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Bad rear brakes

IIRC I've even seen backing plates that were designed to keep the pistons from coming out of the cylinder. You would have a hard time getting the rubber back enough to check for leakage.

That's the brakes!
Seems like I recall seeing something like that but man, it's been a long time lol. I sure hope my brakes don't break :D Been wanting to say that to several folks LOL
 
What sized wheel cylinders do you have in back? Bore size?
 
Rubber brake lines do not collapse when pressurized when applying brakes. They collapse when piston returns and fluid tries to return to the MC.

Is the Proportion valve new? After Market? If it is stuck you won't get any real pressure built up.

Really need to know full set up. I assume Disc/Drum set up. Is it factory OEM type?

I know this may be hard to do, but put a pressure gauge on rear line in front of Prop. Do you get pressure? If not work way towards master cylinder. If you do, measure pressure after prop valve.

You need to find out where your loosing rear pressure. I assume your Brake warning light stays off? Does it work?

You also need to look hard at how you bleed system, including MC.

Thanks for youre thoughts on the matter,
Prop valve new as is all blocks, exp t-joint on rear axl
Disk/drum correct, OEM
Yes ive thought about messure the pressure, as u say, takes some effort/costs
But that would be the correct was to go about it.
Brake warning is off, used to work electricaly, as above the blocks are new.

Yes ive just re-bleed the master, that's My best gues either worn out shoes or/and air somewhere.

Thanks
Linus
 
Double post
 
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How much would be way past their service limit?

I have no idea actually - but I was commenting in light of his comment that his wheel cylinders and the linings don't appear to move much with pressure on the pedal. Depending on where his shoes are at rest, maybe they just can't reach the drums firmly anymore. There's a chance he is dealing with more than one issue. The wear pads on the backing plates may be worn and restricting shoe movement. Some sort of obstruction in the MC or line. Corroded wheel cylinders. Hard to tell. Even a seriously deteriorated, rear rubber hose might be starting to disintegrate inside and blocking flow instead of just collapsing on release. Of course that means at one time they probably weren't releasing well and that would wear the shoes out. Don't know.
 
That maximum cut limit on drums, really just to avoid the brake cylinders from going past their limit. Unless someone just runs those brakes to the end, rarely happens.

Corroded wheel cylinders. Hard to tell.
That's real possible, and easy to find out. Okay, OP, so your in Sweden. Cars in Sweden have brakes, too.

I'd suggest you pull BOTH rear brake cylinders, and take them apart. Simple things can make them not work, so they need to be looked at. Condition of the cylinder itself, maybe needs to be honed. The pistons clean, the rubber cups in good shape, and sealing good. Nothing special about them, besides size, so should be easy enough to find them, where your at. Make sure the bleeders are okay, and clear.
Guessing their gummed, or rusted up. As long as you get fluid to them, no reason those brakes shouldn't work.
 
That maximum cut limit on drums, really just to avoid the brake cylinders from going past their limit. Unless someone just runs those brakes to the end, rarely happens.


That's real possible, and easy to find out. Okay, OP, so your in Sweden. Cars in Sweden have brakes, too.

I'd suggest you pull BOTH rear brake cylinders, and take them apart. Simple things can make them not work, so they need to be looked at. Condition of the cylinder itself, maybe needs to be honed. The pistons clean, the rubber cups in good shape, and sealing good. Nothing special about them, besides size, so should be easy enough to find them, where your at. Make sure the bleeders are okay, and clear.
Guessing their gummed, or rusted up. As long as you get fluid to them, no reason those brakes shouldn't work.

Thanks for the tips,
Maybe i forgot to mention one wheel cyl is new, the other old, both sides have the same problem, so i figurer the problem must be up ahead, either the mc or somewhere on the line/blocks,
The shop has My drums and shoes til 11/7 so i want know until then if My re-bleeding of the mc got results...
Ill be back for an update. Possible a solution
 
Thanks for the tips,
Maybe i forgot to mention one wheel cyl is new, the other old, both sides have the same problem, so i figurer the problem must be up ahead, either the mc or somewhere on the line/blocks,
The shop has My drums and shoes til 11/7 so i want know until then if My re-bleeding of the mc got results...
Ill be back for an update. Possible a solution
!1/7 is July 11th, correct? In US we do month day.
 
one wheel cyl is new, the other old, both sides have the same problem
Okay. Two possible trouble spots, are right together. The brake line 'block' on the rear axle, and the rubber hose, right there. The hose can get old, weak, and collapse...the block can get clogged. (Mine was!) Might at least make sure both those, along with the lines are clear, using compressed air.
Guess you know not to try to bleed the brakes, with the drums off.
 
Okay. Two possible trouble spots, are right together. The brake line 'block' on the rear axle, and the rubber hose, right there. The hose can get old, weak, and collapse...the block can get clogged. (Mine was!) Might at least make sure both those, along with the lines are clear, using compressed air.
Guess you know not to try to bleed the brakes, with the drums off.
A simple test might be to compare the quantity of fluid that you get when you bleed the back vs the front. You should get a pretty good stream of fluid with the bleeder open.
 
Okay. Two possible trouble spots, are right together. The brake line 'block' on the rear axle, and the rubber hose, right there. The hose can get old, weak, and collapse...the block can get clogged. (Mine was!) Might at least make sure both those, along with the lines are clear, using compressed air.
Guess you know not to try to bleed the brakes, with the drums off.
Didnt know, why?
 
A simple test might be to compare the quantity of fluid that you get when you bleed the back vs the front. You should get a pretty good stream of fluid with the bleeder open.
U mean if i depress the pedal, open the bleeder,
Can u tell how much pressure? A squrt or just rinning( don't know the word :))
 
Quantity, how much and the flow rate.
It should squirt out quickly. If it does and your brake pedal stays firm when pressed with the bleeder closed then I would suspect the wheel cylinders.
 
Didnt know, why?
On bleeding brakes, with the drums off?
Without the drums on, the brake shoes have nothing to limit their travel. If there's no 'stop', it's real easy to push the wheel cylinder's pistons/cup seals clean out of the brake cylinders. Make sense?
 
If your distribution block works with the brake warning light and lets say the Master Cylinder Rear Brake piston leaks and does not generate pressure and just collapse to the stop, while the front brakes work, you would see the warning light come on. Meaning a MC problem as long as no other leak down stream on the rear.

If it works and the light stays off that means the MC is giving you equal pressure. So the next part of the system is the proportioning valve. If it is bad and clogged you may just be building pressure up to it and nothing coming out. You can undo a rear brake line and see if you get fluid out when petal depressed. Or place a gauge that can handle the hydraulic pressure of 500 psi and see if you have pressure. If you do, then your issue is with the wheel cylinder/pads/drum. But if neither rear wheel work that means both sides are faulty or in reality it is upstream. So I suspect the proportioning valve or plugged/damaged rear brake line feeding the Tee over the rear housing or master cylinder if your distribution block brake light doesn't work.

You really need to halve your problem to make troubleshooting easier. Which means break the brake line coming out of the proportioning valve and put a pressure gauge on it. If you get 300 to 400 psi out your problem is down stream. If not, it is upstream.
 
Hi i'm Starting to run out of ideas soon concerning My rear drums,
Before anything else is there someone who can tell me if a longer "front to rear brake line" will effect the pressure at the wheel cylinders?
The new line i got from Y1 is about 40cm (sorry i'm swedish) maybe 1,5 feet longer than the original one, probobly cause i have the prop valve on the framerail,
Anyway does this cause the bad action on My rear break shoes or do i need to look elsewhere?
Would be great help!

Linus

Is the prop valve original, or adjustable? The length should not make a difference.
When i added an adjustable prop valve, I cut and re-flared the brake line to fit.
 
Hi here is some update on this thread,
I got the drums back from the shop a week ago, re-furbished (?) and re-lined,
mounted everything on, all new hardware and both new wheel cylinders,
butt still wery week if any break power on the rear wheels,
the way i tested is, Rear end of wehicle in the air, put in gear, step on the brakes.
Here is what i discovered:
The thing i didnt understand earlier was that then i bleed the brakes i could acually feel the shoes go against
the drum, but when i tested as described above, no braked...???
SO what i did, i disconnected the brake servo,
i´ve have tested this correctly yet, just want to gear with you,
IS IT possible that the brakes are better witout the servo, i mean more pressure,
seems like it so far, will test better when i get some help...
 
If your distribution block works with the brake warning light and lets say the Master Cylinder Rear Brake piston leaks and does not generate pressure and just collapse to the stop, while the front brakes work, you would see the warning light come on. Meaning a MC problem as long as no other leak down stream on the rear.

If it works and the light stays off that means the MC is giving you equal pressure. So the next part of the system is the proportioning valve. If it is bad and clogged you may just be building pressure up to it and nothing coming out. You can undo a rear brake line and see if you get fluid out when petal depressed. Or place a gauge that can handle the hydraulic pressure of 500 psi and see if you have pressure. If you do, then your issue is with the wheel cylinder/pads/drum. But if neither rear wheel work that means both sides are faulty or in reality it is upstream. So I suspect the proportioning valve or plugged/damaged rear brake line feeding the Tee over the rear housing or master cylinder if your distribution block brake light doesn't work.

You really need to halve your problem to make troubleshooting easier. Which means break the brake line coming out of the proportioning valve and put a pressure gauge on it. If you get 300 to 400 psi out your problem is down stream. If not, it is upstream.
Hi and thanks for youre insights, sounds like you know what youre Talking about,
Do you think it's possible to put a gauge on one of the bleeder holes in the rear, to messure the pressure after the prop valve?
 
Is that a stock distribution block/prop valve? If it is...kinda remember on some of them, on a two pot type MC, the valve could have a 'shut-off' valve built into it. Check in the service manual. Look at the valve itself, on each end, to see if one is out farther than the other.
Idea behind it was, separating front/rear brakes. If something went wrong with either front, or rear brakes, that sliding shut-off valve would move, closing off fluid to the bad brakes.
To 'fix' it, after the brake problem was cured, the valve has to be manually moved back to center of the block. Might be worth looking at.
 
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