My Rear Disc swap from drums observations

[John Cunningham]

Oh now quit telling stories, everyone knows those drum brakes are totally ineffective. No way you were locking them up.

In this thread I see an odd combination of a whole lot of guesswork and some willingness to do actual research, and input from one guy that actually seems to understand brake systems.

When I see things like misunderstanding the application and role of a proportioning valve (or as correctly pointed out, "combination valve") and the failure to retain parking brake functionality, wow, man, I just.. I.. I'm out. Y'all have fun.. brake systems aren't really for amateur experimentation and guesswork, IMO. Not if you're testing the results on public roads.

Richard

Your right there is some guess work but so are many things. When the factory does not provide you with enough braking then you go to work. I am quite pleased at the rear disc install. I would like to go farther with some knowledge...mostly about how much actual pressure is on the rear disc with the wrong master...if not enough Ill put the correct master cyl and a prop valve...even if I did nothing its a great modification upgrade....but there are always guys out there who dont want to do anything to their trucks unless it came that way....

 

[John Cunningham]

An observation.
Not using the drum e-brake "ever" means that the shoes aren't self-adjusting themselves as they should when the e-brake is set.
These trucks do have somewhat of a prob in that area, though.
GM designed that ratcheting system poorly. The notches on that star-wheel adjuster are too large which means that the shoes to have to be worn down a fair amount before they do self-adjust, resulting in poor brake performance & pedal feel until they do. ...and even then, the shoes do not get a proper amount of adjustment via the self adjusters due to the tooth size.
Top that off with GM's redsign of the brakes with no adjustment tool window on the backing plate in order to be able to adjust the shoes manually, results in having to physically remove the drums so as to adjust via trial-&-error.
Even the old trick of driving in reverse & slamming the brakes on will not get the shoes to self-adjust properly as they do with the older design. The over-sized notches on the star wheel is mainly to blame for that, but the redesign which put the adjuster at the top of the backing plate, instead of the old design where it was on the bottom, also has a finger in that pie.
Want the drum brakes to work properly & consistantly? Pull those drums & manually set them up with the proper drag that they require every couple of thousand miles or so, depending on your driving style.
Yea. GM dropped the ball on the redesign, but when properly set-up, they do work as they should.
While discs are much simpler & easier to maintain, the drum brakes on these trucks are not as problematic as some claim they are, just as long as they are properly adjusted. That requires diligence, which some owners don't seem to want to, know how to, or are even aware of.

That being said, I am putting discs on my '98. Purely for ease of maintenance & aestheics. But, they will be a properly designed set-up, with an adjustable proportioning valve, plus an E-brake. None of this cobbled together, fingers crossed & hope it works guessing game install.
Brakes are not the area to be doing that kinda stuff. There's responsibilty involved here. Not only to yourself & your family, but to every other vehicle on the road & the inhabitants within.

I'm with someotherguy on this one. Way too much guessing & uninformed non-knowledgeable error by trial experimentation for me.

Your right the drums suck from GM........the brake kit I used works fine. I was not sure why he did not suggest a different master cyl and this friday I will have more in depth information about why this is working for folks. He claims he has thousands of these kits sold over the last few years and nobody has complained about non performance. Not much guess work. Install the drums and bleed them......instant difference in stopping and pedal feel. I think his kit could be improved and that remains to be seen when I see how much pressure is in the line. If not enough I will change the master cyl and add a prop valve if needed.
I added some rear discs to a 66 nova about 25 years ago and left the prop valve wide open. Any adjustment I made did not make much difference so I left it wide open and drove that car for years like that.
I drove a 170 mph drag car with 4 wheel discs and a chevy master cyl with a small bore master cyl for the mechanical brakes designed by an engineer and he told me when we built the car what ever you do.........do not use a prop valve in your race car... both front and rear got the same pressure and it worked. I set several NHRA records and won some national events with that car and never did the ass end come around on me and some of these old tracks were very very short. I used a parachute but most of the braking was done with 2 piston calipers front and rear and a 10 inch rotor for weight.

I dont think this is a cobbled together like you say it was. I chose not to have an emergency brake because I have never used one in the last 30 years for anything with an automatic. A stick shift I would have one for sure. I purchased a 2004 Dodge Sprinter new for a work truck and I still have it........I have never used the emergency brake one time in 15 years with that truck. I have 2 other cars and have never use an E brake in those either............so much for the freaking e brake needed.

All I know removing my drums was a good idea and a good upgrade just merely because it stops very smooth with a good pedal... and some unsprung weight taken off to boot.

 

[Crookedaxle]

I drove a 170 mph drag car with 4 wheel discs and a chevy master cyl with a small bore master cyl for the mechanical brakes designed by an engineer and he told me when we built the car what ever you do.........do not use a prop valve in your race car... both front and rear got the same pressure and it worked. I set several NHRA records and won some national events with that car and never did the ass end come around on me and some of these old tracks were very very short. I used a parachute but most of the braking was done with 2 piston calipers front and rear and a 10 inch rotor for weight.

JEEBUS!!! the stuff you are using in this thread to justify your thought process is off the damn wall. Does a drag strip have pitch on the road surface or is it dead flat? Do they have corners while braking down hill? How about some rain or sleet thrown in? A patch of oil? Pulling a tongue hitch trailer? Have a bunch of weight transfer to the front of the vehicle while hauling a load that has a high center of gravity like you're doing in a truck? And on top of all that you're not exactly making a panic stop at the end of a run on the drag strip are you? If you lock up your ass end while shutting down after a run you should probably never be operating a riding lawn mower let alone a vehicle. AND, AND....you used a parachute on your drag car keeping the rear from coming around no matter how hard you tried! LMAO! I've heard of comparing apples and oranges but I think you're comparing apples to pickles in this whole thread. I don't think it's any coincidence that most the people here that seem to know what they're talking about also say there is nothing really inherently wrong with the factory drums either. I was just going to swap in a late model rear end on mine but the more I read some of the posts here by the "experts" I think I'll just keep the stock setup on my '93 GMC K2500. All new brakes front and rear with quality components and I think it'll be as good as any of these crackpot setups. Oh, and did I mention that GM went back to drums or did you already know that?

 

[someotherguy]

but there are always guys out there who dont want to do anything to their trucks unless it came that way....

LOL this right here proves you don't know ME, that's for sure

Richard

 

[Gibson]

Gotta say,, this is, and has been, an interesting thread. I applaud you guys who make the disc conversions to the 400 platform, with having to use a scan tool for the ABS to get proper bleeding, and then having to mess around with E-brakes, it's gotta be a lot of work.
I mentioned before, that for the use my rig gets, ('97 K2500 Sub, 8,600GVW,) that I didn't really "need" discs, and their is a lot of work and cost involved.
I'am actually thinking that, (for me,) an easy way to up-grade the brake system for little money/time, and effort, is to just pull-out the 14SF with its JD7 brakes, (13x2.5 shoes,) and replace the rear end with a 14FF that has the JB8 brakes, (13x3.5 shoes).
This will give 40% more braking effort in the rear, (that's a lot,) and the E-brakes and the other stuff should stay the same.
Ya know, It's almost unknown, but Chevy did have an RPO for a 1ton Sub, (9,200GVW,) I've seen one, it was a factory '96 with the 14FF, JB8,, and the front suspension, brakes, and transfer case from the 9,200GVW pick-up,, kinda rare, the one I saw was an ex Forest Service vehicle.

 

[letitsnow]

Thats an interesting observation and I need to ponder on this information....so you did not change the MC? I think we would be better off with not saying the amount of fluid because that is about volume........the prop valve may cut some volume but it is about pressure I think. The disc requires more pressure than a drum to work properly to achieve the same results.
Drum : More fluid and automatic will get less pressure if the MC is a two bore
Discs: Same MC will get less pressure automaticly because of the larger bore.

That would make sense if you did not change the disc drum MC...you need more pressrue to make the disc function and really you were only getting about 1000 PSI at the most with the prop valve all the way open.

So with your prop valve turned back for the drums your disc brakes were getting hardly anything for pressure at the drum brake prop setting..hence the reason you had to open it all the way up and this is correct.

So this is basic proof you did not change the MC

Correct - I am still using the stock MC.

As far as more or less fluid. There is a knob on the prop valve. If you turn it one way, the rear brakes do more, turn it the other way and they do less.

 

[sewlow]

I chose not to have an emergency brake because I have never used one in the last 30 years for anything with an automatic.

Without using the E-brake, you're relying on this to hold a 4500lb.+ vehicle in place.
A 1/4" pawl stuck into a notch on a 4" diameter 1/8" thick wheel.
A wheel that small doesn't provide a whole lot of mechanical leverage against that weight of the vehicle.
Has that system ever been known to fail?
Ahhh...YEA! Big time. Many times. Even on the smallest of grades.
I've learned about that not ftom Google, but from actual observation & experience.
I've heard that distintive ratchet sound of a failed pawl more than once. Don't even have to see the vehicle rolling to recognize that sound & just what the hell is going on when that is happening.

You must be registered for see images attach

I've seen the results.
This vehicle. Dad's. (He bought it new at 18. His first new car.)
1976. 20 minutes outa the paint booth. Sitting in front of the booth doors & here comes a truck, making 'THAT' sound.
Nobody in the truck.
Rolled a 1/4 block down the slightest grade of a hill (3%? Maybe.) at just better than a fast walking speed, jumped the curbed & plowed directly into the passenger 1/4 panel & door.
Thats the closest I've ever seen the ole man come to tears.
The Insurance Co. wanted to write it off! It took over a year to get that settled.
All because some _____ was too damn lazy to set their E-brake.

You must be registered for see images attach

 

[letitsnow]

Without using the E-brake, you're relying on this to hold a 4500lb.+ vehicle in place.
A 1/4" pawl stuck into a notch on a 4" diameter 1/8" thick wheel.
A wheel that small doesn't provide a whole lot of mechanical leverage against that weight of the vehicle.
Has that system ever been known to fail?
Ahhh...YEA! Big time. Many times. Even on the smallest of grades.
I've learned about that not ftom Google, but from actual observation & experience.
I've heard that distintive ratchet sound of a failed pawl more than once. Don't even have to see the vehicle rolling to recognize that sound & just what the hell is going on when that is happening.

You must be registered for see images attach

I've seen the results.
This vehicle. Dad's. (He bought it new at 18. His first new car.)
1976. 20 minutes outa the paint booth. Sitting in front of the booth doors & here comes a truck, making 'THAT' sound.
Nobody in the truck.
Rolled a 1/4 block down the slightest grade of a hill (3%? Maybe.) at just better than a fast walking speed, jumped the curbed & plowed directly into the passenger 1/4 panel & door.
Thats the closest I've ever seen the ole man come to tears.
The Insurance Co. wanted to write it off! It took over a year to get that settled.
All because some _____ was too damn lazy to set their E-brake.

You must be registered for see images attach

If you wait until stopped before putting the truck in park, those pieces last longer.

 

[John Cunningham]

Without using the E-brake, you're relying on this to hold a 4500lb.+ vehicle in place.
A 1/4" pawl stuck into a notch on a 4" diameter 1/8" thick wheel.
A wheel that small doesn't provide a whole lot of mechanical leverage against that weight of the vehicle.
Has that system ever been known to fail?
Ahhh...YEA! Big time. Many times. Even on the smallest of grades.
I've learned about that not ftom Google, but from actual observation & experience.
I've heard that distintive ratchet sound of a failed pawl more than once. Don't even have to see the vehicle rolling to recognize that sound & just what the hell is going on when that is happening.

You must be registered for see images attach

I've seen the results.
This vehicle. Dad's. (He bought it new at 18. His first new car.)
1976. 20 minutes outa the paint booth. Sitting in front of the booth doors & here comes a truck, making 'THAT' sound.
Nobody in the truck.
Rolled a 1/4 block down the slightest grade of a hill (3%? Maybe.) at just better than a fast walking speed, jumped the curbed & plowed directly into the passenger 1/4 panel & door.
Thats the closest I've ever seen the ole man come to tears.
The Insurance Co. wanted to write it off! It took over a year to get that settled.
All because some _____ was too damn lazy to set their E-brake.

You must be registered for see images attach

I appreciate all the advice about Ebrakes.........I have not used an emergency brake on any car or truck I have owned for 30 to 40 years...for some reason I never had to.

I did talk to a good friend of mine who is an engineer for GM.........and I will quote him " John many of the chevy trucks from the gmt 800,900 etc have gone back and forth with disc and drum brakes for a couple of reasons. Its about warranty claims and thats all. On discs it was because in bad weather they had trouble with one of the pads and getting debris in between rotor and pad so they built a shield to help that situation. The other reason is the E BRAKE seizing up from non use...they could corrode and rust and cause the disc brake to have issues and nobody uses them so they had serious warranty issues........so They decided most trucks did not need discs so they went back to drums which has a better ebrake and is more protected.
So much for the need for an Emergency brake. Disc brakes are superior in every way except the ebrake situation and the trouble they have with them..in my case I never use an ebrake and you can get an ebrake kit but I never use a ebrake so I dont care.
If you have to have an ebrake put it on the pinion with a rotor and caliper.......they are out there.............so ask yourself and be honest......How many times have you used your ebrake the last 12 months......?? In my case I know I have not used my ebrake for 20 years or longer.....not once.

 

[John Cunningham]

Correct - I am still using the stock MC.

As far as more or less fluid. There is a knob on the prop valve. If you turn it one way, the rear brakes do more, turn it the other way and they do less.

Yea that controls the pressue to the rear and if you have the stock MC you dont even need a prop valve. So how do your brakes work? What change did you notice?