JB3 to JB5 rear brake upgrade

[Ronno6]

Should I not be able to resolve the imbalance of my mixed-component braking system (JB5 front; JB3 rear)
the options are:
1.Convert the front discs  back to the original JB3 set up, or
1.Convert the rears to the JB5 option.

I would really like to upgrade the rear if possible.

For the first, would new rotors and calipers be all that is required?? Are wheel bearings and pads the same?
For option 2, would drums,shoes and cylinders do the trick? Would the larger diameter shoes make the drums too large
for the backing plates? Would the wider shoes make the drums too wide to fit without having to have longer axles??
Would the 3/4" wider shoes require a top pivot change?

I really hate having to fix a previous owner's mixing of parts..

[Ronno6]

I have seen where a member called  bd  has done this.


Whacha say, bd ??

[zieg85]

I can tell you the calipers from the larger rotor won't fit on the smaller spindle...  For the hassle on the rear consider going to a disc brake set up. 

[Ronno6]

I can tell you the calipers from the larger rotor won't fit on the smaller spindle...  For the hassle on the rear consider going to a disc brake set up.

The rotor is only thicker...not larger in diameter.
Are yoiu saying my spindle is not the came one as for the JB3 setup?

I have thought about going discs on the rear, but it is pretty expensive..........

[zieg85]

What I am saying is the calipers are different and won't go on the JB3 spindles.  I had a bad caliper and my parts truck had the thicker rotors and I tried using the JB5 caliper and it wouldn't work

[Rattler12]

Also the backing plates are different for JD5 vs JB3...……..    and good luck finding them for JD5

[Ronno6]

Also the backing plates are different for JD5 vs JB3...……..    and good luck finding them for JD5

Ain't that the truth!

[bd]

Read through JB3 to JB5 Upgrade.  The part numbers provided also apply to the 1984 model C trucks.

JB3 and JB5 front disc brake parts are not interchangeable.  Although the pads are the same, there are physical differences in the calipers, rotors, hubs, spindles, bearings, seals, dust shields and possibly the hoses.

JB3 and JB5 use the same master cylinder.  The JB3 and JB5 brake caliper piston bores are similar diameters and use the same friction pads.  However, JB3 uses a single diaphragm vacuum booster while JB5 uses a dual diaphragm vacuum booster.  The dual diaphragm booster provides greater pedal pressure delivery to the master cylinder for decreased pedal effort.  JB3 and JB5 brake options incorporate different combination valves (although I doubt you would notice any difference in performance by using a JB3 valve with JB5 rear brakes).

My 1987 R10 uses 1-3/16" bore (JB8 - 1 ton dually) rear wheel cylinders with JB5 rear drum brakes (11.15" x 2.75") and JB3 front disc brakes through a JB3 combination valve actuated by a dual diaphragm booster and JB3/JB5 master cylinder.  Pedal “feel” is normal and firm.  The vehicle stops on a dime w/o the rear locking up, unless I depress the brake pedal sufficiently to lock up all four wheels.

To find the non-consumable infrastructure you may need to scour the yards unless you are fortunate enough to find NOS.

[Ronno6]

I had stumbled on to that thread before. Good information!

I just cannot understand why I cannot get my rear brakes to quit locking up under normal braking loads.
I have tried about everything I can think of and replaced about everything but the hoses.
I have observed them under vacuum assisted pressure and can see no elongation or swelling.
I think I am going to try the 15/16" bore rear cylinders in an effort to reduce the rear braking.
Those are the ones specified by all the parts houses for the JB5 rear brakes.

I have found JB5 backing plates for a 1987 C10, but am having a difficult time verifying that they will work on my 84.
The various websites for the plates you have spec'd list model years all over the map for various vehicles, but seldom list
either 84 or 87 C10's
Anyone know for sure if they are interchangeable for those years?

[Rattler12]

You might try an adjustable prop valve in your line to your back brakes

[Ronno6]

You might try an adjustable prop valve in your line to your back brakes

That may be a good solution.
For the time being I am gonna try the 15/16" bore wheel cylinders.
The least expensive of all fixes.
Should reduce rear brake pressure by 14% and reduce pedal travel.

[Ronno6]

I have found, on page 861 of the parts guide Cat 52A
https://www.mediafire.com/folder/1zf0zcabliv77/Parts_Books
ALL have 1.28" thick rotors.................
WHAT'S UP WITH THAT ??

[bd]

You have a 1984 C10.  JB1 and JB3 use ~1" thick rotors.  JB5 and JD5 use 1.28" thick rotors.  Both the 1" and 1.28" thick rotors are 11.86" diameter.

[Ronno6]

You have a 1984 C10.  JB1 and JB3 use ~1" thick rotors.  JB5 and JD5 use 1.28" thick rotors.  Both the 1" and 1.28" thick rotors are 11.86" diameter.

I believe that.
Interesting that the parts manual indicates differently:

To determine the correct brake system the following information must be known.
1. Gross Vehicle Weight (GVW). This is given on the identification tag located on the driver side door pillar or on Step Vans attached to the inside face of the dash and toe panel.
2. Model Number.
3. H.D. Power Brakes (RPO JSS). This is an option available on most vehicles. When trucks are equipped with this option, the brake system may be upgraded to the next higher rating. (Example from JB3 to JBS) Trucks equipped with this option can be identified by checking the Service Parts Identification Sticker. '
EXAMPLE:
If the truck had a CIO and 5400 GVW, it would be equipped with JB3 brake system. If the truck was equipped with J55 H.D. Brakes it would have the JB5 brake system.
1979-81 LIGHT TRUCK BRAKE SYSTEMS
RPO # ROTOR REAR DRUM/ROTOR POWER BOOSTER
JB1 11.88* x 1.28* 11* x 2.00’ None
JB3 11.86* x 1.28* 11 * x 2.00* 9.5* Single Diaphragm
JBS 11.88* x 1.28* 11.15* x 2.75* 9.5' x 8* Diameter Tandem Diaphragm
JB6 12.5* x 1.28" 11.15* x 2.75* 9.5' x 8 ' Diameter Tandem Diaphragm
JB7 12.5* x 1.28* 13* x 2.50* 9.5' x 8* Diameter Tandem Diaphragm
JB8 12.5* x 1.53* 1 3 'x 3.50* Hydro-Boost
JB9 14.25* x 1.53' 15* x 4,00* Hydro-Boost
JF-9 14.25* x 1.53* 13.75* x 1.53’ Hydro-Boost
JD3 11.86* x 1.28* 11' x 2.00' Hydro-Boost
JDS 11.86* x 1.28* 11.15* x 2.75' Hydro-Boost
JD6 12.5* x 1.28* 11.15' x 2.75’ Hydro-Boost
JD7 12.5* x 1.28* 13* x 2.50* Hydro-B

[bd]

There is a lot of conflicting information floating around the web.  One thing I'm not certain of is whether there were production changes that affected rotor specifications through the years.  Meaning, truck weights decreased moving forward in time and the weight had to be trimmed from somewhere.  Glass and sheet metal were thinned, frames were thinned, etc....  Decreasing truck mass may have allowed for lightening certain brake components as well(?).

Our "in-house" reference is Brake Tech, what do all the numbers mean..