Author Topic: 78 TX 500 - No Rear Brakes  (Read 6486 times)

0 Members and 1 Guest are viewing this topic.

Offline JohnnyEgo

  • Jr. Member
  • **
  • Posts: 6
  • Karma: 0
78 TX 500 - No Rear Brakes
« on: April 08, 2014, 10:58:04 PM »
Hey everyone.  I just posted my intro to the intro page.  And now the thing that drove me to this forum, which was not my bike, because I have no brakes.  I have no rear brakes.  I found this out as I sailed through a stop sign at a four-way intersection while desperately standing on my rear brake and fully clenched on the front.

After crawling home using a combination of front brake, clutch, and Flintstone method, I noticed that I've got nearly full movement on the rear brake pedal before it engages with the master cylinder piston.  I may be using those part names wrong.  From the master cylinder perspective, it looks like I stepped on the brakes and never stepped off.  The rear brakes themselves are not locked, and the wheel moves freely.  If I press on the rear brake pedal hard enough, I even get a little engagement from the brakes, then they release when I let off.  I just have no brakes at all for most of my pedal travel, and then only very little for what remains.

I am not mechanically inclined, but I am capable of following directions pretty well, and I have a full set of tools.  I guess my primary questions are:

1. Do I need to remove the airbox to add or check brake fluid for the rear disk?
2. Are parts for the rear master cylinder and brake lines readily available?  Is there something more contemporary I can replace them with?
3. I am figuring either the master cylinder or hoses are 'bad', and I can bolt and unbolt things with the best of them.  But is there a better way to troubleshoot this, or a more common way of doing repairs?

I can take pictures of stuff if necessary.  I appreciate any advice or thoughts, and have no worries that you will insult my intelligence in regards to motorcycle maintenance.

Thanks!


Offline jimmer

  • Administrator
  • Hero Member
  • *****
  • Posts: 526
  • Karma: 2
    • Pisgah Forest, N.C. USA
Re: 78 TX 500 - No Rear Brakes
« Reply #1 on: April 09, 2014, 01:52:10 AM »
Check the pad condition and bleed the system asap! Get back to us if that doesn't find your problem.A shop manual is very handy..........................

Offline guylr

  • Administrator
  • Hero Member
  • *****
  • Posts: 1137
  • Karma: 19
    • ATL in the USA
Re: 78 TX 500 - No Rear Brakes
« Reply #2 on: April 09, 2014, 02:07:34 PM »
You should be able to get to the master cylinder cap without removing the airbox but it is tight on a '78 model. Jimmer is right, start with the pads and check them for excessive wear or oil contamination, flush the system with new fluid while you bleed it. It may require a master cylinder rebuild if it won't build pressure after that.

Question for you. Are your front brakes not working either? You said that you sailed trough a stop intersection!

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline CrouchyUK

  • Administrator
  • Hero Member
  • *****
  • Posts: 1026
  • Karma: 20
    • Brigg, Lincolnshire, UK
Re: 78 TX 500 - No Rear Brakes
« Reply #3 on: April 09, 2014, 02:43:01 PM »
Parts diagram gives a good idea of how it all should work.  Pedal should really be returned and position set by the spring and threaded bolt.  Worth checking this early on.

Does sound as though the hydraulics are shot though.  All fixable and parts readily available.

https://www.dropbox.com/s/vixaojr40bw5pvi/XS500E%20rear%20brake%20parts%20list.pdf
1975 Honda CB200T (2) - 1975 Yamaha XS500B (2) - 1976 Yamaha XS500C
1977 Yamaha RD400D - 1977 Yamaha XS500D - 1978 Honda CB550K - 1980 Honda CB400N
1980 Honda CB900FA - 2000 Kawasaki ZX6-RG2 - 2002 Suzuki GSX-R1000K2

Offline JohnnyEgo

  • Jr. Member
  • **
  • Posts: 6
  • Karma: 0
Re: 78 TX 500 - No Rear Brakes
« Reply #4 on: April 09, 2014, 06:55:57 PM »
I didn't realize I was coming up to a stop sign, and was probably travelling faster than I should have.  I was going about 45mph when I saw the sign.  I applied as much front brake pressure as I felt I could without locking up the front wheel, and pretty much stood on the rear brake pedal.  I probably should have downshifted a couple of times, but at the time, I was focused on the fact that I was on the brakes as hard as I could be and yet still cruising through an intersection.  Probably only at about 20 mph, but when you and everyone else are expecting you to stop for the pick-up trucks and fuel tankers traversing the intersection in front of you, it feels much faster. 

Front brake works fine.  I live out in the sticks, or whatever euphemism you good people who live outside the US have for a place that consists of wheat fields, fracking sites, main roads made of dirt, and my house have for the middle of nowhere.  I will head into town today or tomorrow for brake fluid.  Can't see how I could get at the cylinder easily without moving the airbox or getting brake fluid everywhere.  So that leads me to the following additional questions, and I appreciate your patience on these:

1.  Can I unbolt the master cylinder and pull it into a place more conducive to removing or adding fluid, then bolt it back to it's original location?
2.  There are a lot of large animal veterinarians and feed suppliers in town.  I was thinking of getting a giant horse syringe to suck out the brake fluid in the master cylinder without getting it on the paint.  Which then lead me to wonder if I could pull the brake fluid from the caliper to remove, and then push in to replace?

I'll get at the back caliper to look at the pads and take some pictures while I am out there.  Is there a convenient place to get the appropriate brake lines and fittings for our bikes?  I figure whether the lines are intact or not, if it is time to replace my knee, it is probably time to replace the lines.

Thanks!

Offline JohnnyEgo

  • Jr. Member
  • **
  • Posts: 6
  • Karma: 0
Re: 78 TX 500 - No Rear Brakes
« Reply #5 on: April 09, 2014, 08:36:10 PM »
Looks like brake fluid will be tomorrow afternoon at the moment.  In the meantime, a visual inspection of the hoses and fittings didn't identify any obvious leaks.  Also, I think I have the problem isolated to the master cylinder.  I took a bunch of pictures, given my lack of mechanical knowledge, so if anything jumps out at you, please feel free to point it out.


The brake lines have a little plastic ring around them that has 'DOT 8 - 77' embossed on them.  My guess is that they are original.  No obvious indication of fluid leakage at the caliper.


I don't know how the piston is normally supposed to look, but nothing stands out to me.  Piston moves a very little bit maximum break, then returns to position.  I had no difficulties sliding it back on the pads.  Just in case, here is a larger view:



Aside from the missing chunks, it appears I have plenty of brake pad material.  The pads were not locked up.

Good return on the brake pedal spring.  Nothing appears to be out of order there.  On to the master cylinder.


Before pressing the brake.


Pressing the brake pedal until the brake finally engages.


So I have this much free-play before the operating rod engages the cylinder piston (may have that terminology wrong).  Judging by the weathering on the operating rod, my guess is that the piston was originally much lower, and has not been able to return to it's normal position.  Master cylinder rebuild time?

Front brakes engage and release without any problems.  Pads are the same thickness as the back pads.






Offline boostfreak

  • Jr. Member
  • **
  • Posts: 22
  • Karma: 0
Re: 78 TX 500 - No Rear Brakes
« Reply #6 on: April 09, 2014, 08:45:16 PM »
Gorgeous bike. Wish mine looked like that.

I would also try bleeding it. Crack the bleeder screw on the caliper open with some plastic tubing attached so you don't make a mess, then push down on the lever. You should have fluid coming out. If not I'd be looking at rebuilding your master, which it sounds like you need anyway.

Offline guylr

  • Administrator
  • Hero Member
  • *****
  • Posts: 1137
  • Karma: 19
    • ATL in the USA
Re: 78 TX 500 - No Rear Brakes
« Reply #7 on: April 09, 2014, 09:44:21 PM »
Yes you cold unbolt the MC but shouldn't have to. The top cover on the MC has three bolts holding it on. You have to slip an 8mm open end wrench in to loosen them or a flat ratcheting box end. When the bolts are out the cover will slide off after you've given it a light tap to free it. Under that is a diaphragm to remove. Once that's out you should be able to fill the MC reservoir to the "Upper" line. You may need a small funnel with a hose attached to get in there but I'm pretty sure you will be able to.

Your caliper, hoses and pads look good visually.

The free play you indicate is a little more than I like but wait until you have the system bled to adjust it. The push rod is threaded at the bottom clevis fitting. There is a hole in the clevis that you use to help with the adjustment. See service manual.

On the front braking. Once you get the bike up a running well with good brakes front and rear, go to a big parking lot or back road and practice hard braking. 70% or more of your stopping power is in the front end and some times you absolutely do need to bring the front tire right up to locking and even lock it to get the bike stopped in the least distance. Practice it a lot, get confident in what the bike is capable of and it may save your life someday. Also if you decide to keep riding, sign up for an MSF training course. It's well worth the money and will help you learn the skills every biker needs. Sorry, not trying to be preachy, I just want to see you enjoy your bike.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline JohnnyEgo

  • Jr. Member
  • **
  • Posts: 6
  • Karma: 0
Re: 78 TX 500 - No Rear Brakes
« Reply #8 on: April 09, 2014, 10:10:23 PM »
I appreciate the sentiment with which the advise was given.  It's been 20 years since I've ridden this or any other bike, and I knew that as a 'returning rider' I was likely to be in the highest risk pool, so I took the MSSF(?) course when the bike came back to me.  It wouldn't hurt me to take it again, though.  In general, I've spent way more of my limited time to dedicate to the bike in doing maintenance over riding, so I probably only have it out for 20 or so hours in a given year.  I could definitely use more practice.  Now it starts reliably and runs reliably.  Once I get it to stop reliably, I'll have more time to build experience with it. 

In my prior outings, the brakes worked fine until the moment they didn't.  Doesn't appear that I have leaks anywhere.  I have ordered a master cylinder rebuild kit and some new hoses and banjo bolts from MikesSX, which I never would have found without this site, so I figure I'll rebuild/replace those parts anyways.  I guess my question is if it is a brake fluid thing and the fluid does not appear to have leaked, does brake fluid normally fail catastrophically, or does it fade in effectiveness over time?

I'll be replacing the fluid tomorrow because fluid is cheap and it will give me something to do until the new parts get here. Thanks everyone for your help!

Offline JohnnyEgo

  • Jr. Member
  • **
  • Posts: 6
  • Karma: 0
Re: 78 TX 500 - No Rear Brakes
« Reply #9 on: April 14, 2014, 08:17:23 PM »
Figure I owe you good folks an update:


The Japanese must have nimble little fingers.  I had to loosen my airbox and wedge it up to get to the back screw of the master cylinder.


Plenty of brake fluid in the reservoir, but I am pretty sure it is not supposed to be that shade.

Having never bled the brakes on a bike before, it was not a process I was looking forward to.  On my old Pontiac, I'd gravity bleed the front and rear while drinking a beer.  Wasn't sure that would work on this, so I went with the syringe bleed system.

I live in a town in the west where you cannot buy shoes for a human, but have four choices for a horse.  So getting veterinary syringes presented no challenge, and they were only $2 a piece.  A little 3/16" tubing and I was in business.


I ended up running two full syringes through the brakes to make sure I had pushed out a lot of the old crap.  This worked better than I had hoped.  No air bubbles and firm brakes. 


This is what my old brake fluid looked like, diluted no doubt with the clean fluid I pumped in behind it. 

Anyways, got her buttoned up, good pressure with both front and rear brakes adjusted.  She kicked right over despite not being started for a month, and idled well enough.  I got about thirty yards from my driveway when the back tire blew out. 

Now I have a new back tire, which is really a front tire mounted backwards, as that was the only thing available in a 100 mile radius of my house.  But the important thing is that the bike is back up and running and stopping, and I appreciate everyone's help.

Offline wilberforce

  • Full Member
  • ***
  • Posts: 84
  • Karma: 1
    • Tyneside, UK.
Re: 78 TX 500 - No Rear Brakes
« Reply #10 on: April 23, 2014, 11:34:24 PM »
I've just posted on the other recent thread about back brakes.  Never saw this one until after I hit the submit button :-[.

Homer Simpson moment - Dooohhhh
One of the Boys from the Wall.
XS500E - 1978 vintage
Aprillia Shiver 750 - 3,600 miles.
Moto Guzzi Breva V750ie - 2005 vintage - sold.

Offline wilberforce

  • Full Member
  • ***
  • Posts: 84
  • Karma: 1
    • Tyneside, UK.
Re: 78 TX 500 - No Rear Brakes
« Reply #11 on: May 12, 2014, 05:49:23 PM »
 Further to my oops moment.  I've managed to get the master cylinder off the bike but am unable to get it apart due to corrosion.  Therefore I need to find another but can't find one for the XS500.

Anyone any ideas if one from a different model will fit.
One of the Boys from the Wall.
XS500E - 1978 vintage
Aprillia Shiver 750 - 3,600 miles.
Moto Guzzi Breva V750ie - 2005 vintage - sold.

Offline jimmer

  • Administrator
  • Hero Member
  • *****
  • Posts: 526
  • Karma: 2
    • Pisgah Forest, N.C. USA
Re: 78 TX 500 - No Rear Brakes
« Reply #12 on: May 12, 2014, 11:53:45 PM »
I pm'd you a couple weeks back that I have 2 of them.

Offline wilberforce

  • Full Member
  • ***
  • Posts: 84
  • Karma: 1
    • Tyneside, UK.
Re: 78 TX 500 - No Rear Brakes
« Reply #13 on: May 13, 2014, 10:29:27 AM »
I pm'd you a couple weeks back that I have 2 of them.

Did you?  Nothing in my messages in box.
One of the Boys from the Wall.
XS500E - 1978 vintage
Aprillia Shiver 750 - 3,600 miles.
Moto Guzzi Breva V750ie - 2005 vintage - sold.

Offline jimmer

  • Administrator
  • Hero Member
  • *****
  • Posts: 526
  • Karma: 2
    • Pisgah Forest, N.C. USA
Re: 78 TX 500 - No Rear Brakes
« Reply #14 on: May 16, 2014, 01:16:11 PM »
Well if you want one for $25 plus shipping,let me know. Jim