Dual Master Upgrade

vuldub · Post by **vuldub** » Tue Jul 23, 2013 1:14 pm

Current setup
11" x 2" shoes, 11" drums all around (front and rear)
Front wheel cylinders 1 1/8" bore
Rear wheel cylinders 15/16" bore
Single reservoir master 1" bore
Firewall mounted master (upgraded)

Upgrade desired
Dual reservoir master

Several questions:
1) Will any dual reservoir 1" bore, firewall mount, work? I am eyeing a 72-76 CJ5 dual master wo/ power w/front drums.
2) What's the difference or desirableness about Herm's dual master?
3) Does the original 72-76 CJ5 have a proportioning valve (wheel cylinder bores are listed as 1 1/8" front and 15/16" in rear - same as my setup)
4) Can I do without a proportioning valve since my wheel cylinder bores are balanced for more front braking

Post by **wesk** » Tue Jul 23, 2013 6:46 pm

Use Herm's kit. The master cylinder he uses is the stock dual master cylinder used under the floor by the CJ5 1969 thru 72. It's the simplist way and there no need for proportioning valves with that 69 to 72 set-up. The 69 to 72 used the 10" brakes but the 11's you have will work fine.

vuldub · Post by **vuldub** » Wed Jul 24, 2013 7:11 am

Thanks Wes. My master cylinder is not floor mounted, it's on the firewall. The pedals on my m38 have been swapped out along with the steering column. Herm's master looks like it will bolt right into my firewall setup, however I would like to know the bore of the cylinder he uses. I need a 1" bore. I believe the CJ5's from 72-75 used a dual 1" bore equal sized primary and secondary reservoir. But I didn't know if they had a proportioning valve.

Post by **wesk** » Wed Jul 24, 2013 8:55 am

If you plan on staying with a 72-76 CJ5 brake system it would be a good idea to get a 72-76 CJ5 parts and service manual. The 72 manual shows no proportioning valve. Only two residual check valves, one in each outlet port.

vuldub · Post by **vuldub** » Wed Jul 24, 2013 10:59 am

wesk wrote:If you plan on staying with a 72-76 CJ5 brake system it would be a good idea to get a 72-76 CJ5 parts and service manual. The 72 manual shows no proportioning valve. Only two residual check valves, one in each outlet port.

My 11" brakes were upgraded from a 72 CJ5 and the master is a single reservoir from a 66 ford pickup. I would like to replace the master with the 72 dual cylinder however I was unclear on the proportioning valve. Would the residual check valves be integrated with the new master or are they a separate part? I would love to get the service manual, however this jeep is now composed of parts from various vehicles requiring the purchase multiple service manuals.

vuldub · Post by **vuldub** » Wed Jul 24, 2013 11:32 am

Thinking about this more, if I have drums all around and I buy a 72 dual master specific to drums w/o power booster, wouldn't the residual pressure valve already be setup inside for similar pressure (for drums) from both chambers?

PS> I found an 74 CJ5 service manual. Apparently the proportioning valve was added in 74 in a "combination valve" . 72 didn't have one.

artificer · Post by **artificer** » Wed Jul 24, 2013 3:08 pm

Provided the master cylinder is firewall mounted use any firewall fitted Ford or GM 1" bore or other make for that matter.
With the correct size wheel cylinders no proportioning valve is needed so just forget about that aspect.

The master cylinders should be listed, on Rock Auto for example, as with or without residual brake pressure valves [2 for drum brakes or 1 to the rear line & none in the front disc brake circuit].

A master cylinder without 2 valves CAN easily be retrofitted with them.

http://www.rockauto.com/catalog/x,carco ... for%2Bford

RAYBESTOS Part # RMC39468 More Info Reman
Master Cylinder (Remanufactured); 3/4 TON and 4 WHEEL/ALL WHEEL DRIVE Except FT DISC/RR DRUM,1" $12.71

Post by **wesk** » Wed Jul 24, 2013 6:59 pm

Wes,

Posted: Wed Jul 24, 2013 11:32 pm Post subject:
Thinking about this more, if I have drums all around and I buy a 72 dual master specific to drums w/o power booster, wouldn't the residual pressure valve already be setup inside for similar pressure (for drums) from both chambers?

Yes the 72 master cylinder has the residual valves built in to the outlet ports.

Since the brakes on the axles and the hanging pedals both come from a 72 Jeep then just stay with the 72 jeep parts and buy a replacement master cylinder for a 72 jeep CJ5 with 11" drums front and rear. Plumb it up and adjust the pedal rod and bleed and you are all set.

vuldub · Post by **vuldub** » Mon Jul 29, 2013 1:39 pm

Great. Thanks guys. Two thumbs up.

CapnDan · Post by **CapnDan** » Mon Mar 20, 2023 10:57 am

Vuldub: How were you able to mount a master cylinder to firewall? Could you share how you did it, with a picture? Looking at my 54 M38A1 I don't see enough flat area above brake pedal to mount it.

RonD2 · Post by **RonD2** » Mon Mar 20, 2023 12:07 pm

Hi Danny,
Not sure if you noticed this thread is almost 10 years old?
His last post of any kind in this forum was going on 7 years ago.

Just a thought --- you might get better response by starting a new thread to ask your question?

Good luck!

Post by **wesk** » Mon Mar 20, 2023 2:31 pm

Here's a few links to folks that have been there, done that:

https://forums.g503.com/viewtopic.php?t=181801

http://earlycj5.com/xf_cj5/index.php?th ... st-1604134

https://www.jamcosuspension.com/product ... kit-pbbufw

As I recall there is quite a bit of room on the M38A1 firewall with the F134 engine for swinging pedals and a firewall mounted master cylinder.