I am swapping my original drum brake rear for a 3.23 4-channel posi unit from a 2000 trans am. I know there are lots of threads about this, and believe me I have likely read them. However, I have a few questions.

From what I have read, I understand that I need to redo the brake lines to some degree due to my car having drums and the 4th gen 4 channel rears have 2 separate lines to the wheels (no T-block). Can I use the existing lines to the calipers if I tie them into a T block or do I need to replace it all? And about the proportioning valve, it seems like some are fine without replacing it while others say you need an adjustable one. I'm thinking I should get a prop valve/T block combo but not sure if it is necessary. Are there good combination prop valves and T blocks out there for our cars (if it even matters what car)? Which one should I get and could you provide a part number?

Also, I am a little unsure about the ebrake cables. Some sources say the ebrake cables from the 4th gen rear should hook in above the driveshaft with no issues other than a custom bracket/extra support to keep them clear. Is this accurate?

 

The 4th gen rear still has a tee that branches off to both sides. You'll need a simple adapter from the 3rrd gen feed line to the flexible tee connection on the 4th. Hawks sells a set of e-brake cables for a 4th gen rear swap but I didn't have a good experience with them. Sadly, this appears to be a trial and error as everyone solves the e-brake issue differently. As for a proportioning valve, its up to you. The stock 3rd gen set-up doesn't send much brake to the rear so a valve can help utilize those disk brakes by sending a stronger signal back there.

 

I had read that some 4th gen rears, the "3-channel" (no traction control?) will have the T block that splits them. The one I have, the "4-channel" (with traction control?) does not. It has 2 separate lines that do not connect together, it seems as though it had a line to the back for each side. I didn't pull it off the car myself to see, but the guy I got it from confirmed he did not remove it or cut it out.

Regardless of that, is the adapter just some brass fittings that change the diameter of the line? I have not yet removed my current rear and I have the 4th gen one sitting in my garage so I haven't seen it with my own eyes. As far as the prop valve goes, it seems like they (what I saw on jegs) make some that can function as an adjustable prop valve and splitter. This would be a universal part, correct? I don't see why it would have to be specific to a car.

 

You are actually correct and I forgot about ABS cars. I would still rout them to a Tee. By adapter I mean thread pitch. Earl's, Amazon, etc all sell various adapters to get you from metric to SAE, male/female, and vice versa.

 

I have a three channel I'm cleaning up, can confirm there's a t-block, but it's part of the soft line that goes to the body. From there it's hard lines to the end, then soft line again before the caliper. To answer another part, no you can't reuse the existing lines, since the calipers have some movement in them, you'll need the soft lines at the end to allow for that.

 

Ok gotcha. So it sounds to me that if I could find an adjustable prop valve with an input that matches the thread for the 3rd gen brake line from the cylinder and 2 outputs that match the 4th gen lines to the calipers, that would be all I need?

Also to respond to you pirateofms, by existing lines I meant the ones on the 4th gen rear.

 

Always is. On all our cars.

You don't need a prop valve if there's already one in your car. If there's not, just buy the one that fits it.

Yes you can take your existing lines off your 3rd gen rear and put them on a 4th gen one, IFF they're long enough, and all that. Going from drums to discs they're potentially TOO long and it might not be practical to shorten em up. If not, not much of a problem anyway; you can pop in at yer local corner parts store and pick up a stick or 2 of generic line and make new ones up. Should be 6mm w metric bubble flare if memory serves. Very universal, really.

The 82-88 crap rear discs fail to use a rubber hose at one wheel or the other. Hard line straight into the caliper. Pass side I believe it is butt my CRS disease is kicking in and causing a brain cramp. Not an issue in this case though. For a 4th gen disc rear you just need to retain the rubber hoses that came on it (or get new ones) and run your new generic lines to them.

 

Sorry, I don't think I am being clear enough. When I say use existing lines I mean leave the lines currently on the 4th gen rear outside of connecting them to a tee as they are currently separate. Also, this may be a stupid question but is the proportioning valve currently in my car able to be adjusted if I need? If not and I can't get enough fluid to the rears to engage correctly, I guess I need to bypass it and install an adjustable one.

 

Yes, nothing wrong with the 4th gen lines and connecting them to the chassis side of the system.

 

Sure, if they'll reach and all that, why not. The T will be part of the rubber hose that goes to the body. It'll need a bolt to hold it to the pumpkin; obviously the T, bolt, and lines all have to agree on a single place. If that's not possible, just pop in at yer local corner parts store and pick up a stick or 2 of generic line and make new ones up. Should be 6mm w metric bubble flare if memory serves. Very universal, really.

No it is not. However the hydraulic requirements of the PBR discs and your drums are similar enough that your drum one will probably work just fine.

You're really overthinking this in a major way.

 

This is a slight change up of questions, but after more research into how combination valves work it seems that a metering valve/spring in the combo valve holds back pressure to the front discs as the drums require more pressure to engage (is this confirmed to be true or is it the other way around? lots of conflicting information/opinions out there). So if I were to change that spring to one with a lower rate and in turn reduce the amount of pressure it takes to engage the fronts, I wouldn't need anything else? This is a theoretical for when I have the rear brake lines set up.

Don't mean to overthink anything, I just want to be certain and do as little guesswork as possible. Especially when it comes to the most important part about any car, the ability to stop.

 

If you're really worried about it, get the PV for 89-92 w rear discs. Those are arbitrarily near identical to the 4th gen setup.

I'm not a big fan of "it worked for me" as any kind of guarantee, only at best, a glimmer of hope; butt when I put a 91 or 92 rear in my drum 83 L69 car, I left the 83 PV in it, since it's SAE, and there's definitely no suitable one for PBR discs w SAE fittings, other than attempting something aftermarket, which I absolutely DID NOT WANT to step onto that treadmill if I didn't have to. Which turned out, wasn't necessary anyway. Works GREAT. I can't tell any kind of erroneous behavior at all.

I DID have to do some adapting... the OE hard line to the rears in the car was ¼", butt the hose from body to rear had to be 6mm. So I had to make a 6mm <–>¼" section for the rearmost end of the car's line. Kinda a PITA since my flaring tool's ¼" jaw wouldn't grip the smaller line; took a few tries and some aluminum foil; butt I eventually got a piece of 6mm bubble flare line maybe 4" long with a good clean ¼" 45° double flare on one end and the 6mm still on the other, cut off a little of the car's line to accommodate my adapter and re-flared the ¼" line on the car to ¼" as well after I cut it, and hooked it all up with a F-F ¼" flare union.

If you think about what's going on with the PV, it merely requires that pressure build up in the rear system, before it begins letting pressure go toward the fronts. Butt with discs in the rear the pressure builds up almost immediately anyway, meaning there's no appreciable delay to the front; they apply nearly as soon as the rears do. Less delay than there would be with drums, which I'm sure you notice that delay now, right? So yeah...

 

Unless you're planning to incorporate the Traction Control system into your 88, then I'd suggest removing the two hard lines, the two rubber hoses (to the chassis, not the ones for the calipers) and their connection unit from the 4thgen axle and getting a new pair of 89-92 3rgen hard lines and connecting them to your car's existing single rubber hose and tee (or a new hose and tee, but you get the point). Otherwise, you're going to have to find a way to connect the two rubber hoses together to connect them to your car's chassis fitting.

 

Indeed: you could get a set of premade ones off the big brown truck if you want to do that, rather than making them up yourself. You'd still need to make sure that the T fitting on the rubber hose will bolt up to the pumpkin in the same place on the 4th gen rear that it did on the 3rd gen one, for the 3rd gen pre-made lines to fit right. And of course, the 3rd gen lines may well be a little over 1½" too short at the caliper ends, besides; not sure whether you can "stretch" em enough to overcome that.

Personally I'd just visit the corner store and be done with it.

 

Jegs sells repro stainless versions of the three channel version for less than $40, prebent and ready to go. You could probably swap a pair of them on and just bolt it up to the existing rubber center hose. I don't know if the end hoses are the same, however.

 

I haven't seen em mentioned after the Hawk's ones were brought up, so I thought I'd give some input on e-brake cables quick. The 4thgen ones WILL NOT fit on your thirdgen, unless you do some adapting on the handle side. The 4thgen cables use a sorta "T" shaped cable end to tie into the parking brake handle, where thirdgens use a straight plug shape. I initially tried stock 4thgen cables when I did my rear brake swap, ended up giving them to a coworker who had a 4thgen. What I ended up using, keeping in mind that I have a 3rdgen rear with the '98-'02 brakes (2" or so shorter per side on the axles), was a set of the long cables meant for '92 disc rear cars. The caliper end of the cable is the same, they'll fit into your body brackets, they'll fit your parking brake handle fitting, and they did actually clip into the 4thgen cable brackets as well (the ones that bolt in next to your LCAs). The fit might be a little tight with the extra width of a 4thgen rear, but I ended up with some extra length on my cables, might be just long enough for a 4thgen rear if you route em right. They were about $16 each on RockAuto, so might be worth a shot.... again, there are TWO lengths available for the '92 rear disc cables, can't remember the numbers off the top of my head, but I did use the longer of the two for both sides.

Also still using my factory prop valve ('92 drum rear car) with the "upgraded" spring, been working perfectly for me with the full 4 corner 98-02 brake swap.

 

I put a 4 channel rear in my car and just bought pre made 3 channel lines and hoses and hooked into the original rubber hose on the car.