Just Purchased - 1979 R100T /7 with intermittent brakes and other strange issues...

[jchivell]

Hey Forum,

This is my first bmw bike and I'm really excited to start riding it and being a part of the forum! I just bought it over the weekend and rode it around town for the first time - there are some things that dont think are correct and wanted to get some ideas on where to start. The first issue that I want to tackle is the front brake:

Again, 1979 R100T /7

The front brake seems to be randomly and temporarily losing pressure. When the lever is pulled, sometimes it can be pulled all the way in without working. If I pump it once or twice it starts working again. Also seems to lose pressure if I hold it down a long time (ie, at stoplight on a hill).

So, being totally unfamiliar with these bikes (but eager to learn), where should I start? Should I try to bleed the brakes a bit? Is there a way to test the master cylinder? Something specific I should try?

Clymer manual is in the mail, so I thought I would start here while waiting for it to arrive. Please let me know what you think! Once I get this taken care of I'll start looking at the strange oil leak that I have going on.

Jordan

 

[lkchris]

It sounds like you've already (essentially) tested the master cylinder and it's failing.

The only other way to lose pressure is at the caliper and this would be a (probably) visible leak.

It's not surprising that 38-year old systems may be ready for some new seals.

The master cylinder is under the fuel tank, and all it can cost is some brake fluid to bleed the system.

Somewhere on this website there's the ability to locate your nearest BMW club--good idea to get in touch and perhaps find someone with experience with these bikes.

Just to be pedantic ... your bike is either an R100/7 or an R100T. /7 and T are not used together. If it's a '79, it's an R100T ... http://www.omnilex.com/public/bmw78/m1.jpg

 

[20774]

Jordan, welcome to the forum! And congratulations on the purchase. Should be a fun time for you!!

More than likely, given an unknown history, you should definitely bleed the brakes. I would also recommend replacing the front brake line...just the since disk, right? People will recommend aftermarket stainless lines and they could be an improvement, but I've always been satisfied with the OEM rubber line. What's going to happen over time is that the rubber will breakdown internally and could balloon out (might not see it) to the point where you loose the hydraulic pressure to the caliper. So, replace the line before you begin to bleed.

Not sure but I'm guessing the master cylinder is under the tank...I know it is for stock '78 R100/7s. The bleed valve is down at the caliper. So, it's going to be a stretch to reach the valve while pumping/holding the brake lever...it can be done, though. With tank off, top off the reservoir with new fluid. Begin pumping, then hold, release the bleed valve. Close the valve and repeat the pumping. You should probably put a small piece of wood on the handlebar to prevent the brake lever from coming all the way to the bar during the bleed process. It may have happened already, but if the master cylinder is actuated to its extremes, the internal o-rings could be dragged across pitted or rusty spots in the bore of the master cylinder, thus tearing the o-rings...the result is that you can't hold the lever to a constant pressure as the fluid works its way around the tattered o-ring. If you replace the brake line, perform and good brake bleed, and you still can't hold pressure, likely a caliper rebuild is in your future.

Let us know how things go. And upload a picture when you get a chance!

 

[brittrunyon]

Welcome Jordan.
All the above is sound advice at this point in your Airhead Adventure.
Happy Wrenching.

BR

 

[69zeff65]

Brakes are something to not skimp on

Pull the gas tank and give the entire front brake system a good thorough inspection.
Check the brake fluid to see if its mostly clear, free of dirt and other little tidbits.
Check your wire connections for the brake level sensor and brake light, make sure they are clean and snug.
Inspect the rubber brake line for obvious damage or a sign that its the original one from day one.
Check the brake cable for wear, binding and any obvious damage.
Get down on the front brake caliper(s) and check for leaks, rust and worn out pads.

The usual culprit when the brake action is spongy or looses pressure is the master cylinder. I have been very fortunate to have never had to try and rebuild one, I hear it is a hit or miss proposition on success. A new master cylinder for either dual or single disc brakes can set you back a bit if you have to buy one. There is someone out there who makes and installs a stainless steel sleeve in them so that it can be a good rebuild, maybe someone in the forum has some additional info on the guy who does that. If you find a rusty lump of a master cylinder, low and dirty brake fluid you can pretty much count on doing something with the master cylinder.

If the rubber brake line(s) look old or are cracked and damaged just replace it (them). I prefer Spiegler stainless but OEM rubber are just about as good but may cost more depending on where you get them.

When you look at the calipers don't be freaked out about the funny way the pads wear, its abnormally normal if that's possible. Just look for metal on metal, fluid leaks and bad wear on the brake disc(s) if you don't find any of that chances are its all good down there.

My advise is to reach out to the nearby airhead BMW club and reach out to them, they are always willing to help.

 

[ccolwell]

As brakes are important to me, I would rebuild the entire system -- master cylinder, calipers, brake lines. I would start by pulling apart the MC and examining the bore. It's likely fine but if there is any scoring I would replace it. If not, rebuilding it, either replacing just the seals or the piston and seals, is not very hard. It does take patience, particularly on the first go around. Rebuilding the calipers is a bit more work as getting the pistons out and back in can be tricky. You'll need an air pump and hose to get them out -- read any instructions and watch any videos you can. The danger here is firing the piston out of the caliper into valuable metal or more valuable flesh. The right size block of wood is your friend. Once out it's just a matter of inspecting the piston/bore for wear and replacing the seals. Do not buy new pistons until you examine the old ones as they are pricey. Getting the pistons back in is much easier if you use red rubber grease. Get as little as possible as you don't need much and may never use it again. I got the tin from the link below to do my R90S and still have 95% left.

And the big warning is that DOT 3/4 brake fluid will strip the paint off anything it touches very, very quickly.

One other thought -- my R90S did much the same thing. It turned out the PO had used DOT 5 brake fluid. If your brake fluid is purple you definitely need to rebuild the whole system.

http://www.ebay.com/itm/18g-Castrol...063708?hash=item4d45795e5c:g:EboAAOSwhwdVUZwY

 

[jchivell]

Thanks everyone!

Brakes are definitely not something I want to leave to chance or overlook, so I thought I would start here for safety. I will take a look at the master cylinder today/tomorrow and start there to look for noticeable issues.

 

[Na Cl K9]

ATE brake service is all about technique and perseverance

The biggest problem seems to be getting all the air out of the master cylinder but, there are ways... I agree that you may just as well replace the main rubber brake hose from the Master Cylinder to the metal Caliper pipe. No telling what your system had installed fluid wise. Dot 5 will cause the rubber to deteriorate and isn't going to save the metal parts from water incursion. I have had 4 ATE Master Cylinders sleeved in Stainless Steel by a fellow named Mark Frappier in Agawam Main. He does excellent work and will require you to send parts from the M/C rebuild kit so he can fit the bore to the piston precisely. As indicated, the caliper seals might not be leaking but the piston could be rust pitted so to know for sure will require air pressure to push the piston out of its bore - a harrowing experience for those attempting it for the first time as it makes a loud pop and without a "backstop" against the caliper pad holder casting can cause damage on it's violent exit. The tool kit might still have a set of feeler gauges that also has a strange looking two prong fork looking thing attached which is used to adjust the piston travel when everything is back together. Its important to keep the piston from over-travel in the bore using this gauge. Also, when you bleed the M/C, be sure to put a rag over the open top of the reservoir since if the piston is doing its job properly there will be a small squirt of fluid that jets out of the tank while you cycle the brake lever and as noted, dot 4/5 will do nasty things to the painted parts it lands on. The rag will prevent the jet of fluid from leaving the tank. Equally important is the final adjustment of the caliper and pads to the brake rotor to achieve solid contact. Making the bike run is half the fun, the other half is making it stop. When I work on these bikes, I always make sure they will stop first - I don't like surprises.

 

[69zeff65]

PS Strange oil leak

That may be brake fluid leaking down the side of the front engine cover. If its up near the front of the engine and seems to be coming from the top of the motor/bottom of the gas tank I would suggest disconnecting the battery and removing the gas tank right away in order to mitigate any damage from leaking brake fluid. Even if its old and nasty brake fluid it will eat the paint off the bottom of the tank/frame, damage wiring and really screw up wire connections so don't put off pulling the gas tank to long.

 

[20774]

As I recall, DOT 3/4 are sold more or less as the same thing...nothing wrong with DOT4...I forget the difference in specs but it might have a higher boiling point. DOT5 is definitely a no-no, but DOT5.1 is OK...again, I think it's a racer-thing, having a makeup that is suitable for racing. But DOT3/4 is perfectly fine.

 

[ccolwell]

As I recall, DOT 3/4 are sold more or less as the same thing...nothing wrong with DOT4...I forget the difference in specs but it might have a higher boiling point. DOT5 is definitely a no-no, but DOT5.1 is OK...again, I think it's a racer-thing, having a makeup that is suitable for racing. But DOT3/4 is perfectly fine.

Yup, boiling point increases as the number does (3-4-5.1). Any of those will do including a decent brand from the local auto store.

 

[jchivell]

Pulled off the tank today. A few observations... the PO already installed stainless brake lines, so thats good. No signs of leaking near the brakes or along the lines. Brake pads seem worn but still have plenty of life and look good.

On the MC, looks like there has been a very slow leak over time, that has probably stopped. Looks gunked up on the outside, but no signs of fresh fluid. Electrical connections looks corroded but still making contact - probably need to be cleaned. With the cap open, fluid is moving when the cylinder is actuated so thats good. Looks like there is a good bit of gunk/fine debris in the reservoir.

I think I will drain/flush the brakes, refill with new fluids, bleed, and see how they act then!

 

[20774]

Sounds like a plan!

 

[jchivell]

Oil Leaks

Also, the strange oil leak is coming from the Oil Pressure Switch. After doing some reading, this seems to be fairly common. And almost expected. Bought a new one for $20 and will pop it in next week.

There is also oil dripping (just after running, and only a few drops) from both gasket sections on both cylinder heads. Not sure how big of a job that is, but I guess I'm going to find out! Oil change, cylinder head gaskets, and oil pressure switch all planned for the next step once the breaks work! Then if I'm lucky, I'll be able to figure out why the right rocker makes a different noise than the left one...

 

[Na Cl K9]

Master Cylinder service...

There is an O' ring that fits under the master cylinder reservoir. Remove the large steel hex socket fastener seen in the bottom of the tank while your system is empty. This permits the tank to be removed from the M/C body. The O'ring is between the tank and the machined tank mounting boss. These rings become flat after 30 years or so (!) and weep/seep/leak. The O' ring is not a part of the M/C rebuild kit as a rule and must be ordered separately for around $5.00. Don't ignore the opportunity to make this repair.
On the subject of 'cylinder head leaks', it is possible you are looking at a Valve Cover gasket leak. Just a thought. Its an inexpensive thought at that.

 

[jchivell]

There is an O' ring that fits under the master cylinder reservoir. Remove the large steel hex socket fastener seen in the bottom of the tank while your system is empty. This permits the tank to be removed from the M/C body. The O'ring is between the tank and the machined tank mounting boss. These rings become flat after 30 years or so (!) and weep/seep/leak. The O' ring is not a part of the M/C rebuild kit as a rule and must be ordered separately for around $5.00. Don't ignore the opportunity to make this repair.
On the subject of 'cylinder head leaks', it is possible you are looking at a Valve Cover gasket leak. Just a thought. Its an inexpensive thought at that.

Ugh, of course its not included. I got my MC kit from Capital Cycle and its already on the way. Called Capital Cycle up to ask about the O-Ring and they sent me one without charging shipping. Super nice guys so wanted to give them a plug! So I'll be swapping out that o-ring also!

I drained the brake system and tons of gunk/particles came out. Some looked like a copper color? Anyways, refilling and bleeding didnt make an impact so I'll rebuild the MC and see where things stand at that point.

And it is possible that I'm talking about the valve cover. Probably not using the right words here. But there is some oil leaking from both sections (valve cover and cylinder head?), and on both sides. Replacing the gaskets cant be too hard, but there might be some other maintenance that I want to tie into that job. The left side is making a noticeably different (ticking) noise than the right, so I want to do some reading and try to figure out what it could be before I go in there. The PO said he either replaced the rocker or pushrod recently, so that might have an impact.

 

[ccolwell]

And it is possible that I'm talking about the valve cover. Probably not using the right words here. But there is some oil leaking from both sections (valve cover and cylinder head?), and on both sides. Replacing the gaskets cant be too hard, but there might be some other maintenance that I want to tie into that job. The left side is making a noticeably different (ticking) noise than the right, so I want to do some reading and try to figure out what it could be before I go in there. The PO said he either replaced the rocker or pushrod recently, so that might have an impact.

Sounds like the valves need adjusting and you can put new valve cover gaskets in while you're there. Some ticking is normal. And what appears to be leaking from the head gasket may just be oil from the valve cover migrating to the head cylinder junction. I'd do the valves and re-torque the heads and see what that does.