Rear Brake Wheel Cylinder Upgrade?

[KenONeill]

59 minutes ago, Thefeliciahacker said:

inform us

1. Brake systems do not have a "duty cycle". That would imply that there is a maximum quantity of brake fluid they can deliver to the pistons. Ok, you can have wheel pistons that are too large for the master cylinder but doing that is bad engineering.
2. ABS cycles the brakes on,off,on,off but faster than you could read that, when/if the system detects wheel locking.
3. A good ABS system, like on, say, a Skoda Octavia, can cycle each wheel separately, and each side of the car individually. Again using the Octavia, where I have done this, as an example. If you brake hard with one side on gravel and the other on tarmac, the retardation is controlled allowing you to keep steering control. If you then steer the car off the gravel without reducing braking pedal effort, you feel the car slowing faster.

[Thefeliciahacker]

2 hours ago, KenONeill said:

ABS cycles the brakes on,off,on,off

So a duty cycle.

Abs doesnt just use negative feedback, it uses predictive algorithms and thats why if you brake on ice with all 4 wheels abs will function somewhat but will eventually lock up as there is not enough grip causing all 4 wheels to stop simulatniously and thus the car thinking it has completely stop, the reason this doesnt happen in the first millis of the brake application is that the abs uses predictive algorithms and g sensors to avoid such tricky conditions.

Its the same deal as predictive ignition used on all modern ignition systems, you dont fire the spark the time the magnet passes under the hall sensor but rather, you predict the firing point based on the rpms which have come from that feedback loop.

2 hours ago, KenONeill said:

That would imply that there is a maximum quantity of brake fluid they can deliver to the pistons

Not quite duty cycle is the amount of on vs off time, so abs will have a duty cycle that varies depending on grip levels, nothing to do with maximum volume of fluid delivered, a fixed volume will cause a fixed displacment of piston thus excerting a fixed force (not minding line expansion and fluid compression WHICH DOES EXIST albeit very small when compared to line expansion)

Edited 16 January, 2022 by Thefeliciahacker

[R_U_AFA]

So my felicia does not have ABS (I don't think many did have it fitted or not in the UK anyway)

But I may have found a issue with my pressure regulator, because before I started to replace the wheel cylinders I decided to see how much braking I had on the rears

And it wasn't good.

So with both sides of the rear on stands.

I found that the foot brake had to be depressed around 7/8 of it's travel before only a light drag can be felt; and even with the pedel fully depressed the wheels can still be just about turned by hand.

At first I thought that this was being caused by the fact that with the car jacked up the pressure regulator thinks there was no load on the rear axel

So then I jacked up the rear beam axel to simulate a full load, but still no change in the amount of braking effort being applied to the rear wheels

Just to give a comparison 1 click on the handbrake gives a light drag, 2 clicks gives a lot of drag, and 3 clicks I am unable to turn the wheels by hand.

And it is the same across the rear axel on both rear brakes.

I am only measuring the brake effect by hand, no techinical equiptment here.

I have re-bled the brake system aswell, so no air in there.

Also I will just say that my front pads seem to have take a bit of punishment because they are down to around 3-4mm now, and back when I changed tyres i am sure they had around 6mm(although having one of my fronts sieze on one morning can't have helped this)

 

So just a Couple of questions:

1. Has anyone had to replace the pressure regulator before? (load sensitive type)

2. What amount of pedel travel do you have before the rears start to engage/drag? (with or load or without)

[D.FYLAKTOS]

13 hours ago, R_U_AFA said:

What amount of pedel travel do you have before the rears start to engage/drag? (with or load or without)

 

The best feeling was with factory brake pump (brake master cylinder), the worst was with LPR and with Ferodo the feeling was one click lower than the stock (same type of brake pads with the 3).

After replacing the factory (NOT my idea) i had lot of pedal travel with LPR (new brake fluids, no air inside the system) so with first chance i put the Ferodo, the pedal travel is better although it's not as i had with the stock in which things were more ''tight''.

[R_U_AFA]

6 hours ago, D.FYLAKTOS said:

After replacing the factory (NOT my idea) i had lot of pedal travel with LPR

I still have the original master cylinder, it's not been changed

 

6 hours ago, D.FYLAKTOS said:

the feeling was one click lower than the stock (same type of brake pads with the 3).

 

Can you remember what % of pedel travel you had before the rears started to grip before, and then now

 

20 hours ago, R_U_AFA said:

2. What amount of pedel travel do you have before the rears start to engage/drag?

 

I do seem to remember reading a a past thread, where someone said that they had around 50% pedal travel before the rear shoes even started to move, never mind starting to bind.

 

[D.FYLAKTOS]

40 minutes ago, R_U_AFA said:

 

Can you remember what % of pedel travel you had before the rears started to grip before, and then now

 

 

I do seem to remember reading a a past thread, where someone said that they had around 50% pedal travel before the rear shoes even started to move, never mind starting to bind.

 

 

Unfortunately i got no measures in cm of that but the feeling was terrible with the LPR, i wouldn't dare to drive fast in a mountain road wearing this. Even in city traffic i was very cautious for a possible fender-bender.

As a percentage i could say 30% worst at least.

[nta16]

Are you sure you are both not confusing pedal feel and travel with brake efficiency, I have driven older cars that have brake boosters as an optional extra and the braking efficiency has been the same with or without brake booster but the pedal feel and travel different.  Better to anticipant driving conditions and need less from the brakes.  I am not a good driver but as I use an old car I do look ahead more than when driving a modern car all of the time.

 

[D.FYLAKTOS]

2 hours ago, nta16 said:

Are you sure you are both not confusing pedal feel and travel with brake efficiency

 

No ABS: hen you drive at straight line you simply push the pedal with force and keep your steering wheel tight but when you drive at mountain routs you can not brake efficiently with a pedal with ''rubber feeling".

After the first cm (you can hear the sound from the disc brakes depending how hard are the brake pads) the pedal must get stiff, if there is a gap between those senses then you lose precious seconds and you can get out or course.

A lose pedal (as i had with LPR) gives you nothing more that trouble even in a city traffic, yes 5 brands by pressing all the way down the pedal in a highway braking will give you the same brake result but we don't drive is US highways.

The feeling can be different even when you change brake pads (soft-hard) so your whole braking at sport driving.

[nta16]

2 minutes ago, D.FYLAKTOS said:

No ABS

I drive a car where the nearest thing to ABS is a very old and very faded, always faulty, biological computer, the car is without vacuum booster, the car is also light (according to Google, 735kg curb weight against 920–1,060 kg for Felicia).

 

Do you not cadence brake and use the gears.

 

You have to drive your vehicle within the prevailing conditions, if the braking is as bad as you say then you must adjust your driving or get better braking but you can not beat physics, of the brakes or road.

 

The brakes all have to be in balance, front to rear, improving just the front brakes can make the overall braking worse rather than better.

 

Some cars have a soft slow pedal feel others have a sharp hard pedal feel others cars are in between, there can be personal preferences or what someone is used to as to which might feel better but it does not matter as long as the brakes work well (within their limitations).  You must also always factor in the tyres for braking (and many other things like excess weight carried).

 

 

38 minutes ago, D.FYLAKTOS said:

we don't drive is US highways

No we do not see much of that on UK motorways either.  😄

 

[R_U_AFA]

Really this should be started in a new thread

But It's not particularly the pedel "feel" that I have an issue with, it's the amount of pedal travel before the rears are applied, although pedal travel would have an effect on the "feel".

But I believe there does seem to be an underlying issue with the braking system somewhere, particularly with the rears (as my following results seem to show)

 

So today I jacked up the car put it on axel stands and made an attempt to measure the brake force at diffrent stages of the foot pedel's travel

 

Below is the force(in Nm) needed to turn the wheels at diffrent stages of pedel travel(in mm)

 

So total pedel travel from top ot bottom = 60mm

 

                                                                                                 Amount of force needed to turn wheel

                                                                           Front                            Rear(without load)                          Rear(with load)

             Amount of pedel travel

 

                              10                                             0                                            0                                                     0

                              20                                             0                                            0                                                     0

                              30                                             5                                            0                                                     0

                              40                                             25                                          0                                                     0

                              50                                             50                                          1                                                     1

                              60                                             95                                          10                                                   10

 

The same test using the handbrake

1 click = 70Nm

2 clicks= 80Nm

3 clicks= 85Nm

 

In my opinion there seems to be something wrong with the rear hydralic circuits, because of the fact that the hand brake seems to be working ok

My initial thought would be air or a blockage or incorrectly adjusted rear shoes as mentioned earlier.

But I have checked that the self adjusting wedge is free and working, and because both rears seem to be effected equally, and with there being no change with or without a payload, that is what leads me to think that the pressure regulator is at fault.

Also the rubber brake hoses don't bulge under pressure either.

 

I think I may have answered my own questions here but any other thoughts are welcome before I start replacing parts

[nta16]

Certainly with my car the feel and movement of the pedal is dependant on the rear shoes being set well.  Setting the shoes so that they catch enough but not too much is always a bit of a compromise as I have cheap modern made drums.  Cleaning all of the rear brakes and lubricating where required does help especially if it hasn't been done for a good while.

 

I don't know about the force but you seem to me to have a lot of pedal travel slack, I don't know if your cars are the same but on my old car pedal slack can often be the pedal or it's connection (clevis pin in this case) get ovalled and/or wear ridge(s) on one or both, they can have loads of wear and still operate. 

 

My car doesn't have any fancy bias or adjuster, when the rear shoes are set OK I check the handbrake by pulling it up three clicks and if I can just about rotate each wheel heavy hand push (wear gloves) then it's fine.

 

I don't know about your pressure regulator but to test what getting where at the rear you could try clamping off rubber supply to before split to each side if you have it, and then to each side's rubber supply, by opening bleed valves at at rear cylinder, or before union if required.

 

[D.FYLAKTOS]

22 minutes ago, nta16 said:

My car doesn't have any fancy bias or adjuster

 

Nor Felicia.

[nta16]

3 hours ago, D.FYLAKTOS said:

Nor Felicia.

I must be thinking of another model then, I thought there was something added to the system must be my bad memory.

 

[Thefeliciahacker]

The felicia has an Inline pressure adjustment valve and a load based pressure regulator 

[R_U_AFA]

On 08/03/2022 at 17:52, nta16 said:

I don't know about the force but you seem to me to have a lot of pedal travel slack

Yes, I agree

 

On 08/03/2022 at 17:52, nta16 said:

pedal slack can often be the pedal or it's connection (clevis pin in this case) get ovalled and/or wear ridge(s) on one or both, they can have loads of wear and still operate.

Didn't think about this, will be the next thing I check. Also the acting point between the master cylinder and brake servo could wear i guess. I bet this doesn't get lubricated at the factory.

 

On 08/03/2022 at 17:52, nta16 said:

I check the handbrake by pulling it up three clicks and if I can just about rotate each wheel heavy hand push (wear gloves) then it's fine

That is exactly the same as mine, the handbrake test was to show just how little the rear brakes are being applied with the footbrake

 

On 08/03/2022 at 17:52, nta16 said:

Setting the shoes so that they catch enough but not too much is always a bit of a compromise as I have cheap modern made drums

Yes, only as mentioned earler in this thread felicia drums can't be adjusted. Also I have operated the rears with the drums removed and there is no movement in the shoes untill the foot brake gets to around 45mm of travel. Must admit I have not checked the drums for too much wear, but presumed they were within wear limits because of the good operation of the handbrake.

 

[nta16]

The drums don't adjust only the setting and travel of the shoes which has me wondering if you have the correct wheel cylinders fitted and/or inline pressure adjustment valve and load based pressure regulator are set correctly.

 

Have you renew any other brake parts and hydraulics?

 

I totally forgot about the servo not having one on my car.

 

My old drums were cast with minimum thickness lettering and size on them so that you knew if they'd worn think, sadly not so with the cheap modern made parts but if you have some measuring callipers either in a book or on here you could find out if yours are worn too thin.

 

Edited 9 March, 2022 by nta16

[R_U_AFA]

Checked the brake pedel linkages today, and no free play there

 

On 09/03/2022 at 21:28, nta16 said:

The drums don't adjust

Yes sorry I ment to put shoes not drums

 

On 09/03/2022 at 21:28, nta16 said:

My old drums were cast with minimum thickness lettering and size on them so that you knew if they'd worn

Pretty sure mine are originals from factory, again I haven't phisically measured them, but there are no wear ridges on the insides, and if the drums were worn I would expect to see some as seen as the shoes don't act across the full with of the drum

 

On 09/03/2022 at 21:28, nta16 said:

Have you renew any other brake parts and hydraulics?

I replaced the wheel cylinders 5-6 years back, 100% correct parts, even after that the rears were never the strongest but there were a lot better thn they are now.

 

On 09/03/2022 at 21:28, nta16 said:

inline pressure adjustment valve

Doesn't apply to my model type

 

On 09/03/2022 at 21:28, nta16 said:

load based pressure regulator are set correctly

Almost certain that this is the original one from factory so probabley the correct one. But I have tested with it at both ends of its travel with no difference in results which there should be, that does lead me to belive that this is the part as fault, for example it is stuck internally permantly limiting the pressure to the rears or has somehow got cloged with dirt. In fact I believe so much that this has failed I have already orderd a new one, this part failing would also explain why both rear brakes are weak to the same degree.

 

There is also one other thing I have noticed when operating the shoes, and that is that the trailing piston and shoe tends to move before the leading one, but shoudn't they move together at the same time?

 

And just one last thing, the shoe return and retaining springs, I would say are original, so around 20 years old, now I know that over time they would tend to weaken, but is it possable for them to go the other way and get stronger, meaning more fluid pressure is needed to overcome there resisting force.

 

 

[nta16]

3 hours ago, R_U_AFA said:

Pretty sure mine are originals from factory, again I haven't phisically measured them, but there are no wear ridges on the insides, and if the drums were worn I would expect to see some as seen as the shoes don't act across the full with of the drum

Perhaps that suggests they might not have been working well for sometime.

 

3 hours ago, R_U_AFA said:

In fact I believe so much that this has failed I have already orderd a new one, this part failing would also explain why both rear brakes are weak to the same degree.

In that case see how things go after this renewal.

 

3 hours ago, R_U_AFA said:

There is also one other thing I have noticed when operating the shoes, and that is that the trailing piston and shoe tends to move before the leading one, but shoudn't they move together at the same time?

I would have thought so, but I am not an expert, on anything.

 

3 hours ago, R_U_AFA said:

And just one last thing, the shoe return and retaining springs, I would say are original, so around 20 years old, now I know that over time they would tend to weaken, but is it possable for them to go the other way and get stronger, meaning more fluid pressure is needed to overcome there resisting force.

Not really, perhaps if the parts are all old, crusty, rusty and there's muck rather than any lubrication (if required) they 'd be more difficult to but the hydraulics should overcome it unless things are seized.  If you don't know how old the shoes are, or you know they are very old I would replace them with new and also install a complete new fixing kit which will renew all the springs.  Before installation obviously I'd clean and where required lubricate when fitting new.  You could perhaps wait until after fitting the new pressure regulator to see how good the existing rear brakes are.  I always like to give a really good flushing out of the existing brake fluid and flush cleaning before fitting new parts to the hydraulics.

 

Don't forget your tyres are an important part of the braking system too, if they're gone hard from age and/or lack of use and/or very worn they won't help the braking.

 

If your rear brakes are doing next to no work then it follows the fronts will be working harder so having all four corners working properly will balance things out and improve matters overall.

 

Let us know how things go after fitting the new part.

 

[Thefeliciahacker]

Take it for a brake measurment and report back, I think we are missing the reall issue

[RicardoM]

On 08/03/2022 at 17:37, R_U_AFA said:

In my opinion there seems to be something wrong with the rear hydralic circuits

Obviously. Brake cylinders, brake lines, rear brake regulator (if any)

[R_U_AFA]

Changed the pressure regulator today, and it's made no difference.

I am going to try stick a new set of shoes on to just see if that does anything (I've got them laying around any way)

But it's as if there is still air, or something compressable in the system, but I have bled the system mutiple times, is it possable to get air trapped and not be able to blead it?

On a differant note is there a way to tell if the fluid is getting past the master cylinder pistons?

[nta16]

Random thoughts from me I'm afraid.

 

You want the air to go to the highest point and be released.  I don't know the set up on your or if it has ABS(?) but there are different methods to bleeding brakes and clutch system and perhaps some 'tricks' specific to the model such as elevating one area of the car.

 

Another possibility is air sucking in rather than fluid leaking out, of connections or hoses.

 

Another thing I hear of with my type of car is of new cylinders being boxed with the bleed nipple in the wrong opening to get it in the box and is left like that on installation.

 

Different people favour different methods of renewing the fluid and/or bleeding with some using suction. others a loop in the existing system and others like myself just gravity and/or pumping the pedal into a jar with fluid in it to stop air being sucked in.  I also like to put a bit of grease in the threads of the nipples to create a seal around them and stop the possibility of air being pulled passed the threads.

 

Another old trick is to wedge a stick between the peddle and seat front so that the pedal is pushed and held down at least overnight to allow air bubbles to rise.

 

You could also go round and one by one open a bleed nipple and see if fluid comes out as it should, close it off and try the next one in line.  The reverse of that is to look for weeps by cleaning each point then putting some talc, fine sawdust or paper tissue on the areas to see if any wet shows up.  

 

If you mean could the master cylinder be leaking within itself then yes it could.

 

New shoes could make a difference if the current shoes are wrong in anyway and not taking up the gap, same if the it's the wheel cylinders.

 

Can you adjust the shoes out to lock the wheel up?

 

I've just cleaned and lubricated the rear drums on mine and had to completely reset the shoe adjustment which should be easy but first attempt was far too close and second attempt too loose, third attempt I can't remember if it's better or worse than before I started but I will do more then road test each time until it feels about right on the pedal.

 

Could you put in a long high remote bleed pipe and put more fluid through to allow the air to a very high point, I'd be using tube and jam jar with fluid seal.

 

That's me out of ideas, before I started the post really.

 

Edited 3 August, 2022 by nta16

[D.FYLAKTOS]

13 hours ago, R_U_AFA said:

 but I have bled the system mutiple times

 

In what way, manual or with pump?

[R_U_AFA]

I have been using a pressure bleed kit, but when I wasn't happy with that I did it manually using the 2 man method.

But with a pressure bleeder, I believe that air shouldn't be able to be sucked in because the fluid is always under pressure(that is so long as it is attatched to the system)

Anyway today I found a slight drip from one of the unions that I had disturbed, so that could have been sucking in a little air.

I'm going to have another investigate over the next few days.

 

21 hours ago, nta16 said:

I also like to put a bit of grease in the threads of the nipples to create a seal around them and stop the possibility of air being pulled passed the threads.

Seen this trick done before, must admit I had forgotton about it, but again it shouldn't be necessary with a pressure bleeder

 

21 hours ago, nta16 said:

You could also go round and one by one open a bleed nipple and see if fluid comes out as it should, close it off and try the next one in line

I have done this and fluid does come out, my only problem is I don't have a refrence as to what shoud be a correct amount. All it confirms to me is that the pipes are not totally blocked.

 

21 hours ago, nta16 said:

If you mean could the master cylinder be leaking within itself then yes it could.

Was just wondering if there was any obvious symptoms that would indicate this, I not sure if this is at fault because if the master cylinder piston seals were faulty wouldn't I have poor braking on the front axle aswell.(I believe the felicia has a diagonally split breaking circuit)

But also I heard somewhere that if you trap air in the master cylinder it's hard to get rid of.

 

21 hours ago, nta16 said:

Can you adjust the shoes out to lock the wheel up?

No, as mentined earlier in this thread there is no way of manually adjusting the shoes. In theory it is done automatically, I suppose the wedge that does the adjustment could have become worn but it looked ok. Just as a test along this line I could place some shims between the shoes and wheel cylinder it see if it locks up the wheels. Also I will point out that the handbrake does lock up the wheels.

 

Anyway I going to have a tinker and see how I progress, it's just that this is starting to annoy me, and it isn't helping with wear on the front brakes either.

[D.FYLAKTOS]

11 minutes ago, R_U_AFA said:

I have been using a pressure bleed kit, but when I wasn't happy with that I did it manually using the 2 man method

 

Me too, i had a sort of ''sponge feel'' (as we say it here) after the mechanic changed a brake pump.

I told him but insisted that the pump-bleed-add new brake fluid is ''the New way, much better'' etc so by first chance i went to another repair shop with a stictly order ''i want the old-school method with two persons'' and guess what?

When i took my car things were much better then before, by instict i didn't liked the modern method, i wasn't convinced that it can remove completely the air bubbles from the system.