Mopar Muscle Association UK

My memory is coming back a little and i also got some information from the Mopar Action "Swap and Stop" article.

The lightweight master cylinder (which might be easier to fit over your headers but will look a bit too modern) was used on 1979 - up mopars. In any event you WILL need a master cylinder made for disc brakes.

Use an adjustable proportioning valve as the chances that a non-adjustable one is even ballpark close to the right balance is more than slim.

In the mid 1970s Chrysler eliminated the rear brake residual valve from the master cylinder. In its place they fitted "expanders" (dish shaped steel inserts) into the rear wheel cylinders. Any new wheel cylinders should have these in as standard.

Just to further confuse things, the 'lightweight' master cylinder came in different bore sizes too, plus unless you get one from MP a lot of the replacement ones are actually cast iron (even though the originals were ali). The difference is price - probably $30 for an aftermarket and $130 for the MP. You can get the $30 one in aluminium, but it's pot luck.

If that's confusing, let me summarise. If you order one for a late Mopar and you want a specific bore size then you need to know which applications had them - and even then you should check it's the size you want AND aluminium.
If you get one from MP you'll know the diameter (they might do two?), and also that it will be aluminium - but they'll charge you an extra $100 for the identical part.

(PS - go with the manual discs! But the dual master cylinder won't look original in case that's a problem)

I looked in Hausers catalogue and he had a big list of those ally master cylinders. All the part no.s etc.

Thanks for the response chaps. Still weighing up the options & waiting to see what Will & FBO come up with.
Got an answer to my 'comprehensive' enquiry to SSBC thru their website, but answered by someone who didnt appear to know too much about brakes! The m/c in their kit is 1 1/32 bore (he wrote 11/32! that got me going!) and just comes with an adj prop valve.

Thanks for the offer Steve of your 300's m/c but i think we better stick to a new one, once we establish which one's best. Would love to keep the original for appearance but if changing to a disc/drum system you really gotta have a dual master to cope with the extra fluid that needs to be pushed to the discs.
We are trying to keep the changes from stock (ok, a stock clone) to a minimum, and just to those for practical purposes, eg elec ign, front discs, and, thats it I think. If it means we need a different m/c, we can live with that.
PS Look fwd to seeing the 300 next year, Brooklands maybe?

Dave, its comforting to know you opted for manual brakes with discs & drums. Your brakes looked ok in that clip in Members Car Show!
Do you remember how you decided on your m/c bore?
Dont you need a metering valve for the fronts?
MP Brakes reckon drum brake masters have the residual valve at the outlet, and as we have '63 spec rear brakes (so wont have the new wheel cylinders) may need to add a residual valve for the drums once the old masters removed. Sound feasible?
I'll see what Geof H has in the way of m/c's. As long as its the right size stock looking, and fits, I'm not too fussy!

Gav, thanks for the input too. And for pointing me to Mopar Performance, hadnt thought of them for brakes! (presume thats the MP you meant, not Master Power brakes!).
You're right that their lightweight m/c wont look right but their spec is interesting.
They have a 15/16" bore cyl for under 2800lbs cars, that gives "the highest volume fluid displacement while maintaining proper pressure."
Their alternative is a 1 1/32" for cars over 2800lbs and "features a larger bore diameter for an increased pedal feel."
So maybe the cars weight is a consideration too. No mention of pedal ratio tho.

More info to go in the mix.

RobTwin wrote:Do you remember how you decided on your m/c bore?
Dont you need a metering valve for the fronts?

Dunno. What does that do?

I have to have the proportioning valve screwed in all the way to stop the rears locking up before the fronts. Massive rear tyres do not help with this. But now non of the brakes lock at all. Very handy in wet conditions actually because it stops very well in the wet. It used to lock up real easy with the power drums even in the dry. Could be I am still not pressing hard enough though?

You see I have a larger than one inch bore in my M.C. although I can't remember exactly how much more. This is because I got a job lot of parts from the technical editor of Mopar Action magazine and the M.C. was part of that deal. I KNOW how hard it is to press. Which is why I am advising you to go with a smaller diameter.

You should replace those rear wheel cylinders if they are the original ones. Any new ones will work with the modern master cylinder without the need for a residual valve.

The lighweight master cylinder is just over 8 inches long in case you need to measure up.

Another late reply! Started this with 1 eye on the compooter and 1 on match of the day. Then 1 on the GP qualifying. No good at multi-tasking so turned it off now!

Well, now I've been an expert on these things for about a week now, I can tell you (according to MP Brakes again) ....
"A metering valve is used in the disc portion of a disc/drum system to hold off the application of the front discs slightly allowing the slower reacting rears to catch up. This provides rear stability on wet surfaces and reduces 'nose-dive' and excessive pad wear."
And they say an adjustable proportioning valve (what you have) "is used when you have a special rear condition that requires higher or lower pressure than normal conditions. You should always use a metering valve to the front when using the adjustable valve to the rear."
So looks like you've had a good result not fitting this vital part and made the right choice if you dont lock up anymore.

Definitely leaning towards the 1" or less m/c so will push for this in whatever 'kit' we get. Can always go for a larger one (go for a lager? sounds like a good idea) after if it dont suit for some reason.
USA Imports are keen to help us get the right result here and say they'll stick with it till we get that result. Which is nice. Thanks Will/Neil.
Good point about the rear wheel cyls too, I'll bear that in mind when ordering the parts. Mind you, they were new just before we got the car. But so was the torque converter but that was faulty and trashed the trans... but thats another story altogether!

I'll get all the info on what they are quoting Mon/Tues, throw in some of the good advice from here (your experience is vital & much appreciated Dave ) and see if we can get this finalised cos I for one would like to start thinking about something else!

RobTwin wrote:And they say an adjustable proportioning valve (what you have) "is used when you have a special rear condition that requires higher or lower pressure than normal conditions. You should always use a metering valve to the front when using the adjustable valve to the rear."

...the special rear condition is anything that is not factory stock! From the factory, vehicles have a non-adjustable proportioning valve, which is often integrated with the metering valve. They didn't need an adjustable one because they'd built in the correct bias for the factory setup. Once you add discs to a vehicle that didn't have them, use different master cylinder or rear brake cylinder sizes, different tyre sizes to stock (most of us), or different vehicle rake, engine, etc etc then theoretically the factory setting is not correct anymore so you need to tune it for your application (hence the adjustable valve). Some people get lucky (all the changes cancel each other out), some aren't worried about a non-optimal system, some fit the valve.

I guess one option is to see what it's like without and adjustable valve and then if not good enough, fit one. While the system is apart I'd go with the valve myself.

Well, that's phase 1 complete.

Ordered the kit (an SSBC kit) from Performance Suspension Components in Arizona for $799 + $65 for shipping to Kissimmee in Florida. Knowing the carrier was UPS I had them deliver it to a UPS Store (like a post office that does international shipping too) near where we were staying. I had to pay another $50 for the UPS Store to open a 'mail box' so they could hold on to the package securely.
The Store is about a mile down the road from Jeff's villa so we picked up the 2 boxes and distributed the contents in 3 suitcases, and bobs your uncle, disc brake kit home for about ?510.
Normally wouldve gone with USAImports/FBO but having the opportunity to save on the shipping was too good to miss.

All's left to do now is make it work