I need some advice. A good deal has come my way for a rear disc brake conversion kit. It has no backing plates. Car is 70 442 with an O Type axle. The tech support guy says backing plates are a problem, so they don't include them. I can imagine asking for this at a parts house?

Who can help me ?

 

Backing plates are a front disc thing. Unless you are partying in torrential downpours, your rear discs won't get much water on them, nor is their some oil slinging engine or grease chucking suspension right there to throw it on the back of the drum. Is this kit for your car? What do the instructions say?

 

I am looking at buying a kit from a guy who sold his car. I'M looking at getting
a set of instructions and looking to solve the rear backing plate thing..

 

You might consider contacting Quick Performance in Iowa. That looks to be a Ford style rear caliper setup. They might be able to help with mounting hardware.

 

None on my G Body, Never a problem. The only thing they do is shield a bit of road dust and debris. Brake cooling will improve.. The ones you show have the good parking brake mechanism, Not happy with my older BEAR BRAKES RB.

Calipers look like the same ones on my 85 Seville. Has no backing plates in the rear. Would not be much left, if you tried to put on.. Takes a little to adjust parking brake, Videos on YouTube. Drum brakes hold a lot of water

Do not forget to get a disc front and disc rear brake systems proportioning valve, Get a good one!

 

Here's some advice you probably don't want to hear.

Scan this and other forums for all the threads where people have done a rear disc conversion and the car stops worse than stock. Just because a vendor can cut out brackets with a water jet cutter doesn't mean that their kit has any engineering or testing behind it. Simply bolting the parts in place is the easy part. Getting the system balanced so it stops correctly under all possible braking conditions seems to be a skill that many people are lacking. Your call. Know your skills.

 

Backing plates are not strictly necessary. I've been running 4 wheel disc without any plates for a while with no ill effects. They're nice, especially for a daily driver that will see mud and gravel and lots of water, but not strictly necessary. Don't sweat it.

As Joe said, that particular kit is, well, wobbly. Although I did put that on a '70 Chevelle and it worked just fine. It's the cheapest way to get the drums off the car.

 

Joe is right. You need to do an analysis of the entire system and match the components for everything to work correctly. If you just bolt the kit on, you will probably have issues with brake bias and pedal firmness related issues due to incorrect master cylinder sizing.

You do not need backing plates for the brakes. The brakes will run cooler without the backing plates. But, the OEM drum backing plate is what helps set preload on the O-type axle bearings. Talk to Monza / Jim at JD Race for help with an appropriate spacer.

 

THANKS for your thoughts. So you believe I'll need a different axle
bearing retainer?? Do you have a good number for Jim? Save me
some time.................

 

The bearing retainer does not need to change. You need a spacer to replace the thickness of the drum backing plate, which the photo in your first post appears to include as part of the kit.

 

As noted above, it's probably not worth screwing up both the authenticity and the stopping power of the car just so you can say you have four-wheel disc brakes.

 

I believe four wheel disc brake is a better way to go. Even with standard size rotors. Most modern car come standard 4 disc brakes. Drum brake going through deep puddles just stop working. To be clear. On my G-Body going from 10.5'' rotors in front and drum brakes in back. To 13'' rotors in front and 12'' rotors in back. On 17'' rims. Disc front and disc rear brake systems proportioning valve. Properly install and adjusted. Made a huge difference in stopping power.

 

Most modern cars come with four cylinder engines also.

And how often are any of these cars driven in rain, much less through deep puddles.

 

Then it's settled. OP will convert his 4-4-2 to 4 cylinder, 4WDB and then he can drive it in the rain anytime he likes.

 

I see your point. Except in snow and fog. Would drive up and down the east coast in mine for work. In the middle of the night, to avoid traffic and cops. Newer V8 and V6 come with 4 wheel disc brakes.

Have some knowledge of Cadillac from the 1980's. My first experience driving 4 wheel disc brakes cars. I was very impressed how well they stop those big boats.

 

I missed those in the picture the other night.. I still recommend doing a little math to get an idea about line pressure, brake torque, and front to rear bias prior to installation. It will help determine the needed master cylinder bore and if the OP will need an adjustable proportioning valve in the rear line.

 

Adjustable proportioning valve for the rear line. First picture. Took me four short test drives to get balance perfect for front and rear. Second picture disc front and disc rear brake systems proportioning valve. Location on G-body. Baer Brakes had great step by step instructions and support!




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^^^THIS.

I'm going to rant a little here, so people with thin skin should go to their safe spaces.

The large number of posts I see here and in other automotive forums from people who can't even bleed their brakes properly tells me that the vast majority of people contemplating or executing these brake "upgrades" really have no idea what they are doing. Heck, I remain amazed by the number of people who don't even know the difference between a distribution block, metering valve, or proportioning valve, or what those items even do. The fact that a company owns a CNC plasma cutter and can make brackets does NOT mean that they actually have a clue or that the kit has any sort of engineering or testing behind it. Every factory brake system has years of engineering and thousands of hours of testing behind it, and that testing encompasses the entire spectrum of operating conditions - lightly loaded, max load, brand new brakes, worn-to-the-limit brakes, dry pavement, sand, wet, snow and ice. I challenge anyone to show me an aftermarket "upgrade" kit with even a fraction of that engineering and testing behind it. Look, no one will argue that PROPERLY DESIGNED AND INSTALLED disc brakes will stop better than drums, but in my experience, very few of these "upgrades" are properly designed or installed. For example, adjustable prop valves are only useful if you've actually tested the car under the full range of driving and braking conditions and actually adjusted it properly. Bottom line is that if you think you can buy some no-name kit off of ebay, bolt it on, and your car will magically stop like a new C8, you are kidding yourself. Do a search for threads about brake problems, especially after "upgrades".

 

I'll throw in a little OEM factory experience here. Yes, new cars are overwhelming 4 disc brake cars, however, one needs to grasp that the rear discs are not the front discs. For a Corvette, sure, put the big honking rotors on the back for even brake force, but the majority of cars, which are not performance, have only one thing the rear brakes do, which is keep the rear end of the car from swinging around on you. Those OEM rear discs are TINY. They do just the same thing as trailer brakes. The front brakes, with that huge V8 compressing the springs as the front dives to the floor, will do much more.

In short, wider, better tires, and front disc upgrades, will be more bang for the buck for stopping power, than rear discs, and be a lot less hassle.

 

^^^THIS. And to add to Koda's point, the whole point of a prop valve is to REDUCE rear brake force so the back doesn't lock up prematurely.

Let that sink in for a minute.

You'll be spending thousands to convert to rear discs, then limiting their braking ability back down to what the drums already provided. As soon as the rear brakes lock up, the back end is coming around, which kind of negates the "upgrade". And as Koda also points out, tires and weight distribution have as much to do with stopping ability as the brake hardware.

 

And I just have to add this post from one of the Oldsmobile sites on FB, from just a few minutes ago...

 

So you guys are saying. You get what you pay for. Go with Baer Brakes, Wilwood or Brembos. Have a auto mechanic who knows braking systems install. Put larger disc in front. And forget about changing the rears?

https://www.wilwood.com/Tech/TechQA

 

I do believe that you usually get what you pay for, but you still have to break out the calculator for a Bear, Wilwood, or Brembo brake upgrade kit. They kits are not necessarily designed for every single installation. You still need to figure out the correct master cyclinder bore size. Most of the kits these companies offer have to much rear bias out of the box - which is why Baer, Wilwood, etcetera all recommend installing an adjustable proportioning valve in the rear line.

For example, the Baer 14" front Pro Plus six piston front brake kit is supposed to be matched to / work well with the 13" SS4+ four piston rear kit. But, out of the box, the kit has an approximate 60 % / 40 % front to rear brake bias. That is way to much rear brake for any car - including most road racing cars. Our A bodies don't seam to be able to handle much more than a 20% rear bias. I suspect that is because of the excessive front dive under heavy braking which unloads the rear tires. The bias in these kits is not an issue, as long as you install the "recommended" adjustable proportioning valve.

Even the big name kits are put together from a limited number of part variations and the installer needs to understand the system dynamics for the best results.

 

To belabor some of the points, in my opinion if you don't have a stack of paper that looks like the below before you start you "upgrade," then your system probably won't work correctly.

 

You are hired!!!!

I guess I just got lucky. Thousand of miles in wet and dry. Works perfect. No experience in snow, tires too wide to take a chance.

 

If you bought front and rear kits from Baer that are made for your car, they will be close in bias. Baer also provides good recommendations for master cylinder size for thier kits. You also installed the adjustable proportioning valve. The reason Baer recommends the valve with all of their kits is because they know that the kits are in the ballpark with regard to balance, but will need some fine tuning for each installation.

 

You should have worked for GM on there X-body cars front wheel drive. Had a 1980 Omega. On the thread Oldsmobiles you have owned, I mention. Rear of the car would come around at high speed braking or wet roads. Hated that car!

 

70Rocket I have a question that been rattling around my brain for years! Maybe you can answer. With the original 1987 Cutlass and 1972 high output 350 SBO. With radical cam, I did it not have enough vacuum for original brakes.

Had a few scary moments at low speed. After installing the Baer Brakes, it has never been a problem. Nothing else change, but the Baers. Brakes.

 

Vacuum creates a pressure differential across the brake booster diaphragm. Less engine vacuum equals less of a pressure differential and less booster assistance. The booster assistance is added to the pedal input force when calculating force applied to the master cylinder, which in turn is used to calculate line pressure. So, less engine vacuum ultimately means less force applied to the master cylinder, lower line pressure, lower caliper clamping force, and ultimately lower brake torque.

The fact that your problem went away could be related to a number of variables. First, you might have increased piston area which will generate more clamping force at a given line pressure which in turn generates higher brake torque. You might have also increase rotor size which will yield higher brake torque. You may be using a higher coefficient of friction pad which also yield higher brake torque for a given clamping force. It might be a combination of all three offsetting the reduction in force applied to the master due to a decrease in engine vacuum.

 

Thank you so much! One less thing rattling around my brain.

 

Hey joe lightning in va jusy saying hey youve helped me have a great day!!!!!!

 

Is there a front disc brake upgrade for OEM disc brakes? What does it entail? Larger drilled rotors, dual piston calibers?

Any recommendations for improving the OEM drum brakes besides a routine overhaul?