struggling with 81 750 seca front brakes

I solved the carb problem with my 750 seca build and now comes the front brakes.
Last fall I rebuilt all the components of the seca's braking system with Chacal's parts.
All the "0' rings seals etc. were replaced ; anti dive, calipers, new SS hoses (ebay, sorry Len)
Master cylinder, etc.
I filled the lines from below with a syringe and also poured fluid ito the fill hole in the MC.
I have pumped/bled. Vibrated /bled. But no resistance at the lever.The Haynes manual says
open the bleeder one turn and pull the lever to the grip
and watch for bubbles. I tried that repeatedly but no pressure built up. So I tried the way I'm used to,
which is to pump the lever with the bleeder closed to build up pressure, then crack it open to let the
bubbles out. This didn't work either.
I saw that the level in the MC never dropped,so I vibrated the lines with my sander with the lever tied down
but still no resistance. I pulled the MC and the return spring worked but not with it on the bike. I rebuilt
another MC with Chacal parts and swapped it with the same results. Could this have anything to to with
fork rebuild ? I don't remember lining up the holes in the damper with the opening for the anti dive,
Would that be a problem ? Can't find fluid leaking but can't get air out. Help !

 

Sometimes you can bleed the master cylinder. just pump and hold and loosen the banjo until a little fluid comes out then tighten it back. sometimes it takes two or three tries'
Cover anything that can get damaged by brake fluid especially paint.

 

Haynes has errors, and that part of the bleed procedure is one of them.

When bleeding brakes you squeeze the lever first, then crack the bleeder (connected to a length of tubing, the other end of which is submerged in a container partially filled with brake fluid), count to about 3 (you're really looking to see the brake fluid slow down a little, indicating that pressure is dropping) and then close the bleeder again. Repeat until no air comes out. This ensures that the system is under some pressure, and remains under pressure until the bleeder is closed so that no air can get back in.

The way the Haynes manual says to do it will add air to the system, not remove it. That is where the root of your trouble lies.

Remember, you have the most difficult to bleed brake system of any XJ.


It sounds like you did this, but here's a review. You can skip to #8 since brake fluid is already in the system, but it won't hurt to start from the beginning if you think there is a lot of air in it now.

What I do to bleed the system.
1. get a large syringe from a farm store and about a foot of vinyl tubing (you can also use a 2-stroke oil mixing syringe).

2. Cut 6" of tubing and attach that to the end of the syringe. Remove the Syringe plunger. You now have a funnel to fill the master cylinder with.

3. Break loose all four bleed fittings (be sure to put down cat litter or drip pans).

4. Tie the brake lever to the grip.

5. Fill the master cylinder and syringe.

6. Wait overnight (or at least a few hours)

7. You should now see brake fluid coming out. Close the bleeders, and untie the brake lever.

8. Bleed the brakes as normal, starting with the anti-dive bleeders, then the brake caliper bleeders. Remove the funnel.

9. You aren't done yet. There will still be some air in the system. The next step cures that, no matter what method you use to fill and bleed the system.

10. Use a vibratory sander (no sanding pad) and slowly run it along the brake lines, calipers, and distribution block from bottom to top. This will move any remaining air bubbles up into the master cylinder. Tap (or vibrate) the master cylinder to get the air bubbles to come out of the return hole. This process can also be done with a box-end wrench or other similar tool, and tapping the calipers and lines (it just takes longer).

11. Do one final bleed normally, just to be certain that the calipers are fully bled.

12. Use a flashlight to check the fuid level in the master cylinder. It should be below the fill neck. Unfortunately there is no dip-stick or sight glass on this master cylinder, so unless you empty it and measure out the fluid you will need to just eyeball it. If the fluid level is too high the brakes can hydrolock and not release.

 

I overhauled the front brakes on 2 650 maxims, A 650 seca and a Kawasaki 1100 shaft LTD. Bleeding was easy until
I tried to overhaul the front brakes on my xj75o seca. When I pull the lever to the handle , it stays there. How come there isn't
a spring strong enough to pull the lever out again ? what am I doing wrong ? Too bad there isn't same way of either pumping fluid from the bottom
bleeders under more pressure that a veternary syringe. All the vulnerable areas have plastic taped over to protect from fluid spill.
there's no way to prevent spillage whe filling the MC on this bike and attaching and removing tubing at the bleeders spills a bit.

 

There is, and it should already be installed.
Did you polish the master cylinder bore?
Are you sure that you have the piston seal oriented correctly?

Spills are inevetable when working on any brake system (some more than others) clean it up quickly and it won't do any harm. Have you modified a syringe for filling the master cylinder reservoir with (see #2 above)? That greatly reduces the chance of spills while filling.

 

Only thing I use is Mytevac vacuum bleeder it’s great for problem brakes.

 

I like mine as well. I wish that I could remember where I put it though. Somewhere in the garage....probably.
I need more toolboxes.

 

I thought I had the system bled properly by the beginning of sept. last fall. brakes hed pressure and stopped the wheel.
Started to work on the bike again in April but concentrated on carbs. I finally got the carbs done on 7/20. Now the brake lever is floppy again and
I can't get the fluid to go either down or up past the MC piston with the lever tied to the grip. Can I leave the part of the anti dive system attached to the
fork alone and start with the brake fluid side ? I can disassemble all the lines and connections, check all the seals etc. and start over . On the MC piston
side doesn't the flare part of the seal face in ? Since the anti dive part attached to the fork has no fluid, it can't leak, right ?

I disassembled the whole front brake system today down to the individual components. I found the master cylinder piston stuck in the cylinder. I got it out with
compressed air. The bore was very smooth owing to my honing and polishing it last fall, but was still too tight and the rubber cap on the spring and the seal
on the piston were hanging up. When I pushed it in with a screw driver it only came back half way. I'm going to hone it again with 600, 1000, and 2000 wet paper then
use polishing compound. It's funny that the piston sprung back ok last fall when I last polished it but somehow it got tighter over time. Back then I pushed it in several times with a screw driver
an it rebounded just fine. I'm going to need some sort of hone that will fit into the bore and hold the wet paper, any ideas ? Does rubber swell when it's immersed in brake fluid ?

 

The seals should not swell. Where did the rebuild kit come from?

 

I don't remember. I got some parts from chacal, some off eBay, and some off Amazon. I honed the MC bore with an old automotive
brake cylinder hone which held a small sheet of sand paper against an "s" shaped sheet of brass shim stock clamped into a slotted steel rod.
I cut the flaps down to fit into the 17 mm bore and used 400 and 600 wet paper. The bore was smooth and shiney afterwards but there may have been
some fine radial scratching that hung up the the piston seal after sitting for 8 months . That bore is just aluminum, so I'm hesitant to use a hone with stones.

 

Going through the xj4ever catalog, It looks like all the parts for the xj750 frame mounted MCs have been discontinued
so I probably used the piston seal, spring cup and boot over again. I would appreciate tips on where to get these rubber parts.

 

When I clean up a small bore I use a wooden dowel, cut a slot in it, and wrap finishing paper around that.

Bad news about the rebuild parts. That must be a recent change.
It may be time to switch to a conventional master cylinder, or see if Chacal still has any new original-type master cylinders in stock.

 

Great news, I found a 750 seca MC rebuild kit on eBay by "All Balls " I 've used their parts before, mostly bearings and seals
but it all seemed like good quality stuff. At least there were no problems yet. I also found a 2 stone cylinder hone on eBay for less than
ten bucks that sqeezes down to a half inch. I used to make split dowel sand paper holders for furniture making. I will use a dowel rig
for sure if the stones are too aggressive. I would use plastic from a milk jug to back up the wet paper and keep pressure on the inside
of the bore.

 

Last night I also saw a couple of used 750 seca MCs on eBay for between 15-20 bucks

 

Got back to Santa Fe on 8/1 and a 2 stone cylinder hone was waiting in the mail box. With slotted dowel wet paper holder I was ready to hone and polish
the xj750 seca MC. The rubber seals on the spring and piston were hanging up and not returning the lever. After careful honing ( not too much ) I polished
with 600 and then 1000 paper lubed with brake fluid. A tip, fold the strip of wet paper around a doubled over strip of flat milk jug plastic and slip it into the
slot in the end of the dowel. fold the flaps against the dowel in the direction of spin , slip it all into the bore and the paper will be tight against the inside
of the bore. I was using my cordless drill to spin it and dipped it in BF repeatedly. I repeated ; hone, 600, 1000 a couple of times until the spring returned the piston
when pushed in, every time. Then I cleaned the MC with brake cleaner and compressed air. After that I assembled the whole system with new crush washers and
Teflon tape where needed.
OK, so now it's all back together and the lever returns when pumped. Bleeding time again. This time I syringed fluid up from the anti dive bleeders to the caliper bleeders
which were open with tubing into jars. I closed off the caliper bleeders when clear fluid appeared in the tubes then closed the AD bleeders. Now I tied the lever to the
grip and am filling the master cylinder reservoir hoping that fluid will drain slowly into the lines. Am I on the right track ? Correct me if I've messed up or missed something.

 

Won't work, that's for the XJ750 Maxim style master cylinder (16mm bore). P.S. that's also why it lists it as being for 1982 and 1983 models only (which is when the 750 Maxim was made) and doesn't list the 1981 model years (Seca's were made from 1981-83, and they all use the same m/c).

The lever returns because the seals are about 1.5mm smaller in OD than they should be, there is no resistance because there is no real "seal" occurring.

Your methodology for bleeding is correct, but that m/c will never build pressure is my prediction.

 

Joe if you run into problems give me a shout and let me see if I can dig up some spare seals for you.

 

I finally got the front brakes on the 750 seca bled . To Len ; I only ordered the kit to see if I could get a stronger spring, I did not use the rubbers. I used a set I got
from xj4ever last fall. They measured 18.5 to 18.7 mm. Honing and polishing enlarged the MC enough for the existing spring to return the piston and lever every time.
Here's the system I worked out for bleeding. With the lower half of a syringe ziptied to the handle bars and a 1/4" 0d 3/16" id tube fastened to it at one end, I ran the other end of the tube
through a rubber cork and plugged it into the MC filler hole. This allowed me to have an extra brake fluid reservoir ready to fill the actual reservoir avoiding spillage.
The next step was to tie the lever to the grip and fill the afore mentioned syringe full of fluid. Dropping down to the anti dive bleeder on the left, I attached the
hose from my brake bleeder pump, pumped it up and cracked the bleeder. Brake fluid got sucked down from the top and I tightened the bleeder when the bubbles stopped.
I repeated this for the left caliper, the right anti dive and the right caliper, filling the half syringe on top each time. When I released the lever it was already pretty stiff and I
I could only pull it in a half inch. The next step was more traditional. I went through the same sequence but pulled the cork out of the MC filler hole and topped it up with just
dribble at a time through the syringe/tube. Pumping the lever a few times and lashing it down with a bungee, I cracked first the lower left bleeder with tubing attached and fed to a jar.
A little foam came out but no big bubbles. Then upper left bleeder lower right and finally upper right. After that I put the plunger back into the syringe annd sucked fluid out of the
filler hole until the fluid was at the bottom of the tube, Screwing in the plug I was done. Now the brake lever is completely rigid. I won't be able to test the brakes with the
bike rolling until I get the bike off the lift and I take the clamp off the front wheel but I'm guessing the I'm home free now.