The 30mm GM wheel cylinder swap is something I picked up from a bunch of CTD owners. They had been doing it to their trucks. And since all the 3/4 tons and 1 tons use the same type/style of wheel cylinder (with the exception of the ones with rear discs) I decided to do it on my truck, and the results were VERY noticeable and well worth the $30.

It's a simple mod to do and is very effective. You can see in the comparison below how much bigger the cylinders are.
GMC 1 ton -----------= 30mm = 1.18"
Dodge 1 ton----------= 27mm = 1.06"
Dodge pre-'97 2500-= 24mm = .94" (Though they have been found installed on POST 97 Heavy Duty Trucks)

The difference in stopping power between 30mm and 27mm is 23%! That may not seem like much, but it definitely is noticeabe out on the road! I know there are some people that think disc brakes are the answer, but for $30 you can have drum brakes that are just as capable as the disc brakes found on 01+ Trucks. And unlike the disc brakes, the drums don't have issues with mud and gravel getting in them...or slides seizing up. There's a good reason GM switched BACK to drums some on their trucks.

What you'll need for the swap is a set of 1 Ton GM wheel cylinders. Don't go to the stealership to buy them. Head down to NAPA or Bumper To Bumper...or order them from Rock Auto. Below are some part numbers. If you go into NAPA (or somewhere else to get them), DON'T tell them what you're using them for. That will just confuse them!

NAPA: 4637337
CARQUEST: SWC1025
WAGNER: http://www.rockauto.com/catalog/cata...8&a=FR5-F79768

They should run you anywhere from $8 to $15 a cylinder. I have heard of some costing as much as $40. DON'T get those...the cheap ones work just fine. In fact, the guy that came up with the idea specificly said to use the cheapo NAPA cylinders. I used Wagner cylinders in mine (they're probably the same) and I still noticed a huge improvement in braking. A warning though, the first time you use your brakes (after you have them properly adjusted) you will most likely lock up the rears. I know I did. That's beacuse you're used to using brakes that don't function very well. After a while you get used to using a lighter touch on the pedal.

A concern that some have had about this mod is the master cylinder. Some think that it doesn't have the capacity for the larger cylinders, but let me assure you that it has MORE than enough capacity for them!

Installing them is a simple task. Simply remove the springs at the top of the shoes. (You don't need to remove the shoes). The wheel cylinder is held on by two bolts and the brake line. Remove the brake line, and then the two bolts that hold the cylinder on. When installing the new cylinder, it's helpful to start the brake line, then install the cylinder and bolts, and then finish tightening the brake line. After that, reinstall the springs and you're done. You now have larger wheel cylinders.

Alternatively, I've been told you can install them WITHOUT removing the springs by sliding one side of the cylinder into place at a time. Then loosely installing the bolts. After that, install the brake line and then tighten the bolts. I haven't tried this, but if it's possible it does sound like a much easier way to do it.

An optional step is to bleed the system, or at least the rears. You don't have to do this. I did though, just to get some more of the old fluid out of the system (it was really crappy when I bought the truck...sucked mosted of it out with a turkey baster). It shouldn't take more than two or three pump/release cylces to do. A few brake bleeding tips...

- If you use the pump the pedal method, try to resist pushing the pedal all the way to the floor. What happens is the master cylinder travels in an area where it doesn't normally go in normal braking operation and that area is often rusty. This CAN result in torn up seals that can cause internal leaking and a mushy pedal.

- I've always started with the furthest brake away from the master cylinder and worked my way towards it. In other words, right rear, left rear, right front and then the left front.

Some owners who have done this mod have complained that it didn't do anything for their braking, or in some cases made it worse. This is because of two things. The first is the simple fact that the adjusters on our trucks SUCK! They are NOTORIOUS for not working, especially if you live in a climate where there is a lot of road salt used in the winter. The way you are supposed to adjust them is by backing up and then jabbing the pedal, but many have found that method to be unreliable as the self-adjusters often don't work. Like many others, I've found that if you crawl under the truck every oil change...or every other oil change...and adjust them manually, you will have much better braking. The method many use (including myself) is to jack the rear end up. Then, while spinning the tire, click the brake star wheel upward until the shoes just start to rub. That's it. The first time you use the brakes, the shoes will even out and there will be no rub. There are some that claim this method is no good when working with trucks that have Limited-Slip/Anti-Spin differentials because the amount of drag will be different on each side. But you're not going by the amount of drag on the wheel. You're going by the SOUND of the shoes.

The other problem (which I have never dealt with, only read about) occurs on some of the 96.5 and newer models. Why it doesn't occur on them all is something that seems strange to me. It involves the brake proportioning valve that was installed in the rear axles of those trucks. Basically what it does is limit the amount of pressure that the rear brakes receive based on how much weight is in the bed of the truck. The more weight, the better your braking. Well not everyone travels around with a bunch of weight in their truck. Dodge has a TSB out that applies to vehicles with LIFTS ( http://dodgeram.info/tsb/1998/05-04-98.htm ) but from the way it sounds, guys have been doing it to their non-lifted trucks as well. It's been said to make a big difference.

There is a "redneck" way to modify/test the valve, and that's to disconnect the rear axle load sensor (proportioning valve) rod from the axle and tie it up to the frame with a ziptie. Like I mentioned, sometimes the proportoning valve assumes that your rear axle is very light and won't let enough pressure get to the wheel cylinders. It's also possible that proportioning valve could be bad. It's a good idea to try it on a road that's not frequented, as the vehicle could sway or fishtail when applying brakes. There are ways to re-locate the lower joint of the rod for the valve to a higher position on the axle. I haven't read much into them though. Some have even come up with ways to make the valve adjustable with the use of various bolts and nuts.


EDIT:
I found the txt file I was looking for with the drum removal trick in it. Here it is...

 

You Sir, are my Hero. Thanks for the write up. Can we get this pinned or something?

Im going to try the install shortly, when Napa is open [:'(]

 

Well Napa is closed when ever I have time to pick up a set.

What is the application for that Napa number so I can pick up a set from Canadian Tire?

 

1996 Chevy 1 Ton Dual Rear Wheels

Bore Size: 1 3/16"

The single rear wheel trucks only had a bore size of 1 1/16" [:'(]

 

Burning Rom, great post. If I'm following you, this might help the braking power on the 2500 and heavier. I've noticed when lightly loaded, I don't have the brakes necessary to make a hard stop. This happens especially while towing a trailer. You get that uneasy feeling and start coming down hard on the pedal but the braking power still isn't there. Would you think that it might be a faulty brake proportioning valve or the weak rear brake cylinders? The swapping of the cylinders sounds like a good idea. Would like to know more about the BPV and tricking it for more brake force. Thanks for the post.

 

This is a VERY good mod for 2500 owners.

The lack of braking that you have doesn't sound like it's attributed to anything being faulty, but rather a combination of small wheel cylinders and the BPV limiting the pressure that gets to them. That's what it's supposed to do...it just doesn't do a good job of it...or knowing when you really do need the brakes (like towing). [:'(] I will do some more research into tricking the BPV and let you know what I find.

 

Great Rom, I would appreciate anything you find. I'm going to go with the NAPA cylinders and see what happens. Can't be any worse than what's happening now while towing. Without the trailer, I do nose dives. Rear brakes are adjusted but just don't seem to function like they should. Either way, I have always felt, the 2500 is underbraked. I could see how the BPV could screw you up and I never paid much attention to it. Even with a load, I cringe when having to stop quicker than normal. I will post the results on the cylinder change. Thanks again.

 

Alright, I did some digging on the BPV, and I found that there really isn't much to bypassing the valve. I've attached a picture of the "lever" that I found on the internet to this post.

The cheap fix is to zip tie the lever in your pic up to the frame, so it's in a horizontal position. If this improves your braking, then that tells you that the BPV is still functional, and has been limiting your braking ability. I wouldn't recommend this as a permanent fix though as I don't trust my braking to zip ties.

What I would do, based on what I found, is slowly raise the lever with a zip tie (or with some rope...or something else to keep it raised). Move it up little at a time until you find an acceptable adjustment. Then measure the rod length needed to make that position the new default or starting position for the lever. The rod you need to change runs from the bracket to the valve, which is just above the rear end and slightly to the left of center.

You may notice after raising the lever that rear brakes will easily lock up when empty. Not a big deal if you are aware of it and adjust your braking style accordingly. The ABS or RWAL should also help keep it under control.

I've read that some guys fabbed up adjustable rods, but nobody ever mentioned how. I don't have a whole setup to look at, as my truck doesn't have it and I can't find pictures of all the parts, so I can't begin to guess how they did it.

I also found out that not all the trucks have these. Some do...some don't. And even more surprisingly, the newer trucks with rear discs have them as well.

[IMG]local://upfiles/16690/F374C1FD31B148DEB2086E2D68BE90E3.jpg[/IMG]

 

The change over to a GM cylinder is complete. Piece of cake. Burning Rom, you deserve the great cheap tip of the month award. Definitely helped with the braking of my 2500. Although I did do rear brakes at the same time and the old ones were still in great shape due to lack of use for the past 75,000 miles, I still feel the GM cylinders helped in the improvement. Good picture of the BPV and it turns out, I don't have one. The GM cylinders cost me $16 each because the NAPA I went to didn't have the cheapies. They would have been $12 each. No biggie for $8 as it would have cost me that in gas to go to a different NAPA. The salesman said there really wasn't any difference and both were 1 3/16 bore but he didn't have any.

 

TTT for anyone that missed it