Picking right master cylinder for 1 tons (1 Viewer)

[workingdog]

I've put dana 60 in the front and 14 bolt in the rear of my 40 and I'm still trying to get the brakes dialed in. They have great feel, but no bottom, you can't lock them up. I got the LowRange offroad chevy master cylinder conversion kit which has a GM 1 ton truck master cylinder with 1 1/4" bore. However, it's set up for disc/drum (unequal reservoirs) and I have disc/disc. I call wilwood and because I have dual piston front and rear, the surface area of the pistons is so great, they don't even make a MC big enough (their biggest is 1 1/8").

My question is, can I make the MC I have work (and I just need to do more bleeding or some other adjustment), or do I need to find a GM 1 ton MC set up for disc/disc (which I have not been able to do - I know it's out there, just can't identify).

 

[peesalot]

My 1970 FJ40 stock MC pushes 4 GM calipers just fine, and they are not the little metric ones.

 

[whitey45]

Running an early corvette 1969 master( 4 wheel disc from the factory( chevy dana 60)big single piston caliper) 14 bolt with 3/4 ton disc brakes and calipers. Nice firm pedal, stops well. Only complaint is I am using a toyota booster and it needs more assist. Thinking hydro boost is the way to go.

 

[workingdog]

@peesalot - how is that possible - it's like 4 times the total flow. I know - all you ever do is slow down a little bit. I had a stock toyota on the FJ60 with the same axles, it worked okay, but not great. Wilwood said 1 1/4" minimum. The stock toyota is what? 7/8"?

 

[peesalot]

I dunno, I use the bolt on GM calipers ( 3/4 ton or whatever people call em ), IIRC 86' blazer is the parts house application. No double pump or nothin, Now I did not remove the residual valves so maybe thats helping, My MC is the dual resivior not the single. No proportion valve and it stops really good for a 95 wheel base on 38's bias ply. IMO the 80 series MC are great, plenty of 4 wheel discs on those. When you say 1 ton brakes, please elaborate as there are different set ups,1 ton is vague.
If you think about the volume of fluid the MC pushes, and compare the 8 wheel cyl. it was designed to move and the GM calipers that don't gotta move far( prolly cause the res. valves hold em close) the fluid volume is sufficient. FWIW I have had the GM calipers get stuck or sticky, and had to replace which is a pain cause the fronts need a bit of grinding to fit the Dedenbear knuckles. This usually happens after pressure washing, don't pressure wash the calipers.......

NOTE: My memory just flashed and I was incorrect, the rear calipers are the metric GM ones that are a bit smaller than the 3/4 ton ones I have on the front, this may also be a reason the old 70' MC does the job.

 

[cruisermatt]

I dunno, I use the bolt on GM calipers ( 3/4 ton or whatever people call em ), IIRC 86' blazer is the parts house application. No double pump or nothin, Now I did not remove the residual valves so maybe thats helping, My MC is the dual resivior not the single. No proportion valve and it stops really good for a 95 wheel base on 38's bias ply. IMO the 80 series MC are great, plenty of 4 wheel discs on those. When you say 1 ton brakes, please elaborate as there are different set ups,1 ton is vague.
If you think about the volume of fluid the MC pushes, and compare the 8 wheel cyl. it was designed to move and the GM calipers that don't gotta move far( prolly cause the res. valves hold em close) the fluid volume is sufficient. FWIW I have had the GM calipers get stuck or sticky, and had to replace which is a pain cause the fronts need a bit of grinding to fit the Dedenbear knuckles. This usually happens after pressure washing, don't pressure wash the calipers.......

NOTE: My memory just flashed and I was incorrect, the rear calipers are the metric GM ones that are a bit smaller than the 3/4 ton ones I have on the front, this may also be a reason the old 70' MC does the job.

yeah, so @workingdog calipers are about double the piston surface of what you have.

 

[peesalot]

Assuming he is using the stock brakes that came on those axles-

 

[workingdog]

Probably not stock. Dana 60 in front, 14 bolt in rear. All double piston and the pistons are around 2" - 2.1" each.

 

[workingdog]

Okay, I'm bringing this back to life as I have to figure out how to fix this. The pedal feel is great for about 75 breaking, and then the pedal keeps going all the way to the floor and you don't get full braking power. So, you can drive around wonderfully until you have to panic stop or stop on a steep hill. Pumping them up does not help.

I've got an 1 1/4" bore chevy master cylinder. However, I have discs front and rear and the master cylinder has uneven reservoirs (for disc front, drum rear). Is that going to keep the brakes from working correctly? Or do I need to look at something else.

 

[EWheeler]

Okay, I'm bringing this back to life as I have to figure out how to fix this. The pedal feel is great for about 75 breaking, and then the pedal keeps going all the way to the floor and you don't get full braking power. So, you can drive around wonderfully until you have to panic stop or stop on a steep hill. Pumping them up does not help.

I've got an 1 1/4" bore chevy master cylinder. However, I have discs front and rear and the master cylinder has uneven reservoirs (for disc front, drum rear). Is that going to keep the brakes from working correctly? Or do I need to look at something else.

Replace the calipers with the smaller metric ones mentioned above? Do some searching on Pirate4x4 (search, dont ask, everyone with real world experience is long gone from that site, but lots of good tech still exists) there are probably hundreds if not thousands of documented 1-ton builds there. The Billavista tech articles are still up. He may have addressed this in his 14bolt bible?

The master cylinder in my 2002 chevy 2500hd works for discs front and rear. May be worth a look? Who knows if it would bolt up to your booster and then you have to worry about if the brake line nuts are compatible. These are the joys of building custom s***. Or go drop it off at WFO and pay them to solve your problems.

 

[EWheeler]

Okay, I'm bringing this back to life as I have to figure out how to fix this. The pedal feel is great for about 75 breaking, and then the pedal keeps going all the way to the floor and you don't get full braking power. So, you can drive around wonderfully until you have to panic stop or stop on a steep hill. Pumping them up does not help.

I've got an 1 1/4" bore chevy master cylinder. However, I have discs front and rear and the master cylinder has uneven reservoirs (for disc front, drum rear). Is that going to keep the brakes from working correctly? Or do I need to look at something else.

Addressing your specific question about uneven reservoirs, have someone watch the reservoirs when depressing the pedal. Does one empty? I am going to guess no, because no engineer would design a reservior that could be emptied within the possible operating stroke of the master cylinder piston. You have a bore diameter and a stroke = volume. You could do some maths to calculate what your clamping force is for the volume displaced at your master cylinder given number of pistons and diameter of them in the calipers. Im sure there is a generally acceptable number for minimum required clamping force for effective brakes.