Rear disc conversion...has anyone did it?

[Thayer03]

I have a 71 GMC Longhorn 3/4 ton. 8 bolt pattern. I have front discs already but I am thinking of a rear disc conversion. Any thoughts or suggestions on this project?

Randy Thayer

[Jeffs65GMC]

It can be done.

First question to ask yourself...why?

Drums hold better then disks (braking area being equal or some garbage like that ). Look under any big rig and you'll find drums the vast majority of the time. Disks are a selling point. They do clean out better of mud and resist fade.

So, all that aside, if you still want disks, here's the cheapest way to do it.

You'll want the front rotors from a 77 K20. Remove all your drum stuff. Throw it out the window. Then get some AA disk brackets (under $10). The last thing you need is some calipers off the rear of an 80's caddy eldorado. This will give you parking brakes. If you don't care about that, you can use front calipers off of an s-10.

Slide the disks over the wheel studs, and mock up the caliper and bracket. When you are sure it's right, tack weld the bracket on. Pull it all off again, and finish weld the bracket. Bolt it all up, put on some flexible rubber lines, and drink a beer to congratulate yourself on your fab work.

[wibilly]

i have done it on my eaton rear. i bought rear brackets off ebay for a 14 bolt from great laks off road $61 with spacers brackets are nice, spacers were not cut square but was a bolt on deal with grade 8 bolts included, as Jeff said you can weld on front brackets if you align them properly before welding them on. you probably have 9/16 wheel studs so make sure to get roters drilled for them some years had 1/2" i was told 76-78 eldorodo calipers so i found a 76 as a doner and used them for cores and took the parking brake cabel as wellfront roters off a full size chevy truck or any gm with 1.25" roters can be used if you use a driveline parking brake the caddy didn't use rubber hoses at the calipers but rather a steeele line bent in a u shape aprox. 1.5' by 4' to give it a place to flex as the calliper moves. i used corvette hoses because i had them i made brackets for parking brake cabels and brake hoses are off a front wd car cut bent and welded to my axel housing i will probably use a corvette mc when i get to that point to have two large resivoirs and a residual valve set up for rear discs brake line sizes ma need to be adapted depending on parts used but it is a pretty easy swap

[Longhorn Man]

this is a double two sided coin here.
I'll normally be the first to say that disks won't help stopping on your truck but maybe an inch in a 60 to 0. They'll add weight, and the pads won't last nearly as long.
(I do understand that an inch could be the difference between being a close call and an insurance claim)
If your truck is loaded down real heavy most of the time, they'll make a MUCH better improvement over the drums.
If you are in the mud, huge improvement over drums
Bling factor, huge improvement.


However, here is the real flip side to this issue... parts are getting harder and harder to locate, drums are all used up and used is all you'll find. So an upgrade is manditory one day. I'll normally say get a whole new rear, since these eatons are also outdated and getting hard to get parts for, but, in all reality, as long as you keep it full of oil, it's pretty hard to mess one up.


Misled showed me his disk set up on his eaton, and I must say, it looks like a nice set up. I think it is the same as wibilly's unit.

[Thayer03]

Thanks guys. I will leave this project for a while and do everything else for now. Those are some great ideas though! Thanks again!

[wibilly]

andy what do you mean they will add weight? i did not weigh the componits but i'm sure i shaved at least 40 pounds and as far as stopping power as you said without some weight in the rear it probably won't make much of a differance but my truck will be used as a tow rig for awhile i do know i've had a lot of vehicles and have never had anything that will stop like my vette as far as the eaton there is nothing stronger or easier to work on and iv'e been told the 14bolt internals can be put in the eaton housing by simply shortening the axels i need to reserch this more i have an extra 14 bolt and another eaton on the way i did find all bearings and seals to be available for the eaton

[drink2mny]

You know I can't resist. Check signature below.

There are many many options that you can do and many places to get stuff and piece it together.
Ours are complete bolt on package. No guessing and no small tubes not cut correctly for spacers.

You can ask around this board our product and customer satifaction are great.

Do you have an eaton or a dana 60?? I guess I just don't know what comes under a longhorn.

Again we are just an option.
I mean no disrespect of the above mentioned ways to build a rear disc brake kit. People have a choice as to what they want to do..
Good luck
www.blackbirdscustomtrucks.com

[Longhorn Man]

Disk brakes are normally heavier than drums. (assuming the discs are big enough to be comparable in stopping power) this is something that low buck drag racers love about 4 wheel drums. I had thought it was the other way around untill I did a rear disk conversion on old POS Honda I had about 10 years ago.
As for the comparison to the vette in stopping performance, your truck is very nose heavy, sep when you compair it to a vette, where some of the later vettes have an ideal 50/50 weight front/rear, which makes a HUGE difference in the amount of work the rear wheels can perform in traction situations. Not to mention your vette weighs about 3000 to 3500 pounds, and your truck is more like 4000 to 4500 in your everyday set up. (All the junk ant tools and chains you carry in the tool box or what ever) Not to mention the contact patch the wide vette tires have in comparison to the tall by skinny tires your truck has...what, a 9.50 x 16.5? Compaired to a 300/40P17 or so? (guessing on both accounts)
Having a trailer does add weight, and a loaded trailer naturally will add more weight on the rear tires... every pound will make the braking power that much more effective... just as I indicated.
I have also heard about teh 14 bolt guts, but haven't really looked at it yet. I plan to just remove the whole thing and replace it personally. The bearings and seals are in fact still around, I'm willing to bet a punch in the gut that they had to order them, and while I know the pinion seal is still used on other rears (same P/N) I wouldn't be one bit suprised if the bearings are specific for the eaton.
It is a good rear, just getting out dated and parts are getting harder to find every day. It sucks when your truck...esp if it is your only vehicle... is down for something as stupid as a wheel seal, and it'll take 3 days to get one to you.

[Jeffs65GMC]

The drums on a 14 bolt weigh 35 lbs a piece...I'm sure the eaton is similar. I would not replace an eaton. Bearings aren't a problem if they don't wear out. If you are worried, then order up another set as spares. I'd about guarantee that the outer wheel bearings are the same as a d60/14bolt. Put some 14b side gears in and use the shafts from them and you have an axle that you never have to worry about.

[Thayer03]

Great. Thanks for the info guys. How do I tell if I have an Eaton? As far as I know it is a Dana 60 but I could be wrong.

[wibilly]

an eaton has a perfectly round rear cover and a chunk that comes out the front like a ford 9"

[drink2mny]

Axle identification http://www.blackbirdscustomtrucks.com/index5.html

I really need to update this

[ChevyDude]

It's on my list of "to do" things! Nice kit :

http://www.blackbirdscustomtrucks.co...x7.html#910&12

Alex

[MisterMan]

my reasoning: a nice clean truck slamed on 20's dosent look good /w/ drum hubs sticking out in the rear only. But a trucks brakes do feel better /w/ disk all around, and a new booster

--den