XJ750RH Seca - Master Cylinder Rebuild Questions

Hi All,

I'm rebuilding the master cylinder for the front brake system on an XJ750RH Seca.

When I rebuilt the master cylinder on a Honda 750, one of the instructions was to dunk the new piston and piston seals in brake fluid before inserting into the master cylinder bore. Does that hold true for the Seca master cylinder as well? This is the remote cable operated master cylinder.

I have looked for any Master Cylinder rebuild threads and couldn't find much, other than the order of assembling the parts, so I'm asking before doing something stupid.

Thanks,

Charlie

 

Forgot the other question. On the Honda, they recommended running a brake hone through the bore of the master cylinder. Should I do that on the Seca as well?

Thanks,

Charlie

 

Dunking in fluid sure makes it easier to insert...

Hone... Don't know that I would bother unless there is some visible damage. Besides, it's aluminum, and would probably hone down way too easy.

 

JPaganel,
Thanks! When I said Hone, I meant like one pass just to break the glaze in the bore.

Also, since this master cylinder mounts vertically, and I've read about the infamous "Air Bubble" at the top, should I fill the bore with fluid before I put it all together?

Thanks,

Charlie

 

What glaze? You have rubber seals sliding on aluminum at ambient temperature. This isn't the engine cylinder.

Honestly, I've rebuilt a bunch of master cylinders and the idea of honing one never even occurred to me. They all worked fine.

I don't know how much bench bleeding will help, but I'm pretty sure it won't hurt.

 

Pre-bleeding the brake lines helps quote a lot. You may want to use a vacuum bleeder. As a final step, I have found that using a vibratory sander (sans sanding pad) on the lines (beginning at the caliper and working up) with the lever tied to the bar is the easiest way to ensure that all of the air bubbles get out of the system. Be sure to bleed the anti-dive as well.

 

JPaganel

Thanks!!!!!!!

Charlie

 

k-moe,

Thanks for that. I read about the sander technique. Will give it a try. Will also likely try to do a little bench bleeding on the master and brake lines (and hopefully not on me. LOL).

Thanks,

Charlie

 

I know it's been a while since I started this thread, but I have now Rebuilt both Calipers, cleaned out the brake side of the Anti-Dive units and Completely Rebuilt the Master Cylinder on the Seca xj750RH with the "remote master cylinder".

I have put the system back together using all new Stainless Steel lines and New crush washers. Everything was cleaned to within an inch of its life.

I also Filled the master cylinder with Brake Fluid, pre-filled the brake lines and the calipers.

Put the system together and started the bleeding process. I also cleaned the Brake side of the Anti-Dive units. (No leaks but they seem stuck.) Anyhow, they are clean.

I am at the point where I can't seem to get any pressure built up in the system after pumping the Brake Lever well over 30 - 40 times. I also tied the lever back about 2/3 of the way and left it for a few days and still no pressure. Today I took the Master Cylinder apart to check my assembly and it is correct per the diagrams (and pictures I took as I disassembled the original parts).

I need some help figuring out what I did wrong.

Thanks in advance,

Charlie

 

You didn't do anything wrong; they are just a PITA to bleed. Get a large syringe from the farm store. Connect it to a length of tubing, and use it to push brake fluid up to the master cylinder. Once the MC is full, bleed the calipers and then the anti-dive units as normal. Follow up by tying the brake lever to the grip and work your way up the brake lines (starting at the caliper) with something that will vibrate the lines (a sander, rapping with a screwdriver handle, etc.) to move any remaining air bubbles up to the master cylinder. Finish by untying the brake lever and slowly squeezing it to expel any remaining air.

 

Did this procedure yesterday with the 900. (Had a nightmare 2 years ago with my SECA 750 (who was the idiot at Yamaha who decided to "remote" the MC!).
K-Moe is absolutely right. 20 cc luer lock syringes are $1.49, 12 cc are $0.49 at Tractor supply. I bought 2 of each and had to give my name/address (told the sales guy, I'm an RN who works in etoh/drug rehab. My needle using patients want 0.5 cc. syringes, not these. Anyway...) 0.17 tubing was $3.49 for 10 feet, you'll only need one foot. J-B Weld a bleeder screw to the tubing, regular epoxy the tubing to the tip of the syringe. and you will be set for a decade.
Yes, Teflon tape melts when exposed to brake fluid (DOT 3 and 4, don't know about 5), this valve isn't staying so wrap away.
I didn't tie the lever, couldn't get ahold of any friends/ family so could only do one side at a time. Took 30 minutes (not counting time spent tightening bolts successive times (probably excessively careful to not damage the threads in the calipers). If you can get an assistant or two, it'll take mere minutes. Wish I'd been able to use a sander (too far from the house), sweet idea.
Remember, the pistons need to move into contact with the pads. (Keep an eye on fluid level in the MC.) You won't feel resistance until they've moved into place.camera app

 

k-moe & Ross1bd,

Thanks Guys!
I've got a couple of syringes and that's what I used to pre-fill the MC, calipers, anti-dives, and lines.
Did not think about doing the "reverse bleed". But will do it when I get back over to the bike today or tomorrow.
Will also bring a sander!
So, if I understand correctly (and I may not. LOL) my procedure should be to
1. Attach the syringe to the Caliper bleeder screw (probably start with the left side caliper since it's furthest away from MC).
2. Open the cover on the MC.
3. Fill syringe with Brake Fluid and pump in to caliper. (Should the brake lever be tied back????)
I ask because the Honda system has a tiny return bleed hole in the MC that needs to be open to the brake lines so return fluid (and air when bleeding) can come back to the MC.
4. When Fluid is coming back to the MC from left side, close bleeder and repeat on right side.
5. After fluid comes back to MC from right side, get sander going on calipers, then brake lines then the splitter, then the hard line and finally the MC.
6. Close cover on MC and pump up the system.
7. Check Fluid level periodically during process to make sure level stays up.

Does this sound about right???????

Thanks

Charlie

 

Hey Guys,
OK, so I must be stupid.
Today I went over to the bike and did the reverse bleed using the syringe.
Pumped in probably 20cc into each of the calipers. Both calipers extended to touch the rotors. That was good.
Then I started up the sander and held it to each caliper and anti dive unit. Worked my way up to the Master Cylinder.
Never saw any air bubble(s) come out the master. Also did not see the level change in the Master Cylinder.
Put the cover back on the Master and gave it a squeeze before bleeding and it only traveled maybe 3/4 to 1 inch with the brakes locking up the wheel.
OK, so I'm thinking this is good and I'm almost home free.
Bleed the right side and have fluid in a steady stream. Do the anti dive bleed on the right side, same thing.
Brake lever still only moves about an inch.
Go to the left side and bleed the anti dive unit! THen the Caliper. Now the Brake lever goes all the way to the grip, but, the brake locks up after the lever is about 1/3 to 1/2 of total travel.
Do I still have Air in there??????? I'm guessing Yes. Going to let the bike sit for a day or 2 to see if the air will rise to the top if there is air in there.

Comments would be appreciated.

Thanks,

Charlie

 

Hello,

I know it has been awhile however I thought I would try and get some info anyway. I got the rebuild kit for this same set up. Looks like the spring and the piston needs more room in the cylinder. The piston spring that I trying to use is 11 coils not six as shown from factory diagram. The
pictures from the tread that were taken before disassembly. Still got those?. Attached is the diagram.

Thanks in advance.

 

Vacuum bleeder for the win! Every bike owner needs one!
I have one I got from either Amazon or Harbor Freight, can't recall. Originally had borrowed one for the XJ, but when buying other bikes that needed to have brake fluid changed, got one myself.
Hooks up to compressor. worth its weight in gold for maintenance. I used to get the kid to pump the brakes in the car when bleeding them but now, I'll use this.
Just know that it can pull fluid pretty fast and you don't want to empty the reservoir.

 

I will get one once the rebuild kit is installed. Still trying to see how a 1.00" piston and a
spring can fit in a .75 " cyl. (my bike is 80 750 seca with a remote or cable activated master cylinder that mounts on the frame behind the headlight basket). Misplaced the original when taking it apart. Note the previous pictures attached on the last message sent.

 

Hello Charlie,

Still got the pictures of the master cylinder you mentioned. Got a problem putting mine together. Would be much appreciated.


Seca CSM