Rear disc conversion

[letitsnow]

@letitsnow has a Lugnut4x4 kit on his K2500;

I do. I also deleted all abs stuff and replaced with a wilwood adjustable proportioning valve. Am still using the oem master cylinder.

My brakes work good, no soft pedal - but the pedal travel is more than trucks that I have driven with an NBS master installed.

Soft pedal tells me that the OP either has air in a line, or the master cylinder and/or abs stuff isn't working correctly.

One thing to look at is where the rear calipers mount - mine weren't perfectly centered on the rear discs.

 

[Clevor]

Did you change the master cylinder? I know some folks who convert to disc end up moving to the NBS master cylinder since they are designed to apply the correct pressure for a disc/disc setup vs the GMT400 master that are designed to apply pressure for a disc/drum setup.

No I didn't b/c lugnut4x4 says I don't have to. But in the back of my mind, I didn't understand how this could work b/c the disc calipers have much larger Pistons than the wheel cylinder Pistons. Those brakes have been bled many times by a shop that has the abs tool to do that. They are also the ones that did the conversion. I trust them b/c I use to work for the owner in automotive repair. The guy is sharp. They also made many calls to lugnut4x4 trying to get a better pedal. I really don't think it has air in it.

 

[Clevor]

I do. I also deleted all abs stuff and replaced with a wilwood adjustable proportioning valve. Am still using the oem master cylinder.

My brakes work good, no soft pedal - but the pedal travel is more than trucks that I have driven with an NBS master installed.

Soft pedal tells me that the OP either has air in a line, or the master cylinder and/or abs stuff isn't working correctly.

One thing to look at is where the rear calipers mount - mine weren't perfectly centered on the rear discs.

I can look at the brake centering issue tomorrow but in the meantime I think my soft pedal is more of a long travel issue. Unnerving when panic stopping with 3000lb trl. Did the owners of the other trucks happen to tell u what master cylinder they used?

 

[Clevor]

Did you change the master cylinder? I know some folks who convert to disc end up moving to the NBS master cylinder since they are designed to apply the correct pressure for a disc/disc setup vs the GMT400 master that are designed to apply pressure for a disc/drum setup.

I'm also thinking that the soft pedal issue is more of a long travel issue. Unnerving when making panic stop w/3000lb trl.

 

[letitsnow]

Did the owners of the other trucks happen to tell u what master cylinder they used?

They didn't.

 

[Schurkey]

I didn't understand how this could work b/c the disc calipers have much larger Pistons than the wheel cylinder Pistons.

Bigger pistons that have much less travel. APPROXIMATELY the same fluid volume used compared to drum wheel cylinders that are much smaller but travel farther.

Disc brake conversions are often disappointing; either there's pedal height problems, or braking power problems. Sometimes both. Don't get me started on the engineering failure involved in some disc conversions using flat-steel brackets instead of the OEM-style brackets that take caliper thrust in-line between the pads. Some flat-steel brackets over-stress the caliper mounting bolts.

Soft pedal AND dragging could be the master cylinder pistons not returning to their at-rest position as they should. But there's other causes--or multiple causes--as well. By "multiple causes", I mean one problem for the soft pedal, another problem for the dragging.

Is it the front or the rear or both that drags?

 

[Dropped88]

I used lugnuts4x4 on my 99 c3500 srw and having no issues my pedal feels almost identical to when i had drum.

 

[Clevor]

Bigger pistons that have much less travel. APPROXIMATELY the same fluid volume used compared to drum wheel cylinders that are much smaller but travel farther.

Disc brake conversions are often disappointing; either there's pedal height problems, or braking power problems. Sometimes both. Don't get me started on the engineering failure involved in some disc conversions using flat-steel brackets instead of the OEM-style brackets that take caliper thrust in-line between the pads. Some flat-steel brackets over-stress the caliper mounting bolts.

Soft pedal AND dragging could be the master cylinder pistons not returning to their at-rest position as they should. But there's other causes--or multiple causes--as well. By "multiple causes", I mean one problem for the soft pedal, another problem for the dragging.

Is it the front or the rear or both that drags?

Rear, goes away when putting my foot under pedal and lifting with toe after braking. Long pedal travel. Unnerving

 

[letitsnow]

Thinking more about this - The lugnutz disc brake brackets weren't holding my rear calipers perfectly square to the rotors. This was making the rear pads bind because when new, there wasn't enough room for the brake pads to fully retract. There was some sort of shim in with the brake pads that I removed - that gave me enough clearance to run without binding.

I have put a bunch of miles on this set up now, and it works really good - you can tell (when looking at the brake pads) that they are wearing at a bit of an angle, so they will wear out faster than they should, but they still are wearing pretty slow.

Having the adjustable prop valve is probably a big part of making this work though, as I can adjust how much fluid is going to the rear brakes. This might make my pedal travel less than yours.

My rear axle is the SF 14 bolt. I had to grind a bit of the casting flash off of the oem rear axles to get this to work also. At first I was bummed out, then I remembered that 90% of all aftermarket parts that I have ever purchased - they have needed tweaking to get them to work as advertised. Seems to be just the way that it goes.

 

[Clevor]

Thinking more about this - The lugnutz disc brake brackets weren't holding my rear calipers perfectly square to the rotors. This was making the rear pads bind because when new, there wasn't enough room for the brake pads to fully retract. There was some sort of shim in with the brake pads that I removed - that gave me enough clearance to run without binding.

I have put a bunch of miles on this set up now, and it works really good - you can tell (when looking at the brake pads) that they are wearing at a bit of an angle, so they will wear out faster than they should, but they still are wearing pretty slow.

Having the adjustable prop valve is probably a big part of making this work though, as I can adjust how much fluid is going to the rear brakes. This might make my pedal travel less than yours.

My rear axle is the SF 14 bolt. I had to grind a bit of the casting flash off of the oem rear axles to get this to work also. At first I was bummed out, then I remembered that 90% of all aftermarket parts that I have ever purchased - they have needed tweaking to get them to work as advertised. Seems to be just the way that it goes.

Do u remember the Wilwood part number?