Mono shock rear drive large seal leaking

[enigmaT120]

Do your EBC pads squeal? My front ones do sometimes.

[beemered]

Wobbly,
1.No play-15000 miles since new,but one of my R80s had this issue and leak.Probably just old age -30 years.
2.Used BMW gear oil non syn since new,have a case.
3.Got the BMW part from a MB/BMW car dealer -$30 ,the real deal.Have compound similar to P80.
4.Not leaking there,YET !
5.My brother got me some trichlorethane or some such years ago to degrease a frame.Used it with bare hands and in minutes it felt like I had elephants standing on my fingernails.Switched to gloves and they expanded to twice their size,looked like clown gloves.
6.Cant find EBC brakes to fit early 88s with 25mm wide shoes.Definitely not $21 either way.
7.Haha,Yea,I've been playing these games for decades !

[barryh]

Some thoughts...
• Are you using synthetic oil ? Often times synthetics will leak when excellent, name brand mineral oils will not. Modern oils are so doped up with additives that no one on the planet can say where the dividing line between mineral and synthetic is anyway. I suspect you may be paying double simply to gain an oil leak ! Try some Valvoline 75/140 non-synthetic.

I use synthetic oils throughout the bike and have no leaks and that's with every seal original from 1979. Other than high detergent content that might clean sludge from behind a seal I don't think modern synthetics cause good seals to leak.

I very much doubt if Valvoline or anyone else makes a non synthetic 75/140. If they did it would be so chock full of viscosity index improver it would be a very poor choice. You need the inherent high viscosity index of a synthetic base stock to make an oil of that wide a viscosity range.

[Roy Gavin]

There are two types of mono FD, one has a needle roller bearing in the drive side and should have around 2 thou end float, the other has a taper roller bearing and should have 2 thou preload.
Mine has the needle roller and has had shake at the rim for the last 150,000 km, it doesnt leak and shake hasn't changed much in that time.
Mobil M1 gear oil-------------.
I have a spare which I bought as "just professionally rebuilt " - it is also a needle roller type but had been built with around 5 thou preload, could only just be turned by hand, the big bearing stayed with the crown wheel when I removed the cover - it should have been fitted with Loktite 242, and the wipe pattern was wrong .Seal was banged right in touching the crown wheel too.
It is now fixed and waiting to go on, but in the way of these thing the original will probably see me out!

[Wobbly]

I use synthetic oils throughout the bike and have no leaks and that's with every seal original from 1979.

Apologies, but this statement is so broad as to be meaningless. Exactly which brand and nomenclature of oil are you using? The differences brand-to-brand, and even within a single product line, are huge. I get the feeling "synthetic oil" is the new marketing buzz word to simply charge customers a higher price. In the US, there is no legal or label differentiation between highly doped mineral oils and lubricants completely conceived in the laboratory. Even the term "full synthetic" is meaningless here.

I see you reside in the UK and there are brands, types, weights, and specifications we cannot get here. I really think we are talking apples and oranges.

Other than high detergent content that might clean sludge from behind a seal I don't think modern synthetics cause good seals to leak.

My brother bought a '99 BMW R1100S (12K miles) and the PO was proud that he had just paid big money to convert all the oils to "Mobil-1 synthetic". Whatever was in the final drive got all over the rear wheel and FD housing in the first 500 miles. The FD was not over-filled. This was not a drip-drip-drip leak, but an extreme seepage. Before replacing the $42 seal, I suggested we simply change over to Valvoline "synthetic" 85/140 which was on-hand. That's all it took to reduce the issue to a manageable "sweat". That proved to me there was a huge difference between brands.

I also have a 1979 and I'm enjoying a relatively leak-free bike. It's my brother's Oilhead that spends all the time on the lift...

I very much doubt if Valvoline or anyone else makes a non synthetic 75/140.

If they did it would be so chock full of viscosity index improver it would be a very poor choice. You need the inherent high viscosity index of a synthetic base stock to make an oil of that wide a viscosity range.

My point exactly ! Modern oils are so doped-up that it's hardly worth the extra expense of the marketing label "synthetic", or even "full synthetic"... at least here in the USA.

All the best.