Roc87

I got a 9bolt off ebay, and the seller said he'd include the correct proportioning valve. I didn't receive the PV when he shipped the rear end, and he said he'd just mail it. I still haven't received it and I'm wanting to put this rear end in. I know the brakes won't work properly without the correct PV, but what happens? Does the rear get too much pressure or not enough???? I need to know because it's getting bolted in tomorrow if the PV is here or not! Thanks guys

2laneblacktop

I went from a 10 bolt with drums to a 9 bolt with discs and i didn't even worry about the PV valve. I have never been on the brakes real hard yet to see it the backs lock up to soon but I have never even seen a difference. Everybody says you need the PV to make it right or its going to be all messed up but I think it works just fine with the stock drum brakes setup.

Roc87

Cool, Thanks! I wouldn't mind them having more pressure to them, that way I could build more boost before "launching"

RB83L69

It depends on which disks. If they're the PBRs, then you don't have to change anything. If they're the older crappy ones with cast-iron calipers, then instead of merely really weak rear brakes, you 'll basically have no rear brakes at all unless you change the MC and PV.

Definitely do the PV mod, it supposedly is night and day improvement with that old system. Makes them almost work noticeably. And of course, do teh caliper update.

Roc87

How can I tell if they are PBR's? The rear is out of a '89 Trans Am.

MdFormula350

i think the 88 or 89 + thirdgen's disk brakes were the pbr's!!
so you should be fine then!

RB83L69

PBR = aluminum, has these 3 letters "PBR" on them

other = cast-iron

Roc87

(@^%$, then they aren't the PBR's. I had to use a wire brush last night to get the surface rust off of them so I could paint them. What if I do the "Mod" to the proportioning valve I have? (Use the allen head plug, rather than the spring and bleeder, in the end of the PV). Does the mod get rid of any difference between the 4 wheel disc pV and the other one? Sorry if I'm rambling, I think I sniffed too much of the paint I used for the calipers last night!

REVLIMIT

from what i know...the Drum brake PV lowers the line pressure going to the rear drums. Since drums lock up easier than disk brakes. So if you use the drum PV then your not fully using the rear disks.

CrazyHawaiian

Well Revlimit swapped my rear for me in the 90 RS and it works. I went from RS drums to a 9 bolt with discs. Not sure what calipers they are tho. I didnt do a PV either. But I did snag the MC off a 90 IROC with 4 wheel discs and swapped that. They looked exactly the same as the stock one so I dont know if it made a difference or not. The brakes worked good enough for me to drift. But I didnt do any braking tests or anything. It was definately better then when I had drums. Its been a few months now since the change from drums to disks and if you slam the brakes you hear a click noice from the rearend. I think there might be air pockets in there (doh!). I should probably bleed the brakes again (dont think I did it right last time hehe). I suspect I should have done the PV too. Its ok tho because in about 2-3 weeks the car will be down for probably a month while I redo everything (engine, tranny, bodywork, paint, suspension, brakes).

But if you think about it the PV is a relatively inexpensive mod compared to the rest of your car. Your brakes are what save your car from hitting the wall or whatever. So I say its well worth it. Also be sure to bleed the brakes properly. I think I snagged the MC from the 90 IROC for $50.

Roc87

Thanks for the replies and suggestions. I managed to get the 10 bolt/drum rear end out, but removing one of the brake line fittings on the 9 bolt, it broke due to rust. So, I have to replace that brake line before I go on and bolt the rest up. Those that have done the swap, do you have to get different parking brake cables? I haven't really checked, but it seems like the cables for the drums are longer than whats needed for the discs?

lonsal

iTrader: (2)

Yes you will need the e-brake cables that are correct for that disc brake rear end. I ordered new ones from GM. They came with a tight wound spring on them that I had to remove with a Dremel tool and an abrasive cutoff wheel though. Unless you are putting an older disc (non-PBR) rear end into a 90+ car you won't have to swap the e-brake pull-up mechanism. You'll need the kind that has an adjustable center rod at the equalizer (where the two e-brake lines connect together). The 90+ model year cars don't have this adjustment rod. I had to swap in an older style e-brake mechanism as a result.

Lon