Dual circuit M/C

Post by **Bazzalucas** » Wed Oct 22, 2008 2:47 am

Hi, all,
A little while back someone mentioned what a good fit the dual m/c from the 69-74 MGB was. Any pix? How do you solve the reservoir problem? I have a good one from a '74, (non-servo), and would like to fit it. Thanks!

Post by **downsey** » Wed Oct 22, 2008 5:30 pm

Yep that was me. First thing you have to do is a mill a block of plate that will allow you to run brake lines out of the chassis rail and up into engine bay. Second you\'ll have to find a remote reservoir (Volkswagen beetle works really well). Then you cant mount the master cylinder fabbing up a bracket using existing holes (i believe, i cant remember if i had to drill new holes or not). Then the tricky part. The plunger doesnt line up with the lever arm of the pedal so you\'ll have to fab up a linkage system (its not too hard to figure out what it should look like, pm me and maybe i can draw you a picture, or pull up my carpet and take a picture).

Then drill your 2 holes for the the brake lines and your set. Its really not that much work, just seems like a lot. You\'ll definitely be happy with the results, especially if you convert to mgb disc brakes and mgb rear end as well.

Post by **Bazzalucas** » Wed Oct 22, 2008 8:38 pm

Thanks, Downsey. I have Midget discs in front, standard drums in back.
My MGB M/C has a flush-mount resevoir held on by four machine screws. Is that the type you have? If so, how did you plumb the lines to the resevoir on the bulkhead? Drill and tap, or...? Thanks again.

Post by **downsey** » Thu Oct 23, 2008 6:31 am

Yep thats the type that i have. The block that needs to be made will incorporate those 4 machine screws. You'll need some barb house fittings which will thread into the block. Then you'll need some like 5/16 inch fuel line . The lines will be fed out of the rail towards the back of the car. After the lines exit the rail they will need to be looped around 180 degrees and fed up into the engine bay to where you mounted your remote reservoir.

Post by **Bazzalucas** » Thu Oct 23, 2008 12:29 pm

Aha! Hence the "mill a plate", etc. Thanks.

Post by **bmcecosse** » Thu Oct 23, 2008 2:10 pm

Phew - sounds like lots of work -all for twin circuit brakes, which in my experience are useless anyway - hmmm.

Post by **downsey** » Thu Oct 23, 2008 4:12 pm

Its really not that much work at all, and is pretty much just a safety upgrade. The mgb disc brakes are multiple times better than the midget brakes. I know, my dad has midget brakes on his bugeye and they suck. The back mgb drums are great as well, i can pull the e-brake and lock the back wheels up at any speed.

Post by **Bazzalucas** » Thu Oct 23, 2008 4:43 pm

I can lock up the front wheels with my present arrangement! I would just feel that little bit safer with a dual circuit. Besides, the Morris will soon be tucked away for the winter here in the snowy north, and I've got to have SOME project going!

Post by **bigginger** » Thu Oct 23, 2008 8:02 pm

bmcecosse wrote:Phew - sounds like lots of work -all for twin circuit brakes, which in my experience are useless anyway - hmmm.

Would you care to elaborate on that? I've had brake failure on vehicles with both single and dual circuits, and I know which I preferred being in

Post by **bmcecosse** » Thu Oct 23, 2008 8:12 pm

Yep -i've lost brakes before on twin circuit Minis - and the remaining brake power was useless - pedal still went right to the floor and handbrake had to be used for a spin stop! Scary. Also ran my TR7 out at the beginning of this year - and unbeknown to me one of the rear cylinders had quietly leaked away the fluid - stamped on pedal - right to the floor (again useless twin circuit brakes) and again stab at the handbrake saved me running into neighbours fancy Audi across the street! I don't doubt the MGB front disc/rear drum conversion will be excellent - it's the impressive amount of work to fit the twin circuit M/C I find amazing! And certainly not value for effortb in my eyes. I have lost brakes on single circuit cars too - but generally just a slowly developing 'long' pedal - never had a sudden failure - but then only been driving for 44 years.

Post by **les** » Thu Oct 23, 2008 8:54 pm

Your not the sort of chap one wants to see following behind then!

Yep -i've lost brakes before on twin circuit Minis - and the remaining brake power was useless - pedal still went right to the floor and handbrake had to be used for a spin stop! Scary. Also ran my TR7 out at the beginning of this year - and unbeknown to me one of the rear cylinders had quietly leaked away the fluid - stamped on pedal - right to the floor

!

Post by **Onne** » Thu Oct 23, 2008 10:08 pm

Better to have useless brakes than no brakes at all!

You obviously can't expect that if one of the circuits fails that the car will still stop as it would normally do, after all 50% of the brakes are not working!

Post by **bigginger** » Thu Oct 23, 2008 10:55 pm

And commiserations - my single circuit failures have both been sudden and total

Post by **Onne** » Thu Oct 23, 2008 11:01 pm

And I bet wolseley drums wouldn't have been any better

Post by **alex_holden** » Thu Oct 23, 2008 11:46 pm

Onne wrote:Better to have useless brakes than no brakes at all!
You obviously can't expect that if one of the circuits fails that the car will still stop as it would normally do, after all 50% of the brakes are not working!

But will you really still have any brakes if one circuit of a dual circuit system fails? Why is it (in my limited experience of working on modern cars), when you open one bleed nipple on a car with dual circuit brakes the pedal goes to the floor with no resistance?

Post by **M25VAN** » Fri Oct 24, 2008 7:24 am

I too have had brake failure recently when coming off a motorway on a downhill sliproad.

A quick search has found two ways of 'powering' the brakes. A master cyclinder with two chambers as described here.

http://auto.howstuffworks.com/master-brake1.htm

and two seperate cylinders as in this kit for a TR.

http://www.revingtontr.com/shop/product ... RTR4409RAK.

Either way if both work correctly they have to be better than no brakes at all.
I was lucky that my leak was a pipe and not a cylinder as I'd have had no handbrake either!

Post by **leyther8008** » Fri Oct 24, 2008 8:15 am

I,ve imported a kit from the Austrailian member Barry Parsons, which I will be fitting over the winter, looks to be a very comprehesive package and as and when I finally do it I will report back on results.
Apparently in Australia any car over 1400cc regardless of age has to be fitted with dual circuit brakes, hence he developed his kit for minors.
Its not a diagonaly split system as supplied simply seperation of front and rear circuits.

Post by **M25VAN** » Fri Oct 24, 2008 12:15 pm

Sounds interesting. Please keep us posted as this looks like a nice swapover. Glad it's a front/rear split as it would be interesting with a diagonal split on a disc/drum setup...

Post by **eastona** » Fri Oct 24, 2008 8:01 pm

I had a midget, and the reservoir chamber is split so all the fluid isn't lost if there's a failure in one circuit. I did have the master cylinder totally fail. One seal failed, so the fluid stayed in, but it rendered the whole thing inoperable, fortunately I was travelling slowly.

I know what you mean Alex, it does go to the floor, but I think offers some level of braking on the remaining operable circuit. I'd be interested in a decent explanation of this.

Andrew

Post by **bmcecosse** » Sat Oct 25, 2008 1:25 pm

It really shouldn't Alex - it should just go half-way down, although in practice more like 2/3 way down ! Bleeding twin circuit Mini brakes is best done with two nipples open - one on each circuit, otherwise it can take ages to shift all the air.