Upgrading brake on a 96 Dodge 2500 to 3500

I see you've been waiting two days for a reply. I read it earlier but I can't answer some of your questions. What I CAN suggest is the brakes are already strong enough to lock up the wheels, so going to anything larger isn't going to give you more stopping power, including when pulling a trailer. What you will get is larger rotors will build up heat at a slower rate, and that leads me to an important point you should be aware of. A few decades ago, I had a car with a rotor I had cut a total of 1/8" under the legal limit, and under the other rotor. It never caused a problem, however, ...

On the newer vehicles, trucks in particular, two different size rotors will cause a horrendous brake pull when they get hot. Dodge had a 32 page service bulletin about this, and in fact I was involved with three of those trucks. One was a truck the owner had just bought. The previous owner sold it for this elusive problem shortly after having a brake job done. The other two were lemon law buybacks that would have been solved if the mechanics had just followed the service bulletin. Those rotors were about 1 1/4" thick, but on one truck, one rotor was.020" thinner than the other one. On the second truck, one was.007" thinner! That's the thickness of two sheets of paper, but it caused a very hard brake pull after about a half dozen fairly hard stops. The customer's truck got two new rotors. On both lemon law trucks, I cut the thinner rotors to true them up, then cut the thicker ones to match within.001". It's important to note the speed of cut has to be identical too. That results in the same number of grooves, and therefore the same pad-to-rotor contact area. This brake pull never shows up right away or during normal braking. It results from repeated hard stops such as when coming down a steep hill. On the trucks I was involved with, all of them stopped perfectly straight for seven hard stops on the same hill I used, then they pulled real hard on the eighth stop just a few seconds later. The cause was a change in the coefficient of friction that took place at the higher temperature, and since the rotors were different thicknesses, the thinner one heated up faster. By the way, that 32-page service bulletin had us checking everything under the sun from the alignment to replaced suspension parts, then they finally presented the solution on the last page or two.

The next thing to keep in mind is every vehicle has a proportioning valve in the brake hydraulic system that everyone forgets about. That limits the amount of fluid pressure to the rear brakes to reduce rear-wheel lockup. Most trucks and minivans have a height-sensing proportioning valve at the rear axle because they can have such a wide variation in loading. When cars are lowered or trucks are raised, that changes the amount of weight transfer to the front, and that changes the calibration needed in that valve. Lawyers and insurance investigators know all about altered ride height and they will use it to convince a jury that you were partly at fault for the crash when the other guy ran the red light because you were less able to avoid it, and they will be right.

You could run into the same problem with altered brakes. I'm less of an expert on potential lawsuits related to altered brakes, so the best I can share is you will no longer have the carefully-designed-in front-to-rear braking balance. A skidding tire has no traction, so when one does start to skid, you have to let off the brake pedal a little to keep it in traction. Three tires were not yet stopping to their fullest potential, but you let off the brakes a little. That is proof the stopping distance was longer than it could have been.

The first issue I mentioned was heat buildup from pulling a trailer. The second one has to do with the 3500s experiencing rapid front brake pad wear. Front pads should wear out about twice as fast as the rear shoes or pads. We were told that if there was a 3500 that was experiencing rapid front pad wear, we could increase the rear wheel cylinder diameter by 1/16". If there was a truck that was constantly heavily-loaded, we could increase the diameter by 1/8", but there was a hitch. Chrysler never used that size so the replacements had to come from a GM dealer. Those were factory-approved modifications to solve a problem under certain conditions, so there was no threat of a future lawsuit. The original wheel cylinder diameter was the result of those calculations that led to balanced front-to-rear braking.

Some people will tell you to switch from drum rear brakes to disc, but again, that isn't going to gain you any stopping power. On trucks and most older cars, drum brakes are of the "duo-servo" design which means the front shoe's only job is to apply pressure to the bottom of the rear shoe. This is referred to as a "self-energizing" brake and it's real effective. Drum brakes worked great for stopping heavy cars and trucks. The drawbacks are it's harder for heat to escape and they they take a long time to recover after driving through deep water. Disc brake pads are always in contact with the rotors, so they squeegee off water, and since they're in the open, heat dissipates better. Their drawback is they are not self-energizing so a lot of pedal pressure is needed. This is where a power booster becomes necessary. The main reason you'll find disc brakes on the rear is calipers present less moving mass compared to shoes, so they respond better to the pulsing action of an anti-lock brake system.

As for the parts interchangeability you're asking about, I can offer two suggestions. First, I use the Rock Auto web site for reference quite a bit. You can look up parts and compare the part numbers from various manufacturers for both applications. If the part numbers are the same, obviously that part fits both trucks, but when they're different, you don't know why. One could use a ball joint with a larger tapered stud, or it could simply have an additional threaded hole for a brake hose bracket. The next is to visit a Dodge dealer's parts department to see if they offer an off-road upgrade kit. They will also be able to tell you which parts were available as part of an optional brake system. This is where the off-road modification kits are nice. Those will include the proportioning valve, calipers, and wheel cylinders as a matched set, and they will include a master cylinder or specify if a different one is needed. Normally the master cylinder's bore size is a trade-off between pedal pressure and pedal travel. A larger cylinder diameter will move more brake fluid with less pedal travel, but you'll need much more foot pressure to stop the truck.

You DO have to change the master cylinder when changing from drum to rear disc brakes. Drum systems have a residual check valve in the port in the master cylinder. That keeps about ten pounds of fluid pressure on the lip seals in the wheel cylinders at all times. Ten pounds of fluid pressure on a caliper would keep it applied and dragging.

My daily driver is an old rusty trusty '88 Grand Caravan with the optional heavy duty brakes. I use it to pull a tandem axle enclosed trailer that's bigger and heavier than the van to the nation's second largest old car show swap meet, (next week), and I have never even bothered to hook up the trailer brakes. I can't hit 70 mph due to the wind resistance, but stopping has never been a problem. I can't imagine your truck having a problem pulling my trailer. What kind of braking problem are you trying to overcome?

I have a feeling something else is going on here. Do you have rear-wheel anti-lock brakes?

I have a friend with a body shop who specializes in rebuilding one and two-year-old smashed Dodge trucks. Last year he got a 2500 MegaCab from Iowa. We went to Detroit to a salvage yard that buys a real lot of stuff directly from Chrysler. He got a never-installed frame, and an 8' dually box that was used in experiments with running diesels on compressed natural gas. He cut the truck's frame and the new one and used 60 percent of each to turn this truck into a dually diesel MegaCab with 8' box. We know you're not supposed to weld on these, but this was for himself. When he comes to plow snow from my driveway, I wave to him, then have to wait a while for the tail lights to show up!

The point of this sad story is this is still a 2500 but with the dually rear axle, that if I remember right, was from a 3500. The brakes were the same as on the single-wheel axle we removed. He used this truck to move his sister back from Texas to Wisconsin last summer. That was with a 32' goose neck heavy equipment trailer that he built an 8'-high box around, then filled it with her crap, ... Ah, ... Stuff! Halfway home all eight studs broke on one of the trailer's four pairs of wheels. A company that repairs semi trucks and trailers on the road came out, then they had to go back for more equipment because they couldn't lift the trailer with what they use for semi trailers. Now THAT'S overloaded, but he never had a problem stopping that load. Remember, this is a 2500 with standard rear leaf springs, but he did add air springs. He has also hauled those huge round bales of hay you see in fields sometimes, for nearby farmers. He once hauled 40 of them on that trailer, and they say those are 1,000 pounds each. The farmer's kid had trouble with his Ford trying to haul 15 of them. This tells me the 2500s don't suffer from weak brakes, and is why I think something else is going on with yours.

Now, that's not to say there isn't a heavy duty optional brake system with beefier parts. That's why I'm in favor of you visiting the dealer's parts department. At the Dodge dealership where I worked, the people in that department were real happy to look stuff up for people as long as you would give them a day to do it when things were slow. They can also do research through Chrysler's web site for dealers.

One more thing you might consider is asking at the dealership where they send their mechanics for live training. We used to have a training center near Milwaukee, and the instructors used my Auto Shop and those of two other community colleges as remote training sites. Those instructors are extremely knowledgeable about options, modifications, and especially finding solutions to what the engineers and designers messed up. They are usually quite willing to talk with owners as long as it doesn't interfere with their class schedule. They don't have classes every day. In fact, they may go for weeks without seeing students. They use their time researching problems and coming up with fixes for them.

This brings me back to the original suspicion that something else is going on. The first thing I'd check is if the pads are glazed. When the rotors just slide off once the calipers are off, I take a light cut on the brake lathe, then let that roughness chew off the glaze. For "captive" rotors that require removing the wheel bearings, I just use course sandpaper and scrape the glazing off by running the vehicle in gear on a hoist until I burn my fingers!

Obviously if you have four-wheel anti-lock brakes, the wheels had better not lock up. If you don't, you almost certainly will have rear-wheel anti-lock, so it's unlikely you'll get the rear tires to skid.

I hope that gives you something to start with. I'm racing a dying laptop battery so I have to call it quits for tonight, but I'm going to keep thinking on this. I'll check with my friend too and see if there was anything else he modified with his brake system.

Well, we know if that's four-wheel anti-lock brakes, the wheels won't lock up, but that's actually a good thing for stopping. I have a '93 Dynasty with the Bendix-10 ABS system. That will just about tear the seat belts off their hinges! Remember my comment about a skidding tire has no traction, and to get the traction back, you have to let up on the brake pedal even though the other three brakes weren't stopping to their maximum potential? Well, 4-wheel ABS takes care of that. The system looks at the four wheel speeds, then disregards the fastest wheel. Of the other three, it looks for the one spinning the slowest, blocks any additional fluid flow to it, even if you push harder on the brake pedal, then, if it still isn't speeding up, it bleeds off some fluid pressure. Once it's back up to speed, it opens a third valve to reapply fluid pressure. It does that "block, bleed, apply" between 15 and 30 times per second for each wheel. That means every brake is stopping at its maximum potential.

GM used a similar Bendix-9 on the Caprice Classic. The difference is they modulated the two rear wheels together, so it was a "three-channel" system instead of a four-channel system. There had to be some other differences too because I drove one after aligning it, and the system did exactly what it was designed to do, ... Allow you to maintain steering control. As a friend who is a county deputy put it, "if you slam on the brakes, you go and go and go, and they find you in the next county! I was my dealer's suspension and alignment specialist all through the '90s so I drove a lot of Chrysler products, and I never found one to have such miserable brakes. Remember, the purpose of anti-lock brakes is to prevent skidding tires so the front ones can be steered, and so the rear ones don't pass up the front of the truck. The shorter stopping distances is an unexpected byproduct but Chrysler's systems have been much more effective at that than systems on most other vehicles.

My reason for sharing all of this wondrous information is to point out that you have brakes that are already strong enough to lock up the wheels. They just aren't doing that by design thanks to the ABS system. So stopping power isn't what you need more of. What you need is less heat buildup. Even the trailer brakes were hot, so you know they were all really working.

I'd still talk with the guys at the dealer's parts department first, but then you might look at aftermarket parts. I would be willing to bet you are not the first person to have a truck with hot brakes, so there is likely to be someone who developed a solution. I did a search last night for "Dodge truck brake upgrade". A number of interesting things came up, but you have to understand that all manufacturers of brake linings have to design their parts so the same front-to-rear balance is maintained. If you only replace the front pads, those new linings have to work with the original rear shoes. One can't have a higher coefficient of friction, but I don't know how closely they have to watch that at abnormally-high temperatures.

There are different types of brake fade and you may be experiencing one of them. Really hot linings give off a gas that gets between the rotors and pads and acts like little ball bearings. No amount of additional pedal pressure will overcome that. This again is why you should look at reducing heat buildup, not increasing stopping power. I realize the two are related, but solutions come from different directions.

What about a Jake Brake? I don't know much about them or if they're even an option with a gas engine.

It never occurred to me that valve float would be an issue, but after thinking about it, I can see where it would be. Regardless, we're getting into an area I am not an expert on. I've never owned a diesel, and when I've gone on out-of-state trips with my friend to fetch trucks and parts, we've never been loaded enough to need the one built into his truck, so I've never driven with one either.

I promised you I was going to consult him for other ideas but I haven't been able to get a hold of him. I'll be seeing him tomorrow on my way to an old car show swap meet. Last year the wireless internet at the show was terrible, so you probably won't hear back from me until next Monday night. Hopefully I'll have some better ideas.

Nothing of value to report. According to my friend, Jake brakes can be used on gas engines but they aren't nearly as effective. Valve float should not be an issue, because any back-pressure in the exhaust system comes from inside the cylinders. The pistons will just encounter a lot more resistance when it comes to pushing that gas out under pressure. It's true that the valve springs do not need to be nearly as strong as on diesel engines so intake vacuum doesn't pull a valve open, but you also don't have such a high compression ratio either. You still won't build up enough exhaust pressure to push an exhaust valve open. You have to remember, we run into plugged catalytic converters from time to time, and one of the symptoms is an unusually smooth idle, and a steady hiss from the tail pipe. Valve float is not one of the clues.

You're thinking backward about the master cylinder. As you push harder on the brake pedal, the fluid pressure pushes out on the lip seals and makes them seal better. One of the tricks we use is to push lightly on the pedal, and ease up on it momentarily. If the lip seals are worn or torn, the reduced pedal pressure often lets the seals relax and lets fluid bypass one of them. When that happens, the pedal will sink to the floor and the red "Brake" warning light will turn on.

I don't think you have a master cylinder problem. If one seal had internal leakage, the red "Brake" warning light would turn on due to unequal pressures in the two hydraulic systems. If both systems were leaking, you would have no brakes at all at some point. From everything you've described, my mind keeps going back to glazed linings.

The reason I know about the '95 minivans is I have one. It does require a scanner to open some of the valves so air can escape. The slow pedal trick won't work on that. As I recall, you have rear-wheel ABS. Those systems don't require separate bleeding. That valve assembly only blocks fluid flow, then allows it. It doesn't have a separate high-pressure system to apply fluid pressure. The RWAL, (rear-wheel anti-lock) valve is normally open, just like a piece of steel brake line, so air will bleed right out.

If your brake pedal is sinking slowly under light foot pressure, then you may indeed have internal leakage. If you have to replace the master cylinder, start with the new one already bench-bled so it's ready to go, loosen the soft metal line nuts at the master cylinder's ports, unbolt the master cylinder from the power booster, then use it as a handle to bend the steel lines up a little. That will prevent the fluid from running out of the tops of those lines.

Remove the lines, then install them on the new master cylinder. Bend the lines back down so you can bolt the master cylinder to the power booster. Snug one of the line nuts. Have a helper slowly push the brake pedal about halfway to the floor and hold it there while you tighten the nut. Release the pedal quickly so the fluid rushing back washes any air bubbles with it into the reservoir. Loosen the nut and do that once more until you don't see any air bubbles coming out. Do the same thing for the second line.

There's no way air can get in the lines below the master cylinder this way, so there's no need to bleed at the wheels.