ok, if i install a 4th gen rear with disc brakes....how hard will it be to just connect up the discs....in the tech section it sias how to change drums to discs...but since the rear will already have discs...what do u exactly do....i have drums now

 

im in the process of doing the same thing right now, it's a little tricky getting the e-brake to work but everything else bolts in. i found a combination valve (some call it a proportioning valve, though its not) off of a thirdgen that had discs. I modified the valve and placed a proportioning valve inline so i can adjust the pressure to the back brakes.

 

DUDE!!! I'm doing the same swap... I've been totaly lost. can i buy a new valve from a parts store and put it in? also, do i have to cut the lines and flare everything, and all that crap? or can i just bolt the valve in? I'm kinda on edge, because no one around where i live knows how to do half the **** I'm getting into, so I'm figuring stuff out for myself. but brakes is not something i wanna play around with. is your e-brake cable the only thing giving you problems? how did you fix it? IM me at about 12:30 EST... I'll be out of class and back home by then, and I'm really interested to hear what you did. my AIM is flyitlikeustolit.

 

I'm just gonna hook everything up and see how it stops with the factory drum prop valve...if it sucks I'll get an adjustable..

It shouldn't be that much worse than the drum setup...at least I hope!

 

I have the same situation, except I put about a 91 or 92 rear into my 83 drum-brake car. The one you have is equipped with exactly the same calipers, so it should be the same deal as mine.

I left the stock MC & PV. It all works perfectly. The rear brakes are obviously working: they wear the pads at about 2/3 the rate of the front pads, and all 4 wheels will lock up at about the same pedal pressure point. My parking brake (these cars don't have an "emergency brake"..... if you had some kind of emergency while driving, like you lost all hydraulics or something, that hand brake sure as hell isn't going to do you any good) just hooked right up, the later cables just clipped right into the early adjuster thing. The 4th gen ones I don't know about. At worst you'd need to get parking brake cables for a 91 or 92 disk-brake car.

 

Good info.. I was pretty sure I would be able to 'get away' with the stock MC and prop valve...and after your reply I'm quite confident now!

I picked up the 4th gen rear end complete with the brakes and the cables for the parking brake... I haven't looked at hooking up the parking brake yet, but everything else is a pretty easy swap for me.

I'll post when I'm done and take it for a drive... As far as I figure, 12" rear rotors with dual piston calipers should stop a little better than the factory drums and the same prop valve. It couldn't possibly be worse, could it?

 

according to the guy who wrote the tech article, it could be, but i don't believe him anyway. I'm waiting to see waht happens. I get the rear on wednesday. keep us posted on how it goes!

 

From what i've heard the drum combination valve puts more pressure to the rear because drums take more pressure to do the same amount of work as the discs. I might have that backwards though.... someone correct me if i'm wrong thats why i took out the plunger and spring out of mine and ran a proportioning valve i'm still adjusting it though attempting to get the back brakes to lock right after the fronts lock but you can only do so many brake lock ups before the police start creeping

 

plunger and spring? explain. I thought there was just a valve you remove somewhere, like chillin next to the booster or something.

 

I read that tech article the other night because I am going to be swapping rears soon and just have to say that it sucks. It is not that informative at all.

 

I dunno. it was nice to know that the swap is easy, but from what I've found out, there's really no need for a wilwood prop valve. I wouldn't say it's a waste of money, but It's overkill right now. maybe later. I still have wheels and interior to buy, and my wheels/tires are gonna set me back around 2100. and the interior, I'm still not sure. looks like another 700 as well. I really don't want to spend 100+ on a brake valve i don't NEED.

 

The tech article isn't horrible.. I figured out a few things midst the swap but most of the info was right on.

The best tip I can offer anyone on it is to get some of that PB BLASTER and soak the hell out of everything. Wait a few days...spray again. Then when you've got half a day to dick with it follow the tech article and you'll be fine.

I worked on it for a week or two 20 mins here and there spraying **** and then got a friend over and we had EVERYTHING out in about an hour and a half. That includes removing the LCAs from where they bolt to the unibody.

The only other tip I can offer is when unbolting the LCAs unbolt them from the axle first, and worry about the frame bolts after the axle is out. I tried like hell to break those bolts on the frame and never touched them until after I got the axle out and worked everything loose.

Nothing but good to say about PB Blast however...that stuff is like a torch in a bottle.

 

yeah... I have a couple cans of it, it's good stuff. also, Mouse Milk is the **** too. if it can't come loose with mouse milk, it's welded on. when i get the rear on weds., I'll start the swap. I'm ordering some wheels then, and i need to measure the backspacing. Centerline is going to make custom wheels for my car. not custom because they aren't stock, custom because they're unique to my application. (i.e. one of a kind). :lala: :hail: centerline

 

Drum brakes outbrake disc up to 500 psi pressure [when the drums lock up]. Disc brakes will not lock up until @ 1500-1600 psi. So if you have disc/drum, you need to limit the amount of pressure to the rear brakes or else they'll lock up first and your braking distance drops. So the GM disc/drum valve should bias the pressure 70/30 from front/rear.

With disc/disc...its closer to 50/50. I don't know why the GM disc/disc combo valve is not working for you guys. Gutting it worries me a bit, but it seems to work and you keep your brake warning light (as opposed to a aftmkt valve).

But, with the aftermarket prop valve, you have way more control and you are able to compensate for changes in weight transfer etc. For example, in a stock car under braking, you unload the rear brakes much more so than if you had chassis braces, stiffer springs, shocks, struts, etc.. In those cases, the rears can handle more pressure without locking up.

You can rent a brake line flaring tool at your local chain autoparts store. Does not look that difficult. Only pita would be doing it in the engine bay with the limited clearances. But way less pain than changing your spark plugs.

In-line prop valves are not necessary, I don't think, unless you are racing circle track or something and have a need to limit pressure to a particular side of the car. I could be wrong, though.


Good luck with your 4th gen rears...post pics when you finish!

 

so.... can i use a 3rd gen rear disc or a 4th gen rear disc prop vale or not? I still can't seem to figure it out. and where is the valve at? is it part of the booster or something, or what? does anyone know?

 

Sorry if I offend any of you guys, but did ANY of you do a search on "rearend swap" or anything like that? The reason I ask is that it's all been covered before, in agonizing detail.


To answer the topic question,

85C350, You have an '85, right? TO make it work "right", you're master cylinder is fine but you'll need a new prop valve, part number 14089496 for "early" threads. Other than that, all you have to do is fab up a bracket for your 4th gen e-brake cables. Search for threads with replies by DynoDon, he posted a pic of the bracket he made and it works great.


Stolit, you shouldn't have to cut or mod anything if you get the right parts, and you'll be fine with the correct 3rd gen prop valve. Look at Dan Burke's page here. He covers the rear 1LE brake swap but the 4th gen PBRs are essentially the same calipers so all the info will be true in your case also:


http://www.ws6transam.org/1LEbrake.html

FYI, the prop valve is right under the master cylinder, you can't miss it. If you still don't find it, you have no business working on cars....

J/K


Good luck all. If you have any questions, PM or email me.


Ed

 

well if i do all of this....what about the front??? i need discs in the front too....who can cover that???

 

What front brake setup are you looking to go to? If you go with C4s, 1LEs, or C5/LS1s, you will be fine as your current master will work.

Ed

 

well, what is the best 4th gen rear??? should i just get the front off of the same car that i got the rear off of?

 

1le are the 93-97 right???

 

the adj proportioning valve i was speaking of is $35 from summitracing just to limit how much pressure goes to the rear brakes like the stock valve but where i can tune it to my liking and not gm's thats all i was saying

 

Depends on what you want. They're pretty much the same, just different ratios and some come with ABS and TCS, that's all. For a 3rd gen, I'd go with a 3.23 or 3.42 non-ABS/TCS rear for the easiest install. On your second question, 1LE cars began in '88 and went thru '97 I think, I'm not a 4th gen guru.

87, gotcha on the prop valve thing. It's my understanding that guys running adjustable prop valves like you mention remove the stock prop valve all together.


Ed

 

i have heard that for the ls1s, the rears are the weak points on that car....may not hold up?>?

 

you misheard. on an F-BODY..... the rear is usually the weak link. the 4th gen is more exacerbated because the trannies are rated to 400+ HP. the driveshafts are good, high strength units, and the rears aren't 12-bolts. so they become the weak link. a few of my buddies have historically just waited til their 10-bolt crapped out so then they could put in a 12-bolt. they put in heads and a cam, some little bolt ons, get the HP around 4-500, and blow out that rear, and drop in a 12-bolt. 6-speed cars seem to be worse, because of the sudden and instantaneous strain put on the rear every time you shift... an auto keeps the force constant (relatively) under acceleration.

either way, for the $150 I just paid for mine, I can't get a better deal than that.... a posi carrier with 3.42 gears, AND slightly bigger axles (28 splines), plus the instant disc-brake conversion, it's a damn good deal. (and when it craps out, i just buy a 12-bolt).

 

seems as if i just said that they were the weak link????? lol...no harm done....

 

The rears are the weak link on 4th gens, but no weaker than the 3rd gen rears.

 

I wasn't jumpin on ya, just pointing some things out. sorry bro

 

I agree with what RB83L69 said. I've done this myself, and the factory rear drum master cylinder and prop valve work just fine! No premature locking of the rear brakes, no wear problems, and the braking performance is noticably better.

Again, the parking brake cables will need to be addressed. You could fab up a new bracket, like I originally did, but later I replaced the cables with pieces from AutoZone. I got them for a 91Z28, disc rear, and they only cost about $18 a piece...

 

Let me clear Marc's post up. The '93-97 LT1 rears are a direct bolt in with the cables he listed, but the '98-up LS1 rears are not. They use different cables.

Ed