts will be covered in a separate web page when I complete that work.

Engine Stand

I had previously removed the engine so I could powder coat the frame. I had placed it on a cradle using my Park-n-Move dolly when I got it out of the frame.

Another use for Park-n-Move Dolly as Engine Stand

Another use for Park-n-Move Dolly as Engine Stand

I needed a way to work on the engine without it moving around and used my motorcycle lift from Harbour Freight for that purpose.  The engine is light enough to lift by myself as I had removed the heads, cylinders, pistons, air box and starter motor covers.  I lowered the lift as low as it would go, placed some 2×4 across the lift arms and then picked the engine up using my legs to lift it and placed it on the lift.  I strapped it down across the lift arms to secure it and then raised it to a comfortable height to work on from my shop stool.

Make-do Engine Stand

Make-do Engine Stand

Blocking The Crankshaft

As documented in many write-ups, if the flywheel is removed, the crankshaft is free to move forward and can easily be knocked off the thrust washers.

–> http://bmwmotorcycletech.info/flywheelremovalwarning.htm

If you are only removing the clutch, and you are not removing the flywheel, you don’t have to block the crankshaft.  Details on how I blocked the crankshaft are in the “11 BMW R75/5 Remove & Replace Flywheel, Replace Rear Main Seal, Oil Pump Cover & O-Ring” web page.

Making a Clutch Locking Bar

I used a piece of 1 inch mild steel bar stock to make a bar to block the rotation of the clutch so I can remove the bolts around the perimeter without the clutch spinning.  I drilled a 3/8 hole at one end so it can slide over the transmission stud on the top, right side of the engine.  I modified this same bar later to hold the flywheel stationary so I can remove the flywheel bolts.

Making Clutch, Flywheel Removal Bar

Making Clutch Locking Bar to Stop Rotation When Removing the Clutch

I cut the bar stock to length so it would just reach the inside of the engine housing and rest next to a clutch bolt and on the inside of the engine housing. I ground the corners off the cut edge so the edge of the bar wouldn’t gouge the engine housing. Then I mounted the bar so it was between one of the bolts at the circumference of the clutch and the engine housing.

Bar Preventing Rotation When Removing Clutch Bolts

Bar Preventing Rotation When Removing Clutch Bolts

Removing the Clutch Assembly

DANGER:
–> The clutch is under great pressure from the clutch diaphragm spring
–> ONLY REMOVE EVERY OTHER BOLT.
–> DO NOT STAND IN FRONT OF THE CLUTCH ASSEMBLY.

Be safe and work carefully.

By removing every other bolt, the remaining three bolts are sufficient to keep the clutch assembly together against the pressure of the diaphragm spring. After I removed the three bolts, I used three 8mm x 1 bolts that are longer than the original ones with washers and nuts. I purchased these at my local Ace Hardware. I set the nuts so the exposed thread is about the same as the thread length of the original bolts.  Then I threaded the three longer bolts into the three empty holes until the washer touched the clutch housing and I tighten the nut with a box wrench to secure the bolt.

Three Longer Clutch Removal Blts & Original Bolt on Right

Three Longer Clutch Removal Blts & Original Bolt on Right

I removed the remaining three original bolts. At this point the three longer bolts are holding the clutch together. I backed the longer bolts out about 1/2 turn at a time going around to each bolt in turn. The idea is to release the diaphragm spring pressure slowly and evenly.

–> KEEP TO THE SIDE OF THE ENGINE WHILE DOING THIS TO AVOID INJURY

Backing Off Clutch Pressure 1/2 Turn Per Bolt at a Time

Backing Off Clutch Pressure 1/2 Turn Per Bolt at a Time

Despite my care, one bolt came loose sooner than the others and the clutch assembly jumped outward on one side with a loud BANG.  I cleaned out my underwear and continued to loosen the other two bolts. 🙂

Source: Max BMW Parts Fiche
http://www.maxbmwmotorcycles.com/fiche/DiagramsMain.aspx?vid=51885&rnd=04302013

The clutch assembly comes out with the clutch compression ring (5) facing you and the clutch pressure plate (2) behind it with the clutch plate (3) sandwiched between them. The diaphragm spring (1) is last as it presses on the back of the clutch pressure plate.  In between the clutch compression ring and clutch pressure plate are spacers (4) each clutch bolt goes through. You can see one of them in this picture.

Spacer Between Compression Ring and Pressure Plate

Spacer Between Compression Ring and Pressure Plate

I marked the clutch pressure ring and pressure plate so I can assembly them in the same orientation if I decide that the parts weren’t too worn.

Marks on Compression Ring & Pressure Plate

Marks on Compression Ring & Pressure Plate

Here is a picture of how the parts go together but without the spacers: at the bottom is the clutch pressure ring that faces you and at the top is the clutch diaphragm spring that is against the flywheel.

Clutch Parts Order: Bottom Clutch Pressure Ring, Top Clutch Diaphragm Spring

Clutch Parts Order: Bottom Clutch Pressure Ring, Top Clutch Diaphragm Spring

Measuring Clutch Parts and Inspection

I took measurements of the clutch parts and used the information I found at Duane Ausherman’s site to decide the condition of the parts.

Clutch Diaphrapm Spring Condition

Here are pictures of the clutch diaphragm spring showing the condition of the fingers.

Diaphragm Spring Finger-Wear on Edges

Diaphragm Spring Finger-Wear on Edges

Diaphragm Spring Finger-Wear on Edges

Diaphragm Spring Finger-Wear on Edges

Diaphragm Spring Finger-Wear on Edges

Diaphragm Spring Finger-Wear on Edges

Diaphragm Spring Finger-Wear on Edges

Diaphragm Spring Finger-Wear on Edges

One edge of the fingers show wear. I judged them still usable (not badly worn, but certainly worn) based on pictures I found at Duane Ausherman’s site which I have reproduced below.

Source: Duane Ausherman: Nearly Perfect Spring Fingers

Source: Duane Ausherman: Badly Worn Spring Fingers

I measured the finger height above the bench top at 18 mm. Duane indicates that original height is 17.7 mm so mine hasn’t compressed.

Clutch Plate Condition

I measured the clutch plate thickness at the outside diameter at 0.202 inches and at the inside diameter at 0.190 inches. Duane indicates that original thickness is 0.240 inches and he has seen them still working at 0.200 inches. Mine is about worn out.

Clutch Plate Disk Facing Transmission

Clutch Plate Disk Facing Transmission

Clutch Compression Ring Condition

The clutch compressing ring I have looks like the /2 ring shown in Duane’s article

Note: Duane refers to this as the clutch backing plate and Max BMW parts fiche calls this the compression ring, which is the term I am using.

Clutch Compression Ring

Clutch Compression Ring

I measured the thickness as 0.218 inches at the at the inside diameter. Duane indicates the original thickness is 0.234 inches, but mine measured 0.227 inches at the unworn part. He doesn’t indicate what the minimum value is but does show some “worn” values for this plate: outer edger at 0.229 inches; inner edge at 0.225 inches. Mine is less than these and combined with the clutch plate being thin, it wouldn’t be long before the clutch starts slipping.

Clutch Pressure Plate Condition

Duane indicates it should be 0.417 inches for the /5 plate. He indicates that deep grooves are “bad” and I take that to mean deep grooves where the diaphragm spring fingers press on the back of the pressure plate.  I definitely have pronounced grooves.

Clutch Pressure Plate Facing Transmission

Clutch Pressure Plate Facing Transmission

Clutch Pressure Plate Facing Engine Showing Grooves from Diaphragm Spring

Clutch Pressure Plate Facing Engine Showing Grooves from Diaphragm Spring

Clutch Pressure Plate Throw Out Rod Hole

Clutch Pressure Plate Throw Out Rod Hole

Keep or Replace the Clutch?

I decided to replace the entire clutch assembly; clutch diaphragm spring, clutch pressure plate, clutch plate, clutch compression ring and clutch bolts.  I ordered the following parts from Tom Cutter at Rubber Chicken Racing.

21 21 1 250 035 Diaphram Spring (Heavy Duty)
21 21 1 251 801 Pressure Plate
21 21 1 236 332 Clutch Plate
21 21 1 231 666 Compression Ring
21 21 1 231 463 Filister Head Cap Screw (6)

 

11 thoughts on “21 BMW 1973 R75/5 Remove and Inspect Clutch

  1. Pingback: 1973 R75/5 Rebuild: Clutch Removal and Inspection | Motorcycles & Other Musings

  2. very nice presentation! OK, I have a crazy idea and I need help. Want to install a R75/6 motor to a Citron CV transmission. BMW (push pin) type clutch will not work BUT it appears that I might be able to modify the BMW flywheel to take the (throw-out) Citron clutch.

    Any thoughts or am I just nuts!

  3. Hi Brook,
    First of all, I want to say thanks. Your site has been enormously helpful with my own ongoing ’72 R75/5 restoration. Great pictures, easy to understand text, I really appreciate all the work you’ve put into this, and I always read your stuff before I do any work on the bike.

    Secondly, when I was pulling my own clutch, I experienced the same loud “BANG” when loosening the bolts. I realized later (after I’d finished) that I was doing it incorrectly. It’s the inner nuts that need to be gradually loosened, not the outer bolts. That way, the bolt threads, under pressure from the clutch spring, never disengage suddenly from the housing — no bang, no damage to the threads, and the clutch spring slowly releases without causing Dirty Underwear Syndrome.

    Again, thanks for all your help. This is a big job, and you’ve made it a lot easier!
    -Dave

    • Hi Dave,

      Well, your explanation makes sense. BTW, I have a number of “underwear trophies” from my DUS experiences, so welcome to the club 🙂

      Add, thanks for the kind words. I’m glad this material helped you and you helped me by explaining where the load BANG came from.

      Best.
      Brook.

    • Hi Rod,

      Thanks for stopping by and looking at the site. I did not replace any of the transmission studs or fasteners. The studs were secure so I didn’t disturb them.

      Best.
      Brook.

  4. Thank you so much for your information Brook. It has made working on my /5 such a pleasure. Wonderful pictures, with easy to read details.

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