Aaronl84

So as the title says, and I know these have poor braking systems, but we have an 85 iroc and it doesnt panic stop for nothing. You can not lock the wheels up unless its wet out - normally thats be a good thing, but this doesnt have ABS

and it takes way too long for a serious stop on my opinion - now, i habe 4 other older cars, 1970 abody with disk up feon and rear drum an it will throw you out of the windshield if you stood on the pedal…

so far, lwe’ve put new rear calipers on, has new pads, rotors, master and a rebuilt prop valve

i suspect the ebrake issue is partly in the cable, but are these cars really that bad to stop?

aliceempire

iTrader: (14)

I wouldn't necessarily want them locking up under any circumstances but I've had these brakes and I didn't find them as bad as reputation implies. I'm not claiming they're great, just that mine were fine for what I used them for. I did use a proportioning valve for rear drums if that had anything to do with it.
Also noting my park brake has always been fine which leads me to believe your pistons in the calipers are not moving as they should, maybe seized. A brake hose deteriorating would explain bad service brakes but not the lack of parking brake, though you could have more than one problem. I'd say you've got bad hoses and a park brake issue or you have seized pistons. The park brake adjusts the pads so you could be out of adjustment. I'd think the pedal would be soft, as if you have air in the system.

Aaronl84

its got rear disk and the calipers are new as of this morning. So i dont think the calipers are seized

sofakingdom

iTrader: (1)

Did you put the "recall kit" in the calipers?

Have you adjusted them up by using the parking brake about 1000 times?

Have you tried the spring mod to the prop valve?

When you bled them, did you make absolutely sure NOT to let the MC run dry? Did fluid come out both rear bleeders vigorously and profusely?

Aaronl84

1) what is the recall kit?

2) the master definitely did not run dry

3) fluid does not come flying out of the rear calipers like it does in the front. But it does bleeding and there is no air in the line.

4) the prop Val was just rebuilt by old auto restoration, but what is the spring mod?

Aaronl84

Also, we worked the ebrake about 30 to 40 times, but definitely not more than that, When I look underneath at the calipers, the passenger side moves more than the driver side, so I think we need to adjust the cable, although I have not investigated how to just yet. Also, when you pull up the E brake handle, lever only moves about a half an inch on one side and maybe 3/4 of an inch to an inch on the other side.

Saxondale

iTrader: (2)

Subscribed. I have the same questions as Aaron. Because considering swapping my ‘84 3.73 drum axle for an ‘84 3.73 disk axle.

naf

iTrader: (7)

the recall kit was offered by GM to fix issues with the rear discs not resetting close enough to the rotor for the parking brake (and often the pedal) to re-engage the pads.

it replaced the pistons with an improved design.

it may be available somewhere. word is that most new/rebuilt calipers don't have these upgraded pistons installed.

I purchased through GM parts Direct in '05?

Part Number: 18019028 from GM Parts Direct, listed as "Actuator" and included parts for both rear calipers, pistons, springs, seals, etc.

naf

iTrader: (7)

There 'may' be a bracket available from Hawks that allows installation of the better PBR brakes to the earlier D-M equipped axle.

sofakingdom

iTrader: (1)

naf's description of the "recall kit" is spot-on.

The calipers adjust by way of the piston unscrewing itself out. Each time you use the parking brake, the act of letting it off may unscrew the piston a tiny bit, if it's tight enough in the first place. IOW, you have to unscrew it yourself if it's already screwed in too far (which, you have to screw it in to replace the pads & rotors if they've been working, because the piston will be unscrewed far enough that it holds the pads too far out to fit over the rotor), then use the parking brake to dial it in. If you don't use the parking brake, the pistons never unscrew, and the pads sit progressively farther and farther from the rotor as they wear because of lack of adjustment, and become less and less effective. If you start out with this condition from new, they will forever be ineffective.

No idea about "rebuilt" or "by old auto restoration". Could mean just about anything, or nothing. Search this forum for "Grainger spring".

Beeman

Almost 40 yo car did you change all of the brake hoses and the MC? A brake pressure gauge is the only way to know if you're getting enough pressure to stop.

naf

iTrader: (7)

it was not uncommon at some time in the past to see these D-M equipped rear disc cars drive by with rusted up rear rotors.;

Aaronl84

So fad, we’ve replaced all 4 calipers, pads, master, and had the prop valve rebuilt
i have the grainger spring coming - along with a new caliper to replace a new one that is leaking

so im guessing thats why i cant get all the air out

we are replacing the 3 rubber lines when the new rear caliper and spring go in


will report back this weekend

Aaronl84

I started a new thread but
new calipers,
new hoses,
new pads,
rebuilt prop valve with the Grainger spring
new master
bled twice

still cant lock up the fronts or backs on a dry pavement panic stop

pedal still feels spongy to me

any ideas

codyman125

I almost hate to ask, but you did get proper brake line for the rubber hoses correct? Seen it just recently someone complaining about sponge brakes after a change and they had hose clamped gas line in place for their rears instead of buying the correct part.

Aaronl84

i def have the right parts
the only kne i didnt change (becuase i didnt know it was back there) was the under car one that goes to the rear axle

codyman125

I figured. Formerly worked tech support. #1 thing I learned was to never assume anything.

It does seem like the pressure simply isn't getting to where it needs to go. Does the engine stumble at all when applying the brakes? If so, there could be a leak in the diaphragm. That doesn't match up with poor function of the emergency brake though... I am interested to see what the culprit ends up being.

ironwill

So have you since replaced this hose?

GETGONE

Is there any way to know if you already have the recall kit installed? My dad originally purchased my 85 IROC back in 1992 with 42K on it. I have a leak in the caliper seal and bought rebuild kits with new seals.

naf

iTrader: (7)

the pistons were visibly different but I couldn't tell you now which one was which.

maybe an internet search will reveal a pic of the revised piston

https://www.thirdgen.org/forums/brak...epair-kit.html