Drum to Disc brake rear end swap how-to!

[rlith]

Well I got the new rear end in! I had wanted disc brakes for a long time, I came across a good deal on a g80 (limited slip posi) rear w/ disc brakes from a 99 blazer. It only had 33k on the rear and I got it for $180.00 bux! YAY.... So I finally get around to installing it this weekend with the help of Grappler...(Thanx once again bud)...

The install is fairly straight forward: (see notes at the end of this page): So I started by picking up the rear at my local wrecking yard. It's been sitting in mud for almost a year (the back end of the blazer it was on had no wheels and it's a messy yard)...

Here is the rear...As you can see there is a lot of surface rust...



Fortunatly the emergency brake shoes were in good shape as seen here...


Grappler taking a break before the installation... (see ending notes)



The dust shields were toast (rusted and bent) so I pulled the diff cover, then the axels and put new ones on.. In this pic you can see on the left side how bad they were banged up... on the right side I had already removed the dust shield...I also took the opprotunity to change the diff fluid... Sprayed out the casing with 2 cans of brake clean, let dry, then added Valvoline Durablend (dino/synthetic mix) 80/90 weight gear oil.



I used a wire wheel on an air rotary tool to get any scaling and debri (i.e mud) off of the casing. I then used a spray on rust inhibitor/converter/primer and let it sit overnight. (actually a couple of days because I couldn't get back to it). I then put on 2 coats of Rustolium Black w/ hammered finish on to it. This gives the benifit of being less rusty later on (gads I hate salt) and it actually looks good. I may do my whole frame in the stuff.

Here's a pic of it when it was half painted. You can see on the right the finished product while on the left it's still bare. Definatly an improvement.



I then cleaned up the calipers. Ground out the dirt and grease on the calipers themselves (aluminum, not iron, very light weight!) then cleaned and painted the actual caliper frame in the same color as I painted the rear itself.

In this pic I had test fitted the newly cut rotors and the calipers.... They came out very well...



rear side...



Once the new rear was finally ready for installation we of course had to pull the old one... This was simply a matter of diconnecting the vent hose, brake line T, emergency brake lines, u-bolts, drive shaft. Remember when you pull the u-joint, run some tape around both the end caps so they don't fall off when manuervering the shaft around.


Then we jacked it up and slid it out lengthwise....

My baby don't got back...



Here is the old rear in all it's glory (and salt)



Installtion is the same as extraction, just in reverse....

Grappler taking a break before the installation...



Without Caliper but with caliper frame: Note.. I took the opprotunity to install red polyeurethayne bushings on my swaybar to replace the OEM 10 year old rubber bushings....



With full caliper installed.


Angle 2


Finally when you've reattached all your brake lines, simply bleed all the air out of the calipers and lines. Test drive, enjoy!!!!



Some notes and conclusions:

Overall this is not a difficult swap. If I had been less concerned about the type of rear I was getting (g80) there is actually an easier way to do this. The above will work on 84 to current... This will also work... If you want to add OEM stock disc brakes to your EXISTING drum rear without changing the whole rear you would only need the following....

All 98 and up parts (these will work all the way down to 86)

Backing plates (27.00 per side )
Calipers (30.00)
Caliper frames (20.00)
Pads ($20.00)
Discs (36.00 per side at advance auto parts)
OR a loaded caliper from Advance autoparts (includes frame, pads, calipers, bolts, et-al)
Stock bolts
Dust shields (12.00 per side at the dealer)
Brake lines to the caliper...($15.00 each)

Simply remove your old shoes and the backing plates, install the new backing plates then the calipers, etc... Bleed and go...


EMERGENCY BRAKE INSTALLATION..

From the center of the body you will see a bracket where your pedal cable and your ebrake cables. From the bracket to the backing plates, those 2 cables will need to be replaced ($23.00 per side at the dealer) as the drum style has different ends and won't work with the new setup.. (This is only for 95 to current, 94 and below have a completely different cabling system so you would have to figure out on your own on how to go about making the ebrake work)



Definatly better stopping power than with my drums, the overall upgrade was well worth it. Overall time was about 4 hours (this included breaks and what not)

[Forklift]

great man, that lt1 needs to slow down faster, thanks
I need to go pillage soem yards for a g80 soon , like before I start attaching the 4 link

[Grappler]

gezz, whos that lazy bum helpin you?! need to get him off his fat arse and get some work done! now if only the swap went as easily as this write up did!

[rlith]

Quote: Originally Posted by Grappler

gezz, whos that lazy bum helpin you?! need to get him off his fat arse and get some work done! now if only the swap went as easily as this write up did!

All told it was fairly easy (with the exception of the razor blade in your shoulder...and me whacking you in the head with the jack handle! And I keep wanting to work on your swaps dammit!

[Grappler]

swaps? im not doing no stinking swaps. just need a job i get paid the same at and work less.. so i can get my bills paid and get out to clean the garage and get some decent progress done on them.
yeah the razor blade did suck!

[rlith]

Quote: Originally Posted by Grappler

swaps? im not doing no stinking swaps. just need a job i get paid the same at and work less.. so i can get my bills paid and get out to clean the garage and get some decent progress done on them.
yeah the razor blade did suck!

Become a male prostitute... Cmon, afterall you love to whore yourself for parts!!!

[Grappler]

ill remember that the next time you need to work out of my garage.. who the whore is for what..

[rlith]

Quote: Originally Posted by Grappler

ill remember that the next time you need to work out of my garage.. who the whore is for what..

I'll just send "you know who" to move in with you...

But let me say, for the record, I have always appreciated any help you've given me, be it advice or physical help...

k, back to the cracks... giggidy giggidy giggidy

[Park Style]

nice rick............ look andy is alive... wholey hell

[rlith]

Quote: Originally Posted by Park Style

nice rick............ look andy is alive... wholey hell

I prefer to call him...."Undead"...

[freestylebikerguy]

this should proolly be inthe how to section shouldnt it?? very good swap instructions tho, makes me wanna swap my rear end

[nice01s10]

nice work man

[Lenny95NeoN]

I Guess I'll give this a try. I need to get the truck on the road again. I guess I get any axle w/ drums and just swap my discs equipment over to it.

[Watrboy821]

are there any codes on the rears themselves that can give me the ratio of the rear?

[Watrboy821]

nevermind i just searched and i guess there isnt

[Chris H.]

off hand do u guys know if the rear like the one u picked up is the same length as one under a pickup? I am looking to swap my rear out of my 98 pickup for a g80 rear with discs out of a blazer.....

Thanks
Chris

[Watrboy821]

I think the 2wd rears are 2" shorter than a 4wd rear, other than that 2wd ones are the same.

[rlith]

Quote: Originally Posted by Chris H.

off hand do u guys know if the rear like the one u picked up is the same length as one under a pickup? I am looking to swap my rear out of my 98 pickup for a g80 rear with discs out of a blazer.....

Thanks
Chris

If your moving from a 4x4 s10 to blazer or vice versa they're the same length, same for the 2wd to 2wd 4x4 length is longer and the mounting points are different...

[Lenny95NeoN]

Quote: Originally Posted by Chris H.

off hand do u guys know if the rear like the one u picked up is the same length as one under a pickup? I am looking to swap my rear out of my 98 pickup for a g80 rear with discs out of a blazer.....

Thanks
Chris

Also if U are lucky enuf to get a 8.5 rear outta a Blazer the rear is about an inch longer where it attaches to the driveshaft. So U will need a shorter drive shaft, or get yours shortened.

[Watrboy821]

Why is this not a sticky? I will be doing this soon, thanks rlith, your how tos have helped me with a few things. Do you need brake lines from a 98+ or will the 94-97 brake lines work?

[rlith]

Quote: Originally Posted by Watrboy821

Why is this not a sticky? I will be doing this soon, thanks rlith, your how tos have helped me with a few things. Do you need brake lines from a 98+ or will the 94-97 brake lines work?

Best to get the lines from the donor.

[Watrboy821]

alright thanks a lot

[Watrboy821]

Found my 3.73 rear today in my dad's pile of s10 stuff. I now have it all(well i gotta get calipers but i have cores). I should have it done soon and I will post pictures up on my car domain.

[Watrboy821]

got my new calipers and painted up my brackets. The pads are rusty but rather than buy new pads i used some that we had lying around. I will have pics of my rear when i clean it up and paint it tomorrow. And on saturday i am doing the swap so i will have pics.

[juk]

Will the directions for the drum to disc swap (with the axle that is under the truck) work with the 8.5 too? Just curious. I may get around to doing that one of these days.

[Watrboy821]

the calipers on an 8.5in rear are the same calipers that are on a 7.5in rear. I know this because i have a couple 8.5in rears sitting around. The brake change should be any different.

[Watrboy821]

Quote: Originally Posted by Watrboy821

the calipers on an 8.5in rear are the same calipers that are on a 7.5in rear. I know this because i have a couple 8.5in rears sitting around. The brake change should be any different.

I meant to say shouldn't be any different

[teamfu_az]

if you buy all the disc parts and bolt them to a drum rearend how does the e brake work? is the existing shoe setup compatible with the new rotors?

[rlith]

Quote: Originally Posted by teamfu_az

if you buy all the disc parts and bolt them to a drum rearend how does the e brake work? is the existing shoe setup compatible with the new rotors?

We found out after this how-to was done that the flange on the axeltube has to be moved 3/4" back for the bolt on to work... And weather you do it that way or thw whole rear end swap, you just need the cable from the driver door back..

[teamfu_az]

not to be a bug since im new but can anyone post pics of a brake swap instead of a rearend swap. i dont care what car the parts are from as long as ist oem bolt on ill do it. i get smokin deals on replacement parts and i like to keep it cheap. thx in advance

[rlith]

Quote: Originally Posted by teamfu_az

not to be a bug since im new but can anyone post pics of a brake swap instead of a rearend swap. i dont care what car the parts are from as long as ist oem bolt on ill do it. i get smokin deals on replacement parts and i like to keep it cheap. thx in advance

As I said above, in order to even atempt to do it that way you will need to move the flange for the baking plate back 3/4" and reweld it...

[laidoutmini]

i got a 91 s10 2wd so if i swap disk parts from a 98 2wd blazer i need to cut the backing plate flanges and move them inward 3/4". am i reading this right ? thanks

[rlith]

Quote: Originally Posted by laidoutmini

i got a 91 s10 2wd so if i swap disk parts from a 98 2wd blazer i need to cut the backing plate flanges and move them inward 3/4". am i reading this right ? thanks

They need to be moved inwarards, not outwards... You're better off swapping the whole rear

[developed]

This was a really good read!

thnx
developed

[sockjock]

Cool thread. I have a question: If I currently have a G80 w/3.73 gears and drum setup and want to keep it and add the disc brake setup; what about the abs sensors and so forth or do I need a complete donor rear end?

[Soul]

What about the master cylinder? Do i need to install a proportioning valve or diff cylinder? BTW i have a manual brake cylinder (88)

[rlith]

Quote: Originally Posted by sockjock

Cool thread. I have a question: If I currently have a G80 w/3.73 gears and drum setup and want to keep it and add the disc brake setup; what about the abs sensors and so forth or do I need a complete donor rear end?

For the rear the abs sensor is seperate from the rear itself.. And to add stock, yes you will end up needing the whole rear. We found out a bit after this how-to was first posted that to convert a normal drum to disc with just parts, the flanges need to be moved in about 3/4".

[rlith]

Quote: Originally Posted by Soul

What about the master cylinder? Do i need to install a proportioning valve or diff cylinder? BTW i have a manual brake cylinder (88)

No, your stock master cylinder and prop will work fine.

[developed]

Quote: Originally Posted by rlith

For the rear the abs sensor is seperate from the rear itself.

So - does this mean the ABS will work or not?

[developed]

Quote: Originally Posted by rlith

We found out a bit after this how-to was first posted that to convert a normal drum to disc with just parts, the flanges need to be moved in about 3/4".

I thought the flanges had to be moved out about 1/4" using spacers. How do you move the flange in?

[rlith]

yes, it means the abs will still work fine

[DJDAudio]

If you find any more dave 98layinframe is looking for a rear axle for his 2 wheel drive sonoma.

Posi or disk brakes.

[rlith]

Quote: Originally Posted by developed

I thought the flanges had to be moved out about 1/4" using spacers. How do you move the flange in?

If you use the oem 98+ brake parts you will have to grind out the flange welds and reweld them back 3/4" They would have to be move out with the spacers if you went with the F-body brakes

[Davy_Baby9]

Quote: Originally Posted by rlith

If you use the oem 98+ brake parts you will have to grind out the flange welds and reweld them back 3/4" They would have to be move out with the spacers if you went with the F-body brakes

On my 91 it bolted the disk backing plate to the flange. I took measurements of the old drum and backing plate, and the new one. I found the 93-97 F-body rear disk only have 1" hubs on the rotors themselves. It looks likeaccording to my calculations that the 2004 rear disk, with 93-97 rear rotors off of a F-body are going to exactly the way it was with the drum, without cutting the flanges.

More to come though because I'm still taking more measurements...

[sockjock]

I found a complete rear end from a '99 Blazer 4wd for 300 bucks. I don't know what the gear ratio is or if it is limited slip or the mileage. The vehicle was a rollover. All that is left is the rolling chasis. I figured on swapping in my 3.73 gears and limited slip.Is it too much money? How can I tell what gear ratio and if it's a limited slip without the glovebox RPO's? It looks to be in good shape and it has the disk brake setup.

[developed]

Quote: Originally Posted by sockjock

How can I tell what gear ratio and if it's a limited slip without the glovebox RPO's?

I think the only way is to take off the cover and look. You'll need to change the oil anyways. It would be wise to go ahead and pop the axles out and replace the seals too. If this is going into a 2wd, I hope you know the 4wd diff is a couple of inches wider than a 2wd.

[sockjock]

Mine is a '95 Blazer 4wd. So it's a 4wd to 4wd swap.

[Lenny95NeoN]

Quote: Originally Posted by developed

So - does this mean the ABS will work or not?

[Message cliff notes:]
[ABS will Work fine as long as the axle ratio's are the same as stock.]

Because I broke my factory posi by abusing it, I ended up doing the reverse swap of this. I had to swap in a 7.65, open diff, and drum rear, w 4.11 gears, from my stock 8.5-posi diff w/ 3.42 gears. I used the e-brake lines from the donor truck, but needed to use spacers on it due to it being longer than mine are.

The rear hydraulic brake line's threads matched perfectly to my Blazers connection, but the retainer clip was different. I had to devise another way to keep it secured. I just flushed the brake system for the fist time since I had it (about 2 yrs. ) and it actually stops better now even though I basically downgraded the rear braking system.

I did not even get any new rear brake parts. Rear brakes usually last 2-5 time longer than front brakes will. I also had to use the longer, 45-inch drive shaft (measured u-joint to U-joint) from a two door Blazer that had a 7.65 rear. I think they are original equipment in all automatics, and the four door's drive shafts are possibly the same length.



I ran into two problems. Since I changed rear axle ratios, my Speedo is fast by about 15- 25 mph at highway speeds. That would be fine except the abs system uses the vehicle speed sensor in the tranny for the rear wheel abs, and uses independent speed sensors for the front wheel abs. That triggers an abs and brake light from time to time. But it didn't do that at first when I had larger 265/70/15's on the rear axle and smaller 235/75/15s on the front.



To remedy this I just quickly turn the ignition from "run", to "accessory on", and back to "run" to kill the lights. This works while moving and if done quickly enough the motor will not shut off. But this is just temporary. Soon I will use tire w/ a 29inch or taller rolling radius in the rear and anywhere from 28.9- 24 inch rolling radius in the front. By my calculations that will keep the abs computer from giving me the idiot lights, plus I like that raked look and it will make the truck look a lil meaner when I do the 5/5 drop.



I eventually will get a VSS adapter, or a PCM reprogram, since I am putting the same gear ratio or somewhere in between this and stock in the 8.5.



I reaaaaaaalllllllly like the acceleration.

I hate the poor gas mileage.



The other problem probably won't affect you. The older drum brake hub is slightly (like milimeters) larger than my original one, so it was extremely tough for me, and everybody else matter of fact, to get the 2wd aluminum wheels on and off. Especially getting them off.



I eventually got some steel wheels, put them on the rear, and never had a hard time getting them off again. I just got another pair of steel wheels for the front because I'm tired of it looking like that. I'm painting them all black and putting a brushed or painted trim ring on them. I do not like chrome on my Blazer, and all chrome will be deleted.

[Lenny95NeoN]

Quote: Originally Posted by developed

I think the only way is to take off the cover and look. You'll need to change the oil anyways. It would be wise to go ahead and pop the axles out and replace the seals too. If this is going into a 2wd, I hope you know the 4wd diff is a couple of inches wider than a 2wd.

I'd love to use a 2 inch wider 4wd, or even a 4 inch wider zr2 rear axle on my 2wd. Then I could sell mine to someone willing to upgrade. I'd even take a drum 8.5 rear. I'll just get the big brake rear disc from drum upgrade kit anyway, and I don't see how, or if they work when U have rear disc already I can do soo much more as far as wider tire with one of those. Do the spring perches match?

[Dave101]

Any idea as to how this could be done to a GMC Sonoma? I have heard that it is an S-10 in disguise. Any idea's anyone? Thanks!