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Thread: 1973 BMW R75/5 SWB versus LWB

  1. #1
    Registered User b25bsaboy's Avatar
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    1973 BMW R75/5 SWB versus LWB

    Good evening to you all!

    Well I did it again and purchased a new project and it is a SWB 1973 BMW R75/5 so Iím told. If in fact this is a short wheel base, how difficult is it to make it a LWB or can it be done. It not to say that I would but I have the parts that are needed except for the frame tail piece that I bought several years ago. These parts came from an R 75/6 I believe.

    Just thought I would float the question to see what the wisdom says.

    I am looking forward to diving into this project that has been sitting in a gentlemanís garage for the past twenty years. Will forward some photos once they become available.
    Rick MacPherson
    Success is Not a Destination, But a Journey.
    Accredited Motorcycle Appraiser
    1968 BSA Starfire, 73 R75/5 SWB, 2008 Honda GL-1800 Lehman Trike

  2. #2
    Depends on your intended use of it. If you are going to load the back end of it and travel long distances, you might prefer a long wheelbase for increased stability. The parts are readily available and include the swingarm, driveshaft, rear sub-frame, side covers, and seat. If you are using it for lightly loaded sport and recreation riding, I personally think it is more fun with the SWB. Most of the horror stories about the handling are either highly aft-loaded bikes, or the front end is not properly set up. It takes some work to do a rigorous front end setup on one, but it is nothing but time and the details are widely available for how to do it. I test rode one and the steering shook strongly when off-throttle. The seller told me that all SWB's did that. He is wrong.

    For contrast, there is a fairly famous SWB in the museum at Bob's BMW with over 600,000 miles on it - all of them loaded to the gills for travel.
    Lee A. Dickinson - Danielsville, GA USA
    Airheads #3480 | Iron Butt Assn. #8914
    1976 R75/6 - 1992 R100RS - 1993 K1100RS - 2013 R1200GS

  3. #3
    Liaison 20774's Avatar
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    Snowbum has a few pros/cons on this page, Section VII:

    http://bmwmotorcycletech.info/mod4performance.htm

    Matt Parkhouse discusses changing a SWB to a LWB in the July 2004 Owners News.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    MOA #24991 Pauls1150's Avatar
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    Rick, just to help identify what you have ("... so I'm told."), here's a picture (thank you Google) of the difference - look for the "extension" weld 2" forward of the flange where it bolts up to the rear drive. I thought that '73s all had the longer arm & larger battery, maybe not (mine did).
    newvsold.jpg

  5. #5
    Quote Originally Posted by Pauls1150 View Post
    I thought that '73s all had the longer arm & larger battery, maybe not (mine did).
    It was a mid-year change in 1973.
    Lee A. Dickinson - Danielsville, GA USA
    Airheads #3480 | Iron Butt Assn. #8914
    1976 R75/6 - 1992 R100RS - 1993 K1100RS - 2013 R1200GS

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    MOA #24991 Pauls1150's Avatar
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    Thanks, Lee!

  7. #7
    Registered User barryg's Avatar
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    Not 100% sure, but I think that all long wheel base /5's came with the small battery box set-up. I've converted a couple of long frame /5's to the large battery box set up, back in the day.

  8. #8
    Rally Rat 1074's Avatar
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    Quote Originally Posted by Pauls1150 View Post
    Rick, just to help identify what you have ("... so I'm told."), here's a picture (thank you Google) of the difference - look for the "extension" weld 2" forward of the flange where it bolts up to the rear drive. I thought that '73s all had the longer arm & larger battery, maybe not (mine did).
    newvsold.jpg
    That picture shows a /2 swing arm modified to use a later model rear drive and doesn't actually portray the difference between a short and long wheelbase /5 swing arm.
    I don't know where the myth about LWB 73 models coming with a larger battery came from but it is just that, a myth. All /5s came with the same battery brackets and the smaller battery!

    So if you must change from short to long then you'll need the long swing arm with driveshaft, a long sub frame that can either be a /6 or /7 as well as the correct /5 item. The side covers are the same for both but the holding tabs on the sub frame are in a different location on the /6 and later models and they do not line up correctly with the covers. If you look in the parts book you will se a pair of longer bolts and positioning tubes at the bottom front of the fender.
    An original /5 LWB sub frame can be distinguished from a /6 and later by looking at the cross braces at the front of the sub frame. The /6 and later will have a stamped flat plate cross brace. Using this will also require a /6 or later tool tray that will be long enough to span the gap. The actual /5 piece will have two tubes across the sub frame. The rear tube will have the tabs for the rear fender bolts. The forward tube will be in position to support the /5 tool tray that is a bit shorter than the later models.
    Boxerbruce

  9. #9
    Rally Rat 1074's Avatar
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    Forgot to mention that the seat will also have to be changed.
    Boxerbruce

  10. #10
    Liaison 20774's Avatar
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    Some additional defining info on SWB vs LWB:

    https://forums.bmwmoa.org/showthread...Long-Wheelbase
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  11. #11
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    I had a SWB R75/5 in the early 70's and used it for fully loaded long distance travel at high speeds on the Autobahn
    and never had any stability problems. Solid as a rock.
    On curvy roads too, significantly better than Jap bikes at that time.
    I now have a LWB R75/5 but can not comment on high speed. No Autobahn here.
    I would not go through the trouble of conversion.

  12. #12
    Registered User b25bsaboy's Avatar
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    Quote Originally Posted by b25bsaboy View Post
    Good evening to you all!

    Well I did it again and purchased a new project and it is a SWB 1973 BMW R75/5 so Iím told. If in fact this is a short wheel base, how difficult is it to make it a LWB or can it be done. It not to say that I would but I have the parts that are needed except for the frame tail piece that I bought several years ago. These parts came from an R 75/6 I believe.

    Just thought I would float the question to see what the wisdom says.

    I am looking forward to diving into this project that has been sitting in a gentlemanís garage for the past twenty years. Will forward some photos once they become available.
    Good evening everyone,

    Well got the R75/5 back to the shop and this Queen B has done well after being in storage for 20 some years. I was surprised to see the internals of the fuel tank looking none worse for wear. The frame, fenders, side panels and fuel thank look respectable for an old gale of 45 years.

    Check the tell tail sig of the rear of the drive shaft and yes indeed I have a SW. Will start checking what I have to see if I can in fact convert to a LW or if I really want too!

    All in all I am tickled to have another project to work on.
    Rick MacPherson
    Success is Not a Destination, But a Journey.
    Accredited Motorcycle Appraiser
    1968 BSA Starfire, 73 R75/5 SWB, 2008 Honda GL-1800 Lehman Trike

  13. #13
    Quote Originally Posted by b25bsaboy View Post
    Will start checking what I have to see if I can in fact convert to a LW or if I really want too!
    Give it a chance to show its own charm before you turn it into essentially a duplicate in handling character of your R75/6.
    Lee A. Dickinson - Danielsville, GA USA
    Airheads #3480 | Iron Butt Assn. #8914
    1976 R75/6 - 1992 R100RS - 1993 K1100RS - 2013 R1200GS

  14. #14
    John D'oh
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    If you haven't ridden a /5 short wheel base bike then you owe it to yourself to take time to experience the bike as it was designed. Important items to service or are: Fork assembly- clean and service including steering bearing service and springs, swing arm bearings, new or rebuilt shocks, 'euro' style low bars or 's' bars -(the bike was designed to use low bars and they do help with overall control and enjoyment of the vehicle), wheel bearing service and good tires. That gives you the basic factory handling and hopefully proper tension on the bearings will provide what stability is available in stock trim.

    The 750 motor delivers some nice acceleration and the steering angle helps hold a true course on the smooth. I've built them light and tight and have really enjoyed the ride around town and on short country runs. These bikes are what you make of them... you can make a long wheel base bike using a box of /6 parts. You'll be stuck with the /5 battery box unless you can weld and the tail light wires will be too short... and it will be more comfortable. This combination is a hybrid because the wheel base of a /5 lengthened in this manner is longer by about an inch than a standard /6 due to the steering head angle of the /5 being kicked out a bit more.

    If your 73 /5 is actually a long wheel base 73-1/2 /5 then, it will have a drive shaft housing pictured above with the welded in spacer to lengthen it as its primary identifier. Curiously, attempting to take a 73-1/2 long wheel base /5 back to a short wheel base model requires the exact sub-frame from that bike. The rear fender will not fit if any other short sub-frame is used.
    John D'oh

  15. #15
    Registered User b25bsaboy's Avatar
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    Quote Originally Posted by 20774 View Post
    Snowbum has a few pros/cons on this page, Section VII:

    http://bmwmotorcycletech.info/mod4performance.htm

    Matt Parkhouse discusses changing a SWB to a LWB in the July 2004 Owners News.
    Morning Kurt,

    Thank you for the response and where can one find a copy of Matt Parkhouses article?
    Rick MacPherson
    Success is Not a Destination, But a Journey.
    Accredited Motorcycle Appraiser
    1968 BSA Starfire, 73 R75/5 SWB, 2008 Honda GL-1800 Lehman Trike

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