HPP PRX Se pedal problem

[Kek700]

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.
Sorted.

 

[stigs2cousin]

Sorry to hear that. That is probably the seal of the piston sticking to the walls of the master cylinder.

In my motorcycle days I used a "brake cylinder paste" from a big brake manufacturer to get the pistons of my Brembo four pots moving again.

Only worked for a few month, best best solution was a complete remanufacture by a master technician who took everything apart and changed the seals.

(So if the pedal set is new enough " make it the manufacturers problem " and have it serviced on warranty.)

OK, scratch that. Just googled the pedal set, warranty should be expired by now

If you feel confident enough to dismantle the brake master cylinder yourself, this is what I used in the day:

ATE ATE BRAKE CYLINDER PASTE CONTAINS: 180 GRAMS

Buy ATE ATE BRAKE CYLINDER PASTE CONTAINS: 180 GRAMS at Louis Moto for a great price. Top brands ✓ Great selection ✓ No risk ✓ Secure payment ✓ 2 year return policy ✓ Free returns ✓

www.louis-moto.co.uk

It´s not rocket science, doesn´t need a lot of tools and is probably well discribed online.

On the other hand working with DOT brake fluid is a bitch.
You have to keep everything very clean and DO wear glaves/goggles.
( Which I of course totally did in my twenties )
After disassembly and cleaning, lubricating and reassembly you have to bleed the brake exactly like your car, bike, motorcycle.

Good Luck Carsten

 

[metalnwood]

If they have had some use, they could be on their way out. Between myself and a few local guys we all had to get our one rebuilt.

 

[Kek700]

Just to ask, by rebuild do you mean seals, are we talking about the master cylinder or slave, perhaps both?

 

[metalnwood]

What seems to have happened to a number of hpp pedals over the years is that the piston destroys the master cylinder. The theory being that because the geometry of the the way the pedal pushed in the piston which is not straight, it creates some uneven friction over time inside. It does seem to be an issue more for people that brake harder. The three sets that I have used all had that replaced.

 

[Kek700]

I have looked at his latest pedals, they have the master cylinder always angled correctly due to a pivot point at its base.
So I suspect this is as you said a design issue, not sure on my next move, may try and raise the whole assembly to change the master cylinders shaft entry angle.
Unfortunately with out stripping them down and hence not knowing what is going on inside it is all guess work.
Pity Barry Rowland did not do a full strip down in his video.

 

[stigs2cousin]

I know it´s not how it´s done these days, but:

the manufacturer is still active, why not contact HIM for a solution?
The problem seems to be a design flaw, so he should have an interest in finding a solution.

Some companies (cough, Heusinkveld, cough) go above and beyond with after sales service.

So if the walls of the master cylinder are scored the best solution is to replace the whole assembly.
It may be possible to bore and polish the cylinder for oversized piston and seals but that
I´d contemplate for a 1938 Silver Arrow, much to expensive for simracing pedal.

Good luck Carsten

 

[Kek700]

I have tried, not a man of many words in this instance. ( none ) i have just mailed him again pointing out that
I am happy to pay for replacement parts, will reply to this article if anything is resolved.
A beautiful set of pedals they are too.

 

[Kek700]

To report, I stripped it down as far as was necessary, left the slave cylinder alone.
After all it has and does have a perfectly straight path, so scoring should not be a problem.
Looking at the master cylinder and depressing the piston again I could seen no scoring or ridges
What I found was a quite a top class piece of workmanship, have looked at many master cylinders, never seen one so well made, including quite a number from lower ranked formula cars.
At that point, after looking inside I decided to follow the above advice, altering the angle of the push rod attached to the brake pedal to try and reduce it’s diving action and make it’s travel avereage a straighter Path.
Next I used a lot of silicon based grease and liberally applied it to the bore lining and the end of the push rod, finally bolting it back together..
Now I have a smooth hydraulic brake pedal, is hydraulic better than a mechanic load cell.
No, I actually prefer my mechanical load cell peddles, better in almost every way.
But they just do not look anywhere as an impressive bit of engineering, they do not have the more realistic weight to them that these hydraulic pedals have, they also do have a more realistic feel to them, that hydraulic feeling, especially on release.
I am very pleased with my bargain priced pedals, never do I cease to be dazzled by their mechanical appearance, and now I can match my load cell brakes in performance.

I have still got to do a bit more experimenting with a larger variety of rubbers to try and give them a better definition as they pass from min to max pressure.
Hopefully informing me where I am a bit better in their travel, I would like them to tell me that I am at about 80% of their retardation rather than only relying on muscle memory.

Probably just put the kiss of death on the pedals now by saying the above, will be back to where they were next time I use them
But a bit of success is still better than none.

 

[metalnwood]

Excellent news, glad they are up and going I am on load cells now as well, just because I wanted peace of mind.

It hasn't put me off hydraulics, they are still nice but if I ever go back to them it will be with a set that will take easy to acquire parts off the shelf, no more custom hydraulics for me.

 

[Kek700]

He he, I am going to hang on to my HE Pros just in case. This has made me appreciate them more, so good they are too..

 

[blazze]

I have the same issue. Brake is sticking in the beginning afterwards it's fine.
I asked HPP and you can see the instructions below.
I did everything and its still sticking. I even opened them up completely afterwards to give them a clean.

I asked for the seals and this is the one used for the master cylinder:
X-Profile Oil-Resistant Buna-N O-Ring

I'm not gonna send the pedals in for repair and I'm using my old HE Pros for now.
I preordered the Simagic P2000 Pedals, they look quite similar to the HPP.
I will try to order some seals but I'm located in Germany and don't really know where to get them here. If anyone wants to order some of these. Please send me some over.

Edit: Found a shop in Germany, you can contact them in english too

Hi Blazze, You can rebuild the system yourself if you want to.
If you send it in, it would be @ $250 for use to do it.
Below are the bleeding instructions.
These bleeding instructions require a pressure-bleeder or syringe with hose.
Do not use brake fluid, use light grade motor oil. Make sure to wear safety glasses!

Remove the bumpers Press on the brake pedal a few times to make sure everything moves freely Disconnect the brake pedal clevis so the linkage is disconnected from the master cylinder

Remove the master cylinder top plate
Remove the screws on the front plate of the master cylinder, allowing the plate and shaft to be removed
Crack the bleeder valve (on top of the slave cylinder) @ 1/2 turn
Carefully twist and pull out the master cylinder plunger so it is ¼” from the face of the master cylinder.

Use a set of needle-nose pliers, go slow and be careful not to pull it out all the way when it becomes free. This is the hardest step. Twist as you pull.
Be ready for it to want to pop all the way out and avoid that if possible.
Attach the feed tube of the pressure bleeder, or the feed tube from the syringe to the bleeder valve
Slowly pump the fluid into the system via the pressure bleeder or syringe
Slowly feed the fluid until you see it come out of the hole in the bottom of the reservoir in the master cylinder
Close and tighten the bleeder screw
Re-install the master cylinder front plate and shaft back onto the brake pedal via the clevis.
Now use the brake pedal and slowly push the dome part of the master cylinder shaft onto the front side cup of the master cylinder piston.
Press the brake pedal inwards all the way and hold it in all the way (do not release the brake pedal).
While you are holding the brake pedal in this position, re-attach the front plate on the master cylinder.
Test the system by pressing on the brake pedal, ensuring the slave rod moves in-sync with the pedal movement.

 

[Kek700]

At the moment my pedals are okay, many many thanks for the above information.

PS
Where you show the 1/4", I filled it with silicone grease, inside that housing.
I also have free play before the rubbers make contact, the stiction is there when I first press the pedal, but as I have about 1/8" free play I do not need to build any pressure before I depress the pedal and rubbers.

 

[stigs2cousin]

I have the same issue. Brake is sticking in the beginning afterwards it's fine.
I asked HPP and you can see the instructions below.
I did everything and its still sticking. I even opened them up completely afterwards to give them a clean.

I asked for the seals and this is the one used for the master cylinder:
X-Profile Oil-Resistant Buna-N O-Ring

I'm not gonna send the pedals in for repair and I'm using my old HE Pros for now.
I preordered the Simagic P2000 Pedals, they look quite similar to the HPP.
I will try to order some seals but I'm located in Germany and don't really know where to get them here. If anyone wants to order some of these. Please send me some over.

Edit: Found a shop in Germany, you can contact them in english too

View attachment 499807

Man,

that reminds me of fiddling with bicycle brakes .

At least it´s engine oil, thats less nasty thanDot brake fluid.



@Kek700 i can`t imagine where the stiction would originate.??

You greased the piston and the rod, is there a bushing or seal the pushrod sticks to??
And how far in did you push the piston? ( with rubbers removed so that the master and slave cylinder could travel "all the way")
If you just greased in front of the piston maybe you didn´t reach/see the location of a possible scoring?

MFG Carsten

 

[Kek700]

No, it is virtually free-floating, not really convinced about the silicon grease, but it made me feel better.
No again, could only push it in so far, it was really just a look and see, it is quite a confusing issue.
I have just ordered some master cylinder seals from Germany, I may just have to strip it out and see what it is like all the way down the bore.
It is really difficult to think of a possible cause when you have not got a schematic of its internals.
At present I have left a 1/8th inch gap, from the rubbers to push rod, so now the stiction is less noticeable at present on the first application and then generally it appears relative to the amount of use it has on a circuit.
The only odd thing is the piston has more free play than I thought it should have, but I am no brake master cylinder expert.
So if it has created a ridge you can see why it may be possible, I do notice his latest Hydraulic pedals have the master cylinder always in a direct line.
That and what I have just said makes me think you are correct.

 

[blazze]

Behind the plunger is only a spring that pushes it out again.

 

[Kek700]

I am reading as much as I can find. I have now raised the master cylinder up by 3 mm.
I put a rubber bung behind the pushrod.
Now the pushrod is actually pushing on the master-slave cylinder piston further down the bore. ( I really don't know why I did this, probably out of desperation )
I did this after re-reading the above and a couple of reports on this problem, which made me realise that stripping, new seals, etc, etc, was probably not going to be very productive.
At the moment it seems better, but as with all my other attempts I am expecting a failure.

By the time I have gone in a fruitless full circle, I may have actually got used to it and now do not notice it anymore.

 

[blazze]

I installed the new seal today and it didn't help. It's still sticking... I think the cylinder is worn down on the inside and needs a full replacement. I even tried to smooth it down a bit with some steel wool. Not sure what to do next. They are a few years old now and I don't really want to invest any more money into these pedals. With a new brake cylinder it's just a matter of time before it happens again.

 

[metalnwood]

I would move on if I was you ,go to some other hydraulics if you want to stick with them. Might be worth paying him the money to replace it so you can sell it on with some profit as coming with 'new' hydraulic unit. I got it done for free and so did lots of people back then but sounds like hes got past doing that as the number of units coming to him adds up.

 

[Kek700]

I know that it is difficult to explain, but can you attempt to.
It is almost a certainty that I have the same prolem as you.
I put the rubber bung behind the push rod in the hopes that it would push the piston further up the bore, in the hopes that if there was some ridge that had developed it would now by pass it.

So it is useful to me to know what you are trying to achieve by cleaning it.

You can buy very cheaply a small bore honing kit, powered by an hand held electric drill from eBay for about $10 or £6 .
if any of the marks you talk about are not too deep the seal after honing should be okay.