Clutch Master Cylinder Rebuild

I am rebuilding my clutch master cylinder on my 1974 MGB. I couldn't find any instructions online so I will post my progress with pics to help anyone else out who wants the info.

First you have to take off the cover that houses the clutch and brake master cylinder. Two of the three 10-32 screws were rusted and I had to chisel / grind them off.

I next took off the clevis pin that holds the cylinder to the clutch pedal mechanism. First you remove the cotter pin and washer and then tap the pin out. The pin on my car was very frozen and I soaked it for a couple of days in PB Blaster. After that, I was able to rotate it with a nail in the cotter pin hole until it was loose then I tapped/pulled it out.

I removed the hard hydraulic line from the banjo bolt using (I think) a 7/16 inch wrench to loosen it. The wrench is so old it doesn't have any markings on it. I also used an adjustable wrench. It took some patience because it was a tight fit.

The next step was the two bolts holding the MC to the mounting bracket. The top one was easy but the bottom one was difficult to get out because of the spining nut on the back in an unacccesable place. But ( a big but and duh!) there is an access panel behind the master cylinder that pulls out from under the dash which if I removed first, probably would make this whole process much easier. I didn't know about the access panel until I tried to take out the master cylinder. I could not get it out as there was no room. I noticed the access panel and thought it pulled out into the engine bay. I was wrong. When I pushed the master cylinder back it pushed against the access panel which fell out onto the floor of the car.

Well the clutch MC is on the bench and the next step is to take it apart. This is done by removing the snap ring per the attached picture. I have not done this yet. I'll try to do it tomorrow and post another pictue. I would post more pictures but you can only post one per message?

Later,

MG Larry

Good on you Larry. You'll find two rubber seals inside the MC, easy to replace - you've already done the hard part in getting it out of the car. Just remember the hose and slave cylinder are same age as the master cylinder and are probably shot as well.

http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29011

Yep on Jon. You are well on your way.

Next step...Pull the piston assembly and wash it well with your choice of hot soapy water or a petro solvent. In all probability all you are going to find is worn out rubbers, but spend a moment looking at the other metal stuff just to make sure that the tin worm hasn't damaged anything.

Next, wash the cylinder itself WELL with hot soapy water. Pay attention to the insides of the reservoir. Get ALL of the black gunk out. Finish up with a thorough rinse with VERY hot water. The rinse will clean the soap off and the heat will speed the evaporation of the rinse water. Let it dry overnight to make sure that there isn't any H2O hidden anywhere.

Now use a small flash light or what ever to look down in the bore. Look for pitting or scoring. Pitting usually means the kiss of death as it can't be honed out, but VERY light scoring might be repaired with a flap of fine emery cloth on a bent section of coat hanger held in a hand drill. If you have to dress the bore, be sure and go back and clean all of the grit out. COMPLETELY.

Reassembly is a no brainer but remeber to lub everything with fresh brake fluid.

Before you stick the thing back in though look at the eye of the push rod clevis. If it is elongated you can braze flat washers on both sides and use a new pin after drilling the washer to the diameter of the new pin.

Also, take a look at the hole in the top of the pedal. If it is elongated much you will have to remove the pedal box in order to braze or weld up the hole and re-drill it.

While you are in there look at the condition of the clevis for the brake pedal and its push rod. If it is sloppy an ounce of prevention now is worth a pound of cure later.

Jack

I've had excellent results using isoprophyl alcohol, instead of the hot, soapy water w/hot water rinse. Also, instead of the emery cloth & coat hanger & drill, I use a wheel cylinder hone, which gives you a very nice, uniform bore surface. I've found that you can actually hone out light pitting with that set up. If you can't get all the pitting polished out, it may still "hold" a seal. I've been pleasantly surprised, in years past, when I've reused slightly pitted clutch master & slave cylinder cores and they've always held up fine. Of course, you have to be the judge of what constitutes pitting that is too severe to take a chance on.
The guy that taught me how to rebuild hydraulic systems was an aircraft hydraulic systems mechanic for a major airline, so I got some real good information that has served me well.
Also, for getting at that lower mounting nut, I use a manifold wrench (a.k.a. "half-moon" wrench) and it works very well.
Bud

Also, as suggested by some wise folk here, if you have a tap set, tap the bottom mounting hole of the M/C with a larger size bolt thread (do a search for the correct recommendation) so to eliminate the nut/washer in that impossible-to-reach location. Makes it much easier to reinstall.

when I took mine apart there was a plastic cover on the spring,the cover had snapped away from the spring but a fisrst glance it looked like that was how things are meant to be.

thought it might be worth mentioning.

Listen to me very carefully. If your clutch MC is good enough for a rebuild, be very careful where you source your parts. Half of what is out there is ch----K sh----t. I just rebuild a super clean clutch MC, with parts from VB!!!! and they failed and leaked all over within 1200 Miles.

I bought a new one from basil at a good price. Original type from england.