Rear Drums Anyone??

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kylenautique

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Out of curiosity, did you actually go out to an empty road and mark your braking distances before and after? Did you nab the disc brake proportioning valve along with everything else? My guess is that your drum brakes weren't adjusted properly and your disc brakes - which are barely functional with a drum brake proportioning valve, aren't that much better, but the truck drives nice and you don't have all that extra play in the pedal any more.


Discs need more pressure and volume. If it were simply a question of more pressure or more volume you could change the master cylinder to caliper ratio and get the right pressure. But discs need both pressure and volume, and that's why brake power boosters became standard when cars went to disc brakes.


All the above said, I prefer disc brakes. I just don't like throwing out drum brakes for boy-racer disc brake kits or incomplete upgrades.
I've read that you don't have to change the ABS out to make the disc brakes work properly. That being said, I deleted my ABS due to the proportioning valve failing before I did this install. Its real fun driving on the freeway, pressing the brake pedal, firm pedal, and you don't really stop. The whole ABS system went in the garbage. I'm using a Wilwood adjustable proportioning valve on my rear brakes which allows for 100-1200 PSI I believe. When I still had the drums, I ran it at almost the lowest setting. Any more and they would lock up under heavy breaking. If I was towing/hauling, I would increase the pressure a little bit. When I went to disc brakes, I run the valve at full allowed pressure. The braking is better and smoother. They don't lock up very easy and yes, I can stop faster and safer. If they get wet, they still function... I could try a higher pressure valve, but I don't really feel the need. 1200 PSI works great.

I'm also using a 1 ton hydroboost system and 1 ton calipers. My truck has pretty awesome brakes. The NBS brake system is IMO, the best swap for disc brakes on these trucks. It keeps everything simple to replace, and gives you a stock GM silverado parking brake. All replacement parts are from a 99-2003 Silverado 1500, which will always be available at any parts store.

The reason I did the install was because I was having an issue with my left drum constantly locking up. After diagnosis, I found that I had a warped backing plate causing the issue. Since I had to remove the axles to replace it, this was a great time to do the install. I'm not a huge fan of drum brakes. I know how to properly install them and adjust them. I just don't enjoy messing with the springs, and if they get wet they become useless. Plus, they fade a lot easier due to heat from heavy braking. With the disc brake install, its not a HOLY SH*T braking upgrade difference. But, its smoother, they don't fade as easy under heavy braking, and they are so much easier to service.

The NBS install is the way to go. It looks factory and functions great.

 
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kylenautique

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You need to change the master cylinder to do this properly., the drum brake master cylinder in your truck powering the discs will cause them to drag. I dont know how GM did the residual pressure , iirc it was through the ABS unit (Someone like @Schurkey should be better suited to fact check that?), or in a valve on the master

The discs also need more volume than provided in the rear portion of a master thats disc/drum

Either drag or not enough take up would be what happen , assuming no changes are made
Just copying over my previous answer...
I've read that you don't have to change the ABS out to make the disc brakes work properly. That being said, I deleted my ABS due to the proportioning valve failing before I did this install. Its real fun driving on the freeway, pressing the brake pedal, firm pedal, and you don't really stop. The whole ABS system went in the garbage. I'm using a Wilwood adjustable proportioning valve on my rear brakes which allows for 100-1200 PSI I believe. When I still had the drums, I ran it at almost the lowest setting. Any more and they would lock up under heavy breaking. If I was towing/hauling, I would increase the pressure a little bit. When I went to disc brakes, I run the valve at full allowed pressure. The braking is better and smoother. They don't lock up very easy and yes, I can stop faster and safer. If they get wet, they still function... I could try a higher pressure valve, but I don't really feel the need. 1200 PSI works great.

I'm also using a 1 ton hydroboost system and 1 ton calipers. My truck has pretty awesome brakes. The NBS brake system is IMO, the best swap for disc brakes on these trucks. It keeps everything simple to replace, and gives you a stock GM silverado parking brake. All replacement parts are from a 99-2003 Silverado 1500, which will always be available at any parts store.

 

BBslider001

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Well, nothing like doing drum brakes twice in less than a week, smashing the absolute F*** out of your pinky when pushing on a drum and it slips away from me, and having to buy new shoes two times. I was on my way to a doc appt this morning and pedal went to the floor in traffic. I blew out the passenger side wheel cylinder and ruined those brand new brakes I just did this last weekend, so I did both cylinders and shoes on passenger side…..AGAIN LOL. I brought it to a local guy who told me he is pretty familiar with the GMT400 platform and would bleed/flush the system for $75. I really really hope he knows what he is doing. Bleeding is not something I wanted to tackle, it if I eat my words and he can’t do it right, I’ll do it myself and y’all can chastise me later. ANBS delete may be in my nearer future than I thought.
 

Schurkey

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Well, nothing like doing drum brakes twice in less than a week
That sucks.

having to buy new shoes two times.
Couldn't clean the brake fluid off the shoes with aerosol brake cleaner? That works...sometimes. Especially if you catch it early, before it soaks deeply into the pad material.

pedal went to the floor in traffic. I blew out the passenger side wheel cylinder and ruined those brand new brakes I just did this last weekend
Pedal may have been low, but the front brakes should still work 100%. If not, there's more wrong than just the wheel cylinder.

I did both cylinders and shoes on passenger side…..AGAIN
Did you previously replace the wheel cylinder? And if not...you'd better replace the left-side wheel cylinder soon.

I brought it to a local guy who told me he is pretty familiar with the GMT400 platform and would bleed/flush the system for $75.
'94 Suburban? Should be a 3-channel ABS, not the RWAL that the pickups got.

First impression is that that price is way high. But thinking about it--GM calls for a gallon of brake fluid, and the need for a suitable scan tool. So $75 is reasonable, if he does a proper job of it.



ANBS delete may be in my nearer future than I thought.
Deleting the ABS is probably a mistake.
 

BBslider001

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That sucks.


Couldn't clean the brake fluid off the shoes with aerosol brake cleaner? That works...sometimes. Especially if you catch it early, before it soaks deeply into the pad material.


Pedal may have been low, but the front brakes should still work 100%. If not, there's more wrong than just the wheel cylinder.


Did you previously replace the wheel cylinder? And if not...you'd better replace the left-side wheel cylinder soon.


'94 Suburban? Should be a 3-channel ABS, not the RWAL that the pickups got.

First impression is that that price is way high. But thinking about it--GM calls for a gallon of brake fluid, and the need for a suitable scan tool. So $75 is reasonable, if he does a proper job of it.




Deleting the ABS is probably a mistake.
I’ll respond in the morning, but real quick, brakes feel amazing. Better than they have since I bought it. I won’t be deleting anything. I’ll go into more detail. Live and learn.
 

BBslider001

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That sucks.


Couldn't clean the brake fluid off the shoes with aerosol brake cleaner? That works...sometimes. Especially if you catch it early, before it soaks deeply into the pad material.


Pedal may have been low, but the front brakes should still work 100%. If not, there's more wrong than just the wheel cylinder.


Did you previously replace the wheel cylinder? And if not...you'd better replace the left-side wheel cylinder soon.


'94 Suburban? Should be a 3-channel ABS, not the RWAL that the pickups got.

First impression is that that price is way high. But thinking about it--GM calls for a gallon of brake fluid, and the need for a suitable scan tool. So $75 is reasonable, if he does a proper job of it.




Deleting the ABS is probably a mistake.
So to respond, yes, the shoes were soaked. I wish I could have saved them. From the side, the fluid went almost down to the backing. It was bad. I did replace both wheel cylinders. Should have done it when I had it apart, but they looked kinda new and I didn't want to get into bleeding....lesson learned. I did have front brakes to be able to get home and then to the shop after I replaced everything. That surprised me. They feel GREAT now, better than they have and the fluid is nice and clean. That $75 was well worth it for me after having done them 2 times and smashing my hand. I was way over it.

I agree about the ABS. At first it seemed like a good idea, but from my reading and watching vids, it doesn't seem to always work. It is way low on the priority list if I even decide to do it, which at this I am shelving the idea.

I appreciate your feedback. I have worked a bunch on diesels and other platforms, but I am in the middle of learning the ins and outs of this one. This forum is wealth of information and good dudes willing to help. I love this truck....most days, but age and wear and tear are what comes with a 30 year old truck and its my DD. Next up, steering gearbox and Cunningham shaft. I am ordering parts this week. Also going to replace the cat with a high flow and Flowmaster muffler. The truck seems down on power and I suspect the exhaust needs some TLC. It looks all original. I know these aren't hot rods, but the engine runs good, fuel delivery seems good, but it struggles to stay at 70 going up gradual hills without a good bit of throttle. It also doesn't have a whole lotta pep in his step when you get on it. Maybe it's just how these drive?
 

AuroraGirl

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Not even sure what this means. Any answer is whatever it is…and will be handled with no issue. LOL....ok....side note, I meant it in jest. Maybe I should have put "LOL"? Been a helluva a week.
what i said is a joke, as if the answer to what you asked is something scary/beyond our/your ability to cope/handle it
 
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