Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Plus 8 brake issue

Hi . I have just had a similar problem on my 1974 plus 8. I drove the car out of my garage and on braking my foot went straight to the floor so I put in a new master cylinder. We then went away in it for a few days, returned put it in the garage. When I next went to drive it the same thing happened again my foot went straight to the floor.
I bypast the servo and the brakes have worked fine since. At present the servo is waiting to be sent to Terry Foxton for rebuild but the brakes don't feel any different than they did,so I'm not in any hurry.
Just my expereance in case out helps.
Steve.

Steve - I had this once on my MGB with the remote servo. Backed up the drive and the pedal went to the floor. Fortunately our drive is uphill to the road.

It turned out that a pinhole in the diaphragm had sucked the fluid out of the master cylinder, and the servo air chamber was full of brake fluid.

Air is compressible so first push compresses it and subsequent pushes then have more effect on the fluid. I put my money on entrapped air somewhere.

Or also old flexible hoses that expand.

I use a Mityvac vacuum pump for brake bleeding, one of the best tools I have ever bought.

Try bleeding the brakes with the engine running.

Arwyn

Howard i read all of the previous and suspect your friend has looked down these avenues, where i would be looking is at the shoes themselves, if the head of the shoe where it sits against the piston of the cylinder is worn down, x that by 4 on one hub then x2 for both rear hubs that is a lot of travel for those small pistons to move before they hit the shoe head, this was notorious in the 80s when Brake manufactures were cutting costs by asking you to part ex brake shoes so they only had to replace the lining, the metal part didnt get replaced, i spent many a time having to put a dollop of weld on the end of each shoe then refile, this will push back the pistons into the cyclinders and give a good stroke first time.

"The 1970 +8 did not have a brake servo at all. But I think it was the first at MMC to feature split circuit brakes and hence the more complex master cylinder with an outlet pipe to each circuit"

Err no, not exactly; all Moss, 4 Speed Rover [and I understand some early 5 speed cars] did NOT have split line brakes. For these cars there is no shuttle valve.
They may or may not have had servos originally fitted.
Air is easy to get trapped in the single line servo system and is a pain to get out. Try bleeding, re-bleeding and re-bleeding again.
The servo adds only a little assistance [60%?] compared to moderns [+300%] consequently as Dogmog notes you can bypass the servo, a simple length of pipe suffices to replace the missing servo.