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Old 06-22-2019, 11:50 AM   #1
mplecha
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Default 4 speed leak.. again

I have a 78 FLH. I recently bought a new mainshaft and had the MDG bushing fit to it. I put the transmission together, and all was well for about a week. Now, I have a puddle under the bike again. Before I pull the transmission out, I'd like to know if there is a way to remove the output shaft seal with taking the whole thing apart again. I've never been able to get that little seal out without removing the main drive gear. I'd rather not do all that again if I can avoid it.
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Old 06-22-2019, 12:35 PM   #2
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Default Re: 4 speed leak.. again

You need to figure out which of three likely spots it's leaking from:

1) clutch pushrod where it exits mainshaft - fix is to make sure carrier bush in mainshaft is not worn out, then use a good seal (often there's room to put two seals here) where the pushrod exits, and make sure the pushrod is polished up with no grooves or gouges

2) mainshaft where it exits main drive gear - fix is make sure MDG bushing is fit closely enough to shaft, shaft is polished with no gouges/grooves, good seal is used. Bonus points for a MDG spacer that is machined for an o-ring.

3) main drive gear spacer to seal - fix is to use a good double-lipped seal, make sure the spacer is smooth, makes sure seal is square in the case (co-axial with MDG), sprocket is installed tight enough and locked down to prevent axial movement of MDG and spacer. When it gets loose and moves inward and outward, it acts as a hydraulic pump causing a leak.

Have fun.

Jason
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Old 06-22-2019, 01:52 PM   #3
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Default Re: 4 speed leak.. again

Quote:
Originally Posted by JasonMcElroy View Post
You need to figure out which of three likely spots it's leaking from:

1) clutch pushrod where it exits mainshaft - fix is to make sure carrier bush in mainshaft is not worn out, then use a good seal (often there's room to put two seals here) where the pushrod exits, and make sure the pushrod is polished up with no grooves or gouges

2) mainshaft where it exits main drive gear - fix is make sure MDG bushing is fit closely enough to shaft, shaft is polished with no gouges/grooves, good seal is used. Bonus points for a MDG spacer that is machined for an o-ring.

3) main drive gear spacer to seal - fix is to use a good double-lipped seal, make sure the spacer is smooth, makes sure seal is square in the case (co-axial with MDG), sprocket is installed tight enough and locked down to prevent axial movement of MDG and spacer. When it gets loose and moves inward and outward, it acts as a hydraulic pump causing a leak.

Have fun.

Jason
To add to Jason's excellent advice;

I've had really good success with using O rings as "extra" protection, I like you changed every seal as suggested by Jason and still had a weep. I added O rings which were a real tight fight and I never had a single drop come out of it after. Trick is getting one or two in there to aid with the seals. Not saying it's going to work every time but if there's a little wear it eliminates any possibility of a weep!
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Old 06-23-2019, 01:16 AM   #4
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Default Re: 4 speed leak.. again

having difficulty picturing where the 'O' rings are to be placed on MDG spacer, internally against shaft or externally up against oil seal?
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Old 06-23-2019, 04:21 AM   #5
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Default Re: 4 speed leak.. again

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Originally Posted by Thunderbird View Post
having difficulty picturing where the 'O' rings are to be placed on MDG spacer, internally against shaft or externally up against oil seal?
Internally! Sorry should have clarified. I used 2 which needed a little grease and effort to get on but it worked a treat.
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Old 06-23-2019, 11:56 AM   #6
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Default Re: 4 speed leak.. again

There are pics of the o-ring modified MDG spacer here: http://www.caimag.com/forum/showthre...ain-drive-gear

Jason
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Old 06-24-2019, 12:18 AM   #7
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Default Re: 4 speed leak.. again

How tight is your primary setup?
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Old 06-24-2019, 08:42 AM   #8
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Default Re: 4 speed leak.. again

How tight should it be? I've run two on this bike. there's a BDL 1.5" belt on it, now. It's tight. Maybe an inch of travel in the belt. I've been using the inner primary to set the transmission in place according to BDL's instructions. I had a 2" belt on it before that with the same technique had a hell of a lot of slop.
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Old 06-24-2019, 08:46 AM   #9
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Default Re: 4 speed leak.. again

I put a new mainshaft and MDG bushing in this thing 2 weeks ago. I'm going to assume it's one of the two seals. If it is the seal on the MDG, can I get it out without disassembling the whole transmission?
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Old 06-24-2019, 09:57 AM   #10
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Default Re: 4 speed leak.. again

Quote:
Originally Posted by mplecha View Post
How tight should it be? I've run two on this bike. there's a BDL 1.5" belt on it, now. It's tight. Maybe an inch of travel in the belt. I've been using the inner primary to set the transmission in place according to BDL's instructions. I had a 2" belt on it before that with the same technique had a hell of a lot of slop.
Sounds pretty good, I can almost pull my belt off the pulleys cold.
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Old 06-24-2019, 05:59 PM   #11
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Default Re: 4 speed leak.. again

Sounds like its not to tight...

Ive seen fresh transmissions get leaky quick if the is belt to tight.

Personal preference for me is to be able to twist the belt at least 90*. Chains I like 5/8-3-4” on the coast side. Like I said, this is just me... with that and 5 bucks, you can get a decent 20oz beer most places.
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Old 06-25-2019, 05:45 PM   #12
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Make sure that the notch in the spacer isnt touching the lip on the seal. Adding some RTV between the spacer and 4th gear groves helps stop weeping there too.
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Old 06-25-2019, 06:14 PM   #13
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Default Re: 4 speed leak.. again

What i did on mine was faced the back of the MDG spacer, new MDG bush honed to size, and placed an O-ring in the existing groove on the MDG. I have previously machined a groove in the spacer for a seal but still had leak problems due to the O-ring picking up on install.


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Old 06-26-2019, 02:52 AM   #14
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Default Re: 4 speed leak.. again

all good tips. hey NZT100, what size and section O ring did you use?
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Old 06-26-2019, 04:49 PM   #15
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Default Re: 4 speed leak.. again

Quote:
Originally Posted by Thunderbird View Post
all good tips. hey NZT100, what size and section O ring did you use?
TBH i cant remember, i took the gear to the seal shop and had the tech match one for me. Sorry i cant be more help there.
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Old 06-26-2019, 05:50 PM   #16
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Default Re: 4 speed leak.. again

There's some good o-ring design notes here:

https://www.marcorubber.com/o-ring-g...iderations.htm

From that page . . .

Compression of o-ring in static use (which is the case for MDG and MDG spacer as they move as one) is 18% - 25%.

Stretch is 0% - 5%.

Fill percent generally 75% filled by o-ring with 25% void.

So, you can design your groove (known as gland, apparently) to a known o-ring you have or can calculate need o-ring diameter and cross-section for an existing groove.

Some more good design notes here: https://www.applerubber.com/src/pdf/...sign-guide.pdf

I've always used "squish it but don't mash the shit out of it" in modifying parts for o-rings, but now I've seen some actual engineering info . . .

Have fun.

Jason
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Old 06-26-2019, 07:37 PM   #17
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Default Re: 4 speed leak.. again

Word forms: (regular plural) glands. (Mechanical engineering: Fluid engineering) A gland is a device that stops a fluid leaking along a rotating shaft or reciprocating rod passing through a boundary between areas of high and low pressure.

Gland definition and meaning | Collins English Dictionary

... Learn something new every day or, um, decade in my case.
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Old 06-27-2019, 03:44 AM   #18
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Default Re: 4 speed leak.. again

thanks for that Jason, it took me two goes to get correct O ring size for S&S carb' to manifold and that's with machined part that is just a butt fitment. Machining the spacer and having correct tolerance with MDG for O ring ID is enough to give my own gland a nervous twitch.
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Old 06-27-2019, 02:21 PM   #19
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Looks like my leak is coming from the large seal. Could the cork have failed? I drove the seal and spacer in with the Jims tool.

Last edited by mplecha; 06-27-2019 at 03:43 PM.
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Old 06-28-2019, 03:24 AM   #20
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Default Re: 4 speed leak.. again

I understood all that was available now is the upgraded double lip large MDG seal and usually cork seal is replaced at the same time. If not mentioned before, that when the MDG seal is replaced also replace the MDG spacer as it gets grooves worn in.
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