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Discussion Starter · #1 · (Edited)
I have been a lurker and occasional poster here for many years, and have spent countless hours searching the posts for information when I've needed it. Now I want to give something back. :)

This is my write-up on a rear disc brake conversion that I completed on my 1999 Astro using parts sourced from the 1990s era Caprice and 1990-early 2000s Blazer. I didn't come up with this coversion...I borrowed this idea from a couple of different posts I found here:

I was not able to find a comprehensive write-up on how to do this, so I decided to document exactly what I did so tha other M/L van enthusiasts can benefit. Of course it goes without saying that you should know what you are doing when you decide to mess with the braking system on your van. If you make a mistake it could be dangerous and even deadly! Your mileage may vary, so on and so forth...

Rather than make you wait until the end, I will start with my synopsis of the results: I love how the brakes feel on this van! The "pedal feel" seems to neither too hard nor too spongy. There is great stopping power without being overly grabby. It really feels like the van came from the factory this way and I am glad I completed this conversion.

I am probably somewhat unique in that I have completed three different rear brake upgrades on these vans:

  • The 11.2" Rear Drum Upgrade (on my 1995 Safari)
  • The Stainless Steel Brake Company A117-2 Rear Drum to Disc Brake Conversion Kit (on my 2001 Safari)
  • This Caprice/Blazer Factory Parts Upgrade (on my 1999 Astro)

I feel that this rear disc conversion is the best of the three conversions, followed by the 11.2" drum upgrade and then the SSBC kit. I'll talk a bit about the other two upgrades:

- The 11.2" Rear Drum Upgrade: This one is probably the most natural upgrade and more info can be found by searching here. The overall brake feel is very good and the upgrade can ba accomplished with factory parts from other GM vehicle lines, however finding the correct backing plates and parking brake spreader bars has become very, very difficult.

- The Stainless Steel Brake Company A117-2 Rear Drum to Disc Brake Conversion Kit: I don't think I would recommend this "upgrade" at all, really. This kit uses smaller rotors and calipers that I think may have been sourced from an early 2000's Thunderbird. Getting the parking brake to work with these calipers is not easy and the overall brake feel and stopping power is disapponting. The kit was very expensive (over $750), and I don't think I would go this route again. I don't think it matters anyway since it looks like the kit is no longer available.



For reference, here is the list of parts that I used. You could certainly save money by using some different components. For instance, I opted to use the Power Stop kit with the fancy performance minded calpers, pads and rotors. I love my vans and I tend to like to use higher-end components when I am adding things. I guess it could be considered getting carried away, but I don't think anyone can argue with trying to have the best possible stopping experience... :) :


1 - Part No.: 15064302
BRAKE ASM-PARK (LH) $159.61 (GM Parts Giant)
Driver's side backing plate and parking brake assembly.

1 - Part No.: 15064303
BRAKE ASM-PARK (RH) $87.91 (GM Parts Giant)
Passenger side backing plate and parking brake assembly.


1 - Power Stop KC5064 - 1996 Caprice
Caliper, Rotor & Brake Pad Kit $ 229.99 (+ $55 core) (Rock Auto)
Kit contains:
- 2 Rotor - Drilled and slotted $48.00 ea ($96.00)
- 1 Brake Pad Set - Carbon-fiber ceramic - $38.00
- 2 Calipers - Red powder coated - $46.19 ea ($27.50 core) ($92.38 + $55 core)
- 1 Brake Lubricant $ 3.61

2 - Rear Caliper Brake Hoses 1997 - 2005 4WD Blazer
-- Duralast 70757 $15.49 (AutoZone)
11" length, 3/8" 24 female fittings at pipe end, 10mm banjo fitting at caliper end.


1 - Right Rear Parking Brake Cable - 1999 Blazer 4 Door Blazer
AC Delco 18P1984 $20.89 (Rock Auto)

1 - Left Rear Parking Brake Cable - 2005 Blazer RWD; 2 door or 4WD; 2 door; without High Rider Package (ZR2)
AC Delco 18P2574 $14.31 (Rock Auto)

1 - Parking Brake Cable Connector - 2005 Blazer (essentially the same as Astro/Safari)
GM Genuine 15714661 $1.84 ea (Pack of 5 $9.20) (Rock Auto)

1 - Parking Brake Cable Equalizer - 2005 Blazer (essentially the same as Astro/Safari)
GM Genuine 15714664 $6.26 (Rock Auto)

1 - Rear Differential Gasket
Fel-Pro RDS55072 $2.84 (Rock Auto)

1 - Smartsails 2PCS M8 X 1.25-Pitch 25mm Length 304 Stainless Steel Metric Hex Coupling Nut
Pack of 2 $6.29 (Amazon)

1 - uxcell M8 x 1.25 x 250mm Fully Threaded Rod, 304 Stainless Steel, Right Hand Threads
$8.59 (Amazon)

4 - Caliper Bracket Bolts (GM Fuel Tank Strap Bolt)
Part number: 11515767 - Pack of 10 $15.98 (Amazon)
10 x 1.0 thread, 35mm long. These are the same bolts used to mount trailer hitch.

8 - High-Strength Class 10.9 Steel Hex Head Screw, Black Ultra-Corrosion-Resistant Coated, M10x 1.5 Thread, 50 mm, (2 Packs of 5)
Part number 94863A212 - $14.72 per pack (McMaster - Carr)

8 - High-Strength Steel Distorted-Thread Flange Locknut, M10 x 1.5 mm Thread Size, (1 Pack of 10)
Part number 3528N13 - $5.71 per pack (McMaster - Carr)

8 - Spring Lock Washer, Conical, Black-Phosphate, for M10 Screw, 10.5 mm ID, (Pack of 10)
Part number 95221A206 - $7.92 per pack (McMaster - Carr)

8 - Flat Spacers, Aluminum, .375 in. Inside Diameter, .500 in. Length, Pair
Part number AAF-ALL18746 (Mfr. #: ALL18746) - $3.99 per pack of 2 (Summit Racing)



PART 1: REMOVING EXISTING REAR DRUMS AND AXLES:

Lift the rear end of the van, place on jack stands and remove the rear wheels. I put the stands under the rear axle housing out near each and of the housing. You will need to remove all of the exising drum hardware, including the parking brake cables. The most time consuming and tricky part is probably removing each axle so that the backing plates can be removed. I found it was easiest to do this part first, and then I removed the entire backing plate from each side with all of the hardware attached.

To remove the rear axles, you need to remove the differential cover and drain the fluid. There is no drain plug, so this can be messy. I found it easier to loosen the bolts, but not completely remove them and then pry the cover away from the axle housing to drain the fluid into a pan. I have an open (non-positraction) rear end on this van, and the rear axles are held in place with large "C" clips. Once the cover is off you need to rotate things so you can remove the bolt that holds the pin in place. This bolt has an 8mm head. GM recommends replacing this bolt, and I bought a replacement at AutoZone. Once the pin is out, you can push each axle in towards the center of the van and the c-clip will generally fall out on its own into the differential housing and you will need to feel around in the oil and retrieve them. At this point you can then carefully remove each axle from the housing. I decided to remove and replace the rear bearings and seals during this project, but if you don't want to do this, be careful when removing the axles so you don't damage the bearings or tear the seals.

With the axles out, it is now just a matter of removing the brake line , the four nuts and bolts holding the backing plate onto the axle housing and the parking brake cables. The nuts used here are "interference fit", I assume so the backing plates won't get loose from vibration...and it make it more challenging to remove them. As you loosen the nut from each bolt you never really get to a point where they spin freely, so this part is really a pain!

I chose to remove the backing plates, shoes and springs all as one unit. Once you remove the brake line from the back of the wheel cylinder, you can use a rubber mallet to break loose the backing plate from the axle and it should come off the axle. I also removed the parking brake cables at this point as well, since different cables will be used with discs.

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PART 2: INSTALLING THE DISC BACKING PLATES AND AXLES:

At this point you can start putting things back together!

The backing plates are stamped with TL and TR. The one with TL goes on the driver's side and the one with TR goes on the passenger side. It is during the installation of the backing plates where I made some mistakes...and hopefully everyone can benefit from my experience!
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Tire Wheel Automotive tire Automotive lighting Vehicle brake

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ISSUE #1: As had been discovered by prior research, this conversion requires that the backing plates will need to be installed with a 1/2" spacer of some type so that the calper and pads will be centered over the rotor. I quickly found out that the factory bolts that held the drum backing plates on will NOT be long enough. I believe someone is making and selling spacer plates that can be used for this purpose on Ebay, but I instead chose to use .5" aluminum spacers I obtained from Summit Racing and #10 metric bolts along with lock washers and interference fit nuts that I got from McMaster-Carr. I decided that the factory probably used these for safety and it seemed like a good idea to use these for the conversion. One issue is that the M10 bolts were too big in diameter to fit through the center of the spacers I used. I ended up drilling out the spacers slightly so that the bolts would pass through them.

A WORD OF ADVICE HERE: I ORIGINALLY USED SMALLER DIAMETER BOLTS TO GET AROUND THIS ISSUE AND IN A SHORT TIME THE FORCES GENERATED BY BRAKING CAUSED THE BACKING PLATES TO SHIFT BACK AND FORTH SLIGHTLY SO I REMOVED THEM AND PUT IN THE M10 BOLTS, WHICH SEEM TO BE THE SAME SIZE AS THE FACTORY BOLTS

Yeah, it was dumb to use the smaller diameter bolts in the first place.
Tire Wheel Vehicle Automotive tire Crankset

Once the backing plates and the parking brake shoes are installed, you can then reinstall the axles, and seal up the rear end cover. Don't forget to put in the rear end oil before you make your first voyage to test the brakes!


ISSUE #2: This one is a sneaky one and had me fooled for a bit. When you install the rotors and test fit the calpers and shoes you may notice at this point that the shoes don't appear to be centered on the rotor. I came to believe that the 1/2" of space added behind the backing plates was incorrect, but that was not it. I wasted a ton of time going back and forth with this before I realized what the real issue was...

If you look at the center of the axle that protrudes through the center of the rotor you may notice a slight ridge. In my case, this ridge was just enough to keep the rotors from seating against the end of the axle shaft. There is about 1/8" of space between this ridge and the flat area where the wheel studs are. I have no idea if all Astro/Safari axles are like this or not, but I had an old axle shaft from my '95 laying around and it also was made like this. I figured there were two solutions: either grind this 1/8" area down so the rotor would fit over it, or grind the inside area on the rotor to accomplish this. I decided to grind the axle shafts so I wouldn't have to do this every time I eventually want to change the rotor.

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Gas Automotive wheel system Automotive tire Auto part Metal

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PART 3: INSTALLING THE CALIPERS AND BRAKE LINES:

Once the backing plates, axles and rotors are safely in place you can install the calipers and pads. I believe the calipers are switched from their factory Caprice position, using the driver's side on on the passenger side and vice versa. The idea is that you want the bleeder to face up when the caliper is installed, not down towards the ground. Then comes plumbing the brake lines to the calipers. After some research I found that the '97-'05 4WD Blazer rear caliper rubber lines had the proper SAE 3/8" 24 female fitting at the end where the pipe connects and the 10mm banjo bolt fitting at the caliper. I own a hydraulic brake flaring tool, so I used this opportunity to run all new custom made brake lines across the rear axle, however I believe with some creative careful bending, you could use the existing factory lines with these hoses. I did not use any kind of bracket to hold the hoses in place; I ran them over the top of the leaf spring and they seem to be pretty secure this way. Once all the pipes and hoses are tightened, you can bleed the brakes. I have a vacuum bleeder, to get things started, but I always have a helper get in and do the "press the pedal down and release" method to get the last few air bubbles out and finish things off. I've read in the past that a Tech 2 is necessary to "exercise" the ABS valve to be able to properly bleed the brakes, but I did not find that to be the case.


PART 4: INSTALLING THE PARKING BRAKE CABLES:

The final piece to this conversion puzzle is to get the parking brake functioning. I spent a good deal of time comparing the lengths of the original cables to the multitude of different length Blazer cables that exist out there across the different years. You can save time and use the part numbers I have listed here and get it right the first time! ;) I used Blazer cables because I knew they would have the correct end on them to interface with the parking brake lever at each wheel.

DON'T BE FOOLED INTO THINKING THE '03-'05 ASTRO CABLES WILL WORK...THE END THAT CONNECTS TO THE PARKING BRAKE LEVER IS DIFFERENT AND IT WILL NOT FIT (ask me how I know! :) )

Installing the cables is pretty straight forward. The mounting bracket at the passenger shock that keeps the cable from flopping around was not on the Blazer cable, but I was able to pry this off the original Astro cable and attach it to the Blazer cable. The only real challenge that I ran into was that the threaded rod that connects the cables to the cable and equalizer coming from the parking brake pedal was not long enough. My solution was to buy an M8 x 1.25 couping nut and an M8 x 1.25 threaded rod to in effect lengthen the threaded rod on the cable so that it would reach the nut on the equalizer. I used a 250mm rod here that I found on Amazon and I was able to get everything hooked up and adjusted so that the parking brake actually works! The one thing I don't know is if or how these cables may have changed across the different year Astro/Safari vans...so you may find you have to improvise here.

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CONCLUSION:

Once you double check that everything looks okay, you can reinstall the wheels and test. I found that the rear wheels were much harder to turn by hand than when the drum brakes were installed. This drove me crazy for awhile and I did quite a bit of checking to make sure the calpers looked centered, etc., but nothing looked wrong. I think this was due to the brand new brake pads being so thick and the tolerances being so close with the disc brakes. Once I did some driveway testing and eventual road testing everything seemed to then seat properly and I didn't hear or smell any unusal dragging.


I now have several thousand miles on this conversion and I am very happy with it. I have not found the brakes to be overly grabby and the brake proportioning seems to be what it should be. The van stops very well even when towing a trailer. I would definitely do this conversion again if I end up with another Astro/Safari in the future!
 

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Discussion Starter · #2 ·
There seems to be a limit of how many pictures I could add to the thread. Here are a few more in no particular order:

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Nice Work.(y)
Mine is waiting for the axle rebuild.

Now add the 98-02 Camaro rear disc to the list,
Just remember to get the parking brake cable brackets
 

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This confirms the S10 backing plates with the Caprice/Impala calipers & rotors. Well done!!
 

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Did you have to do anything to the master to get adequate brake pressure/ volume to the rear. We put a wilwood kit on the rear and found even with your foot on the brake with the wheels in the air they would still spin. Did some digging and found the master from the vans that came with rear disc was a different part number. So I tried putting that on and still weak brakes in the rear
 

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Ironically, I'm trying to figure out how to get my rear drum brakes to stop locking up before the front discs. No lack of braking power with my stock drums.
Have you considered the big caliper upgrade for the front?
 

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Have you considered the big caliper upgrade for the front?
No not really... I'm running Power Stop calipers and commercial grade pads, which I can also lock up.
Once the tires lock up and stop turning.. I figure the brakes are doing their job.
But who knows... I may consider it one day
 

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ISSUE #2: This one is a sneaky one and had me fooled for a bit. When you install the rotors and test fit the calpers and shoes you may notice at this point that the shoes don't appear to be centered on the rotor. I came to believe that the 1/2" of space added behind the backing plates was incorrect, but that was not it. I wasted a ton of time going back and forth with this before I realized what the real issue was...

If you look at the center of the axle that protrudes through the center of the rotor you may notice a slight ridge. In my case, this ridge was just enough to keep the rotors from seating against the end of the axle shaft. There is about 1/8" of space between this ridge and the flat area where the wheel studs are. I have no idea if all Astro/Safari axles are like this or not, but I had an old axle shaft from my '95 laying around and it also was made like this. I figured there were two solutions: either grind this 1/8" area down so the rotor would fit over it, or grind the inside area on the rotor to accomplish this. I decided to grind the axle shafts so I wouldn't have to do this every time I eventually want to change the rotor.

View attachment 282078 View attachment 282079 View attachment 282080
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The Astro/Safari used the same drum for all 85-02 so this will be a common issue.
The 94-96 Caprice/Impala rotor has a 3.07" (78.1mm) pilot bore where the 85-02 Astro/Safari drum has a 78.6mm (3.09") pilot bore. This hub register will need to be turned down to use the 94-96 Caprice/Impala rotors.

PART 4: INSTALLING THE PARKING BRAKE CABLES:

The final piece to this conversion puzzle is to get the parking brake functioning. I spent a good deal of time comparing the lengths of the original cables to the multitude of different length Blazer cables that exist out there across the different years. You can save time and use the part numbers I have listed here and get it right the first time! ;) I used Blazer cables because I knew they would have the correct end on them to interface with the parking brake lever at each wheel.

DON'T BE FOOLED INTO THINKING THE '03-'05 ASTRO CABLES WILL WORK...THE END THAT CONNECTS TO THE PARKING BRAKE LEVER IS DIFFERENT AND IT WILL NOT FIT (ask me how I know! :) )
I am hoping you got a picture comparing the different eyelets. The only real difference I can see is the spring goes over the eyelet on the 03-05 Astro holding the cable to the arm.

Inquiring minds need to know (You did say to ask).
Does the 03-05 Astro eyelet not fit over the Blazer arm?
Or is the style of the arm such that the spring causes the eyelet slide off the arm?

Note: 94-96 Caprice/Impala, 98-02 Camaro/Firebird, & 97-05 S10/Blazer all use the same DIH parking brake system with differences in cable mounting. The cable eyelet attachment is the same. The 98-02 Camaro/Firebird uses a separate bracket for cable mounting.
 

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Discussion Starter · #11 · (Edited)
Did you have to do anything to the master to get adequate brake pressure/ volume to the rear. We put a wilwood kit on the rear and found even with your foot on the brake with the wheels in the air they would still spin. Did some digging and found the master from the vans that came with rear disc was a different part number. So I tried putting that on and still weak brakes in the rear
It's funny, after I posted this I realized that I didn't address the proportioning issue. I did some research awhile ago and the later models seem to have been built with some kind of electronic/automatic proportioning built in. Of course now I can't find any references to it. I think it is part of the ABS system. I know earlier models don't have this...but I am not sure which year it changed. I want to say maybe '96 or '97 and up? I can tell you that I didn't do anything as far as proportioning is concerned, or use a different master cylinder and the braking feels very well balanced to me.
 

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Discussion Starter · #12 ·
The Astro/Safari used the same drum for all 85-02 so this will be a common issue.
The 94-96 Caprice/Impala rotor has a 3.07" (78.1mm) pilot bore where the 85-02 Astro/Safari drum has a 78.6mm (3.09") pilot bore. This hub register will need to be turned down to use the 94-96 Caprice/Impala rotors.


I am hoping you got a picture comparing the different eyelets. The only real difference I can see is the spring goes over the eyelet on the 03-05 Astro holding the cable to the arm.

Inquiring minds need to know (You did say to ask).
Does the 03-05 Astro eyelet not fit over the Blazer arm?
Or is the style of the arm such that the spring causes the eyelet slide off the arm?

Note: 94-96 Caprice/Impala, 98-02 Camaro/Firebird, & 97-05 S10/Blazer all use the same DIH parking brake system with differences in cable mounting. The cable eyelet attachment is the same. The 98-02 Camaro/Firebird uses a separate bracket for cable mounting.

I am sure I have some pictures somewhere, I will try and locate them. I have been planning to do this write up since probably July and with the holidays here I finally had time to sit down and do it. I had the lists of part numbers I saved, but I have to sift through pictures on my phone to find the relevant ones. :)\

I recall there were two issues: The eyelet on the end of the cable was too large to fit through the mounting hole. I had considered grinding down the eyelet or drilling out the hole, but I seem to remember that the spring was much different and it didn't look like the length between the mounting point and the parking brake lever was correct either. I am not opposed to modifying things to make them work, but the more I looked at it, the more it seemed more trouble than it was worth when the Blazer cables were available and relatively cheap. :) The bottom line, I guess is that the Astro disc cables might work with some mods.
 

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Discussion Starter · #13 ·
The Astro/Safari used the same drum for all 85-02 so this will be a common issue.
The 94-96 Caprice/Impala rotor has a 3.07" (78.1mm) pilot bore where the 85-02 Astro/Safari drum has a 78.6mm (3.09") pilot bore. This hub register will need to be turned down to use the 94-96 Caprice/Impala rotor
Yes, turning them down would be the right way to do it. At the point where I realized the problem I had already had the rear end apart and the axles out twice, so I opted for a cutting bit on a Dremel, it made a mess with the steel shavings in the driveway, but it was effective in the end. :)
 

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it's great to see your post of working 5-bolt rear disc brakes.
i have a both a '96 caprice 11" drum setup and a '94 impala SS rear disc setup from JY expeditions sitting in milk crates.

after seeing your picture of the backing plate spaced out from the axle tube flange, a dim bulb lit up in my head......
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when i pulled the parts at the JY it never occurred to me to reinstall an axle afterwards and measure the distance from the axle tube flange surface to the axle flange surface to get the exact rotor placement measurement - duh.......
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i noticed in your picture that you have 15" wheels and they fit over the calipers - that is great to know because the impala SS had 17" wheels and i didn't think 15" wheels would fit.


this is a picture of the small parts kit for refurbishing the SS rear discs (part # 18021516) that i don't have. sadly it seems to be made out of unobtanium......
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this is a picture of the small parts kit for refurbishing the SS rear discs (part # 18021516) that i don't have. sadly it seems to be made out of unobtanium......
No worries
Centric 118.66003 Rear Parking Brake Hardware Kit
Caprice/Impala, Camaro/Firebird, S10/Blazer

Dorman 924243 Parking Brake Lever Boot
 
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this is more great news - i was kinda bummed about ever actually collecting the parts to refurbish the SS rear disc setup enough to actually use it. thank you and happy new year MI_Ghost - i'll send you a PM in the next day or so.....


No worries
Centric 118.66003 Rear Parking Brake Hardware Kit
Caprice/Impala, Camaro/Firebird, S10/Blazer

Dorman 924243 Parking Brake Lever Boot
 

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And the Parking brake shoe
Parking Brake Shoe-Rear Centric 111.07840
 
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