75 r75/6 transmission advice

Discussion in 'Airheads' started by dilandau, Sep 25, 2013.

  1. disston

    disston ShadeTreeExpert

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    The OP is not trying to rebuild the transmission himself. He is willing to take it to somebody. It's important at this point to suggest what most of us know by now that the local gear head is probably not a good choice for someone to have look at your Airhead transmission.

    "Ill probably bring it to an experienced local hand and pay for an opinion."

    It can be an expensive lesson to learn about these bikes.

    No mention of how many miles yet on this bike. The original rear oil seals are 37 years old. They almost always leak by the time the transmission bearings are going out or the clutch is worn out. But a figure on mileage or suspected mileage may be helpful.

    No word yet on how much oil is under the trans on the shelf. The trans is already out. Was the shelf area cleaned? This is sometimes used to determine if further investigation would be advisable.

    Part of the original post was mention of "noise" suspected to be transmission bearing and the PO has already pulled the transmission because of this. There was also a mention of "loosing power" This sounds more like a slipping clutch than any transmission problem.

    Send the transmission in the box or take it to Ted Porter. Is this trip doable for you? It looks like an hour away to me on the map but maybe it's two hours. If they know you are coming they can probably look at it and give you advice on what to do next that will fit the situation and condition of this box.

    If you take the transmission to Ted make sure you have all the pieces with you. He will attach the output flange when the rebuild is finished but if you forget to bring it it becomes difficult for you to have to do because it takes a special tool to take this part off or put it back on.

    They will be able to mail the completed trans back to you.
    #21
  2. supershaft

    supershaft because I can

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    There are at least a couple of other well qualified airhead tranny guys around the Bay area. I use to be one of them but I am not one of them right now. Then, of course, there are plenty others outside the Bay area. You just don't see their names all over the net.
    #22
  3. disston

    disston ShadeTreeExpert

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    I only have what I know or hear about to go on. I had forgotten that you were in the Bay Area SS. But I have no other contact info or Web Page or address to say where your garage is. Everybody is getting busy right now or getting ready to be busy. What, are you retiring SS?

    I know Ted porter personally and I know how to contact him. I also think he is a cut above even good.

    Suggest somebody closer to Oakland.
    #23
  4. supershaft

    supershaft because I can

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    I was always busy enough while trying to stay off the radar. I suspect that is the case with others I know in the Bay area. I would want to call up the couple of people I would recommend and ask them if it was alright to mention them on the idiotnet. I suspect it wouldn't be. There's an inmate here that I would recommend but he quit working on trannies. I can't say that I blame him. Hypoid stinks!!!! His good work has made a good name for a number of businesses in the Bay area. Good work is almost always not about where but who? Unless, of course, it's a one man operation. Personally? I am on sabbatical. I am shopping for a house and I could NEVER afford one in the Bay area and, if I could, I would never want to put myself in a corner like that. I have seen what it does to people and it usually isn't good.

    FWIW, I think the four speeds being more robust than five speeds is an idiotnet/urban myth. I don't think I know anyone that actually works on and has ridden both say so. That is people I trust. For starters, the five speeds shift MUCH better than four speeds and that is just the tip of one big iceberg.
    #24
  5. Plaka

    Plaka Brevis illi vita est

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    You did.

    Beats me, ask Matt, he did my last transmission. He's forgotten more about them than I'll ever know. I may also be mistaken and he was talking dogs or something. Tranny was popping out of 1st or second @about 110k miles. I'll ask him when I see him next. I have a crap 5 speed and rear drive that need attention. That garbage from Mike is really something. I'm tempted to crack the box just to have a peek, but I know how little mechanics like you bringing them them pre-monkeyed with stuff in boxes.

    Yes.

    Yes.

    Any idea if the pushrod tubes through the heads are the same OD as the pushrods in the jugs?
    #25
  6. supershaft

    supershaft because I can

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    They have two OD's. If I remember right, the smaller one is the same.
    #26
  7. disston

    disston ShadeTreeExpert

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    The bike is a 1975 /6 with a 5 speed transmission. I suggest you do not consider any 4 speed transmission swaps unless someone gives you one of these free. This is a waste of energy and band width to consider this. The OP is willing to learn how to remove a trans and wants working bike. Not your Hot Rod BS. The GD 4 speed fans will do this every time a Noob shows up needing a 5 speed.

    Do not buy a 1974 transmission. You will most likely regret it.

    An option is a used transmission from Ebay. Not always the best option for somebody new to this. Better would be a used transmission from a wrecker that gives you a guarantee so you ended up with a working bike sooner. Another transmission from a wrecker should be a little cheaper than a rebuild but maybe not by much. You would have to call around and check prices and availability.

    You mention a 60,000 mile figure for transmission life. This figure was used a number of years ago for the original transmission as a minimum. I think very few transmissions only lasted 60,000 but it may have happened. A rebuilt from one of the transmission experts should go more like 100,000 or close to it.

    You have the opportunity to do this right. You have said the money can be available to build a reliable bike. One of the areas that needs attention on Airheads is the transmission. I mentioned Ted Porter as somebody I know is close enough to you and he is a BMW Guru, much respected with years of experience building these bikes. He is an Airhead transmission expert.

    I forgot to put the link in the post I made mention of Ted so here is the link to his shop.

    http://www.beemershop.com/

    I strongly suggest that you do not try to have this work done by anybody that does not come with credentials for Airhead work.
    #27
  8. CaptainCrunch

    CaptainCrunch Been here awhile

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    FWIW, I remember reading the "60K-ish means time for a rebuild soon" thing as well. I think it was Snowbum's site or a link from it. It also said that using full synthetic gear lube delayed this significantly.

    He didn't pluck that number out of thin air.
    #28
  9. Plaka

    Plaka Brevis illi vita est

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    Can you find that on his site?

    (better you than me :D)
    #29
  10. disston

    disston ShadeTreeExpert

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    Snowbum edits his site so often that if it was there at one time it may not be there now. I do think he is the likely source of that figure tho. i think I have heard him write it years ago that way. It's not a bad figure for the lower limit of the OEM trans.

    It is often said by many reliable sources that a transmission correctly rebuilt and accurately shimmed will be better that the original
    #30
  11. dilandau

    dilandau Been here awhile

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    thanks for all of this guys. sorry I have not been quick with new information as its "mother in town extended weekend".

    as noted, I am in the bay area and there are a couple of people around these parts who know their way around an airhead. I also have a lead on a 79 5 speed for $300, and if that seems legit and not in terrible shape I might pick it up just because.

    but still going to bring this one in first to get a professional opinion. as soon as my mother leaves and i can make some phone calls.

    thanks for the links above and I'll post more info when it comes in. Odometer is broken on the bike- clocks in at 43k but estimated from the PO to be about 50k. of course no way to verify.
    #31
  12. disston

    disston ShadeTreeExpert

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    Turns out I have to change my tune.

    [​IMG]

    The one on top matches the one in the transmission I am rebuilding. The one on the bottom is the later model, I believe. All of my spare transmission parts except for the one seem to be the early 5 speed variety. i.e. 1974.

    Somebody else warned earlier that the 1975 trans should or may have early parts. I seem to have more early parts than later and I don't seem to have any late model forks. Don't seem to have any spare forks for that mater.

    I'll continue looking through my junk and see what I can learn. (wonder where all the shifting forks went?)
    #32
  13. 190e

    190e Long timer

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    I suspect some of the info on gearbox life and 4 vs 5 speed came from this on Duane Ausherman's web site. These comments are attributed to
    <!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:punctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <w:DontGrowAutofit/> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--> Rick weber. http://w6rec.com/duane/bmw/trans/index.htm



    <!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]-->
    <!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--><!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:punctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <w:DontGrowAutofit/> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]-->"The secret to long tranny life is using synthetic gear lube, Spectro is the one I've used and had the most experience with. Usually 50k to 75k seemed average life span for the bearings getting regular oil changes with petro based lubes. You can at least double that with synthetic. I had one customer who had used nothing but synthetic and wanted me to inspect his gearbox that had 135k miles on it, and never had been opened. I swear it looked like brand new inside, no gray sludge, no metal on the drain plug. The 4 speed gear boxes seem to go longer than the 5 speeds, so I'd think the 4 speed could have a longer interval"
    #33
  14. CaptainCrunch

    CaptainCrunch Been here awhile

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    That's exactly what I remember reading, though I couldn't find it.

    Thank you.
    #34
  15. dilandau

    dilandau Been here awhile

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    so did my due diligence on the clutch: looks like everything is in an acceptable range. so its all going back in:


    diaphragm plate looks clean. friction plate needs to be roughed up a bit but im just gonna put it all back in as is. which is a good thing because its like $600 in parts to replace it all.
    these numbers look alright?

    spring: .690"
    backing plate: .303"
    friction plate: .236"

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]

    and i got a 79 transmission that seems smooth and fine. I might just stick it in because I want to get riding. meanwhile Ill see how much it is to fix the old one.
    #35
  16. disston

    disston ShadeTreeExpert

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    Wash the clutch plate with Brake Cleaner. Lightly sand.

    Wash the pressure plates with simple green or brake cleaner. Sand the faces of both with 80 grit.
    #36
  17. dilandau

    dilandau Been here awhile

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    maiden voyage today- still some kinks to work out but shes back on the road- pulls nicely and feels fine. transmission is way smoother than my old r100- so i'm thinking i lucked out with that $300 used but "in good shape" purchase.

    a few little things to sort out- clutch lever perch is cracked- need a bungee for my side panels, i rather not have chincy chromed starter cover and airbox. but all and all- im pretty damn stoked!

    [​IMG]
    #37
  18. 685

    685 Scarred Adventurer

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    Now that the OP has reached a satisfactory conclusion, I'll continue the thread and introduce my trannie problem.

    Mine is a 76 R90/6, according to the engine number it was manufactured November 1975. I'm assuming, hoping in fact, that it's all the later 5 speed trannie components.

    Here's the picture. Won't stay in first gear under load, tho on the centerstand it works just fine. Jumps out of 1st under load at anything more than idle speed. All the other gears are smooth and stay in the selected gear.

    From what I've read, it's the 1st gear shift dogs. I haven't been inside the box yet, but found a 1976 complete lay shaft assembly (is that right?) the complete output shaft assembly. For about $100. Shaft, gears, bushings, etc. all still on the shaft as it was taken out of the trans and clean and unmolested.

    Side note, the p-o built out the engine from a 900 to about 1050 cc, it has Mikuni VM38's, and electronic ignition & 2 spark plug heads. He did a lot of work, before he abandoned the project. I basically got it for nothing--a bike for my brother to ride when he comes to Tucson and he's paying for the parts while I provide the labor. The transmission is the main thing wrong with the bike--as long as I don't try to start out on a hill, starting in second seems to be okay.

    I was hoping it was a matter of cracking the case open, pulling the old layshaft out (I have sources of heat, btw,) and putting the new one in, and buttoning it all up. From what I read on this forum, it sounds like rocket science--I've never done an airhead trans. but have done 4 & 5 speed automotive trannies. I can read a bunch and there seems to be a lot of specific info on the internet. I'm a newbie to airheads. Not a newbie to mechanicals, tho. I have a stable, well lit work space, a drill press and welder to fab. tools if needed, and stuff for taking accurate measurement. Air, airtools, and many, many mechanicking tools as well.


    Is it really that unforgiving and complicated?
    #38
  19. Plaka

    Plaka Brevis illi vita est

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    You need some special pulling tools to get it open. See the home made tools thread. Also various support and alignment plates.

    You need a depth mic. to set up the bearing preloads---that's the critical part.

    Sometimes the shift dogs can be salvaged. They were on my 4 speed with the same symptoms.

    If you want a tranny you can count on for a long, long time, have a seasoned pro work on it rather than taking it to a beginner just learning, and making their first mistakes, on your transmission. Let 'em learn on somebody elses. There are judgement calls to be made after looking inside. The pro can make them well. The newbie, unless very well supervised, cannot---indeed, won't even know what to look at or what they're seeing when they do.
    #39
  20. disston

    disston ShadeTreeExpert

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    There is a special tool to remove and replace the output flange. Make your own or buy from the several after market tool suppliers. I use tools from Cycle Works a bunch. I have the flange puller from them.

    [​IMG]

    http://www.cycleworks.net/index.php?main_page=page&id=3&chapter=1

    However this tool doesn't seem to be in the catalog anymore. maybe Dan has some or will make more? You could always ask. Maybe I don't know how the read the catalog?

    It does sound like the problem is the dogs on the Lay shaft. But you have to look. $100 for those two parts is a good enough deal that I think I'd get them now before they disappear anyway.

    Aside from being able to spot the several special problems that may be present and information is very scant about, the big deal is proper shimming of the trans. Some kind of holding fixture should be used to keep the shafts straight while measurements are made. There is a tool made for this also from Cycle Works.

    The clutch should be checked, couple more tools, some of these are found at the corner hardware store

    If there is wet oil on the shelf under the trans the the rear main engine oil seal and the cover O-ring from the oil pump should be replaced. Make sure you understand the issue about blocking the crank before removing the flywheel.

    That's enough to get you started I think. Do you have a Clymer's or Hayne's Manual?
    #40