1960 FC170 and a 68 M715?

[66stepside]

Some rules of thumb:

You probably know this stuff but I'll post it anyhoo:

Smaller MC pistons mean more power but require more travel and vice versa.

Bigger wheel pistons mean more power but require more MC piston travel and vice versa.

Increasing the ratio of the pedal pivot to pedal length vs the pivot to master length increases power but with greater pedal travel.

I just went back and looked through your thread. With the massive K30 front calipers you need a 1-1/4” bore master cylinder. My go to for that is for an 85 K30. There are 2 models, hydro boost and vacuum booster. They are the same specs exempt for the depth of the piston. The hydro unit is flush and the vac unit is recessed at the piston.

I’ve run those calipers with 1” and 1-1/8” bore cylinders. Both will work but will make you feel like you need a change of underwear when the pedal slaps the floor when you really need brakes, good news is they are usually locked up, but still squishy and scary. More volume is the only fix.

As a note about bore size some K10 and all K20 use 1-1/8” bore. I’ve only found 1-1/4” on 78-91 disc brake K30’s. I’ve played with this extensively, those calipers need 1-1/4” bore minimum to have a good pedal feel.

Thanks guys!

I’m running k30 hydro boost on my M715 (k30 drivetrain) and I’ve been using that as a reference for what I’m doing for the FC. The M stops on a dime with the hydro boost set up, so my braking expectations are stupid high for the FC.

I’m stewing on those numbers, diameters and facts you provided. I appreciate the info. And I have a sinking feeling major MC mods will be required, or I’ll have to swap in an 8 lug Dana 44 to replace the Dana 60 front (I don’t want to swap out the front axle! Lol).

I do have the new inline valves coming sometime this week and then I’ll dig further into the squishy brake syndrome.

Meanwhile I am pouring over the details and researching build threads on the Dana 60 front axle swap in all kinds of trucks to see what solutions others have come up with to get their rides to stop properly.

I appreciate the info!

[Yeller]

Another consideration is Parts Mike sells a kit to put k20 rotors and calipers on the d60 front, or at least they used to, I did not look to confirm they still offer it. The kit allows 15” wheels to fit.

[66stepside]

Another consideration is Parts Mike sells a kit to put k20 rotors and calipers on the d60 front, or at least they used to, I did not look to confirm they still offer it. The kit allows 15” wheels to fit.

I saw that on one of the Chevy forums today- thanks for the tip! I’ll be adding that to the list of options for sure.

Thanks!


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[66stepside]

I doubled checked both the lines to ensure they’re routed properly to the proportioning valve and that the front brake line had no RCV, and that the rear brake line did have the valve properly installed.

Everything checked out. More bleeding, more fluid, better braking, but no where it should be IMHO.

The Willwood valves came in:


Custom lines are needed to to get them integrated into the existing lines. No one had the right fittings to mate them together. So Monday I’ll head over to house of hose and have something made.

The space in-between the structural brackets of the dash is too narrow to fit any other type of MC.

Willwood offers a 1 1/8” bore version of the same unit I bought (I bought the unit mentioned on the FC Connection).



It’s 3x the price. But worth it if it can stop the FC!

I also saw these:



This truck originally came with one. I might have to try one.


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[Yeller]

I’m assuming you can push the pedal all the way to the floor by hand? You can feel them apply but it just keeps going? The only cure is more bore but then you will need boost.

I have a similar issue on my bronco, really need hydro boost but it doesn’t fit, need a larger bore master but the reservoir hits the hood. Lager master cylinder requires hydro boost, it is a very vicious cycle, played with it for a long time. Started with a stock 1” bore and no booster, phenomenal braking power with little effort but scary, pedal literally hit the floor. Went to a 1-1/8, significant improvement in feel, still uncomfortable amount of travel also added a stock style booster, 8” dual diaphragm. Found a 1-1/4 bore, pedal feel was much improved but needed more boost, found a 9” with a deeper dual diaphragm, it is satisfactory enough I’m done messing with it. I would really like to go to a 1-3/8 or 1-1/2” bore master with hydro boost but it adds too much length and I can’t find a master that doesn’t go through the hood. Using a 1-3/8 bore with hydro boost and JD2 calipers on my J truck and it is spectacular.

[66stepside]

I’m assuming you can push the pedal all the way to the floor by hand? You can feel them apply but it just keeps going? The only cure is more bore but then you will need boost.

I have a similar issue on my bronco, really need hydro boost but it doesn’t fit, need a larger bore master but the reservoir hits the hood. Lager master cylinder requires hydro boost, it is a very vicious cycle, played with it for a long time. Started with a stock 1” bore and no booster, phenomenal braking power with little effort but scary, pedal literally hit the floor. Went to a 1-1/8, significant improvement in feel, still uncomfortable amount of travel also added a stock style booster, 8” dual diaphragm. Found a 1-1/4 bore, pedal feel was much improved but needed more boost, found a 9” with a deeper dual diaphragm, it is satisfactory enough I’m done messing with it. I would really like to go to a 1-3/8 or 1-1/2” bore master with hydro boost but it adds too much length and I can’t find a master that doesn’t go through the hood. Using a 1-3/8 bore with hydro boost and JD2 calipers on my J truck and it is spectacular.

Yeah, it goes all the way to the floor for about pumps 1-3, then it firms up on about the 4-6th pumps- repeat process. Lol.

It looks like I’ll be doing the same thing you had to do!

I’d love hydro-boost for this application, too, but even the Astro van version is too big to fit. The 90 degree stuff won’t work either as the heater is in the way on one side, and there isn’t enough space toward the driver’s side.

A remote booster is up next if the valve checks don’t work well enough. There are electric booster versions, too. More research will be needed.


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[SJTD]

Seems to me in the deeps of time a read about a "fast fill" master. Has a big bore that moves the brakes agin the drums then the smaller bore gives it the pressure if I remember correctly. Seems to me my '84 had it before I switched to hydroboost. Still got it lying around somewhere I you wants to mess with it for shipping cost. Was new about 20 year ago and only used when I towed the GW from where it was to where it is. Had sillycone (DOT 5) fluid but everyting seemed ok when I disassembled it for a look when I removed it a year or three ago.

Obviously only helps the rear piston which is the rears. I think???

[66stepside]

Seems to me in the deeps of time a read about a "fast fill" master. Has a big bore that moves the brakes agin the drums then the smaller bore gives it the pressure if I remember correctly. Seems to me my '84 had it before I switched to hydroboost. Still got it lying around somewhere I you wants to mess with it for shipping cost. Was new about 20 year ago and only used when I towed the GW from where it was to where it is. Had sillycone (DOT 5) fluid but everyting seemed ok when I disassembled it for a look when I removed it a year or three ago.

Obviously only helps the rear piston which is the rears. I think???

I’ve never heard of that type before. I’m glad you brought up that idea. I appreciate it!

I left the clutch pedal in place (which I normally do not do with an auto conversion) in the event I had to run another MC on the clutch side... like maybe running separate brake lines from two separate MC’s to maximize pressure? It’s a crazy thought, but I might need some crazy ideas in order for this hodgepodge of parts to all function properly.


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[66stepside]

The inline residual check valves are installed. Filled the two reservoirs. Gravity bled the lines, several times.


I Re-bench-bled the MC 3 times. Massive air bubbles at first, then solid fluid. Then I gravity bled all 4 wheels again. Then had the wifey don the winter parka and snow suit (I like working with the shop door open) and she helped me do the initial bleed-the-brakes-process.

I topped off the reservoirs a few times, too.

It stops much better, but she’s still a spongy pedal. I did go back and forth 3 or 4 times 75’ up and down the side drive.

I am tempted to take her for a spin around the block.

Next up, remote booster. Then new 1 1/8” remote res MC swap.


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[Yeller]

At speed it will probably stop well, just make you panic when you first start stopping

[Stuka]

Sounds like the master cylinder is maybe undersized (sorry if this was already mentioned up above).

And just a quick note on your hard lines. The OEM normally has some loops so that vibrations from the chassis don't transfer up into the connections on the MC (acts as a spring of sorts to allow movement). I am by no means an FC expert, so maybe those are farther down below, or maybe you have flex line before it gets to the frame. Just figured I would note it.

[66stepside]

At speed it will probably stop well, just make you panic when you first start stopping

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[66stepside]

Sounds like the master cylinder is maybe undersized (sorry if this was already mentioned up above).

And just a quick note on your hard lines. The OEM normally has some loops so that vibrations from the chassis don't transfer up into the connections on the MC (acts as a spring of sorts to allow movement). I am by no means an FC expert, so maybe those are farther down below, or maybe you have flex line before it gets to the frame. Just figured I would note it.

That a great observation. They were not coiled to begin with, but are coiled closer to the proportioning valve.

Yes, I agree that the MC is probably underpowered. This is a 1” bore, whereas the K30 bore is 1 1/8”.

I did order a remote booster, but the money was refunded due to it being out of stock.

So, I can order another one from a different supplier (like from Willy’s Amercia), or buy the 1 1/8” version of the Willwood MC I have. Ahh, decisions, decisions.


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[Yeller]

I’d do the master cylinder. The booster will not improve pedal feel. In fact it will feel even worse, you just putting more power pushing on that sponge. I’ve ran those calipers on 1-1/8. With a normal dual diaphragm gm booster (90 k5 blazer parts) I could push the peddle to the floor with my hand, but in actual use never got there, I ran it for 5 years, even daily drove it a few of those without complaint. A few buddies drove it and commented the peddle was low but how phenomenal the brakes were.

[66stepside]

I’d do the master cylinder. The booster will not improve pedal feel. In fact it will feel even worse, you just putting more power pushing on that sponge. I’ve ran those calipers on 1-1/8. With a normal dual diaphragm gm booster (90 k5 blazer parts) I could push the peddle to the floor with my hand, but in actual use never got there, I ran it for 5 years, even daily drove it a few of those without complaint. A few buddies drove it and commented the peddle was low but how phenomenal the brakes were.

After the remote booster order cancelation, I’m ordering the new larger bore MC.

I am detailing the interior and putting the stock seats back in, but snipped a piece of tattered cloth off the driver’s side in order to match it up for some new seat covers:







The following pics are of the piece I cut and had washed repeatedly (they’re still wet from the washing):




Here’s a similar pattern I found online:




Not sure if it is close enough for me.


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[66stepside]

More shakedown runs.

For more willy’s parts:


Then for propane... and I wonder how many of these I’ll see pop out of the cracks and crevices?




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[66stepside]

Working on the property:




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[BaldBeardedBastard]

Working on the property:




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This is a great picture.

[66stepside]

Working on the property:




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This is a great picture.

Thanks!


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[5jeepsaz]

Beautiful! Nice to see the truck enjoying some work out there