Rear Drum Brake Conversion to Disc

[kboehringer]

Hello Trans Am Friends,
Recently, I posted in the "Show & Tell" section about my recent experience towing with my T/A ('79 looks like a '78)
http://www.transamcountry.com/community/index.php?topic=85003.0

Several members provided guidance on upgrading the OEM Drums to OEM WS6 Disc on the rear.   I've done some searching on the forum and haven't found much information.   There are several that have performed aftermarket and Corvette upgrades but little information on an OEM drum to OEM Disc conversion.  Looks like I'm going to need some help so I moved the discussion to the appropriate forum area. I'm hopeful the guys that provided the initial guidance will follow to this thread as the work begins.....

I've purchased and received the MAJORITY of the BIG components that are going to be needed including: Rotors, Calipers, Backing Plates, Brake Pads, Parking Brake Cables, Brake Hose(1).  Basically, everything listed on RockAuto for this set-up.



RockAuto is not listing a proportioning valve on their website and the brake booster is out-of-stock.  I would like to replace ALL of these related components but my booster WAS new several years ago and SHOULD serve the purpose for temporary.  Please provide your input on this as if this is an OK plan or highly ill-advised.   

The backing plates were a rusty mess so they've been cleaned in phosphoric acid, primed, and painted.   I have a concern about a couple of the threads for the caliper mounts so these will likely get helicoils.  I know I'm going to be missing some hardware likely the bolts from the drum backing plates will need to be acquired and it's also likely some of the small cable support brakets for the cables will need to be replaced.   I should have no issue fabricating replacement steel brake lines.

Unfortunately, I have THREE T/A manuals including a factory service manual from '78 and NONE of these manuals (Haynes, Chilton, OEM) provide not even one page of instructions, photos, drawings, of the disc rear set-up.   I've scoured the forum and found a few pics but mostly of non OEM upgrades.   I guess I'm the fool trying to go OEM....

In addition to the brake upgrade, I plan to replace all the bearings & seals as I'm already in there might as well even though these were replaced during the initial rebuild (~15 years ago) and the car has actually seen very little miles since.  Again, just seems like a no-brainer.

I'm going to start rippin' and tearing down the rear end this holiday weekend (actually in a few minutes).  If anyone has some photos of the OEM set-up stored in their C: drive, please post a few when your time allows.  Without a sample to follow, this could get a little ugly quickly.

As always, your input(s) are very much appreciated.

Sincerely,
Kurt

[roadking77]

Wish I could help but I cant, good luck will follow along though.

[kboehringer]

Hi All,
Managed a LITTLE progress today and was able to "Mock-Up" the LR.   No issues with the used backing plates (so far) and the rotors fit the axle properly.

I've ordered some new G8 hardware for the backing plates from McMaster-Carr (3/8-24 1-1/4").  The old hardware would have worked but was a bit rusty.  Also seemed the drum backing plate fasteners were a bit shorter than I prefer (1").  The new hardware will be here on Friday....

Off with the old......


On with the new.....


I am a bit concerned about the orientation of the parking brake bracket..... points rearward which seems to be the only option otherwise there is an interference with the axle housing.    Looking for photos of this now across the board....

Also discovered that a new brake line will be easy peasy to travel from the splitter to each caliper.  Would prefer SS hose and will see if Summit offers such a thing for this bird.....

Unfortunately, my garage is full of bikes and the working area is a little tight.... Gonna need to move some stuff around to get to the RR.  LOL.


Kurt

[roadking77]

Kinda looks like my garage, I count 6, same as mine LOL.

[kboehringer]

"I count 6, same as mine LOL."
Actually, to the FAR FAR left in the photos there is a Gold '81 next to the Burgandy '79... It's tank is barely visible.    I have seven more inside my office with the remainder on the back covered porch......  A two-bay extension to the existing garage is planned!

Regarding the new RockAuto calipers (NuGeon V1 97-17234AL & V1 97-17234AR) the brackets for the emergency brake cables are WRONG!   These won't work.  Unfortunately, I went and painted the calipers making them non-returnable.  To make matter worse, I quickly shipped the worthless cores back to RockAuto with the original T/A rusty and beat-up brackets on them.   As bad as the brackets were, they could have been cleaned up and used.   

I've reached out to the manufacturer (NUGEON). Perhaps they can provide the right brackets.  Otherwise, I'm screwed.

Kurt

[Wallington]

Won't find a lot in 78 and earlier manuals since the rear disc option of these appeared in 79.

https://forums.maxperformanceinc.com/forums/attachment.php?attachmentid=402000&d=1436061263

https://www.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/08/11/ae/large/0900c152800811ae.gif

https://live.staticflickr.com/65535/52277975951_7d698ea9a6_b.jpg

[kboehringer]

Won't find a lot in 78 and earlier manuals since the rear disc option of these appeared in 79.

Hi Wallington,
Thank you very much for providing those links to diagrams. I've downloaded and saved them all. 

My factory service manual is from '78, thank you for mentioning the Disc Rear was not available until '79 I was not aware of this.  However, my other manuals (Haynes, Chiltons) are SUPPOSED to cover up to '81 and have no information on the rear disc setup.

The diagram you provided verifies my suspicion that the L & R calipers have different internal components (Thrust Screw & Operating Shaft).  In another post I found on this site, a poster stated that both calipers operated clockwise to apply the parking brake.   I thought that was incorrect as the LR (Driver Side) must operate CCW while the RR (Pass Side) must operate CW.   

Now, the brackets provided by the remanufacturer of the calipers I purchased will have them operating incorrectly opposite.  I'll need to swap these clipers from L->R to assure they work correctly.  If swapped, the bleed port will remain in the proper highest point location and then operate the parking brake in the correct rotation. Hopefully, the remanufacturer will be able to provide the correct brackets.

I was extremely discouraged when I realized the problem with the new calipers and my stupidity at sending the cores back so quickly.  However, I can completely assemble everything except the parking brakes.  I believe I can even bleed and test everything else just leaving the parking brakes off until the correct brackets can be acquired.   Worst case, I need to purchase another set of calipers with the correct brackets.  Unless someone here has them for sale?

Kurt

[kboehringer]

Trans Am Guys,
I've made some progress and with the help of 81Blackbird realized there is nothing significantly wrong with the calipers or their brackets received from RockAuto.   They did however have the calipers set-up incorrectly for the sides (L vs. R).  Thankfully, I had purchased both and was able to transfer the brackets to the calipers with the proper rotation (CCW vs. CW).    That problem solved, I'm moving forward on the other side and replacement of the parking brake cables.



Recently, I've been tossing in the garbage more than a decade of accumulated spares for both the TA/Firebird, my '82 Z-28, and the various motorcycles.   I'm trying to turn from PACKRAT to only retaining valuable and possibly useful spares.    I'm thinking, unless this DISC Upgrade goes completely sideways there is no reason to retain most of the crap pulled off related to the drum brakes.   If it does go sideways, I'll retain only the backing plates and a couple smaller items I'm not certain can be obtained in a drum rebuild kit.   I can purchase as this crap new (drums, pads, kits, wheel cylinders, etc.) if that emergency "put it back together" event occurred (1% chance of that).

I'm pretty certain I know this answer, is there any real value in the crap pile (right side of photo)?

Kurt

[twov8sandat4]

I did the Corvette disc conversion on my 74 so I can't offer much help.  However; one thing I had to address were the wheel studs.  With the discs I lost a few threads on the studs as compared to the drums, so I had to change them out to longer studs for the lug nuts to grab.  Mock up your wheels with the discs to see if you run into the same issue.  There are some extended length lug nuts if you run into this problem and don't want to change the studs, but they require the holes on the wheels to be slightly enlarged to make them fit.  Since the discs on mine required 18" wheels, I just changed the studs to match the front Corvette spindle studs.

[kboehringer]

Hi T/A Guys,
I'm in final assembly phase and running into a problem at the RR.

There is NO WAY (I can think of) that the lower pin can be inserted into the backing plate without excessive force which will certainly result in damage.



Am I not holding my mouth right or what?  Some crazy trick here?

The favor of a quick response requested.   Trying to get her back on the wheels today.....

NOTE: When I purchased the backing plates & misc. off e-bay the seller provided the caliper bolts.  One of the bolts was cut shorter.   I now understand why.  The last guy had the same question and then just cut the bolt shorter.



Kurt

[kboehringer]

SNIP** However; one thing I had to address were the wheel studs.  SNIP**

twov8sandat4,
You are correct.   The studs were a little shorter they were with the drums.   I believe there is enough "MEAT" on each stud to make this machine safe to use.   However, I will be changing to a slightly longer stud ASAP for extra safety sake.

With the help of a vacuum brake pump and my wife on the petals were able to get this fully functional.   The parking brakes work perfectly and the hydarulics seem to be perfect as well.   Fortunately, the OEM drum lines were easy to re-work and use with the calipers.  I suspect the factory did the same thing using only one set of lines regardless of the brake system selected. 



Looking forward to a real test ride to determine if the booster, master, and prop. valve will need replacement.

Kurt

[737driver]

Won't find a lot in 78 and earlier manuals since the rear disc option of these appeared in 79.

Hi Wallington,
Thank you very much for providing those links to diagrams. I've downloaded and saved them all. 

The rear disc info in the factory manual is actually a 1979 Supplemental Manual for 1979. The supplemental manual from 79 addresses the differences from 78 to 79 model year.
In the brake section it does go over the rear disk brakes since they were optioned on the 79 TransAm
Jim