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86 K5 Drum to Disk Brake Conversion Questions...

PWagon

PWagon

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I've been kicking around the idea of doing a rear drum to disk brake conversion for a while now. I wanted to get some feedback and suggestions from you guys (and gals) before I make any decisions though. Here are my questions and concerns.

  1. Will my factory brake booster be sufficient for rear disk calipers?
  2. Will I need to pull my rear axles to install the disk conversion?
  3. Will I need access to a hydraulic press to press the parts together?
  4. What manufacturer would you recommend I go with? (SSBC, Baer, etc?)
  5. I'm running 15" wheels. Will rear disks require larger diameter wheels?
  6. I'm guessing a rear disk conversion will cost me about $700-$800. Does that sound about right to you?
 
A fair number of those question answers are "depends" unfortunately.

Are you intent on purchasing a complete kit, and are you wanting an e-brake?

Could probably put something together for less, but going to cost you in time. And no e-brake will probably make it a lot easier to put together.
 
Dang-it! I hadn't thought about an emergency brake. :doah: It would be nice to keep it, but it's not a deal breaker. Just having rear disks would be more beneficial, so I guess I could give up the e-brake.
 
You should ask yourself why you want to convert.

I've done disc conversions on two trucks, and ended up UN-doing one of them, reverting it to drums. Properly set up, drum brakes provide perfectly adequate stopping force, good parking brake function, and don't require re-engineering the rest of the brake system or changing parts. (Remember your front brakes provide most of the stopping force, so you're doing a lot of work for not much gain, comparatively.)

Now, on the one truck I kept disc, I love it. Drums are heavy (insanely so on the 14BFF), require more maintenance, are a royal pain to adjust, discs can be higher performance, etc. I had to replace the master and booster, etc as part of converting to hydroboost anyway, so switching components had to happen in this case.

But if you're running the stock 10-bolt axle, you should consider keeping it stock. Yes, drums require a bit more maintenance and adjustment, but those drums are relatively small and IIRC just pop off (you don't have to remove the entire hub like on a 14BFF.)

If you do convert, start by keeping your existing booster and master cylinder. If you change the whole system willy-nilly and then don't like the results, you have no idea what component(s) is at fault.

Once you have the rear calipers dialled in and the parking brake, if any, set up to your satisfaction, then look at changing the hydraulics as required (new combo valve or adjustable proportioning valve, different master which may require different booster, etc.)

Been there, done that, made myself miserable, on the one truck anyway. The one I kept disc stops well and the parking brake works even on an incline ... but it's been a TON of work (and even more $$) getting it there.

I know on the 14BFF's you need 16" wheels to clear the calipers. I don't know what rotors are used for the 6-lug axle conversion, so you'll want to check with whoever makes your kit about clearance.

Finally, I have no direct experience with 10-bolt disc conversions, but you can also look at TSM's stuff. Pricey, but their kits tend to be all-inclusive and they do have snazzy p-brake calipers that are upgraded from the small Caddies.

-- A
 
Giving up e-brake is pretty much a simple matter of buying a disk kit that contains non-parking brake (front) calipers. The right ones will clear 15" wheels since that is what they came on.

As mentioned, for most people, the only benefits from rear disks would come with a lot of weight over the rear axle. Outside of that, they don't do a lot of work, which is why the drums/shoes last about forever.

If you haven't, get in there and adjust the drums, perhaps that's all that's needed to get better performance. I dug into mine a few months back as I was getting some squirrely handling under hard braking (and locking up rear), and it was a simple matter of getting both sets of shoes adjusted properly. Back to normal.

Disks are cool, but cool enough for the effort/cost/benefit? Up to you.
 
My right rear drum has always work half-ass. It just won't stay adjusted (I literally have to adjust it once a week). It really sucks when you're trying to avoid an accident by pressing really hard/quick on the brakes, and the truck wants to swap ends (meaning it pulls freaking hard toward oncoming traffic (not good Mav)). I've figured out that the auto adjust mechanism just isn't adjusting. I've replaced all the internal springs, and parts (drum rebuild kit) as well as the hydraulic cylinder. The damn wheel just won't stay adjusted right. :mad: The local brake repair shop want's $800 to "rebuild" both back brake drum assemblies. My thoughts are that a disk conversion would cost the same plus I wouldn't have to worry about adjusting disks. The stopping power of disks over drums is not even arguable. I'm trying to get my truck ready for Colorado mining road exploring this summer, so I need to figure this out before I go.
 
PWagon said:
The stopping power of disks over drums is not even arguable.
Click to expand...

Mm. You're right, not worth arguing, as obviously you've made up your mind :D But I'd put the 14BFF 3.5" drums up against any disc that'll fit on the axle.

More helpfully, it sounds like you've replaced most everything there is ... except the hardline from the center softline to the wheel cylinder. That could be clogged or kinked, preventing that side from activating. It's also cheap to replace. Does mean bleeding the brakes which is a miserable task, IMO, but for < $10 I'd think it's worth it.

Your local shop is just going to re-do what you've already done, no sense in paying somebody else for that. Plus at the end of it, they'll have the same problem you do and have to go on to diagnose the problem.

Anyway, my .02, which with inflation and taxes is worth precisely nothing :)

-- A
 
Well, no, I haven't made up my mind yet. Like I said, I just want some feedback and suggestions from you all. It's a good thing to hear other points of view. I really don't want to spend $800 if I can avoid it. I'm just exploring my options.
 
PWagon said:
My right rear drum has always work half-ass. It just won't stay adjusted (I literally have to adjust it once a week). I've figured out that the auto adjust mechanism just isn't adjusting. I've replaced all the internal springs, and parts (drum rebuild kit) as well as the hydraulic cylinder. The damn wheel just won't stay adjusted right. :mad:
Click to expand...

It's been ages since I've had drum brakes, but are you sure you have the correct adjustment wheels on the correct sides? Rockauto lists a right and left adjustment wheel. So if you have say a left one that's on the right wheel, every time you step on the brakes going forward it'll adjust - the opposite of what it's suppose to do. Someone who has drums will chime in on this hopefully.
 
Oh sh!t. Yeah, the adjusters are side-specific ... and so are the shoes. I always forget this, and it's hard to tell by looking at them. But there's one larger/longer shoe that goes on at one end, and one smaller or shorter that goes at the other, and if you get them wrong, weird things happen. You may know this, as it's supposed to be second nature... but I always end up forgetting.

I actually have a deep-seated hatred of setting up drums because of their mechanical complexity, but once set up I've found them to be perfectly reliable. Really. :surepal: :haha:

-- A
 
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PWagon said:
My right rear drum has always work half-ass. It just won't stay adjusted (I literally have to adjust it once a week). It really sucks when you're trying to avoid an accident by pressing really hard/quick on the brakes, and the truck wants to swap ends
Click to expand...

BTDT, you are right, when the rear brakes aren't working right, they are dangerous when you need them.

Often felt that going disk would be cool, but I won't run a set without e-brakes, and the only economical options so far appear to be the early or later Cadillac setups, and IMO both of those suck, which is why all the late disk brake rears have drum-in-hat e-brake.
 
dremu said:
Oh sh!t. Yeah, the adjusters are side-specific ... and so are the shoes. I always forget this, and it's hard to tell by looking at them. But there's one larger/longer shoe that goes in front, and one smaller or shorter that goes in the back, and if you get them wrong, weird things happen. You may know this, as it's supposed to be second nature... but I always end up forgetting.

I actually have a deep-seated hatred of setting up drums because of their mechanical complexity, but once set up I've found them to be perfectly reliable. Really. :surepal: :haha:

-- A
Click to expand...

Actually the short one goes in the front and the long one goes in the rear.

And you are correct, you did end up forgetting. LOL.
 
I've been thinking about this a little more, and I think I stick with my rear drums. But, I'm going to upgrade my front disks. I plan on using cross drilled and slotted rotors (to help prevent heat fade), and I want to find good quality calipers. I'm done with the Autozone/Oriellys rebuilt calipers. I'm gonna spend some real money on a set of Wilwood calipers this time. Does anyone know what size the front brakes are on an '86 K5 Blazer? The best I can tell it's either a GM D52 or a D154 (http://wilwood.com/Calipers/CaliperListLanding.aspx). Can someone tell me what style/model number I need for front calipers?
 
The D52 in the 1.28" rotor should be what you want. You can measure your rotor thickness easily enough. (The D154 caliper is the smaller "metric" caliper and you don't want those, this I know.)

I'm actually using these on my Blazer, front and rear. That's part of a total brake system re-do, so obviously I can't say that any single component is the end-all to human existence ... but these are nice calipers :D

For the eight-lug 10 bolt front I have a set of the 120-10936.

-- A
 
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