My Rear Disc swap from drums observations

[John Cunningham]

Application is an 8 lug K3500 1 Ton SRW 1997 silverado with the big 3.5 drums and hydoboost

For years I have heard that swapping to disc was a waste of time and money and you would not see any difference in stopping power.

Most HD trucks switched to rear disc brakes years ago so what will it hurt. If there is no improvement at least I lightened a few things up.

I performed the swap today using a JB6 caliper and ceramic pads and the typical 12 inch rotor.

Did a scan of the ABS and bled the brakes.

My old pedal with a hydroboost was a very hard pedal and you really had to stand on it to stop which annoyed me.

New Observations:

Pedal completely changed to something more like a newer truck and not real hard feeling ..I did not question it just went with what I had...I wold not call it spongy just different ...like 100% different.

I broke in the pads and noticed an immediate change in the way the truck stopped. No longer did I have to stand on the brake pedal to get it to stop and no more hard pedal feel

Very smooth and much easier to stop with not near the pedal feel I had before. It takes half the effort from leg muscle feel to stop which is huge. I did not do a 60 to 0 stop distance like a magazine article would... but I do feel the truck is more enjoyable to drive. It might not even have secured better stop times but by feel, I would say it is stopping sooner and a much better brake feel and worth doing.

So sometimes you should not listen to folks that say this is not worth doing and find out yourself. Prove it to yourself which I wanted to do and it was something I would do again in a second.

Since I will pull a large trailer I am moving up to GMT900 front brakes with a 13 inch rotor and larger dual piston calipers. It will require some 17 inch rims that I am pulling from a GMT900...changing the steering knuckle to a 99-2000 and reaming upper and lower ball joints and then using all the GM parts.

But if you have a drum brake rear truck...its worth the swap. Dont let anybody BS you that has not done it....

 

[R422b]

The one thing i worry about increasing rear breaking power without increasing the front is if you ever really get on it the back end may have a tendancy to try to drift especially in corners.
Have you noticed any tendancy for the back end to lock up first?
If not sounds good. How complicated was the swap?
I would like to do something similar on my future truck if i find the drums have too many issues but i would want to be positive that i wasnt adversly affecting the brake bias.

 

[someotherguy]

Lol.. So you replaced malfunctIoning brakes and this confirms your belief that drum brakes are trash.

Richard

 

[letitsnow]

Mine stops much better with rear discs also. I can drive it like a car in stop and go traffic now. The drums seemed pretty inconsistent and not very sensitive/didn't modulate well - which is a terrible combination when paired with the crappy oem abs system.

But, I will admit that my rear drum brakes weren't new. Maybe perfectly functioning drums would be the same, for the week that they functioned perfectly?

 

[John Cunningham]

The one thing i worry about increasing rear breaking power without increasing the front is if you ever really get on it the back end may have a tendancy to try to drift especially in corners.
Have you noticed any tendancy for the back end to lock up first?
If not sounds good. How complicated was the swap?
I would like to do something similar on my future truck if i find the drums have too many issues but i would want to be positive that i wasnt adversly affecting the brake bias.

Mine stops much better with rear discs also. I can drive it like a car in stop and go traffic now. The drums seemed pretty inconsistent and not very sensitive/didn't modulate well - which is a terrible combination when paired with the crappy oem abs system.

But, I will admit that my rear drum brakes weren't new. Maybe perfectly functioning drums would be the same, for the week that they functioned perfectly?

My drums were working fine I adjusted them but here is the better way to describe this:

The truck wanted to nose dive during a stop before, now it wants to squat or in other words there is more 4 wheel braking. I did not use a prop valve unless there is one in the system. Its comes to a more smooth stop and as just said its easier...much easier to drive in traffic because the pedal is so much different which actually was a bonus I did not plan on. I will continue to upgrade the front to a 13 inch rotor and dual disc calipers but if your not going to pull or carry anything heavy you will be pleasantly surprised at how great the truck is to drive without doing the front upgrade especially for a half ton or 2500. A friend of mine drove it a day before and after the swap. He has a 2016 3/4 ton chevy pickup. On his before the swap drive he admitted it was a terrible pedal and not much fun to drive. After the swap he was as shocked as I was and said it stopped more like a late model truck. I also know that these GMT400 are pretty light and if you do this your losing at least 10 pounds a side in unsprung weight and that is huge! This contributes to this different feel as well. I guess if your happy with your drums you would want to keep them. I fall in the small percent that hate the drum feel and would do this without hesitation every time.

An opposite illustration is folks that switch to 20 inch rims are not really happy with their brakes after the switch because of the increased weight. Light is might and a non nosediving truck is worth the effort. I have nothing to gain from this post just sharing what I found out and yes my drums worked fine as I just adjusted them and pulled the drums to make sure all was well. I did not want to compare it to some non adjusted drum. Now just think.........forget about ever adjusting your drums again...never lose brake power cause your in water........lots of great benefits and every med to heavy truck on the road today has rear discs...I dont have to sell this..........

 

[John Cunningham]

The one thing i worry about increasing rear breaking power without increasing the front is if you ever really get on it the back end may have a tendancy to try to drift especially in corners.
Have you noticed any tendancy for the back end to lock up first?
If not sounds good. How complicated was the swap?
I would like to do something similar on my future truck if i find the drums have too many issues but i would want to be positive that i wasnt adversly affecting the brake bias.

Your post made me smile..........this is not a drift race truck...If anything when I start to drift race someday I am sure ill like it better...The swap itself is an hour and the line work and bleeding about another 1.5 hours...so start around 9am and be driving by noon........its a real simple swap 3 hours tops. Your not going to hurt anything by this swap...I would not get to technical with yourself. Drums suck and if you want a better feel while driving dont hesitate.

 

[John Cunningham]

Mine stops much better with rear discs also. I can drive it like a car in stop and go traffic now. The drums seemed pretty inconsistent and not very sensitive/didn't modulate well - which is a terrible combination when paired with the crappy oem abs system.

But, I will admit that my rear drum brakes weren't new. Maybe perfectly functioning drums would be the same, for the week that they functioned perfectly?

I agree with the not very sensitive part. We cant say for sure it stops faster unless we do a technical test but it sure is smoother and more enjoyable to drive. I know we will have the naysayers out there or those who are happy with the drums and I am happy for them. But anybody that does this swap will be glad they did. Its not expensive and kindergarten easy to do....stop and go traffic with this pedal is very very nice.

 

[R422b]

Good to know i am filing this away for future reference. Right now i only have a 2002 tahoe and it has 4 wheel disk but i am hoping to buy a 1988 1/2 ton GMC this spring and i want it to drive as good as the 2002 when i am done fixing it up. I realy apreciate your mention of the reduction of unsprung weight that alone would be worth it to me. I drive gm because i like parts compatibility and a smooth ride.

 

[R422b]

I didnt see your reply to me till i already hit post. That sounds great although i am shure it would take me longer, my 2002 tahoe front end took me 3 days. I have a knack for making projects slow. ☺

 

[Gibson]

I agree with the OP,, I did the same thing on my old 8,600 gvw squarebody K2500. It had the JD7 brakes, with a 14ff axle in back, but used vacuum assist.
I pulled the residual valve out of the master cylinder port that fed the rears, switched to a disc/disc proportioning valve, added a Willwood adjustable in the rear line, and the brakes went from ok to great.
You only had to move the pedal enough for the pistons in the master to close-off the compensating ports and the pedal became rock hard,, I think spending a lot of time in bleeding, along with a lot of fluid being used made the pedal hard,, their couldn't have been even a pin-head sized air bubble anywhere in the system.
You might still have some air,, many times a bunch of microscopic sized bubbles over time will gradually move up-hill until they "merge together" to form a bubble that gives you a softer pedal.
If the fluid column is absolutely 100% "solid" the pedal will be solid.