New problems

[davidpdx]

     I rode over to the BMW rally in John Day Oregon last weekend and had a great time. It was about 800 miles at 65-75mph and my bike came up with a couple of new things for me to work on. I changed all the fluids before I left and the final drive is leaking fluid onto the rear wheel. I just drained it and I lost about 1 oz. If it will not get on my brake shoes and I can just keep it topped up until winter I will ride it this summer and fix it later.
      The other problem is a strange one to me. Sometimes when I turn the key on but before I hit the started I will get a little backfire. It is just a real small pop so I was ignoring it until this trip when we stopped for lunch and started out again it popped my carburetor off. It is a 1984 and my friend thought it might be the electronic ignition firing before it should. Any thoughts? The pipe coming out of the air box pulled out as well, can anyone tell me what should hold it in? I was able to get the carb back in place with a couple of ty-raps and rode it home OK but need to get this one fixed before I do any more long rides. I just got the Clymer book so feel better ready to tackle jobs now. Thanks for your help, David  

[Bob_Roller]

The oil leak from the final drive most likely is the o-rings that seal the brake camshaft, a common failure .

Your popping when you turn the key on, is 'normal', when you turn the key on, the ignition system fires, kind of a quirk with our bikes, if a valve is open and enough fuel is present, a pop or a 'wheeze' is quite normal .

It sounds like you possibly have too much fuel, as in a float needle valve not shutting off completely due to debris in the seal area, or possibly the float isn't adjusted properly or has absorbed fuel and isn't floating like it should, or possibly the hose clamps on the intake tubes were a bit on the loose side to begin with .

[davidpdx]

I pulled the back wheel off yesterday and sure enough the back brakes area is full of oil. On the up side they are near the condemn limit so replacing them is not a waste. I pulled the shaft for the rear brake cam but can't figure out how oil could get in from there as it looks like a straight tube through the finial drive. I have the O-rings on order so will replace them and clean everything up in hopes that will solve the problem.

[Bob_Roller]

When you get the replacement o-rings, only two will work, there may be 4 or 5 grooves in the brake camshaft, only two that are deep, will accept o-rings, don't know why there are extra grooves, but they are .

[montmil]

... I pulled the shaft for the rear brake cam but can't figure out how oil could get in from there as it looks like a straight tube through the finial drive...

Earlier BMW final drives had a straight through bore for the brake cam shaft. Routine maintenance chores included pulling the shaft and greasing it. Later models and final drives, like your '81, have an opening into the gear oil reservoir for a little "splash lube".

Unless a PO has modified the cam bore with a piece of tubing, or replaced the final drive with an older unit, you should be able to spot the opening. There's also a felt washer that's supposed to go between the final drive housing and the rear brake arm.

The oil leak could also be due to a worn out oil seal behind the cardan cover.

[donbmw]

My final drive on my 75 R90 would leak on the brakes every now and then. What I found is the pivot bolt would come loose and let oil seep around it. I would tighten and use Locktite on it every time. I have had this bike since 85 and every time the rear will is off this is something I check.

[davidpdx]

Well I replaced the O-rings and the oil seal and I have ridden about 300 miles at freeway speeds and so far no leaks. When I changed the finial drive oil for the first time it was kind of sparkly. I wonder what experiences anyone has had with swapping out final drives? I have seen a few on e-bay for as little as $70 and have seen rebuild prices anywhere from $400 up to a grand. Thanks for your help, happy to be able to ride the rest of this season without wet rear brakes.  

[montmil]

Caveat emptor, y'all. I'd be very leery of a final drive offered for $70 . Gaskets and O-rings would be the least of my concerns. And the word "rebuilt" means different things to different folks... In the hot rod world, that can be taken as meaning a rattle can job on the block and shiny new valve covers.

Reputable and vetted vendors -or have your own unit overhauled- are the best way to be sure.

Sparkly oil is likely nothing more than aluminum 'dust'. Oft times seen in engine oil, too. A magnet can detect steel trash in the oil which are often bigger bits. You should be good to go.