Doom86

coming home today on a very twisty turning rolling hill area I had to brake hard in a very sharp turn (15mph) and the rear end brakes locked, the front's were not, and the car went sideways. After avoiding the utility truck that as blindly parked in the turn and getting the car under control nothing was lost but a bit of pride, and maybe some rubber.

when the car is cold even going 10-15 mph and just bearly hitting the brakes trying to slow to a stop causes the rears to lock up. It does it really bad since I have a gravel drive way, but does it on pavement as well. The rear drums look good, I took them apart and everything looked good and in the right place according to my manual.

The PO looked to be trying to track down a braking issue the car had when I bought it a month ago. It had symptoms of bad brake hoses which were replaced right after I got it, and fixed the issue. The MC and combination valve look to be new they are nearly spotless, and look out of place next to everything else. Is there anyway to check the combo valve to see if it's the right one? I think if they put in one for a rear disk brake setup that it would put too much pressure to the rear brakes, is that true?

JamesC

iTrader: (5)

The bias increases from drum to standard disc to 1LE, so the combination valve in the car may well be incorrect.

JamesC

Doom86

Also I wanted to add is there anything else that could cause the rear brakes to lock up way earlier then the fronts? It's always done it since I first bought it. Even when driving straight the rears lockup way early when you get on them. The PO said "it had brake work with life time warranty blah blah" but no idea what was actually done. The pads and shoes look rather new too.

Doom86

Can I get some help here please? My family rides and drives this car I can't have it acting like this.

Gumby

Could be as simple as its hooked up backwards, fronts are on the rear brake port of the prop valve n vise versa.........

JamesC

iTrader: (5)

This from my 85 shop manual:

Grabbing or Uneven Braking Action:

1. All conditions listed under "PULLS (Incorrect tire pressure, Front end out of align, Unmatched tires on same axle, Restricted brake tubes or hoses, Malfunctioning caliper assembly, Defective or damaged shoe and lining (grease or brake fluid on lining or shoe), Malfunctioning rear brakes.

2. Malfunction of combination valve.

3. Malfunction of power brake unit.

4. Binding brake pedal mechanism.

JamesC

Doom86

Thanks for your help you two

Looking at it close it certainly isn't as "new looking" as I thought orignally.

The brake lines do appear to be in the correct places on the valve. Thanks for that idea.

The brake hoses have been changed 2 times in like a month and like I said before it fixed the hoping caliper issue. The second time I changed them I had put Russel's braided brake hoses and they were junk, caused caliper hoping under hard braking and had some scary reviews after some research. The rubber one's on there now have been working great for weeks.

The front brakes seem to work fine, though they do seem kind of hard to lock up going 30mph or so, this could be normal I'm no brake expert. The back brakes will lock up at 10-15 mph under light-moderate pressure, even when you try to ease in to the brakes "just enough" to make it stop from a slow roll. After it heats up though it doesn't do this so bad but still very rear brake biased.

From what I've researched if the front's aren't getting full pressure for whatever reason that the rear will seem to be having a problem but it's really the fronts. Anyway to test the calipers? They are pretty cheap perhaps I should change them and see if that's the issue.

All the pads and shoes look to be wearing normally and don't have any contaminants getting on them.

Gumby

Could be just bad, I got a bad prop valve right now, have for a while, everything but it has been changed. But mine just acts like manual brakes.
And being a stick I can engine brake so I haven't done much about it.

can ya post pics of your setup?

you can get some lifetime warranty reman stock calipers for like $10 each at any corner auto store. If your looking for a cheap easy test on those.

Gumby

And a stock prop valve is expensive, not sure how easy one can be rebuilt, I was going to get a disc/drum hotrod brass prop valve and plumb it in.
Like $30 on ebay.
Good enough for a HEMI in a bathtube, ok for me

Doom86

I got someone to watch my wheels as I tried to make them lock up on a dirt road. The rears do lock up much easier then the fronts do. The fronts will only lock up if you jam them hard, it stopped a few times with the fronts not being locked at all and just the rears. It pulls really hard *** end to the left when you slam on the brakes. In reverse though the fronts lock first every time.

Anyone have any insight on that? I don't have the funds to start throwing money at the problem just yet.

Gumby

https://www.thirdgen.org/forums/brak...ster-shot.html

ownor

iTrader: (5)

sorry there's not much i can do to help you with this, just letting you know i had a similar problem when i still had the stock drums in my '89. the rears really liked to lockup when the car was still cold. never found out why they would do that though.

RBob

iTrader: (1)

Three things that I can think of. First, on the drum brakes (rears) is the shoe with the longer lining toward the rear of the car? It needs to be. IOW: the shoe with less lining goes on toward the front of the car.

It is also important that all the levers, springs, and gadgets in the rear drums are properly assembled. Since someone else has been in there, this can be an issue. The best way to check is against another vehicle.

If the wheel cylinders have been replaced, maybe they put the wrong ones on. W/C's with a larger bore will cause early rear wheel lock up.

Last but not least: front pad and rear shoe material. The front pads could be a budget material that lacks braking. While the rear pads may be a better, or even incorrect material, that provides too much braking.

This would cause lack of front brakes, and an over abundance of rear brakes.

If you want to test the lines and combo valve. Need a high pressure gauge and a fitting to go into the bleeder port. Then the pressure is checked at each caliper/wheel-cylinder.

RBob.

Doom86

Rbob and ownor thanks for the information.

I checked all the drum hardware against my haynes and it looks right, but that doesn't mean it is. Here is some pictures of the rear drivers side brake for reference. Also a picture of the wheel cylinder.

When I was doing research someone mentioned backing in reverse with parking brake on for a bit to fix the issue (adjusting??) they were having. After I tried it the fronts started locking first. Tried 6+ times and the fronts were locking just before the rears on a dirt road. I then took it for a test on the road and on a secluded 20mph right turn I locked them up and it stopped straight but the longest tread marking on the pavement was by far the rear passengers tire.

When I got back home tried some more on the dirt road and it was stopping correctly every time.

I'm going to test it again tomorrow after its gotten to cool down and see if it's still good or not, I'm doubtful its "fixed".

Brakes are not something I'm good at so thank you all for your help.

Doom86

different angles

ownor

iTrader: (5)

the only thing i can tell you is that it was always the rear right drum that locked up first on me as well. god, i hate drum brakes..
btw, something that happened to my buddy with this '79 fox-body: he purchased a new brake hose for just one side of the rear brakes and ended up having a lot of bias to one side (in austria, the yearly inspection demands to have less than 20% braking variation on an axle). after some time we came to see that the new brake hose was a bit bigger in diameter, hence the pressure difference.

RBob

iTrader: (1)

They look to be assembled correctly. Although, without being there I can't say for sure. It may be that they were so far out of adjustment that it caused the lock up.

Usually, to adjust the rear brakes one backs up and pumps the brake pedal. Do this when the brakes are cold. As the drums expand when hot and over adjusting can be the result.

RBob.