Hey guys I need some help. big time. I bought a 4th gen rear end out of a 99 z28. My car had disk from the factory as it's an iroc-z. the brakes never were anything to brag about in the first place. the swap went smooth. only thing i reused were my steel lines from my stock rear. i used the rubber hoses from the 4th gen and everything bolted right up. is that ok? I hooked everything up and bled the brakes systematically (DF,PF,DR,PR) and there was fluid coming out that was clean with no bubbles. i put all the wheels back on. started the car and the brake pedal goes to the floor. it will hold the car stopped with the pedal fully depressed. if i let up slightly she moves. ive pumped them, checked the reservoir, and checked for leaks. all checks out. I acquired a 1LE proportioning valve online and I'm wondering if this is the problem? I know this is a brake question but it came about from a rear end swap so i figured it would be ok to post it here. any ideas would be greatly appreciated. i'm at my wits end fellas.

 

wait a minute. the bleeder screws stick straight off the back of the caliper. should the bleeder be above or below the hose?

 

Try this: Unplug the brake light switch on the prop-valve, then unscrew the brake light fitting off the valve. You should feel a pop or maybe hear it. Screw it back in and plug in the switch again. Now, bleed the brakes using VACUUM ONLY. Don't use the pedal technique. The small piston inside the valve must be stuck.

This happened to me when I did my swap and couldn't find an answer until I decided to inspect all the fittings on the valve.

 

The bleeder valve should be above the brake hose.

 

Best of luck Jake, you're onto this swap much sooner than I anticipated! -Jesse

 

First of all, good call on the later rear end. 9 bolt and wider so no need for spacers. Camaromike said just what I was thinking. The proportioning valve is also a safety valve that will shut down fluid to front or rear in the event of pressure loss on that part of the system. You can sometimes reset the valve by pumping the brakes once the system is free of air. Other times, you have to physically release the valve. Camaromikes method for releasing the valve sounds good.

If the bleeders are below the hose, you will have trouble bleeding the calipers. The brakes on many early Asian cars were built this way. What works for me on these is to make sure that the piston is completely bottomed in the caliper. This minimizes the volume of the caliper and allows for getting the most air out. I also use a low pressure bleeder on these cars.

If you are going to use a vacuum bleeder, one thing That I find helps is to seal the bleeder screw threads with caliper grease to prevent air reversion past the threads under vacuum. Also, when using an air powered vacuum bleeder like the Vacula, I use an air pressure regulator and run the tool at only 40psi to reduce vacuum. This seems to help reduce cavitation that can occur with too much vacuum.

 

I switched the calipers(bleeders above the hoses), replaced the proportioning valve with the 1LE valve and bled the brakes thoroughly. Same thing. I don't notice anything leaking anywhere around the master cylinder or any of the calipers. could it be that the master cylinder is bad? i know it cant be the booster because the pedal isn't like pushing against a brick wall. also i want to reiterate that i used the old lines and hoses from my stock rear. that isn't the problem is it? should i have replaced the crush washers for the hoses? I really hate to just start guessing and checking.

 

If the crush washers are the problem, you will have leaks. If it were a collapsed hose lining, which is alot more rare than you might think, you would have a hard pedal and no brakes, or a locked wheel. No pressure with the pedal pressed is either a bypassing master cylinder or alot of air in the system. Did your brakes work with that MC before? If so, it's odd that the MC would suddenly have failed. What method of bleeding are you using? If you're using the pump and squirt method, how are getting air and or fluid out at the wheels if you don't have pedal pressure?

I am wondering if you have lost prime at the master cylinder. Detach the lines from the master and install bleeder plugs. The master on your car is a bypass type so you bleed it using plugs instead of lines. With the plugs installed, fully depress and release the pedal slowly until you can't depress it. do this with the engine off and go easy on pedal pressure so you don't blow the plugs out. When you can't depress the pedal, the master is bled. Remove the plugs and reattach the lines and then bleed your brakes.

Not that it's ever made any real difference but the prescribed sequence for brake bleeding is RR, LR, RF, LF. Always start at the wheel farthest from the MC and work your way up to the closest.

 

Roger that ASE Doc I'll get on that. any idea what threads are on the MC?

 

The bleeding kits are available at most parts stores. They also come in the box with any new MC. The plugs are plastic and while the threads are a decent fit, they're very forgiving of an imperfect fit. The MC threads are metric and very hard to match up. I have not been able to buy them over the counter anywhere but at a specialty hydraulic pipe and tube supplier.

 

I went and picked up my new MC today and installed it. problem solved. idk why it decided to go bad while i was swapping the 4h gen rear in. brakes work just fine. went from 2.77's to 3.23's :-) it'll turn sideways shifting into 2nd now. love it! thank you all for your help and I hope to see you all at thirdgen fest this year!

 

Awesome! Now, my turn to find another rear, but this time with 3.73's. ;.)

 

Glad you got it solved.