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HPP PRX Se pedal problem

Kek700

Premium
I have some HPP PRX pedals, I really wanted to see if all the positive reviews are justified about hydraulic pedals.
Unfortunatly mine have a lot of initial stiction, you could say a notch‘y start.
After that they are rather good, but every time I press them I have to go through a notch‘y start.
This is very annoying, it spoils their overall affect.
Has anyone got an answer, I have tried silicon spray, i just put it on the master and slave push shafts to some affect, soon back to that notch’y start.:mad:
 

Kek700

Premium
The reason I am putting a spacer under the master cylinder is because the push rod has an angle to the piston, which is certainly enough to cause the piston to be tilted in the bore when faced with a force. Is that the case? I don’t know, but it does for the time being helped quite a lot..
I am trying to do this and keep the integrity of the brake, I do not want a none working system.
As I really like these pedals.
If all else fails I will be going down the honing route.
 
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Neilski

Staff
Premium
I'm very curious about how the mounting for the cylinder is creating an angle on the piston. Is there by chance a photo in circulation which explains the problem?
 
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stigs2cousin

Premium
I havn´t found a good picture let alone a technical drawing for the problem, but I think you can visualize with this view:


The pivot on the brake pedal travels on an arc, in this case on the picture it will go down slightly when depressing the brake.
So then the pushrod should exact a downward force on the piston and cylinder wall.
I guess thats why HPP redesigned the cylinder assembly and put it on a swivel so it can stay straight to the movement of the pushrod al the time.

Here you can see the "exploded view" of a brake master cylinder (for a MZ motorcycle, an East German prime example of "achieving more with less" :cool:):


You can clearly see there is a swivel joint between cylinder and pushrod.

So the bigger the backward angle of the pedal is the more force it directs to the cylinder wall and the bigger the stiction and the danger of scoring.

( Flash thought: would it be possible to change the pedal to a 90° angle to the master cylinder and get the desired pedal position by changing the mounting solution.
Second thought: you already did that by raising the master cylinder :redface:)

I think the only long term solution without involving spare parts from HPP would be to bore out the original assembly and "sleeve" it with a more durable steel insert.
( The cost of which would surpass the value of the pedal set by a great margin.)

About a cheap honing set I´d advise caution, the things have to be manufactured to a very high precision or they could make things worse.
If your desperate you could try a wooden dowel with a very fine sandpaper on a drill ( polishing quality) to try and even out the cylinder bore.

MFG Carsten
 
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Kek700

Premium
I checked the fluid levels, I now have a leak, honing it is then.
Edit, just read your last post. :-/
Glad I kept my HE Pros. :)
 
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I got the same pedals a year or so ago used with very little miles. Within a year, both the orange rubbers failed and thankfully a buddy made some poly ones which work.

I have a lot of free play before the pedals stats to register pressure and probably due to fluid loss. Being in the UK, shipping them back isn’t an option.
 
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I checked the fluid levels, I now have a leak, honing it is then.
Edit, just read your last post. :-/
Glad I kept my HE Pros. :)
I just bought a set of these pedals 2nd hand. the quality is good as well but it seems the pedals have the same issue as is being explained here.
How did u check the fluid level? do you just open the cover on the top?
why would we fill the system with engine oil and not DOT brake fluid?
also why are we filling fluid through the bleed screw from the instructions posted on page 1?
 
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Andrew_WOT

Premium
By reading all these threads makes me wonder if hydraulic pedals really belong to sim racing at all?
What do you gain from them versus "dry" pedals like HE Ultimate for instance. Do they really feel better when all the feel feel is in a rubber stack and hydraulics serve only to transfer pressure to load cell?
 
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metalnwood

Premium
I have had the hpp's and now the he ultimates. Before the HPP's I had the old CST load cells.

I guess that the HPP's still feel like other hydraulics and they do feel different. I guess its a matter of taste because performance wise they are the same for me and from anyone else I have heard from.

I got the HPP's because the CST's were a bit dated on looks and I really wanted to see what hydraulics were like. The feeling was nice but once I had the problems I had no problem going back to load cells for peace of mind that I wouldnt have any issues that would take me out for a long time.

I think that once you go to really hard rubbers on hydraulics they start to feel a lot more like load cells anyhow.
 
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Kek700

Premium
I found the leak, it was due to the piston seal going past the fluid level hole allowing the fluid to run onto the piston and out the back of the master cylinder. ( I had mistakenly put dot 4 into the reservoir ) :( Makes me think the reservoir should not have anything in there ? Maybe an occasional bit of oil to lubricate the piston,no instructions, so who knows.:O_o:
I get a feeling that some oil will bleed onto the piston lubricating it, the use of brake fluid was so runny that it just poured out of the piston.
I am experimenting at the moment with fluids, I checked the master and slave cylinders for wear, they are perfect.
I have noticed using dot 4 there is a lot of initial stiction on the pedals. I think it is known as stick slip.
I have a feeling that using oils as opposed to brake fluid may possibly reduce this. ( again who knows )
my next step is to try mobile1 0 W 30 as I have some.
bleeding is easy, just open the bleed screw wide, pour fluid into the master cylinder with it vertical and it naturally bleeds itself.
Using oil will be a big advantage as dot4 is nasty stuff.
I have been using my HE pros in the mean time so I can make a reasonable judgement, I just much prefere the hydraulics for feel and a much more life like feeling to them, but as mentioned above that is with the soft rubbers, with the two black rubbers I do not think I would get the same response.
Anyone got any oil suggestions.:)
 
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stigs2cousin

Premium
I found the leak, it was due to the piston seal going past the fluid level hole allowing the fluid to run onto the piston and out the back of the master cylinder. ( I had mistakenly put dot 4 into the reservoir ) :( Makes me think the reservoir should not have anything in there ? Maybe an occasional bit of oil to lubricate the piston,no instructions, so who knows.:O_o:
If you have a look on the "exploded view" i posted you can see the working principle of a brake cylinder.
It´s supposed to go over the "fill hole" because if i didn´t it couldn´d built up pressure.
The oil would just evade into the reservoir.
It´s also ok that the piston gets oil on the sides through the fill hole because that should lubricte both seals and prevent sticking
( at least in theorie.)

I was just thinking that this problems are related to the lower brake forces compared to cars with brake boosters where the stiction would be "overwhelmed" by the boosting forces.

The use of any kind of engine oil should be fine, it does not have the temperatures we see in an engine and there arte no bearing pressures to consider.

But i can´t give advice what lube to use on the seals my first idea "assembly lube" would be washed away by the oil eventually.

MFG Carsten
 
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Kek700

Premium
Took your advice, just used mobile1 0W40, at present cannot see any reason to experiment.
There are hydraulic fluid that are expressly used for stick slip in hydraulic sysyem.
I may go down that route , but I am not sure that I want to get over involved.
Oiled the the cylinders before assembling after throughly cleaning.
The stiction is much reduced, after talking to HPP there is normally a small amount which should go after the first application.
Also as advise above I have a small amount of free travel , so the pedal only needs to initially deal with the stiction before building pressure.
Not sure if that is much help.
Will put them back and see how it goes, the Dot 4 certainly gave a more immediate response, the oil gives it a softer feel.
 
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Anyone able to tell me if there should be a seal where the pushrod of the brake pedal pushes against the master cylinder?
I noticed some black stuff running out the front when I got them in the mail and the shaft of the rod was really sticky (No pun intended lol)

Took the front cover off and I can't tell if its grease just hardened up or if its an old seal that has destroyed its self. Any ideas?
20210904_004148.jpg
20210904_100041.jpg
20210904_100104.jpg
 
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stigs2cousin

Premium
That looks like old and dirty grease to me. I don´t think a seal could desintegrate there without some pieces remaining.

Is the pushrod contained by a bushing or are the pedal and the piston the only contact points?
From the picture I´d guess there is no bushing because the pushrod is not centered in the "lid part".
If that is correct the stiction is between piston and cylinder and I´m out of ideas.:(

Sorry Carsten
 
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stigs2cousin

Premium
Will put them back and see how it goes, the Dot 4 certainly gave a more immediate response, the oil gives it a softer feel.
From my perspective the pressure feeling should not differ much as fluids should not be compressible.
The special properties of DOT are holding up at higher temperatures and for the last 25 years be viscous enough for the very small valves of ABS/ESP systems.

Maybe you can try to bleed it after the instructions as there might be an air bubble somewhere.
(Which again reminds me of faffing around with bicycle brakes, thank god Maguras, so mineral oil, not DOT .:cool:
You had to position them right to leave no cavities under the oilsurface and pump the oil in and out to "find" the last bubble.)

MFG Carsten
 
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Here is the issue I'm having. Sorry for the **** quality of video.

There is a substantial amount of movement in the pedal before the hydraulics engage the slave cylinder to pull the rod of the slave cylinder.

 
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Kek700

Premium
I am only a one day expert, as far as I can tell there is no bush, at least mine does not have one.
If the piston moves too far forward it will leak as shown in yours.
Easy job, remove master cylinder after disconnecting the pressure sensor from the electronics board, photo it first to see where they go.
Remove the four bolts from the slave cylinder, pull it apart including the piston with spring.
Now pull the master cylinder piston out with its spring.
Now check for scoring in both cylinders, should be none.
Though cleaning, then tip the unit so that the master cylinder is vertical after replacing the slave cylinder piston and spring with the four Allen bolts, making sure to lubricate the bore with a low viscosity oil, I used 0W40 mobile1.
This is what you are going to use, not brake fluid.
Open the bleed nipple, removed mine, fill the master cylinder with oil.
It will virtually bleed itself, tighten the bleed nipple.
Push the master cylinder in release the bleed nipple slightly and with the piston push the fluid through making sure all the air has expelled.
Tighten the bleed screw.
The master cylinder piston should be about flush with the master cylinder housing, bolt it back and you are good to go.
If your bores are scored, the above is of no use, you can buy honing stone for this bore diameter from eBay.
Then apply the above.
I have short cut the description because it will all become apparent as you go.
Took me about an easy hour to do the above.
 
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