Opinion Wanted: Dual Master Cylinder

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northcoastsailor
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Opinion Wanted: Dual Master Cylinder

Post by northcoastsailor » Mon Oct 28, 2019 11:57 pm

I'm at the point in my MB restoration where the chassis is nearly complete, and I can move onto working on the engine and transmission and transfer case. The last sticking point is my braking system.

Background:

A previous owner upgraded all four wheels with 11" drum brakes of a 70s CJ5. It ran the original single reservoir master cylinder until I stripped the vehicle. I had driven close to 500 miles on these brakes and they seemed to perform well.

My jeep is being rebuilt to be a driver. Short stretches on the freeway with speeds up to 55 mph, and around 40 miles per day. Some longer road trips in the Western US and Canada are also planned. I normally keep to the back roads and maintain 45-50mph.

I am currently on the fence about installing a dual MC.

I am wondering if the safety benefit is worth the hassle of fitting and what not. My main concern is that this jeep is driven more frequently and further than the average jeep on this site, and thus any measure of safety (especially in the congested Bay Area) is worth the time and money.

Thoughts?

PS: I already have a kit from Herm on my shelf and have played around with test fitting it; without engine or steering components, however.
GP-MB-2A "Old Crow" (Mostly MB 432554)

Klaas
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Re: Opinion Wanted: Dual Master Cylinder

Post by Klaas » Tue Oct 29, 2019 4:28 am

As you intend to use your jeep as a driver and it already has the bigger brake drums on it, I would go for the dual braking system.
It is always nice that you will be able to stop if anything fails in one of your brakes or brake lines and don't have to rely on the woefully inadequate handbrake.
I would also replace all rubber components and all brake lines with new ones and fill the entire system with silicone brake fluid so you don't have to worry about the hygroscopic nature of the mineral brake fluid and don't have to change it every couple of years.

Don't let the jeep police near your jeep though :D
Klaas
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W. Winget
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Re: Opinion Wanted: Dual Master Cylinder

Post by W. Winget » Tue Oct 29, 2019 4:54 am

Single reservoir worked fine for 75+ years...
If you have dual it's a nice comfort, but if a single failed you have gears and (theoretically) an emergency/parking brake)

If brakes are maintained, (i.e. tested before departing the driveway, no rusted lines under clips, rubber lines in good shape, no leaks on wheels onto driveway) there is no need for a dual reservoir.

Your only adding a comfort, as driving habits with the old Girl should be conservative in the 1st place slowing down before stops, etc.

If I "had" the dual brake reservoir, it would not be on the shelf, but I would not go out of my way to buy and refit one.

Caveat: My 3/4T Command Car I upgraded 3rd members to 4:30 ratios and achieve 62mph...I went to all 4 disc brakes and a dual master out of a Corvette (they actually had a dual master non-powered master cyl available in '78, go figure) Bottom line: I upgraded it and the increased mass I felt prudent to stop with more than the original master could handle, that was a proper choice for safety and not seen by anyone unless they look into the backside of the wheels or down into the engine compartment. I won't be refitting it back to drums....in my lifetime, but still need to get a proportioning valve I think to make it 100% worthwhile, they seem spongy and can't lock up (Silicone perhaps doing that).

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JIMN
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Re: Opinion Wanted: Dual Master Cylinder

Post by JIMN » Tue Oct 29, 2019 8:59 pm

Just installing a dual master cylinder doesn't get you the safety you think it will. Basically if a brake line breaks with the dual system, your pedal will still go to the floor, and you still aren't going to be able to stop, you will have about five percent of your braking ability left, not fifty percent.
Newer vehicles supposedly now have some sort of valves that make the dual cylinders work better, you can investigate that for yourself.

A better reason to upgrade your master cylinder would be to get away from the crappy vented system. Your fluid would last much longer and the system will stay much cleaner.

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W. Winget
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Re: Opinion Wanted: Dual Master Cylinder

Post by W. Winget » Wed Oct 30, 2019 5:47 am

I would disagree with percentages, I blew the rear line (rust under the clip) on my '97 Mercury Mountaineer at a stop light, had to pump twice, maybe three times in the emergency and stomp the parking brake to stop but then got pressure up on the front pads, after checking the fluid I drove it another 60+ miles on front brakes alone before getting a chance to replace the rear line.
There is a small wall in the reservoir basin on most dual masters preventing complete loss of fluid from the master if one or the other gives way.
I would have certainly ran the redlight if there was only one reservoir.

Friend had a brake shoe anchor nut come off (Surplus Deuce) he lost all brake action and put it in a ditch to stop her, that's a little more drama, checked the other anchor bolt nuts and several were loose (military maintenance)
Something to add to a PMCS annual checklist.
V/R W Winget
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northcoastsailor
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Re: Opinion Wanted: Dual Master Cylinder

Post by northcoastsailor » Fri Nov 01, 2019 12:21 pm

Has anyone tried stopping with the E-Brake / Parking brake?

I've got 2.5 months at sea ahead of me to stress about this issue. Just got the brake lines installed to the master cylinder area yesterday.
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Papi Phil
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Re: Opinion Wanted: Dual Master Cylinder

Post by Papi Phil » Sun Nov 03, 2019 12:02 pm

WHICH DUAL MASTER CYLINDER TO USE PLEASE ? I am new to this forum and this is my first post. I just bought a 42 MB and want to install a Dual Master Cylinder....Decades ago I almost got killed when a brake line broke on my M-38 so I don't want to take a chance this time...So I say it is worth it.

But can anyone please tell me which Dual Master Cylinder to buy? Kaiser Willis has one , is it any good? and I see this name "Herm" mentioned but do not know what it is ? Is there another brand? Can anyone help please? many thanks to all.

85jeepcj
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Re: Opinion Wanted: Dual Master Cylinder

Post by 85jeepcj » Sun Nov 03, 2019 2:28 pm

Lots of information on CJ2A page about brake upgrades.
General consensus is no proportion valve needed, larger diameter wheel cylinders used up front vs the rear accomplishes this task.
A dual master brake cylinder isolates front and rear brakes.

ozm29c
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Re: Opinion Wanted: Dual Master Cylinder

Post by ozm29c » Wed Nov 06, 2019 9:46 pm

Northcoastsailor,
Here is an option to consider if you decide to stay with a standard MC. In the photo is an inline vacuum booster that I have recently fitted to an Amphibious Jeep. There was a noticeable improvement in the braking. As I said this is only an option. Cheers.
Attachments
Brake Booster R.jpg
Brake Booster R.jpg (128.2 KiB) Viewed 88 times
GPW 135997
M29C 7333
M29C 4338

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