The Stovebolt Site Forums The Shop Area General Truck Talk UPDATE: 1958 Chevy Drum to Disc conversion.

Well folks, my original MC is leaking again. I have rebuilt it once, a while ago, and now it is leaking again. I don't think another rebuild will do the trick, so I am thinking of converting to duel MC, power and disc. I have been reading the archives and seen come good info. I was wanting to know anyones experience with the different kits and ya'lls suggestions. I came across the kit on Performance Online and it looks like a good kit with everything I would need. Are there any issues with the stuff clearing a manuel transmission? Thanks for info and advice!

Manual transmission... no, ebrake cable... yes

Thanks BigBad. In theory rerouting the cable will be easy, but we all know about theories on these trucks lol.

LOL at the theory line. Found it to be very true. In theory it will only take a few minuets or cost only a few bucks. We all know how that gos.

I have see a few guys stories were they only installed a brake booster and left the drum brakes. They say it works great if your not racing around and you dont haul much. May save you a few buck if you dont want to do the hole conversion right away.

My 58 had all that on it when I got it, but the pedal was low & soft. It uses the small bolt pattern 5 hole & I have a Firebird rear end. I put a checkvalve on the rear & bled it all real good & they work real good now. If I was to do it myself I think I would do like Grandpa says & leave the drums. Unless you are going to do some serious driveing thats all a guy needs.

If any of you drum enthusiasts would drive my '56 with drums then drive my suburban with front discs I think you'd have to admit that even though the drums are "adequate", you'd much rather have a truck that stops like the burb does.

I agree with Cletis. I'll take the disc brake conversion anytime. Of course not everyone has to deal with the Honda crazies on So Cal freeways. Before you do the conversion, plan it out. In most cases you will have to replace the wheels. Some kits for 6 lug use your existing hubs so you probably need new bearings. The kit I used has 5 lug rotors and I had the rear axles redrilled to match. Mine has the booster/master under the floor and there are no clearance issues with the 3 sp OD trans.
Fred

I would like the disk someday, but money it the issue. I agree with all of you and think I may just go the powe drum route. My 66' Fleetwood Caddy has power drums and stops fine. I always drive according to what I am driving. I drive my dad's sky roadster different than my old truck. Don't push your equipment past it's limits.

I have gotten my new Duel MC and Booster. I think I have what I need to swap, but I remembered reading about check valves. Will I need these on a drum/drum set up? Or, do you only need them on the disc/drum setup? Or, do you need them when the MC/booster are mounted under the cab? Thanks for the help folks and if I need them where is a good place to buy from? Thanks again!

I switched to a dual master on my 55.2. Cleared the tranny with room to spare. The e-brake cable needed to be modified. I had to move the little round junction thingy back about 6 or 7 inches. I also had to drill a new hole in the ebrake arm.
These two images show how that junction interfers with the master cylinder.
Unmodified
Unmodified

Unfortunately, I don't have a picture of the modified position but it is 6 -7 inches back. I also had problems with the cable interfering with the transfer case, which you will not have a problem with as yours is a 2wd.

jomichael- Thanks for the info! That looks like the exact setup I bought. Did you have to use some residual check valves to stop bleed back from happening?

Not sure what bleed back is, but mine is drum/drum since I have original 4wd. It is probably different than drum/disc. You can see from the photos that you have plenty of room to add anything in order to take care of that problem. What is bleed back? The higher pressure of discs vs. drum? If so, I bet that is taken care of internally.

Most master cyl. designed for drum brakes have the check valves in them. You might be able to see them Or poke something in & feel them. They go right behind the brass insert in the outlets. If it does not have them you need to mount some inline. They are available at Summit or Jegs,

Id also really like to know this to. I just ordered my kit. I have wilwood disc brakes and lines coming for my new rear. Still running the drum's on the front. Now is it mandatory to go to a 2 chamber master cylinder? Im not going with booster like OP. But curious on the valves etc. Been reading a bit about that but can't find a solid answer either.

You will need a 2 psi residual valve for front and a15 psi residual for the back if mc is mounting on frame ..

That's when the the mc is lower than calipers fluid can go back into mc and overflow it that's why u need residual valves to prevent that

Sal, If he has discs on the BACK and drums on the FRONT-shouldn't your figures for pressure be switched?

Now thats a combination I never would have thought of

I wouldn't advise it. I have never heard of a factory set-up like that and I'm sure there is a reason for it.

sounds like it'd be scary with hard braking, the front wheels provide 60-90% of braking

Bill

I have owned a vehicle that did have a setup like that, with drums in the front a disk in back. However, it was a Yamaha Moto-4 ATV, not a street driven truck.
I'm in 100% agreement, do the brakes right, with disks on the front to match the rear, as well as the proper master cylinder.

Discs are a better system. Putting discs on the rear with front drums would cause your rears to do more of the braking, which would be scary.

Your first post says you were thinking of dual, power, disc. Then it sounds like you purchased dual, power and are staying with stock drums. Assuming I got that right, and you bought from a well known vendor, they would be the ones who would advise on residual valves, If you told them what you are doing they should have sent the necessary parts in the kit (IF you bought a kit).The kits come with different valving depending on drum/drum, disc/drum or disc/disc.
Just remember, there are three components we are talking here. The dual MC is for safety, the power booster is for brake pedal pressure and the disc is for safety/quicker stops. Put them all together and you have a great safe combo that will stop quicker with way less foot pressure. Dual, Power, drum brakes are not all that great of an improvement in actual stopping ability. I don't think you will notice any change except foot pressure. Boosters are kind of for disc brakes anyway. You will really, really like the Power front disc brakes. You will find a great improvement as Cletis and others indicate. I have done that kit on several TF trucks.

Residual, or check valves, are used to keep slight pressure on drum brakes because the return springs will pull the shoes too far away from the drum unless you keep adjusting the shoes. Also fluid can't return to the MC with a slight pressure always applied and they being a check valve. They are used on disc but meant for drum. Different pressure values are used for front and rear.
The proportioning valve is used to apply less pressure to the rear brakes. They require less force than the front and, as said, the front do more stopping than the rear. (weight and weight shift)

The residual valve on discs is a lower pressure than for drums also, so that you don't essentially lock up the front brakes.

Someone correct me if I'm wrong but I think for drum/disc set up the supplier usually recommends 10lb. and 2lb residuals for the front......that is what PirateJack's brochure said when I read it. I put my m/c and booster under the floor while I was putting in my new "system".

^ You are correct. 10lb for the drums and 2lb for the discs. I'm in the process of installing the CPP conversion on my '51 now.

I just did that conversion for the AD. Big discussion on it in Drivelines. I will be interested in what you think.

Who, me?
I already know I'll like it. As others have said, properly maintained drums are adequate, but discs are superior. I was initially just going to switch to a drum/drum dual MC but the effort to go to discs is the same.

Read the thread in Driveline about it. I know I will like it too, but there are issues it wouldn't hurt for anyone to know. Yeah you! There pics in the photobucket for mine.

Haha. Ok, I'll take a look at it. What kid did you use Deve? Mine is the CPP 6 lug I bought the residual valves and some "universal" line from the proportioning valve to the T's but I'm wondering if I should upgrade my lines running from the T's to each wheel too. If so, what size line for front and rear?

mine is the 6 lug kit. I got the Dual MC with the proportioning valve for rear drum/front disc. Because I have an overdrive transmission, there were clearance issues so I had to make my own lines from the prop valve to the MC. I got the MC bracket WITH prop valve bracket that is just below the MC.

At the brass T that is located approx. adjacent to the front crossmember, I disconnected the rear lines and capped it off to separate the front from the rear, then ran my rear lines to the front side of the transmission crossmember, across and to the prop valve. The front disc brake lines seem to be 3/16 to work best. My stainless lines from a few years ago are 1/4 so I had to get some adapters at the front hoses for the larger lines to work. So, if you are plumbing everything all over again, use 3/16 for the front, 1/4 for the rear. The line that runs across the rear end from rear wheel to rear wheel is 3/16.

I wont use stainless again because there is a much nicer nickel copper line that shines up about as nice and bends and flares much nicer while still having the corrosion proof qualities of stainless. You can always look at the pics in the bolt bucket to see how I did it. If you need pics of something else, lemme know.

Also, I just got my test wheel in today from Wheelsmith. Havent had a chance to evaluate it yet. The stock rims especially if they are 15 inch will not fit over the new calipers. So, remember that you have other choices to make.. like what new rims to purchase. Disc brake rims are shaped differently than drums.

So, you can get two new wheels, but then you have to have TWO spare tires. One for the front and one for the back, or, the new disc profile wheels work fine on drum brakes, so 3 new wheels is the most sensible. The cost for my stock looking vintage wheels was $90 a wheel without paint. Then, their wheels don't have clips for the stock hubcaps so they will modify your hubcaps or you can purchase new ones from them. With the hubcaps, about $120 a wheel. It never ends does it? LOL!

Since I a very picky and these wheels DO look a little different than the originals if put side-by-side, I got 5 new ones so the set is the same.

I have the same proportioning valve and bracket and plan on running my own lines from the valve to the brass T's but was hoping to use a pre bent line from the T's to the flexible lines.
Spoke with Van at CPP today and he said not to worry about the line size for the front. 3/16" is all that is necessary for the discs, so the larger stock drum lines will work fine and since I'm using the residual valves they'll stay at the correct pressure.


Where did you find the nickel copper line?


I have the stock 4x16" wheels and I was planning on using a 1.5-2" spacer on the front and something a little larger on the rear. So I'm not too worried about the wheels clearing.

I just read this. The residual pressure valves are there so that when you push the pedal, you're not pushing the piston on the drum or disc brake all the way from it's minimum position. This is to make up for pad or shoe wear.

You can get your nicop lines at the Brakequip store. I am sure there are lots of other places to get it.

Isn't Proportioning Valve and Residual Valve the same thing? I have NO idea. Learning this as I go. Even with the dual MC located below the floor it is still higher than the calipers. Can't see where the worry of backfill would apply.

think of parking on a hill.....

I know what the prop valves primary purpose is, but doesn't it also keep backfill from happening? A long time ago on Horsepower TV they had a tip on inline residual valves. I think they were pushing something from Summit Racing.

The residual valves maintain a minimum constant pressure in the system, for disc brakes it keeps enough pressure to keep the caliper full of brake fluid but not enough that the brakes drag. If they are not installed your master cylinder will not have enough capacity to apply the brakes with one stroke of the master cylinder.
The proportioning valve is used to set the amount of fluid that is sent to the rear brakes vs the front brakes. It helps prevent rear brake lock up. On performance vehicles a proportioning valve is used to adjust the amount of brakes to either the front of the vehicle or the rear of the vehicle. It is used as an aide to get a car through the corners faster by helping steer the vehicle through the corner by using the brakes.

The disc brakes on a 47-55 using the standard kit, the calipers are about 3.5 inches lower than the lowest point on the master cylinder and about 1.5 inches lower than the prop valve when installed just below the MC. So, do I need still need residuals? I still wonder if there is any worry about backfill since the fluid would have to get thru the prop valve first. Maybe I am overthinking it. Wouldn't be the first time.