MGB & GT Forum

I am replacing the clutch and brake MCs on my 1970 MGB. When I removed them, I simply cut the brake lines, since I knew that I was going to replace them, as well. That made it easy to simply unbolt the pedal box and remove the assembly intact. I took it to my shop, cleaned all the parts and painted them.

Now, as I prepare to reinstall everything, I realize that, in order to attach the clutch line and maybe the rear brake line, it will be easier to remove the rubber plug in the firewall, right behind the MCs.

First question: does the plug pull into the engine bay or the passenger cabin? It looks to have a "handle" or sorts molded into the back (passenger) side. How flexible is that rubber supposed to be? Mine feels rather stiff and maybe a little bit brittle, probably from age. I'm afraid to pull or push too hard for fear of breaking it.

Second question: Does Moss (USA) carry a replacement? I can't find it in their online catalog. Moss-Europe has it. They call it the Master Cylinder Access Grommet, part number 14B630. I want to be sure that I can replace it if I break the one that has been there for 54 years.

Paul, Moss has it PLUG, firewall $3.49 Part # 282-970



Edited 1 time(s). Last edit at 2024-04-18 09:37 PM by Watauga.

Before you start setting up the MCs tap their flange to 3/8 UNC (or m10 x 1.5 if you're not fussed) then screw in a bolt from the front. That way you don't have to fiddle with fitting a nut to the OEM bolt. IYDK there's numerous topics about this time saving mod.

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Mk1: CKD 11/66 first registered 8/5/67; owned since 3/77. 18GB +40 balanced. Peter Burgess BVFR head. Piper 285. 123. FidanzaFW. 4synch c/r box. Lots more as I did a nut and bolt rebuild; finished 2015. Tartan Red.

GT: December '78. VW Golf guards, flush fit front and rear valances. Torana XU1 vents, frenched indicators & Mk1 rear lights. 'Worked' Rover V8 with Monsoon ECU for EFI. GM4L60E, Lokar tiptronic & Quick4 controller. Vintage Air A/C. FC IFS. CCE 4 link rear. Salisbury with Quaife. Jaguar Storm.

This grommet should be flexible, not hard and brittle. You need to be able to bend it a bit to place it in position as it is a tight fit. That would not be possible if it is brittle: it would break. The side of the grommet that has the handle goes below the dashboard. The flat side goes towards the master cylinders.

Use a heat gun to warm and soften the rubber. Carefully though, it's a fine line between warm and melted.

I thought of that. I took a slightly different approach. I used JB-Weld to attach a nut to the back of the MC housings, sort of a home-made captive nut. The end result is the same. I can now simply screw a bolt in from the front.

I remember trying to remove the MC. Reaching that lower nut is virtually impossible. I ended up cutting the brake/clutch lines and removing the entire assembly. It was easy to get to the nuts/bolts that way.