[Neil Roy]

Hi Guys,
This is my first post, or rather query to Team BHP public forum, although I've benefited enormously from the modifications which many forum members had done to their boleros' and I've incorporated the same after clarifying with them by Private messages.
My ride is a 2007 model Bolero SLX. Ive installed Bilsteins thanks to Jose Peter's review and his personal advice. I'm faced with an unique problem. Right from the time I purchased my bolero, I've observed that at speeds in excess of 50, when you slam the brakes the rear locks up. The entire braking circuit was serviced completely while under warranty twice but the problem still persists. The reason given was that it is an inherent problem with all Boleros, same as the vibrations we get when you cross 60 in 4th gear or 70 in 5th gear. One must live with it- or at least that's what the service engineers were discreetly trying to tell me. After installing the Bilsteins, the handling and ride comfort is enhanced, leading to increased speeds. So what was an irritant at 60 (rear Wheel lock) has become a nightmare at 80-90. Now when I'm driving on highways, I have to be extra watchful as I know that my vehicle cannot stop as quickly as I want it to. Ive narrowed down my query for increased braking into Four components.
1) Tyre Size Upgrade - Has anybody done that with reference to this specific problem and got positive results.
2) Booster / Master Cylinder Kit Upgrade - Again has anybody done this to solve this specific problem
3) Front disc Rotor/Caliper Assembly - This is where this discussion gets interesting. Bolero Storm, CRDE has got a bigger Disc Rotor- Caliper assembly with Twin Pistons. Has anybody done this.
4) Adjustable Proportioning Valves - The Bolero comes with stock proportional valves for the rear. Has anybody tried adjustable proportioning valve to their vehicle.
There is an interesting article regarding this topic, but I do not know whether posting such links is allowed, as these guys are advertising their products also(Obviously).
So guys, I'm waiting for your valuable inputs, and please include the cost component also.
Mods : I tried searching for this specific query with regards to bolero, but couldnt find any.
Neil Roy

[G-BoleroBoy]

I had faced similar problems. Now mostly it is solved, however sometimes rear tends to lockup and screech (noticeable only in office basement kind of quiet and smooth surface). I dont exactly remember what has solved this problem, as I did way too many things.
1. Tyre size - changed to 235/75 R15
2. Cylinders were replaced recently (after 60K kms) as earlier ones were completely worn out as brakes had jammed
3. Front disc - replaced some 5K kms earlier as they were warped and were shuddering endlessly while braking
4. Not sure of this.

[SPIKE ARRESTOR]

Originally Posted by Neil Roy

Hi Guys,
I've observed that at speeds in excess of 50, when you slam the brakes the rear locks up.
3) Front disc Rotor/Caliper Assembly - This is where this discussion gets interesting. Bolero Storm, CRDE has got a bigger Disc Rotor- Caliper assembly with Twin Pistons. Has anybody done this.
4) Adjustable Proportioning Valves - The Bolero comes with stock proportional valves for the rear. Has anybody tried adjustable proportioning valve to their vehicle.

Roy, your vehicle comes equipped with a Gravity Proportionate valve (GP Valve) get it checked if it is working properly/blocked etc.

Bolero Storm does not come with a Twin Pot caliper, it is Single pot.

Spike

[Neil Roy]

Thank you guys for your inputs thus far. As I understand it, barring a tyre size upgrade which may or may not solve this specific problem, it is safe to assume that the crux of the matter lies in the brake bias or more importantly, the role the proportioning valve plays in determining this brake bias.
Spike Arrestor, you mentioned that Bolero SLX comes with Gravity Proportionate valve. To quote the definition given in the world wide web “The Gravity proportioning valve is a safety device which is installed at an angle of 45 degrees. What this does is, during sudden braking, it reduces the air pressure sent to the front brakes by half so that the driver is able to steer the vehicle even during sudden braking.”

Gravity Proportioning Valves Exporter,Chennai,Tamil Nadu,India

However what everybody mentions about the role of the standard proportionate valve is this –
“Proportioning Valve
The proportioning valve reduces the pressure to the rear brakes. Regardless of what type of brakes a car has, the rear brakes require less force than the front brakes. The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight on the wheel. More weight means more brake force can be applied. If you have ever slammed on your brakes, you know that an abrupt stop makes your car lean forward. The front gets lower and the back gets higher. This is because a lot of weight is transferred to the front of the car when you stop. Also, most cars have more weight over the front wheels to start with because that is where the engine is located.
If equal braking force were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force. If the proportioning valve were set to 70 percent and the brake pressure were 1,000 pounds per square inch (psi) for the front brakes, the rear brakes would get 700 psi ".

HowStuffWorks "How Master Cylinders and Combination Valves Work"

Now I’m thoroughly confused. What gives here? Both are contradicting each other.
On a similar vein, the main spares dealer for MM in Chennai told me that Bolero Storm has twin pistons. If you are sure that it is single Piston, is it possible to have a direct Bolt On Switch of Rotor and caliper with the existing brake circuit assembly from Storm to SLX? And more importantly will it get the desired result of increasing the front bias? The same dealer said that it is possible, but after spike’s feedback I’m not sure I can take the dealer’s word for the same
Regarding Adjustable Proportioning Valves here’s the link.

Proportioning Valves - Proportioning Valve

The options these guys give are mouth watering and the rates very affordable compared to my existing options, but with brakes being involved, “Half a brake is better than none” – What say?

Mods : Links given are just for technical understanding. If I've inardvently broken any of the rules of the forum, that was not my intention.

[nitrous]

The problem seems to be with the brake bias.
Need to check with headers ( Mahindra's unofficial test driver ) if he's got the issue as well.
Then, it could be an issue with all the Boleros.

The danger with this kind of rear bias'd brakes is not in straight-line braking. But, its on the turns.
Any vehicle whose rears lock up when braking in a straight line will easily spin out if you're braking on turns.
And you decide how dangerous spinning out on a curve is.

Usually, passenger cars' brakes are well biased to the front just like how the suspension is set to understeer for safety.

[GTO]

@ Neil : Here's an excellent thread that you might benefit from.