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Author Topic: more brakepower at the back  (Read 10557 times)
Oskar
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« on: August 16, 2008, 01:54:09 pm »

i wounder how to make the rearbrakes more effective.
I think i need to move some brakebias to the rear, now the front left locks when the rest doesnt.

is there a valve or something?

ive recently done the rearbrake ovehaul without problems
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peugeot 205 gti
murena 1.6
Anders Dinsen
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« Reply #1 on: August 16, 2008, 03:35:38 pm »

I'd strongly recommend against making any modifications to the brake system as you can quickly make it worse, and unless you have free track access to perform a good deal of testing, chances are you will.

That said, however, you could have a problem. Though, I also find that it is very difficult to lock the rear brakes on my Murena too - and I know they are in perfect balance. The reason is that there *is* a valve. It's located in front of the right rear wheel. The is a small bias towards the rear on both the 1.6 and the 2.2 (though I think it's more on the 2.2 due to the brake caliper being mounted a bit further out than on the 1.6 - but that would matche the heavier engine), but when the brake pressure rises above some 17 bar, the valve starts reducing the rear brake pressure. This is to compensate for the shift of load from the rear towards the front during braking, and is absolutely necessary on a car with powerful disc brakes on the rear. (ABS would make the valve unnecessary, but that's another story.)

The valve explains why you generally cannot lock up the rears on dry road with good tyres.

If you'd like to have better braking, I suggest you change to EBC Greenstuff pads. They give excellent bite. They need a slight bit of warming up to bite fully, but nothing serious, and once they're running, they give you far better braking than many modern cars! They like being used Cheesy

Cheers,
Anders
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1982 Talbot Matra Murena 2.2 prep 142
2017 BMW i3 "Charged Professional" 94Ah

Used to own:
2001 Renault Matra Grand Espace "The Race" V6 24v
1997 Renault Matra Espace 2.0 8V
1987 Renault Matra Espace J11 2.2
Oetker
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« Reply #2 on: August 17, 2008, 12:31:48 am »

Or change the valve for a T piece and mount adjustable valve in the front in between the rear pipe, so you can adjust the balance ideal to weathercircumstances.
I noticed in the weth that a bit more bite on the rear would be welcome.
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I feel like Jonah, only my fish looks different.
Murena 2.2 Red 1982. Murena 1.6 black on places.
matramurena
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« Reply #3 on: August 17, 2008, 10:05:18 am »

I use this one. Works great!

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1983 Matra Murena V6 (AR engine)
2003 Matra Avantime 2.0T Expression
2003 Matra Avantime V6 Privilege
Anders Dinsen
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« Reply #4 on: August 17, 2008, 11:57:39 am »

I wouldn't touch any of this!

It's illegal to tamper with the brake balance on a road car, and Matra spent a lot of time testing the car on track, so I still feel it's a bad idea to change anything. Certainly not to improve the car in the wet, where you don't want any bias towards the rear. The Murena becomes completely uncontrollable if the rears are allowed to lock up!

I once did a 180 degree spin on a wet road in a corner. I was a bit too fast and the rears lost traction because I lifted my foot from the trottle. This caused a bit of engine braking, and the car went off-limit and out of control. I went from driver to passenger in a fraction of a section, and I never got a warning before it happened.

It was NOT funny, but I'm glad I've tried it. It did it on a training track, fortunately, and I must admit that Roy and I were deliberately pushing things Wink

But this is where the Murena can become a dangerous car: It performs so excellently, but unlike a front engined car, you don't get any warning before disaster kicks in. The steering wheel becomes a bit lighter when the front end starts loosing traction, but that's about the only hint you will get that you are nearer to the limit than you were before.

On a road car, I'll always prefer understeer from oversteer. I can react to understeer during braking by getting off the brake and back on, and I'm still the one *driving* the car. Oversteer, however, is dangerous, because when you loose grip on the rear end, there's nothing that can bring it back. Have you seen what happened to Minassian during the test weekend before Le Mans?

Oskar, I know you're going to Sturup next weekend (I wish I could be there!) and obviously you'd like to outperform a few fellow cars. The track is extremely 'curvy', so you might have a chance, but it will be difficult. Murena is a lot of fun (!) and a good deal of comfort, but it's not a 'super-fast' car. It was just never designed to be so.

- Anders
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1982 Talbot Matra Murena 2.2 prep 142
2017 BMW i3 "Charged Professional" 94Ah

Used to own:
2001 Renault Matra Grand Espace "The Race" V6 24v
1997 Renault Matra Espace 2.0 8V
1987 Renault Matra Espace J11 2.2
roy4matra
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« Reply #5 on: September 07, 2008, 12:05:20 pm »

i wounder how to make the rearbrakes more effective.
I think i need to move some brakebias to the rear, now the front left locks when the rest doesnt.

is there a valve or something?

ive recently done the rearbrake ovehaul without problems

I'm sorry but altering the brake bias is not something anyone should be doing on a road car, and I agree with Anders, leave this alone.

If you have a front left locking up then that only proves the brakes are not correct nor as they were designed.  I have had my Murena from new and know that if the brakes are correct as designed, they are brilliant and do not need any modifications.  However, you can improve them easily by fitting green (or redstuff) kevlar pads.  These should only be fitted at the front or all round - do not fit them only to the rear.

Anyone must rectify their problems first before starting to look at modifications.  The car didn't need improvement before so why should it now?  The reason is they are not correct, and carrying out modifications will only hide the fault, until something fails...

Roy
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krede
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« Reply #6 on: September 10, 2008, 08:07:33 pm »

If you have trouble with the front end locking up I have one word for you before you change anything else...

Tires!!!

When I bought my car the front brakes would lock up all the time... it was quite scary.. and horrific under steer  was also an issue..

A new set of tires made so much of a different you'd have to experience it to believe it!

Shock absorbers and suspension bushes might also be worth checking. 
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Oetker
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« Reply #7 on: September 10, 2008, 08:42:42 pm »

I have to agree with Krede, just standard wheels 185x15 en Michelins do a lot.
In the past there was a saying.
French cars, French tyres.
I keep to that.
Also I puted on new stab rubbers and the rubbers unther and above the shocks.
All togheter it made a world of difference.
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I feel like Jonah, only my fish looks different.
Murena 2.2 Red 1982. Murena 1.6 black on places.
Anders Dinsen
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« Reply #8 on: September 10, 2008, 09:23:28 pm »

French cars, French tyres.

That's rubbish... sorry Wink It might have been correct back in the time when the car was built, but modern tyres are just so much different than the ones used 25 years ago: Compounds are different, carcasses are built differently, and tyre patterns are different.

And Michelin is today a big business (the worlds largest tyre company, I think?), and they supply tyres everywhere: German, French, Japanese cars etc.

Further, I think Michelins are generally relatively hard in the compound. This favours fuel consumption and mileage, but not performance, and to be honest, I don't care as much about the two former factors as I do about the latter. My car does no more than 5000 km/year, so I'm looking for soft compounds - and chose Japanese tyres: Yokohama. I know they aren't french or original to the car, but I can live with that! And I don't have understeer or lockup problems, even when I'm pushing it!

I know Krede has a different make, but the real difference comes from the age of the tyres. Old tyres become hard and no longer grip well to the surface. I think that was also the point Krede was making.

- Anders
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1982 Talbot Matra Murena 2.2 prep 142
2017 BMW i3 "Charged Professional" 94Ah

Used to own:
2001 Renault Matra Grand Espace "The Race" V6 24v
1997 Renault Matra Espace 2.0 8V
1987 Renault Matra Espace J11 2.2
krede
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« Reply #9 on: September 10, 2008, 09:42:00 pm »

Krede's point : Fitting a new set of tires improved breaking tremendously. 

And krede would like to add that the the tires he discarded weren't at all "worn down".... they had plenty of track left... but , as Mr.Dinsen points out, they were old and "hard".

Claiming that French cars run better with French tires , is pure nonsense to me.

Ps: Krede's car is on Michelin tires.
« Last Edit: September 10, 2008, 09:45:20 pm by krede » Logged
Oetker
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« Reply #10 on: September 10, 2008, 10:11:51 pm »

I don't have to much material to compare.
In the past I had so many shitty tyres unther my cars
You can't ask to try them first.
Compared to the Firestones that were not old, and not at the end at all, the Michelin energy 3A  210km/h feels fine for me at the front.
Not hard at all.


The other choice would have been Pirelli P6.
On the other hand, there are a pair very old Viking tyres on the back, that make the car almost comfortable.
It is a personal choice, and I always fall back on Michelin, whatever.
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I feel like Jonah, only my fish looks different.
Murena 2.2 Red 1982. Murena 1.6 black on places.
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