A forum for owners of Yamaha TTR250 trail and enduro bikes!

Out of interest, did you put a repair kit in the master cylinder? It is unusual for the master cylinder to give trouble. Are you sure there are no air leaks on the joints?

Cheers

Brian

I tried a rubber band overnight on my kids quad when I couldn't get it to bleed, thought that maybe with air rising it would bleed out, didn't work at all, tried bleeding the usual way but there was so much air in the system I couldn't get it to compress enough to pump out the air. Ended up reverse bleeding from the caliper bleed nipple, used a 100ml syringe with a length of clear hose to see when the air had cleared the hose, worked brilliantly, you need to watch the Master cylinder for overflowing though. It looked to me like the air bubbles didn't have any problem rising through the brake fluid in the syringe so am confused as to how a normal bleed works, I have bled cars before and had bubbles come out, can anyone shed some light on what is happening.

Sorry but I can't find any pics of the real thing - only this from the manual which I have edited:

Looking at the seal in a new kit, there "ridged" section should face into the cylinder such that it will open against the reservoir wall and seal when under pressure.

Brian

That looks fine.

I have had a couple of front brakes that were a pain to bleed. Almost every refurb seems to have needed a new front brake hose hence I have done a few 

It really takes a lot of pumping to move the air in the top loop of hose. 

I tend to persuade/blackmail/bribe Trish to come and help as it can take a while to shift the air from the system.

To get a really solid brake after the basic bleeding, I leave the TTR overnight with the brake lever held in against the grip with a rubber band and that seems to allow the last few small air bubbles to escape the plunger.

Brian

My method of bleeding goes like this...

Before bleeding I take the caliper off and push the piston all the way in using a g-clamp (preferably one with plastic protectors). This is important because the piston can get an air-lock if it is pushed out as per when the brakes are bled (in other words-the piston will have pushed out a little once bled and the brake pads are seated).

 I fill the master cylinder with dot 4 brake fluid (der of course). I then proceed to bleed the brake line by using the brake line bolt as the brake nipple IYKWIM. I do this until fluid leaks from the brake line. It will not leak much, just enough to notice it. This serves to bleed the brake line.

I then proceed to install the caliper and bleed the brakes as usual from the brake nipple.

This almost always works for me but in some cases I have had to take it for a ride on a rough surface to bleed the front brake. Waiting overnight sometimes works as Brian says with the lever held in with a cable tie.

This was taken from the manual and good to keep in mind-

Jarrah

 

Anything to add on bleeding the rear brake line? Glad to hear I'm not the only one who has trouble getting all the bubbles out -- my current method, apparently, is (1) bleed incessantly, (2) wipe out, (3) bleed incessantly again, (4) wipe out, (5) bleed again ... 3 times now I've had to adjust the rear brake linkage mid-ride, each time it seems a horizontal dismount loosened up some bubbles or something and the rear brake got squishy. I was able to get most of the rear braking back by extending the travel on the brake lever so its not a complete brake failure and I don't think its the calipers. I keep thinking I've got a leak somewhere but can find no evidence of it. I disassembled the calipers and lubed, etc., a few weeks back when I first had the problem.

Perhaps I'm particularly unskilled at bleeding the rear line, like I'm always leaving a bubble in there and shifting 90 degrees lets it out? Or maybe when I drop the bike I'm losing something out the reservoir (suggesting a bad master cylinder, yuk)?

I could just stop dropping the bike, thought of that too.

How unfortunate. 

In all my years of riding motorcycles (passed my test in 1963) I have never heard of a broken sight window on a master cylinder. 

I have never seen a replacement window for sale but I have seen plenty of master cylinders, new and used. 

I would advise a search in breakers' yards or eBlag as your answer.

OR - take a look on YouTube HERE

Good luck.

Martyn

Yamaha WR 450/250,Yamaha Serrow, TTR600. Id be pretty confident any of those would fit...

Probably cheapest to get a used replacement from a breaker.

Brian

Hi Paul

That's a fairly common problem I am afraid. The original screws almost weld themselves in!

After a bit of searching around I sourced some Allen-headed stainless steel ones - see here

Because of the p&p they are probably only worth buying if you need some other parts to go with them in the parcel!

Brian

You need M4 bolts/screws 

You could try this guy on ebay (I see he also has a rare oil cooler on the bike he's breaking)

www.ebay.co.uk/itm/Yamaha-TTR-250-TT250R-Breaking-1993-Road-Legal-Random-Bolt/252766030299%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20131017132637%26meid%3Dc629515ba6484f2bac90c61e1e225095%26pid%3D100033%26rk%3D5%26rkt%3D8%26sd%3D232155974026

Several also on ebay from the States. I've found recent transactions for parts in the USA on ebay to be suprisingly pain free!

Afraid I don't know what other models might fit, sorry. WR?

My first attempt at a guide is here - http://ttr250.com/Front_master_cylinder_seals/TTR250-front_brake_master_cylinder_seal_replacement-how-to-guide.htm

As usual, comments, criticisms, spotting any omissions and suggestions for improvements appreciated!

Brian

How unfortunate. 

I think I've seen a thread that TTRfan did on the boards regarding this problem but a quick search hasn't come up with it.

Not to disappoint you I trolled Youtube and found this CLICKY repair quite similar on a YamWR250R which may be of use.

Good luck and please let us all know the results.

Martyn

Took a chance and bought an "18mm sight glass" from the universal shop.

(Just search ebay - there are thousands, all the same, just the prices vary!)

 

I was slightly skeptical of it working, but had to do something to stop the seepage.

 

 

Prised out the old plastic carefully without damaging the aluminium surround and cleaned it all up carefully, removing all the crud with a fairly sharp screwdriver.

I removed the inner ally baffle from the new sight glass (popped out easily, and I didn't want it)

Smeared the new o ring with flange sealant and pushed it in to the bottom of the seat, added more thin smears to the inner edge of the hole and the outer edge of the new glass. Popped it into the hole and tapped it in as far as it would go with a hammer and an appropriately sized socket.

Looks good. We'll see if it leaks later!

 

 

-- Edited by mossproof on Sunday 21st of June 2020 04:40:20 PM

-- Edited by mossproof on Sunday 21st of June 2020 04:42:05 PM

Slightly off the main topic of replacement but I may be headiong down that path 

The  sight glass window on a master cylinder was opaque so I tried polishing up the aged plastic with Solvol Autosol. It is now possible to see the level of fluid which I guess  is all that is needed but the plastic is crazed. I was surprised how thin and flexible the window is.

  

Hi melPV and welcome to the forum!

The GreyWulf forum and information pages were excellent. It is a shame if they are not going to continue 

With regard to your question, all of the internal components are readily available (either genuine Yamah parts or AllBalls kits) through Totally TTRs and Yamaha parts suppliers so I doubt anyone has tried to swap parts but I am happy for an owner to prove me wrong 

I am intrigued as to why you need a new cover. What has happened to yours?

Best regards

Brian