Fairly urgent master cylinder query!

Anonymous · Post by **Anonymous** » Wed Sep 21, 05 11:49 pm

Stu & are looking into getting a front disc conversion kit for the Polara.

One of the suppliers of these kits (SSBC I think) said that "anything larger than a 1" bore master cylinder can lead to an extremely hard pedal. The smaller the bore the more pressure that is output to the wheels".

I mentioned this to someone at Performance Suspension, whose kit we're quite keen on cos of price and what's included in their kit, and his reply was "OURS HAS A 1 1/8 INCH DUAL BOWL, IT IS DESIGNED FOR THIS SYSTEM AND WILL WORK JUST FINE"

Any brake experts out there know how the bore diameter affects braking/pedal feel?
Which of the 2 above would be preferable, 1" or less, or would the 1-1/8" be ok, as suggested?

We want to get this kit ordered quite soon so if anyone can help......

Ashley · Post by **Ashley** » Thu Sep 22, 05 7:23 am

Rob, I have just got a Booster and master cyl from Summit for a Disc conversion it has a 1 1/8" bore they told me i would need this to pump more fluid into the calipers anything smaller wouldn't do,Hope this help's

Alex · Post by **Alex** » Thu Sep 22, 05 7:32 am

I agree with Ashley, under 1" and you will run out of travel due to the size of the cylinders in the front calipers.

Anonymous · Post by **Anonymous** » Thu Sep 22, 05 8:24 am

Thanks guys, sounds like someone's telling porkies!

Just wondering if it mite have something to do with the type of calipers. It was Master Power Brakes that said less than 1" is best, see link (4th question on this list of FAQs)
http://www.mpbrakes.com/mpfaqmasters.htm

MP's kit has a single-pot caliper but the SSBC & PerformanceSuspension kits have 4-pot.
Would a single pot caliper need a different size bore to a 4-pot?

They have a lot of info on that site about master cyls, valves, etc but if they got that bit wrong, which bits can I believe?!

I'd rather rely on the knowledge & experience of yous guys than some salesman 4000+ miles away!

Cheers

Anonymous · Post by **Anonymous** » Fri Sep 23, 05 2:17 am

Still puzzling over this, too many differences of opinion!

Anyone know anything about pedal ratios?

Apparently, according to Master Power (MP) Brakes,
"As a general rule of thumb your pedal ratio should not exceed:
6:1 for manual brakes with a 1" bore master cylinder
4:1 for power brakes with a 1-1/18" bore master cylinder.

Going by that, and as we're keeping manual brakes we need to be looking at 6:1 with 1" bore. As the master cylinder will be a new part & the pedal won't, I could do with establishing what the pedal ratio is for a '63 b-body, and hope it's 6:1. But that means we're back at 1" bore which Alex & Ash thought too small!
Any records out there about pedal ratios?

Ash - a difference in our applications is that you got a booster and we aint; this may affect what size bore is needed ? Just a guess.
Thinking about that whole dia thing, isnt the bore size a bit like for any fluid passing through a hole, the smaller the hole the greater the pressure?
And high pressure is better than low here isnt it?

The troubleshooting bit in the MP Brakes catalog says for manual brakes with discs front & drums rear, if you got:

Spongy Pedal could be (amongst other things)
Small master cyl bore dia

Hard Pedal could be
Master cyl bore too large

Shows either way if you get it wrong the pedal feel wont be right, and thats certainly something we need to be improving!

Any more ideas?

And I havent started on metering/combination/proportioning/residual valves yet!!

Ashley · Post by **Ashley** » Fri Sep 23, 05 7:23 am

Sorry Rob don't know what the ratio is on your car maybe Alex will ?
Second it dosen't matter whether your using a booster or not it's just there to make it easier for you to stop the car, you still need 1 1/8" bore to give the caliper more fluid

Third you will need a proportion valve in the rear brake line to stop the rear brakes locking up before the front get maximum effort, if you don't the disc conversion will feel POO

Dave-R · Post by **Dave-R** » Fri Sep 23, 05 8:31 am

With manual brakes you want a cylinder bore of one inch or less or you will have to put a huge amount of effort into the pedal to stop. Use an MP adjustable cylinder push-rod (you might have to modify it) to adjust the pedal height so that you have enough travel and also so you can adjust the pedal to a comortable height for your foot.

Been here done this.

Anonymous · Post by **Anonymous** » Fri Sep 23, 05 8:35 am

Thanks Ash
According to my info (from MP Brakes, all learnt within last coupla days!), as you say, you need a proportioning valve for the rears, and likewise a metering valve for the fronts. Also a 10lb residual valve should be in the rear brakes line.
Confusion comes when I read that a combination valve can be used in place of both the proportioning & metering valves. So which system's better?
And also that a proportioning valve can be adjustable. Some sell their kits with an adj version but MP say "not to use one if you can help it. The adj valve will only provide the proportioning function & not the metering that is needed."
Fair enough, if thats right, but all their examples of disc/drum installations circuits with a proportioning valve show an adjustable one! .......Aaaagghhh!

I've sent these queries to SSBC by email so I'll see what they say. MP Brakes cant be contacted by email so cant ask them without phoning.
And in any case their kits dont fit our 14" wheels - I'm just using them to get some knowledge before buying.

See where I get with the emails & help here then I'll get on the blower.

Anyone else out there in MMA land had experience with any of this??????

Anonymous · Post by **Anonymous** » Fri Sep 23, 05 8:41 am

Thanks Dave
That evens it up. 3-3.
You, Paul Knight & MP say 1" or less, Alex, Ashley & Performance Suspension say 1-1/8" !
Are you of the smaller bore - more pressure school of thought then?

Dave-R · Post by **Dave-R** » Fri Sep 23, 05 8:46 am

Rob.

4000lb car x Manual brakes = Holy Crap I'm not going to stop in time

You need all the braking force help you can get if you drive fast. Otherwise you have to really push hard on the pedal.

I use a 1" bore. I think? Can't remember now because it was so long ago.

I have some more information on this at home. I will see if I can dig it out tonight or tomorrow.

Anonymous · Post by **Anonymous** » Fri Sep 23, 05 8:51 am

Rob

Put all the information as to what you have i.e. the car and set up now and what you specifically need to acheive into an email to me and i'll get Don at FBO to sort out what's needed, no obligation quote.

I can supply it and get it into the UK cheaper than most due to our shipping rates

Anonymous · Post by **Anonymous** » Fri Sep 23, 05 9:43 am

Dave, you're right about the 'holy crap' & pushing hard on the pedal bit!
As they are now, at best they work enough to pass an MOT (gawd knows how tho), but at worse theyre downright dangerous. You have to push down quite a way till anything happens then if you need to stop quick-ish and push the last bit (by which time you havent really slowed down at all) harder, it easily locks up. Not so bad for gentle pottering around and with plenty of forward planning, but it's the emergencies you gotta cater for too!

Till now, cos of the engine probs, we've only pussy-footed around, but when its back on t'road it should be better than new (performance wise), and with the odd 1/4 mile pass quite likely, must get the brakes sorted so that the car will stop safely from 100+ mph.

You still got manual brakes then? Can you check what valves etc?

Will, thanks for the offer.
It's a '63 Dodge Polara w/426 Max Wedge running gear. It has the original brakes, ie drums all round (cant remember exact dia but 10-11") manual, single circuit.
We have the original 14" wheels that we want to keep. MP Brakes only do a single pot caliper for these cars so do not fit within a 14" wheel, must be 15 or larger. Others (SSBC & Performance Suspension) do a 4-pot kit that works with 14".
We'd like a stock looking master cylinder, cast iron type, with the brake lines exiting on the drivers side.
Gotta watch we dont get too close to the exh manifold tho. See pic. Cant take any measurements cos the engines out!
I'm not going to quibble about the odd ?? here & there, just want it to work (nearly) 1st time and be a vast improvement.

See pics.....

Anonymous · Post by **Anonymous** » Fri Sep 23, 05 9:58 am

Oops. just realised you said email you the info Will, so have just done so too.

Dave-R · Post by **Dave-R** » Fri Sep 23, 05 10:43 am

RobTwin wrote: You still got manual brakes then? Can you check what valves etc?

Still? The Challenger had power drums all round. I decided on manual brakes with front discs.

The master cylinder is the lightweight later Mopar version. They come in various bore diameters. Easy to fit with a simple adaptor.
I use an adjustable proportioning valve in the line to the rear brakes and later versions of the wheel cylinders in the rear drums.

That is all. You don't need anything else.