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post #1 of 8 (permalink) Old 05-16-2019, 06:45 AM Thread Starter
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Weak Brakes after Replacement

I have a 2008 sportsman 300 that I bought for my daughter to ride. the brakes worked fine but after inspection the pads were thin and there was some pretty good gouges in the rotors. So i bought a kit from race driven for rotors and sintered pads front and rear. everything came apart fine and went together fine. I adjusted the pads per the service manual and tested with the quad in the air. everything seemed fine. But when I took it on a test ride I have to squeeze as hard as I can and the machine very slowly comes to a stop. Same thing with the foot brake. I did the bedding in routine hoping that would help but it didnt. I bled the brakes per the service manual and still nothing changed..

What am I missing??? I have never seen this happen before.

I am going to vacuum bleed the system again this weekend but I dont think its going to help.

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post #2 of 8 (permalink) Old 05-16-2019, 09:18 AM
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I hate to be the bearer of bad news but this may be a classic example of "You get what you pay for"!
I tried RD brakes ONCE. That was 2 in 1 for me... First and Last!
Did you clean the new rotors with brake cleaner to remove the grease/oil film put on them during manufacture to prevent rusting while in storage? If not, the pads are now contaminated.
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post #3 of 8 (permalink) Old 05-16-2019, 09:32 AM Thread Starter
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Yes I cleaned the rotors. It is my first experience with race driven but I know a few guys who had great luck with there brakes so I thought I would give them a shot.

2017 Sportsman 850SP (Mine)

2014 Sportsman 570 (Wifes)
bearclaw HTRs 25x8 and 25x10
QSC clutch Kit
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post #4 of 8 (permalink) Old 05-16-2019, 01:36 PM
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Sintered pads last longer but require higher pressure to stop - take the pads out, wash them and the rotors in lacquer thinner, sand the rotors in a circular pattern with 80 grit emery cloth - sand the pads perpendicular to rotor rotation (inside to outside edges of the pads) - if the rotors are drilled, more pressure is required. The only way to increase pressure is to decrease the diameter of the master cylinder, increase the surface area of the caliper piston, change the fulcrum point of the brake lever or make the brake lever longer.

Note: organic (soft pads) stop with less pressure, wear quickly and are less efficient when wet - sintered pads last longer, are less affected when wet, require more pressure and are hard on rotors - rotors that have ridges worn into them effectively have 1 or 2% more surface area for better stopping ability - drilled rotors have less surface area, but run cooler and help carry water away from the pads, but the holes can fill with mud which is abrasive and will accelerate pad wear.

I think if you manage to get all the air out of the system the braking will be much better. Maybe flushing out the DOT 4 brake fluid and replacing it with DOT 5.1 might help also. Run the vehicle with the brakes slightly on until they are smoking hot and that will help cook out any residual oil and improve the feel also. In addition, getting the brake fluid to near it's boiling point or even boiling the fluid a bit will improve brake feel when it cools down because hot fluid will contain a lower % of water.

God luck

2006 Trailboss 330
2002 Sportsman 90
2005 TRX400EX (FOR SALE)
2003 LT-Z400 (needs engine work & is for sale)
2004 CRF250X
1971 Triumph 650 Bonneville (has 5 original miles)
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post #5 of 8 (permalink) Old Yesterday, 09:11 AM Thread Starter
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just an update.......I vacuum bled the system and that did not change anything and cleaned the pads and rotors again. also sanded the pads and rotors. It did not improve at all. So I swapped the pads for some organic EBC pads and its works like it should. So it was the sintered pads causing the problem.

2017 Sportsman 850SP (Mine)

2014 Sportsman 570 (Wifes)
bearclaw HTRs 25x8 and 25x10
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post #6 of 8 (permalink) Old Yesterday, 02:14 PM
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Glad you got it. Yeah, same holds true on your automobiles. Hard pads last longer but are harder on rotors and won't stop as good. Soft pads wear faster but feel much better and don't wear the rotor as bad. Everything mechanical is a tradeoff.

Last edited by polman500; Yesterday at 05:03 PM.
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post #7 of 8 (permalink) Old Yesterday, 05:19 PM
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Quote:
Originally Posted by latebird View Post
Sintered pads last longer but require higher pressure to stop - take the pads out, wash them and the rotors in lacquer thinner, sand the rotors in a circular pattern with 80 grit emery cloth - sand the pads perpendicular to rotor rotation (inside to outside edges of the pads) - if the rotors are drilled, more pressure is required. The only way to increase pressure is to decrease the diameter of the master cylinder, increase the surface area of the caliper piston, change the fulcrum point of the brake lever or make the brake lever longer.

Note: organic (soft pads) stop with less pressure, wear quickly and are less efficient when wet - sintered pads last longer, are less affected when wet, require more pressure and are hard on rotors - rotors that have ridges worn into them effectively have 1 or 2% more surface area for better stopping ability - drilled rotors have less surface area, but run cooler and help carry water away from the pads, but the holes can fill with mud which is abrasive and will accelerate pad wear.

I think if you manage to get all the air out of the system the braking will be much better. Maybe flushing out the DOT 4 brake fluid and replacing it with DOT 5.1 might help also. Run the vehicle with the brakes slightly on until they are smoking hot and that will help cook out any residual oil and improve the feel also. In addition, getting the brake fluid to near it's boiling point or even boiling the fluid a bit will improve brake feel when it cools down because hot fluid will contain a lower % of water.

God luck

Everything I've read says not to use DOT5.1 in a DOT3 or DOT4 system.

Yes... it's glycol based fluid... but according to the articles I've read it's not backward compatible like DOT4.
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post #8 of 8 (permalink) Old Yesterday, 08:43 PM
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[QUOTE=hatzie;1428445Everything I've read says not to use DOT5.1 in a DOT3 or DOT4 system.

Yes... it's glycol based fluid... but according to the articles I've read it's not backward compatible like DOT4.[/QUOTE]

Don't know where you got your info, but here's the info I got from one brake fluid manufacturer:

DOT 4 and DOT 5.1 are both glycol-based brake fluids and are used widely in the automotive and cycle industry. They are controlled by standards set out by the Department of Transportation (DOT) - hence the name.

The main difference between these two brake fluids is in their boiling points. Part of the standards that need to be met by the manufacturers of DOT fluids are the minimum dry and wet boiling points. These are the minimum temperatures that the brake fluid must perform at before the brake fluid starts to boil, which can lead to complete brake failure.

Remember, these are only the minimum standards. Brake fluid manufacturers can and often do improve on these figures and it is possible to find DOT 4 brake fluid with a higher boiling point than some DOT 5.1 fluids on the market.

Since DOT 4 and 5.1 are both glycol-based brake fluids they are compatible with each other, which means they can be readily mixed without harming your brake system. It is important never to mistake DOT 5.1 (glycol-based) with DOT 5 which is silicone-based and should never be mixed with any other DOT fluid.

Silicone based DOT 5 is the odd one out and is not compatible with any other DOT brake fluid. By mixing DOT 3, 4 and 5.1 brake fluids, assuming it is fresh fluid, the worst thing that can happen is a drop in the boiling point of the whole fluid.

Some brake manufacturers, such as Hayes and Formula, pre-fill their brakes with DOT 4 brake fluid from the factory. Others including Avid and Hope, choose to use DOT 5.1 in their brakes. Many riders with DOT 4 in their brakes will opt to bleed with DOT 5.1 to benefit from the higher boiling point and improved heat resistance.

2006 Trailboss 330
2002 Sportsman 90
2005 TRX400EX (FOR SALE)
2003 LT-Z400 (needs engine work & is for sale)
2004 CRF250X
1971 Triumph 650 Bonneville (has 5 original miles)
1972 Triumph 650 Bonneville (undergoing restoration)
1979 Honda CBX (6 cylinder)
1970 Kawasaki G3SS 90cc Bushmaster
1976 Suzuki RE5 Rotary (not running & FOR SALE)
1981 Kawasaki KZ305-A
1981 Suzuki GS450T (undergoing repair & will be for sale when done)
1982 Kawasaki KZ750-H (FOR SALE)
1989 Honda VT1100C
2007 Vectrix VCTX Electric Scooter
1965 Montgomery Ward 3 1/2 HP Tecumseh Mini Bike
1970 Triumph T25 250cc Trailblazer
1968 Triumph 250cc Flat Tracker

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