Thomas Stahel

iTrader: (1)

Hello

When I was at the vehicle inspection they told me that the difference in braking pressure on the rear brakes is too high.

Front is: 24/26 (left/right)
Rear is: 10/18 (left/right)

The handbrake strangely is okay (18/18). I mean both the hand and the foot brake go to the same brake shoes. So what could be the reason? Is there a brake pressure distributor on my car? The brake cylinders don't look wet, so no leaking.

How should I proceed to find the cause?

Thanks,
Thomas

sofakingdom

iTrader: (1)

Adjust them as high as they can go, and still be able to get the drums back on.

Thomas Stahel

iTrader: (1)

Thanks for your reply. What do you mean by "as high as they can go"?
And how can I adjust them? Actually they should self-adjust themselves... Why is the park brake power balanced but not so the foot brake power? Both apply pressure to the brake shoes in a similar way...

camaromike222

The parking brake works using levers and springs and a cable to expand the shoes. The brake pedal uses brake fluid to apply pressure to the wheel cylinder inside the drum assembly which then expands the shoes when braking. Same method of slowing the drum brake, but different ways of expanding the shoes.

Thomas Stahel

iTrader: (1)

Yes, I understand but that's the reason why I don't exactly understand why and how I should adjust the brakes. In the end, what happens IN the brake is basically the same with the park brake as with the foot brake. The brake shoes are always in the same position. So what has to be adjusted?

Iff the pressure on the left side is less than on the right side, it can actually only have to do something with the wheel cylinder, hoses or the master brake cylinder. If it had something to do with the brake itself, the uneven effect should turn up in both cases (park brake and foot brake).

Camatruder

I have the exact same problem. 50 % less braking power on the right rear wheel. Parking brake operation results in more equal pressure.
EVERYTHING on both sides is new : drums, shoes, pistons, springs, adjuster,...
I adjusted the automatic adjuster like described in the Haynes and Hiltons. I performed all stop and go procedures mentioned in these books.
There is only one brake line to the rear, how can there be so much pressure difference?

Thomas Stahel

iTrader: (1)

Hi Camatruder

Well with me it was the left side but I've resolved the problem. It was easy. The guy at a cheap shop asked me whether the car wasn't moved for a while which was true in my case because I repaired the steering linkage and it took me quite a while. So he suggested driving a longer distance and applying the brake firmly several times. And when I was at the car inspection even I was surprised because everything was quite back to normal again without doing anything.

But in your case... hm... I could only think of the brake line. I mean there is a junction at the rear where the line is split between the right and the left side. Maybe there's a problem.
Did you also check the parking brake cable?
What about the front brakes? Is there any difference between left and right? There is a brake power distributor but I don't know how it works exactly.
Did you put the new brake shoes correctly? The longer ones to the front and the short ones to the back?
Has the difference changed in any way from before and after you changed all the parts?

Thomas

Camatruder

Front was ok.
I think the short shoes need to be installed on the front side.
When i bled the brakes, the fluid came out nicely on both sides.

Thomas Stahel

iTrader: (1)

Oh yes sorry, I misinterpreted the picture in my manual. The short ones should be to the front.

Seems that I'm no further help to you . The replacement of all parts didn't change the pressure distribution in any way? I only thought that this could have been an indicator for what to look at a bit closer. But since you replaced everything... it's getting difficult.

Camatruder

Well i'm out of ideas. I checked everything. When the car is on my lift and i have an assistant push the brake pedal in gradual steps, at each point it feels like i need the same amount of force on both wheels to turn them.
Is it possible that the problem only occurs when the car is on the ground and/or is rolling?
Any input is highly appreciated.

Camatruder

Because i doubted the main cilinder i replaced it, bench bled it and bled all the lines thoroughly but the problem is still there.
50 % less braking power on the right rear wheel than on the left rear wheel. Hand brake is ok (equal braking there). Since everything is new (see post 6), it has to be something with the pressure in the lines coming from that T-piece on the rear axle. Is that T-piece equiped with some kind of safety valve that directs all pressure to one side in case of failure at the other and can this be defective?
Can those steel lines fail? Bleeding went fine, the fluid really spurts out when pushing the brake pedal.

sofakingdom

iTrader: (1)

Did you adjust them up as high as they can go and you still be able to put the drum back on, yet?

Camatruder

Yes i have.

sofakingdom

iTrader: (1)

Do both pistons in the slave cylinder on the affected side move freely?

Camatruder

Yes they do.

82TransAM84

Hello,

I'm in the same boat...

2 years ago, I've had the same problem (rear right wheel braking more than the rear left wheel). I've changed everything (braking lines from the T to each wheel cylindrer, wheel cylinders, drums, springs, shoes, adjusting screws, all the hardware and the 2 e-cables).

I passed the inspection on the edge. I've thought that as everything was new it had to do some break-in period before everything would be fully operational.

Today I went to the inspection, and it happened again (right wheel braking more than the left wheel).

So I wanted to know if some of you solved the problem on their cars.

For your information, the e-cables are disconnected, to be sure they aren't used during the braking and the adjusting screws on each side are set in a way I can barely install the drums in place.

I am thinking about uninstalling the T between the left and right lines, because it is the only thing that comes to my mind.
I believe it cannot be a bad thing to check if it is clogged a bit, explaining the pressure difference.

loopy

iTrader: (1)

Funnily enough I have this same problem too! Even my mechanic couldn't find a fault. Totally new brakes cylinders etc all round on my car.

Right side weaker than left. Any ideas?

Camatruder

Sorry for not replying what resolved it in my case. I took my new (Summit) drums to a shop who rounded them precisly and after that i passed inspection easily. The hint came from the inspector himself who told me that he could not get a steady reading probably because of out-of roundness of the drum. Next inspection is in march next year, i'm already wondering if i"ll pass this time...

loopy

iTrader: (1)

Ok. I doubt that is my problem as my pressure is stable just low on right side. The drums are GM replacements too, with new wheel cylinders and shoes. Got me stumped.

82TransAM84

Hello,

I've found the problem on my car.

It was coming from the passenger side wheel cylinder which braked too much and not from the driver side cylinder, which I believed at the beginning was too weak when braking.

The problem on the passenger side wheel cylinder was a seal which was not installed correctly. When I mean seal, I am talking about the circular rubber piece, inside the cylinder, which is between the spring and the piston. The seal was not perpendicular to the cylinder and was stuck in its position. So it prevented its assigned piston to be forced out of the cylinder, reporting all the brake pressure on the other piston, which was the one in contact with the primary shoe. It created a very big difference in braking power between the left and right side.

For your information, the part was new when installed nearly two years ago and didn't leak at all, even with the seal not in the right position. But as the problem happened as soon as it was installed, I think it was badly assembled from the factory.

From now on, I will always check inside a new wheel cylinder before installing it.

loopy

iTrader: (1)

Excellent, good to know. My wheel cylinders are new too so I guess I will have to check inside for this.

Thanks

Beeman

How are they testing brake pressure at each wheel? Where is this at?, we don't have any inspection here in TN.

82TransAM84

Here in France, during an inspection, they don't test the brake pressure on each wheel but the force of the braking on each wheel.

They use a device which looks like a dynamometer but instead of measuring the power of the engine, it measures the braking.

If, on the same axle, one of the wheel is braking more than the other, you can record it. Above a certain value (in France it is 30% of difference), it is considered you have a braking problem on one of the wheel.

loopy

iTrader: (1)

^^^^^ Same system is used here in New Zealand but the allowed imbalance is only 20%..

Beeman

That's interesting. I have been a state certified inspector in 2 different states working at GM dealerships. Our inspections in the states that actually have them are generally a quickie and all visual, no dynamic testing. The only actual test was emissions in the states or counties that required it.

loopy

iTrader: (1)

Funnily enough we don't have emissions testing although if your vehicle smokes a lot it can be failed. There is a standard to assess smoke duration /quantity but I'm not sure what it is exactly.

82TransAM84

We have the following tests here : dynamic tests (suspension, main brakes, parking brake) + emissions test + good working of all the main devices (headlights, tail lights, turning lights, brake lights, wipers, horn, seat belts) + visual / hand inspection (VIN plates, body, underbody, rust, windshield, leaks, wheel bearings, steering linkage / ball joints, tire wear, exhaust system).

loopy

iTrader: (1)

82trans........that's pretty much the exact same format our tests follow.

Ours are 6 monthly for older vehicles and for post 2012? (I think (not sure about this)),1 yearly .

82TransAM84

We have this inspection every 2 years for all the cars which are at least 4 years old, and it doesn't matter when the car was built (50 years ago or 4 years ago).

But it depends on the kind of title the car has : regular or oldtimer.

If it is regular (like my car), it is like I said above.

If it is oldtimer (it must be at least 30 years old, but this title is not mandatory for a car older than 30 years), since 4 years, they should have an inspection every 5 years.
But it is quite unclear because 4 years ago, they didn't have to pass an inspection at all to allow them to be driven, and I know some people who are still driving them without trouble and who haven't done an inspection yet

Chevy2035

loopy

iTrader: (1)

Thanks I'll check That too

Camatruder

Mine is just a T-piece.

loopy

iTrader: (1)

Just thought I would update this post with my fix.

My brake shop was stumped as to my problem. He tested everything couldn't find a fault. Finally in an effort to eliminate step by step he machined the weak side to remove glaze, made it worse, machined the strong side, problem fixed.

What a relief. Finally passed inspection.

JamesC

iTrader: (5)

The combination valve (proportioning valve) is underhood on our cars.

JamesC

Camatruder

Well i guess it was the same solution as mine!
Had a new inspection last week and passed it easely.

vortech2

I had the exact same problem with the rear drums on mine too with right wheel stronger brake force than left side resulting in failed w.o.f. Had me stumped too for a while. I knocked the plugs out of the backing plates and adjusted the shoes manually. What this did was change the braking force around and I ended up having more braking on left rear than right! Now I really thought about this for a while and have realised that the self adjusters only work when the car is reversed. What I did then was do several hard reverse stops and Presto! Perfect brake force both rear wheels. Cant guarantee that this will work for everyone but its certainly worth trying as you don't have to get dirty.