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Thread: 1971 R75/5 Missing Subframe Tab - Fabrication advice?

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    1971 R75/5 Missing Subframe Tab - Fabrication advice?

    Hello BMW MOA Members!

    Long story short, I just acquired a very dusty, somewhat complete '71 R75/5 (my dream bike). I got it for somewhat of a steal, but it's definitely not without some issues. This is my first BMW so I'm still learning pretty much everything about them as I go.

    The latest head scratcher/epiphany from today is that my subframe is missing the seat-pin latch tab. I don't have a good picture on hand at the moment, but I'll post one tomorrow morning when I get to my shop.

    First question, is this a common break? Has anyone encountered this before?

    Second question, would anyone recommend fabricating a new tab or finding a new subframe? I'm trying to be somewhat thrifty/wise about what I sink $ into for this build.

    Third, Has anyone had experience fabricating and welding missing/broken tabs onto their frames?

    And lastly, would anyone be so kind as to provide the dimensions of the tab in question as to help me in making it?

    Any guidance would be greatly appreciated. Thanks in advance for the help. I'm very excited to be a part of the community, although I think I'll feel like more of a member when this bike actually runs .
    Last edited by jrussakis; 02-11-2016 at 10:00 AM.

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    Administrator 20774's Avatar
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    Welcome to the forum and Airhead-dom!
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    Don't know about the short sub frame, but a used long one should run around fifty bucks. AFAIK, they should be the same with the tabs till about ?. Two cents.

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    Registered User barryg's Avatar
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    Registered User barryg's Avatar
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    Sorry about that. I took some pics of a '71 R50/5 subframe at the latch area ands this come up when I loaded it. Sorry.

  6. #6
    What? Me Worry? gromulin's Avatar
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    I'd start a saved search on eBay for "R75 subframe" or different variations on that. I found a perfectly matching front fender, pinstripes and all in great condition, for my 72 /5 for $67 shipped. You can find all kinds of stuff on eBay, it just takes patience, and running a bunch of saved searches to catch all possible descriptions.
    72 SWB 75/5 Toaster. Craven Golden Arrow luggage.

    I got held back in the fourth grade myself. Twice! Look at me, man! Now I drive the school bus! - Otto Mann

  7. #7
    Registered User PAS's Avatar
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    The one listed on the MAXBMW fiche states the following: "Applies to LWB twin-shock models from 8/71 up to 1984 (except for R65)."

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    What? Me Worry? gromulin's Avatar
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    71 model year was short wheel base, and 72 models manufactured at least until 12/71 were SWB also.
    72 SWB 75/5 Toaster. Craven Golden Arrow luggage.

    I got held back in the fourth grade myself. Twice! Look at me, man! Now I drive the school bus! - Otto Mann

  9. #9
    Registered User barryg's Avatar
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    '71 R50/5 Short Wheelbase Subframe

    Picture 001.jpg
    Latch on the short wheelbase subframe. Mine cracked on the flat part where it attaches to the round part of subframe.

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    Thanks all for the replies! Barryg thanks for the picture! Yep that's exactly what I thought I was missing. I tweaked my back something fierce this morning at the gym so I wasn't able to make it over to the garage today (talk about 24 going on 70...). However I did do plenty of research couch-side. Found a few subframes on eBay one for $150 and another for $83 (plus $30 for S&H). I feel like both of those are steep, or is that just me?

    In my state I couldn't get over to snap a pic of my subframe, but I did come across a subframe that looks an awful lot like mine in that it's missing the seat pin tab.

    Frame Pic.jpg Here's the Ebay Listing

    I'm wondering if bike's subframe is broken or it's just wrong for the bike it's on. Now that I know what a SWB subframe is supposed to look like I need to confirm that I have all the tabs and posts that I should and that I'm not just missing the pin tab. I'm suspecting that I'm missing the two posts on the right hand side of the subframe that secure to the seat pivot hooks (excuse my inaccurate terminology). This is really turning out to be a mystery. Thanks again for everyone's help!

  11. #11
    Registered User barryg's Avatar
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    The piece is rather flimsy. I've cracked mine.

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    What? Me Worry? gromulin's Avatar
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    ...that doesn't look right. The pins you see on the lower side of the picture (LH side of the bike) are to hold a hand air-pump (I just found this out last year after owning my /5 since 1987!). The seat hinge pins on the RH side of the frame are a weak point. If the rubber bumpers wear or fall off the seat, it puts way more load on the seat hinge pins than it was designed for, and they break off. I had my rear one welded back on sometime in the early 90's and it's still good. The rear subframe of the /5 is one of the crappier-designed parts of the bike. The threads on the tip of the camshaft, by far, being the winner of the "Friday Afternoon Engineering Team" crappy design contest for the /5.
    72 SWB 75/5 Toaster. Craven Golden Arrow luggage.

    I got held back in the fourth grade myself. Twice! Look at me, man! Now I drive the school bus! - Otto Mann

  13. #13
    Airmarshal-IL James.A's Avatar
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    There was a SWB rear sub-frame on IBMWR recently.
    1973 R75/5

    1988 R100RS (available)

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    Quote Originally Posted by James.A View Post
    There was a SWB rear sub-frame on IBMWR recently.
    Thanks James.A, I just sent the guy an email. Much appreciated for the tip!

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    Quote Originally Posted by gromulin View Post
    ...that doesn't look right. The pins you see on the lower side of the picture (LH side of the bike) are to hold a hand air-pump (I just found this out last year after owning my /5 since 1987!). The seat hinge pins on the RH side of the frame are a weak point. If the rubber bumpers wear or fall off the seat, it puts way more load on the seat hinge pins than it was designed for, and they break off. I had my rear one welded back on sometime in the early 90's and it's still good. The rear subframe of the /5 is one of the crappier-designed parts of the bike. The threads on the tip of the camshaft, by far, being the winner of the "Friday Afternoon Engineering Team" crappy design contest for the /5.
    Thanks for the insight Gromulin, good to know what I'm getting myself into! I guess it's good to have a frame with all the parts at first that way I can weld them back on when they fall off haha.

    So happy to have you MOA members around to offer your tutelage!

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