A couple ?s

[ThatOneGuy]

First question
Does anyone know if a first gen clutch master cylinder has the ability to properly actuate the slave cylinder of an m50d, or do I need to use the 93 master cylinder.

Second question
I am going to be swaping in an 8.8 l.s. disk brake axle. If I were to use a 98 expo brake master cylinder, can I use the 83 brake booster, or can I use a 91 booster, or does the booster also need to be from a rear disk expo. I know I could use the 83 brake booster and master, but it would cause excelerated rear pad wear, however I would like to run the correct parts if it's possible. The other question is if I use the latter disk brake booster and master does anyone know if it's direct bolt in. I've read alot of articles, and posts. But these are some points that were either not too clear or I forgot. It's been alot trying to prepare for this swap. I'm hoping to have everything ready by the time the block is done.

 

[scotts90ranger]

They started using the M5OD in '87 on the 4 cylinder Rangers, so I would imagine that might not have changed, the hose might have...

When I went to disc brake on my '90 I didn't change the master cylinder, given I don't drive it much anymore so I haven't noticed the rear pads wearing fast or anything the breaking is extremely predictable... pads are cheap unless you are going to be putting a bunch of miles on it... if I put one of the explorer axles I'll have at my disposal on my '97 I wasn't planning on changing the master, but maybe I would since I'll have one on hand...

 

[sgtsandman]

I think the only difference between a rear drum brake master and a rear disc brake master is the proportioning for the rear brakes. I would make sure everything looks the same between the two before you commit. Take pictures of your original and compare them to the proposed replacement just to make sure. Look at the connections and the mount. I think ABS is all handled by a separate module but better to be sure before you start wrenching.

 

[Uncle Gump]

I think disc brake master cylinders use a larger bore piston then drum brakes masters.

At least every system I installed in the dune buggy world did. Larger surface area on the caliper pistons required larger bore masters.

I'm not positive this holds true in factory applications... but I believe it does.

 

[Fast Eddie]

I see you updated your avatar to the Bronc you scored. How'd that all go and what's next for you? Don't see a build link in your sig.

 

[Uncle Gump]

I see you updated your avatar to the Bronc you scored. How'd that all go and what's next for you? Don't see a build link in your sig.

I was kinda waiting to post it up after it was delivered... I planned to post how I went about it in the thread. Craziest thing I've ever done. It's on a truck headed here and should arrive Wednesday. Stay tuned for more details.

 

[RonD]

If the larger master fits on the booster then it will be fine, booster is just an assist mechanism for applying pressure to master

Yes, the proportioning for a pickup truck is usually 70/30(front/back) because there is less weight in an empty bed
Cars and SUVs use 60/40

And because disc brakes are less likely to lock up a wheel 60/40 might be better
And even switching to an adjustable proportioning valve on the rear brake line is a good idea so YOU can adjust it for your driving and braking habits


I don't think the fluid capacity of the slave/caliper would be an issue since any master would have enough fluid to apply pressure to all 4 wheels equally as proportioned
After bleeding the brakes there is more fluid in a caliper than a wheel cylinder(drum brake) but its there now, so not a factor in braking

 

[don4331]

I think the only difference between a rear drum brake master and a rear disc brake master is the proportioning for the rear brakes.

The biggest difference is the drum brake setup holds 10 psi on the drums line as they have significant springs to release the pads upon release of application, while the disc brake setup only holds 2 psi residual as there are no springs on the disc brake setup.
The extra 8 psi will wear the pads on the disc calipers faster than normal - noticeable if it is your daily driver and you are doing mostly city driving. If it's your toy/mostly hiway, you won't notice.

 

[Uncle Gump]

When I was a distributer for CNC I spoke to them before placing my first stock order. Their recommendations and pedal assemblies were configured with a 5/8 bore for drum brake applications and 3/4 bore for disc brake applications. They stated the pedal effort was to high for the drum brake master to properly operate disc brakes. These were non power assist systems but I have always followed their recommendations and I guess always thought disc brake master cylinders were larger bores.

 

[don4331]

@Uncle Gump: Something in there is bass ackwards. Assuming disc brakes operate at 1,600 psi

The 3/4" bore requires ~700lbs at rod or 140 lbs at pedal (assuming 5:1 mechanical advantage between pedal and rod).​

The 5/8" bore only requires ~500lbs at rod or 100 lbs at pedal (same assumption).​

​

So, the larger bore requires almost 40% more effort on the pedal!​

Specific cases:
For the Explorer, the piston in the rear disc brakes is 50mm, while for the Ranger drum brakes, its more like 21mm. But the extra diameter of Explorer discs is offset by larger distance the Ranger drums have to move, so the volume is actually very close.

When Mustang brakes are used, as they have a much smaller, 38mm, piston, they do put more pressure to the rear brakes faster as volume is smaller, accelerating rear pad wear. Smaller piston size and smaller rotors means that even though they are activating the rear brakes more, they aren't causing rear lockup - they're just too small and RABS or ABS will release pressure if they do.

 

[Uncle Gump]

Ya know Don... I'm no hydraulics expert. The conversation I had with them was nearly thirty years ago. I may have something wrong in what I said but I'm pretty sure that was what I was told.

However... there is no disputing the fact that their disc brake masters were 3/4 bore and their drum brakes master were 5/8 bore.

 

[scotts90ranger]

I'm pretty sure the answer to this is changing master cylinders is probably the "right" way to go but will it matter significantly? Marginally I imagine, as noted above if daily driven and towing and such you might get better feel and pad life. I can guarantee you it isn't a game changer, just having power brakes puts you in the right direction I'm sure... Then again, I'm all for shortcuts especially if they work reasonably, sometimes I do things the right way but I don't think it's unsafe or anything to use the stock parts...

 

[ThatOneGuy]

Thank you everyone for the input and thoughts. Now most of the responses have been about my brake questions. Is there anymore input as to my clutch master question, there has to be someone who has put an m50d into their first gen and can verify whether I need to swap to a modern master cylinder. I've got one response saying the 83 master should work, which I hope for due to not being sure if a 91 clutch master is bolt in. Don't want to modify if I don't have to again thanks for all the help you have all given me on this project.

 

[sgtsandman]

I think the lack of response on the clutch is because no one knows the answer. I certainly don’t.

 

[ThatOneGuy]

I think the lack of response on the clutch is because no one knows the answer. I certainly don’t.

I was afraid of that lolwell I guess I'll just be the source of knowledge on that one when it comes time to put the trans in