Another Thread About Rear Disc Brake Conversion Options

[MavMark]

Yes, I know this subject has been brought up many, many times, but my many searches have not yielded definitive information.

I am looking for info specifically about rear discs that have been sourced from other vehicle lines. I have done quite a bit of searching and have seen more than one mention of the 1990's Caprice/Impala as being a source of a "tried and true" disc brake conversion, but I've never been able to find anything that verifies this. Has anyone here actually successfully DONE such a swap?

This old thread has lots of part numbers and there is talk of Blazer/S-10 rear discs as being a possible option, however when I investigated the backing plates, they appear to have a "trapezoid" bold pattern where the top bolts are more widely spaced than the bottom ones where it fastens to the axle tube and as I recall, the Astro/Safari has mounting holes that are evenly spaced at the top and bottom...so I don't think these would work, at least not without doing some kind of full rear end swap and I am not looking to do that:

https://www.astrosafari.com/viewtopic.php?f=45&t=116274

I own two Astros and two Safaris and I have done both the aftermarket SSBC rear disc conversion as well as the 1990's police/taxi 11.2" drum conversion..so I already know about these options. I am also aware of the factory '03 - '05 rear discs, but I don't want to do a conversion to 6 lugs and all that. I am looking to upgrade the rear brakes on one of the two that I haven't done yet (a 1999 high top conversion). I believe I have the parts to do another 11.2" drum upgrade, so I will probably go that route...but while I am waiting for the winter to end, I am kicking around other possible rear disc options.

Anyway, if anyone has any info on a swap that is confirmed to work, that would be great!

Mark

[stent]

i am looking for info specifically about rear discs that have been sourced from other vehicle lines. I have done quite a bit of searching and have seen more than one mention of the 1990's Caprice/Impala as being a source of a "tried and true" disc brake conversion, but I've never been able to find anything that verifies this. Has anyone here actually successfully DONE such a swap?

hi MavMark,
i too would love to find an installation writeup about the Impala SS rear disc swap. i happened across a '94 SS with the rear disc setup intact on a junkyard run and took it all off.
here's a few pics off my phone taken at the JY (the orientation corrects when you view the pics separately) :

here's a parts list from the Impala SS Forum :

reardisc1.jpg (253.67 KiB) Viewed 762 times

as with the 11" rear drum swap, the backing plates seem to be the most difficult & critical pieces to find.
calipers, pads, rotors, parking brake shoes, parking brake cables, fluid flex hoses, all show up on ebay.

some of the small parts in this kit (kit part number 18021516) might be unavailable :

i have put the stuff i got at the JY in a box for now & haven't really examined everything closely but i can take some pictures or make measurements if you want.

[CopperFiremist]

IIRC markmitch did a thread on the 11" rear drums and all you have to get from a JY is the backing plates.

[markmitch]

and the hardware. The springs, shoes, drums and wheel cylinders are still available new.

[AstroWill]

here's a parts list from the Impala SS Forum

Nice!

Will throw it here in text.

REAR
18021517 - CALIPER, unloaded, new (LH)
18021518 - CALIPER, unloaded, new (RH)

18037499 / 18037500 - CALIPER (L/R)
ACD reman, loaded (with pads) includes guide pins, boots, bolts, “H” clip (has CORE CHARGE)

18021521 - PAD KIT, OE - RPO JL9, ACD PN 171-725

17999642 - HOSE, caliper hydraulic (LH)
17999643 - HOSE, caliper hydraulic (RH)
(OE production, complete assembly, rubber, includes mount bracket, fluid fitting and seal washers)

18037216 - HOSE, caliper hydraulic--hose only, rubber, fits both sides of above assembly, ACD Durastop

10286122 - FITTING, caliper hydraulic, fits rear ONLY, included with above assembly

21012386 - WASHER, SEAL, caliper hydraulic fitting--2 per caliper required

18028256 - ROTOR, ACD Durastop 18A656

18039377 - ROTOR, ACD Durastop HP 18A1036 (LH)
(cross-drilled & slotted)

18039378 - ROTOR, ACD Durastop HP 18A1037 (RH)
(cross-drilled & slotted)

18022147 - PIN, caliper guide

14067552 - BOOT, caliper guide pin

14067559 - BOLT, caliper guide pin
(has thread locker pre-applied)

12337902 - BOLT, caliper bracket to backing plate
(2 per bracket, has thread locker pre-applied)

10228897 - WASHER, caliper bracket, use with 12337902 bolt above

18021519 - BRACKET, caliper abutment for 9C1 (cad plated)

18021945 - BRACKET, caliper abutment for Impala SS (black finish)

18021515 - SHOE KIT, park brake (1 shoe)

18021516 - REPAIR KIT, Major, for park brake (1 per car)

10223644 - CABLE, park brake (LH)
10223645 - CABLE, park brake (RH)

18034273 / 18034274 - CABLE, (L/R), park brake, ACD Durastop (alternate)

[MavMark]

Unfortunately I don't believe the Impala SS backing plate will work. Take a look at the bolt pattern on the backing plate...the holes are not evenly spaced; one set of holes (I think the top ones) are spaced wider apart and this won't fit an Astro axle tube. Without backing plates that fit, none of the other parts really matter.

Like I said in my original post....I do know about the 11.2" rear drum swap, and I believe I even have all the parts to complete it on this van. I've just been curious about the disc brake options. In my experience the hard parts to find are the correct backing plates and the parking brake spreader bar.

Mark

[stent]

Unfortunately I don't believe the Impala SS backing plate will work. Take a look at the bolt pattern on the backing plate...the holes are not evenly spaced; one set of holes (I think the top ones) are spaced wider apart and this won't fit an Astro axle tube. Without backing plates that fit, none of the other parts really matter.

i also have an 11" caprice drum brake setup in my stash of parts. when i get a chance i'll measure both the disc & drum backing plate bolt patterns & post the measurements, also some side-by-side comparison disc-vs-drum pictures.

caprice 11" drum brake backing plate

[AstroWill]

Take a look at the bolt pattern on the backing plate...the holes are not evenly spaced; one set of holes (I think the top ones) are spaced wider apart and this won't fit an Astro axle tube.

What are the measurements for your bolt spacing?

[AstroOafAdventurer]

If three of four holes line up in the backing plate with the axle, looking at the trapezoid pattern on the backing plate looks like the hole not aligning up could be slotted?

[stent]

this comment from 2018 by MI_Ghost :

his comment is in this thread :
https://www.astrosafari.com/viewtopic.php?f=45&t=135924

more tidbits :
https://www.astrosafari.com/viewtopic.p ... n#p1293066

more :
https://www.astrosafari.com/viewtopic.p ... n#p1207994

we should get in touch with him...

[MavMark]

i also have an 11" caprice drum brake setup in my stash of parts. when i get a chance i'll measure both the disc & drum backing plate bolt patterns & post the measurements, also some side-by-side comparison disc-vs-drum pictures.

The attachment CAP9.jpg is no longer available

Ahh, okay...I am remembering now. It isn't that the Astro/Safari mounting holes are equally spaced from top to bottom, but they are closer together than some of the other ones out there....but the spacing is still a "trapezoid" pattern. I'm sorry that I've created more confusion with my bad memory!

I found a picture from my '01 Safari axle tube end I took in 2016, the last time I did a rear brake upgrade, which looks to my eye like it matches the backing plates from your stash:

Here is a picture of the wrong spacing that I am remembering:

Wrong Drum Backing Plate

2001 Safari axle tube end:

Astro Axle Tube End

As it turns out, at the time I discovered that depending on whether the Caprice had the Taxi/Police/Heavy Duty options or not there are two different axle tube types/backing plates that were used, and the one with the wider spacing can't be adapted to the Astro/Safari mounting points. Ask me how I know. I bought a set of the 11.2" backing plates, media blasted them and finished them really nicely and when I started the upgrade project I discovered the incorrect spacing of the mounting holes and had to put everything back together until I figured out what to do about it. If there was ANY way I could have made them work, I would have. I ended up finding the correct backing plates but eventually decided to use the SSBC disc upgrade instead. That's how I ended up with this extra set of 11.2 drum parts in MY stash.

I don't have any of the correct backing plates handy right now to take measurements of the mounting holes. It would be really cool if you could still compare the drum/disc backing plates and see if the mounting holes match!

Mark

[AstroWill]

These could be your measurements.

[stent]

I don't have any of the correct backing plates handy right now to take measurements of the mounting holes. It would be really cool if you could still compare the drum/disc backing plates and see if the mounting holes match!
Mark

i'll get everything together & do pics & measurements - give me a few days. this thread could evolve into a good reference for the impala/caprice 11" drum & rear disc brakes.

here's a link to the markmitch 11" drum thread that CopperFiremist mentioned :
https://www.astrosafari.com/viewtopic.php?f=45&t=82673

here's a junkyard sticker tag pic with the VIN number for the 1994 Impala SS i got the disc brakes from :

'94 SS tag

here's a junkyard sticker tag pic with the VIN number for the 1996 Caprice i got the 11" drum brakes from :

'96 Caprice tag

Caprice with brakes still attached

These could be your measurements.

Thank you AstroWill !

[MI_Ghost]

this comment from 2018 by MI_Ghost :

RRD.jpg

his comment is in this thread :
https://www.astrosafari.com/viewtopic.php?f=45&t=135924

more tidbits :
https://www.astrosafari.com/viewtopic.p ... n#p1293066

more :
https://www.astrosafari.com/viewtopic.p ... n#p1207994

we should get in touch with him...

Just be careful how hard you touch!

Here is a pic posted of the Impala disc
https://www.astrosafari.com/viewtopic.p ... 97#p185233

Unfortunately life and work have put my conversion on the shelf for a while but all my information is in the links you posted.

[markmitch]

All my 11" drum parts were scavenged from a Buick Roadmaster and fit just fine. I think the year was 95 or 96. I would have to look in my notes if anyone needs to know exact year. let me know. Mark

PS I did the swap because I found the Roadmaster in pick n pull and because I hope to tow a trailer with my van in the future.

[stent]

i dug out the rear disc & drum sets from storage. now i have to lay everything out - bear with me

[stent]

this comment from 2018 by MI_Ghost :

The attachment RRD.jpg is no longer available

his comment is in this thread :
https://www.astrosafari.com/viewtopic.php?f=45&t=135924

more tidbits :
https://www.astrosafari.com/viewtopic.p ... n#p1293066

more :
https://www.astrosafari.com/viewtopic.p ... n#p1207994

we should get in touch with him...

Just be careful how hard you touch!

Here is a pic posted of the Impala disc
https://www.astrosafari.com/viewtopic.p ... 97#p185233

Unfortunately life and work have put my conversion on the shelf for a while but all my information is in the links you posted.

hi MI_Ghost,
thanks for checking in and posting the additional link !!!!
from your link it looks like Astronaut87 did the Impala disc swap on an '87 Astro in 2013.
i dragged out one of his pics from that thread and added it here...

Astronaut87's impala rear disc swap