robs_seven

iTrader: (1)

Okay i did some searching but still have some ?s. I have a 79 with 81 front and rear discs and calipers. I swapped over the brake booster, master cylinder and proportioning valve. The car is not driven much in traffic or in any close quarters so i have not noticed this until this weekend. I was driving and a lady in front of me on the on ramp stop dead in her tracks waiting for traffic to let her in. Well I was looking for a opening when i looked and saw her stopped. I stabbed the brakes and the car NOSE DIVED hard and to the right almost not stopping me. I started looking at things and noticed the front right hard line goes to the mc and the rest to the pv. I looked on the discs that are coming from the pv and they have less wear and the rear discs barely any wear compared to the front right. Could this be from a messed up proportioning valve. The brakes have been bleed multiple time, i have a brand new master cylinder and all new pads, and brake lines. If this could be a problem with the pv what actions do i take? Can it be disassembled and cleaned or repaired? Thanks in advance
Robby

diabolical1

iTrader: (3)

sounds like you've been pretty thorough except for one part of the system ... the calipers themselves. they may be sticking. when it happened to me, both fronts went out at the same time, except they were stuck in the "braking" position so i kept chasing my decreased engine power for about 2 weeks before i thought about checking the brakes. give them a once over.

justint5387

iTrader: (1)

Did you locked up the brakes?

robs_seven

iTrader: (1)

diabolical1 both front and rear calipers have been removed and cleaned before installing them on my 79. I bench tested them, as fas as have full movement with no restriction. They seemed ok but it could be different when stopping a car.

No i did not lock up the brakes. After all this happened i did some hard braking test on my way home on some country roads and the same thing happened. The car nose dives and favors the right side. The car has sat a few weeks before taking her out on sunday so there was a little surface rust on the rear brakes and when i got home it was still there. Seems like there is not enough real pressure being applied by the hydraulic system. I have put it up on stands and had my wife hit the brakes, with it like this i cant turn the wheels, but under the weight of the car and at speed they are not slowing down enough. has anyone taken the proportioning valve apart and cleaned it if so what did you use and what is the best way to do so?

justint5387

iTrader: (1)

I think the tires and alignment could cause this also

DivinDriver

iTrader: (15)

The proportioning valve is probably the least-mentioned part in the FSMs. I don't think Mazda ever thought of them as anything but replaceable units. No testing instructions, no assembly or repair instructions - - just removal and replacement.

Looking at the parts fiche for the 79-80, it looks like the front LEFT caliper is supposed to go to the MC... and the rest to the proportioning valve. There are changes between 79 and 80 regarding pipe routing, and the MC was different as well.

Are you sure your plumbing is correct?

t_g_farrell

iTrader: (1)

I have a similiar issue on my 80 SA. It will favor the left front wheel when I brake hard and pull slightly to that side. Whenever I have had this be a problem it usually means I need to adjust the rear drum brakes and do a bleed while I'm at it. Once the rear brakes are back in adjustement it seems to be much better and will eventaully come back over time. On the SA,as Divin pointed out, the left front is the directly connected brake line to the MC and the others go thru the pv. Opposite of how your works. Maybe 81-85 thats correct for the plumbing.

Since you are using all 81 brake components I would think the PV should be able to deal with the rear disc. Not sure if the PV part number is different for a drum or disk brake on an 81 rear end. Maybe its a PV for an 81 with drums?

Also it could be all the other calibers are binding. It could just be your not drving it enough and things are getting stiff. Brakes will do that. I run silicone DOT 5 fluid for just that reason. Keeps my rear drum cylinders from seizing due to moisture trapping in them. Of course if you convert over to silicone you may need to rebuild all the components as old fluid gets absorbed into the rubber and doesn't play well with the silicone.

82transam

iTrader: (18)

The plumbing is the same on FB's, the left front caliper goes right to the MC, the rest of the lines come off the PV. Could be incorrect plumbing or as the others saidt he brakes are getting a big stiff. I had problems with that on my one FB after it sat for the winter, right front had basically locked up making it pull like crazy...

t_g_farrell

iTrader: (1)

Robbie are you sure the pv is centered. When its not you can still bleed one end fine but the other end will get very little pressure. I've had this happen to me before. If the system has been completely opened up then you really have to bounce on the pedal a couple of times real hard to recenter that damn pv valve. Otherwise there will remain a lot of air in the rear (usually its the rear that this happens to) and brakes will not feel right.

Not sure if this applies just throwing it out there.

boyee

iTrader: (3)

So if the PV is not centered you'd have to really step on the brake pedal hard (meaning it is very stiff to push down?) to center the valve?

Can the valve be out of whack if say, one were to bang it a little to remove the master cylinder?

And by brakes feeling funny does that mean that the pedal goes to the floor when stepped on?

Thanks for your input.

cpa7man

iTrader: (2)

You could always do what we do with our race cars. Get rid of the stock PV and install a cockpit ****.

http://www.streetperformance.com/par...866-a0707.html

trochoid

iTrader: (6)

The PV is a very simple device. It has a spring, a needle valve and a seat. Remove the large nut, pull out the spring and valve, clean them and the inside with brake cleaner, rebleed brakes. Sounds like the valve is sticking and not allowing fluid to the rear.

boyee

iTrader: (3)

Thanks for your input trochoid.

So what you're saying is if the valve is sticking not allowing fluid to the rear, this would cause the pedal to be really firm since the fluid is just being compressed at two wheels rather than all four, correct?

trochoid

iTrader: (6)

Yes, but with a difference. The left front brake has it's own seperate brake line. The 2nd brake line from the Master supplys the proportioning valve, which feeds the remaining 3 wheels. If the valve is stuck and blocking fluid to the rear, (not sure if that's even possible), then the fluid headed to the rear would go to the right front caliper. This would cause the front caliper to lock up before the right.