So you're thinking about the LSMFG Rear Disc Brake Kit? Here's my .02... (Tips and Tricks Guide)

[Curt]

Hey everyone,

To start this off, this isn't going to be a step-by-step DIY for the kit, but rather a tips and tricks guide along with my $.02 about it. If you don't want to read the whole thing and just wanted to hear my opinion skip to the end, I will also include extra parts I needed for the install at the very end.

As it goes with working on any car, YMMV but for reference I have a Pro Comp 4" lifted suburban with the 6 lug 11" drum brakes in the rear. I purchased this kit specifically with the 3.6" axle offset, parking brake calipers, and braided stainless lines (https://www.littleshopmfg.com/gm-88-00-k1500-rear-disc-brakes-6-lug-11-drum/ ). I also purchased the parking brake extenders which ended up being a complete waste of money (more on that at the very end).

The customer service rep at LSMFG was doing his best to try and help out in the entire installation process but obviously won't be able to help me in the trickier stuff. Aside from recommending me to spend and extra $44 on some useless extenders, his overall advice was helpful.

In their kit, LSMFG includes this set of instructions ( https://drive.google.com/file/d/1dFIFn9I2rAjt2-B5xIq9m7UDXWLr20uy/view?usp=sharing ) to get you started, but I later learned from the rep that these instructions are not specific to their kit, so that was very interesting to hear.

Before you get started, you will need a GMT800 disc/disc MC. See this thread for more info: https://www.gmt400.com/threads/how-to-nbs-master-cylinder-swap-for-firm-brake-pedal.17998/

It wasn't terrible swapping it in, but I learned the hard way that our MC is not capable of pushing enough fluid to the rear calipers. My ACDelco MC was only a year old and was installed by a professional mechanic. The brake pedal feel was terrible until I did the swap. Here's some pictures of the swap that I haven't seen uploaded yet.

Here's a shot of the old MC on the top, and new GMT800 on the bottom.

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To install the GMT800 MC, you must re-bend the brake lines to go into the MC. I don't have the adapter on in this picture, but to show you how much you must bend them check out this picture for reference.

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From here on out, I'll be referring to the LSMFG rear disc brake instructions provided for my tips and insight.

Steps 1-6 are pretty straightforward and easy, no issues there.

Step 7: do yourself a favor and REMOVE THE AXLES. I spent hours trying to cut the backing plate off with no success. There isn't enough room to maneuver a cordless cut-off wheel to cut the drum brake backing plate completely off. You can see my failed attempt cutting the plate once the axle flanges got in the way.

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Step 8: With removing the axles, you will realize that their kit is misleading. They state you can install the kit without removing the axles but their caliper mounting bracket is unable to slip over the axle housing. Maybe this is an issue with the 6-lug trucks only but I cannot see how you can make that metal bend enough to fit over the axle housing if you do not remove the axles. I wish I took a picture of what I mean, but if you attempt this install my words will be as clear as day.

Step 9-10: They do not include any torque specs with the kit. I torqued them down to 100 ft-lbs. One huge benefit of removing the axles is I could get a torque wrench on em and be comfortable with the tightness.

**IF YOU HAVE PARKING BRAKE CALIPERS, WATCH THIS VIDEO**

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When adjusting the calipers, make sure you don't have the caliper piston facing the ground. Mine popped out on accident and created a nightmare for me. I won't go into detail but MAKE SURE THE CALIPER PISTON DOESN'T FACE THE GROUND!!

Here's where things start getting interesting...

Of course I had to learn all this the hard way but hopefully I can save you guys some grief here.
They fail to mention that the caliper bleeder valve needs to be positioned at the 12 o' clock position in order to get all the air out of the caliper. The instructions stated bleeder valve must be parallel to the ground but the customer service rep told me their instructions are incorrect and it must be 12 o' clock. I am skipping forward some steps here, but bear with me here.

When the caliper is installed on the vehicle and all buttoned up ready for bleeding, the caliper looks like this:

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Notice how the bleeder valve is at the 10 o' clock position? Well, you can't just rotate the whole mounting assembly to the 12 o' clock position... why? Your brake line will not be able to reach it.

Without knowing the 12 o' clock deal... I was able to bleed the brakes with no air coming out of the calipers, and wasted a ton of fluid. After spongy brakes and contacting them, I found out what I'm telling you guys. I drew a little picture of what's going on to make things a little more clear.

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So, what did I do? Luckily I had some spare aluminum laying around and I made a shim to go in-between the brake pads so I can hold the caliper in the air to get the bleeder valve at 12 o' clock while my dad pumped the brakes and my brother bled the brakes. It was a 3 man process.

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I had to get creative to get all the air out, I wish there was a simpler and universal way. It seems like the 5-lug guys say rotating the caliper mounting bracket works, but I had already torqued them down to 100 ft-lbs and had the axle back on. If you try rotating your caliper bracket and it works, let me know! Back to the steps...

Steps 11- 16: Straightforward.

Steps 17-18: Cut the ears next to the rotor hat off. They will most likely contact the rotor hat and that isn't good.

Steps 19-22: Straightforward. Knowing the bleeding procedure now, you should have done all this before final assembly.

Before bleeding the brakes, do this:

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. This only applies if you swapped out to the GMT800 MC, or want to make sure there is 0 chance of air being trapped in the ABS before bleeding. Re-bleeding these rear calipers aren't fun... ask me how I know.

Steps 23-24: This is where I was extremely disappointed in the kit. I was told my parking brake cables would work and I would not need to spend an addition $300 on some Wilwood cut-to-fit cables. The rep told me that the extenders would work, etc. etc. After sending him pictures of my drivers side cable coming up short. He recommended the $300 kit. To have completely transparency, the rep did offer to cancel my extender order and refund me, but I told him I wanted the extenders to see if I could somehow make it work. After receiving them, I cannot see how these would be useful to anybody.

So how did I get my cables to work? After taking a month off working on the brakes, I used my brainpower and did some research. Thank the man upstairs when I found out 2 different length parking brake cables were produced for the suburban. The factory cables on the 1500 suburbans are 86" long. I managed to find a different version made for our trucks that is 91" long. This step is really only needed if you have a lifted suburban.

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It wasn't a direct plug-and-play, and I had to grind down a little part of it to make it fit in the adjuster. Here's a pic of it marked out and cut.

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After grinding down the adjuster, the mounting slot for the cable on the caliper was too small for the cable. I had to take a grinder to those as well and widen the slot for the cable to fit.

To install the parking brake cable, you must snip off the parking brake cable ends and remove the spring. I used some bolt cutters to cut the cable. Then, use their included parking brake cable ends to install the parking brake cable.

Since you have an extended drivers side cable, the housing snaps right into the caliper. The passenger side? Find the two bolts attaching the cable housing to the rear axle housing. Once the cable housing is free floating, adjust the cable length from the parking brake adjuster. Snap the housing into the caliper and re-position the brackets holding the cable housing to the axle housing. Connect up your cable to the mounting plate (after grinding it open) and you're set.

Once the parking brake was installed, the installation is complete. Now here's my .02 on the kit.
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So I guess the big question is, was it worth it?

If you're looking for an upgrade in braking performance, then no, it wasn't worth it. It at most reduced my stopping distance by like 5 feet, if that. I never did any baseline tests, and I almost wish I had. For almost $650, I feel like you could spend the money elsewhere to get better stopping power. The only thing I really like about the brakes now is the pedal, but that's mainly due to the MC... not the kit.

If you're looking for to do this as an aesthetic mod, then 100% worth it. I love seeing some rear discs poking out from the rear of the truck. Just brings it one step closer to the 21st century and I love it. As an added bonus the kit pushed out the wheels 0.2" and the fitment of the rear wheels is perfect.

If you're looking to do this as an easy DIY project, it's not as easy as my thread makes it seem. Lots of troubles along the way and honestly, I don't even think a professional brake shop could've got this done. So many stupid hiccups and quirks with this kit that aren't mentioned to begin with. Everything in the thread seems like I did all of it chronologically. In fact I had to re-bleed the calipers 3 times (once for the initial, twice for the 12 o' clock position, then the third time after the GMT800 MC was on) and was informed/found out about most of the other stuff way too late. I want to save you guys the hassle if you decide to tackle a project like this.

Now here's the additional parts list that I needed to make everything work, I will include part numbers, but obviously can be purchased at the store of your choice:

1500 GMT800 disc/disc MC (Duralast NM3089)
MC Adapter (BLF-26C)
DOT 3 Brake Fluid (obviously haha)
Extended Parking Brake (Carquest BCA95545)
Parking Brake Cable Connector (Dorman 21123)
Rear End Gasket (FEL-PRO RDS55028-1)
Rear End Gear Oil (80W-90, GL-5 rated)

If you have any questions about the kit, feel free to ask and I'll reply to the best of my knowledge.

 

[1997]

nice work and posting all the info. Too bad it doesn't stop on a dime now, lots of work. That's quite the leaf pack on the rear.

 

[Curt]

nice work and posting all the info. Too bad it doesn't stop on a dime now, lots of work. That's quite the leaf pack on the rear.

Thanks! Hopefully others who decide to get this kit read this and prepare themselves for the headache ahead. I agree, I expected better braking performance but it is what it is. I added an add-a-leaf back in 2016 but I don't think she'll accept another one haha. They're the ones that came from factory so it's probably long overdue for a replacement with all the hauling and towing I do.

 

[delta_p]

Great writeup!
What do you mean when you said, "our MC is not capable of pushing enough fluid to the rear calipers."? I know the rear proportioning inside the combination valve pack that sits on the inlet to the ABS packages is set up for drums with a limit rear pressure so they don't lock up. Does the kit say anything about that for the disc setup?

 

[df2x4]

Thanks for the write-up and honest review of the product. Makes me feel a little better about being lazy and sticking to drums on my upcoming axle swap. The discs do look nice, though.

 

[Curt]

Great writeup!
What do you mean when you said, "our MC is not capable of pushing enough fluid to the rear calipers."? I know the rear proportioning inside the combination valve pack that sits on the inlet to the ABS packages is set up for drums with a limit rear pressure so they don't lock up. Does the kit say anything about that for the disc setup?

I should've included that was my speculation, my bad.

After following the LSMFG advice to have the bleeder valve at the 12 o'clock while bleeding the calipers, I managed to get the rear calipers bled 100%. The pedal feel was absolute garbage with the disc/drum original MC. It was extremely squishy and I was througly displeased after knowing I got 100% of the air out of the system this time around (this was my second attempt bleeding all four corners and the ABS). I did a test where I put the truck in gear while the rear end was in the air to see how much pedal travel it took until the rear wheels stopped under idle. It took about 65-75% of the brake pedal travel to get the rear wheels to stop in 1st gear idling. I assumed the GMT400 MC didn't have a big enough piston to get enough brake pressure to the rear discs. Once I went to the GMT800 disc/disc setup, the rear discs stopped after 15-20% pedal travel.

As far as the proportioning valve goes, they do make a note of it on their install at the very end. I inquired about it and they said it really isn't needed but I could add it if I wanted to. I'm sure adding the adjustable proportioning valve would've helped though, unfortunately I can't say for sure.

Thanks for the write-up and honest review of the product. Makes me feel a little better about being lazy and sticking to drums on my upcoming axle swap. The discs do look nice, though.

No problem. I really thought the rear discs were the way to go, but maybe I just chose the wrong kit. Love the look of the kit, but definitely not the hole it burned in my wallet, along with the massive headache haha.

 

[delta_p]

As far as the proportioning valve goes, they do make a note of it on their install at the very end. I inquired about it and they said it really isn't needed but I could add it if I wanted to. I'm sure adding the adjustable proportioning valve would've helped though, unfortunately I can't say for sure.

I went and read the instructions. Not sure your getting the full benefits of the rear disc if only the MC is changed. Did you do anything to the stock rear proportioning?

When I read the instruction I took it as you either run new adjustable rear proportioning valve or you modify the one that is already in the system at the ABS. Currently, with no mods and running through the combination valve at the ABS (which has a rear prop valve) it's going to try to limit the rear pressure to around 300 psi or the pressure that would otherwise lockup a rear drum. Under light braking like cruising up comfortable to the red light or in parking lots it shouldn't matter. The disc calipers are going to work better under a more aggressive pedal apply at much higher pressure. So the seal and the spring can be removed and allow full pressure to the rear. It noted that the rear shouldn't lock up before the front, and it shouldn't because there is a front metering valve already in the original combo valve. But the instructions noted if a separate adjustable rear proportioning valve is used it can be adjusted to compensate some for that if needed. I took the instructions as you don't run both the original or an adjustable valve you either remove the seal and spring from the original, or you run from the MC to an added adjustable valve to the rear.

The instruction I was looking at were these.
http://littleshopmfg.com/content/DBC GM C150010.pdf

 

[Curt]

I went and read the instructions. Not sure your getting the full benefits of the rear disc if only the MC is changed. Did you do anything to the stock rear proportioning?

When I read the instruction I took it as you either run new adjustable rear proportioning valve or you modify the one that is already in the system at the ABS. Currently, with no mods and running through the combination valve at the ABS (which has a rear prop valve) it's going to try to limit the rear pressure to around 300 psi or the pressure that would otherwise lockup a rear drum. Under light braking like cruising up comfortable to the red light or in parking lots it shouldn't matter. The disc calipers are going to work better under a more aggressive pedal apply at much higher pressure. So the seal and the spring can be removed and allow full pressure to the rear. It noted that the rear shouldn't lock up before the front, and it shouldn't because there is a front metering valve already in the original combo valve. But the instructions noted if a separate adjustable rear proportioning valve is used it can be adjusted to compensate some for that if needed. I took the instructions as you don't run both the original or an adjustable valve you either remove the seal and spring from the original, or you run from the MC to an added adjustable valve to the rear.

The instruction I was looking at were these.
http://littleshopmfg.com/content/DBC GM C150010.pdf

For right now, I'm going to leave it alone. They work just as good as stock, but I expected more out of it for a $640 brake job. I don't think I'm getting the full potential of these brakes (because of the prop valve), but if the brakes are not up to par under heavier loads, I'll modify the proportioning valve accordingly. With the way it sits as-is the brakes work and I'll live with them. After I installed the brakes, I pulled the ABS fuse and tried to lock up the rear wheels and haven't been able to so that's a good sign.

 

[Gibson]

but I learned the hard way that our MC is not capable of pushing enough fluid to the rear calipers.

With discs the "pushing" of fluid is extremely small, once the piston in the MC covers-up the compensating port their is only a transfer of pressure thru a medium.
With drums you DO have to move a relatively large amount of fluid to expand the wheel cylinders before the shoes even start to exert any useable braking effort.
The discs are already in contact with the rotors, the movement between no brakes to full brakes can be measured in thousands of an inch.
Basic Hydraulics 101.

 

[SAATR]

Out of curiosity, what pads are you using? Front and rear?