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MG MGB Technical - Questions for the Experts

I have a couple of problems with my 68 MGB that I want to take care of.

1) I am leaking brake fluid around the push rod of my dual line non-servo brake master cylinder. The fluid ens up on my shoes. I have ordered a rebuild kit from Bob at Brit-Tek. Is this a fairly staight forward job or am I biting off more than I can chew?

2) My oil pressure reads about 45lbs all the time (except zero when not running) and doesn't change with RPM's. I would like to change the OP sending unit. Where is it? Do you think that this is the most likely culprit?

Thank for any advice you might have.

Rick Bartell
Rick Bartell

Rick,

1. The dual line non-servo master cylinders can be rebuilt, but it is a bit tricky. You have to be very careful taking it apart so as not to destroy parts that are not included in the rebuild kit. My preference is to buy an already rebuilt unit. I do a quick bench bleed, put it in, and have an instant firm pedal.

2. The sending unit is a small metal can with a bracket bolted to the side of the block just forward of the distributor. You should see a small braided steel line about 12-16 inches long coming up from the rear of the block and attaching to the bottom of the can. This small can is the sending unit, and yes, they are a frequent cause of improper oil pressure readings for these year cars (68-72 I believe). You can get a direct reading gauge from a 72-76 car and pipe a line to duplicate the setup. The gauge looks the same as the electric one and mounts in the same place, so is virtually invisible.
Paul Konkle

Rick:

No not an expert, but I've worked on these buggers for awhile now.

1. I've rebuilt several master cylinders and some have come out OK and some still leaked. Depended how badly scored the bore was in the cylinders. My suggestion (and because pulling these things out of their cubby is quite difficult) would be to go ahead and replace it with a complete new one. Alot easier. If you want to, buy a rebuild kit (only $3-$4 bucks) after and rebuild the old one in case of emergency (although you new one should last for a good long time. Check out Victoria British, just received a catalog from them that have both clutch and brake cylinders on sale. Oh, don't forget to bench bleed before you re-install or you could be there for ever.

2. Are you sure your oil pressure doesn't fall on idle? should read at least an acceptable 25psi at idle. If it just sits there only two things come to mind. Either the pressure relief valve is stuck (buy a new one, installation is also a bugger). or your sending unit or guage is busted. See if you can borrow a working after market unit to check your real pressure. It should be different at idle and at start-up. Tour year MG (like mine) has a special oil pressure sending unit connected in the engine compartment by a hose. If thats bad, its replaceable (Vicky Brit $99) if its the guage, its not, and you'll need to check used parts places.

If any gurus are around maybe they can add to what I have (or correct me if i'm wrong).

Good luck

Luis
Luis

Bugger, Paul K. got here before I did. Paul, you fingers must fly over the keyboard.

Luis
Luis

Dumb question. How do you bench bleed?
Mike

Mike,

When you get the new/rebuilt master cylinder out of the box, chuck it up gently in a vise. Fill at least halfway with brand new fluid from a freshly opened bottle. The last one I bought had plastic adapters and a length of plastic hose included. Fit these up to the M/C with the free ends in a bottle/jar/can with clean brake fluid in it, so as not to draw air back up. Stroke the master cylinder by hand until all the air comes out. Remove the hoses and adapters, and quickly and carefully reinstall the new M/C, fitting the brake lines first to minimize the chance of spilling fluid on the paint.

Luis,

I'm actually not that fast, just lucky timing! Hope you are well!
Paul Konkle

If you reverse bleed - push new fluid from the nipple at the wheel to the master cylinder - do you still need to bench bleed ?
.

Rick: If the cost of a new sending unit for that electric oil press guage is too much, you can take a mechanical gauge from a 72-76 B and replace the gauge and all. I did this years ago when repro sending units were not plentiful and have never regretted it. You will need the braided hose, the metal tubing, and the firewall mounted connector fitting of the 71-76 cars to complete the job. I would look for a good junker to pull this off of, that is what I did. Just an alternative for your consideration.
BobMunch

This thread was discussed on 18/01/2002

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