Back right tire locks up under hard braking?

[Rizzo]

I did a search but could not find anything like this. I was on the track on Sunday and on the first lap the back right tire would lock up when I did some hard braking. It left some nasty black strips on the track and the tire smoked bad. Im fairly sure I flat spotted the tire a bit as I have a bit of a vibration over 80 mph now. This is on a stock 98 GTS. No ABS and stock brakes. I just put new rotors and pads on at the end of last season so they are like new. I flushed the brake fluid last week so I know there isnt any air in the lines. I've been thinking about upgrading the back brakes anyway but I dont want to go and spend a bunch of money until I know what the problem is. Any ideas or any ideas on how to diagnose what the problem is? Is there a proportioning valve on the GTS' that could malfunction? Thanks for any help. Also. What do you all recomend to upgrade the back brakes. I have the stock rims and want to keep them and I understand that Dave's Big Brake kit has to have 18 in rims? Mine are 17 in.

[bluesrt]

could have a collapsed brake hose,inner liner gets weak and collapses,just a thought--so when you brake it has a tighter quicker reaction-it does happen...

[Tom, F&L GoR]

Yes, there is a proportioning valve. It is integral to the valve block mounted below and forward of the master cylinder. From there is regulates the pressure to the single rear brake line (splits again at the axle), so it can't affect one rear caliper without doing the same to the other.

Are you absolutely sure it was a rear brake? It is common for the right front to lock since the battery and driver are loading the left side. The rear locking means you had the clutch in? To be sure you might look at the the tire. A vibration is easily felt from a front, less easily on a rear.

Does the parking brake work normally? I have seen the parking brake lever arm shaft (where it passes into the casting) get rusty and return spring is not strong enough to disengage the parking brake. You should be able to move the brake lever by pushing it with your palm. Maybe it's dragging a little.

You don't have to spend big bucks to get over 1.0 G braking and keep your 17" wheels.
40mmBrakes Home

[Rizzo]

Originally Posted by Tom, F&L GoR

Yes, there is a proportioning valve. It is integral to the valve block mounted below and forward of the master cylinder. From there is regulates the pressure to the single rear brake line (splits again at the axle), so it can't affect one rear caliper without doing the same to the other.

Are you absolutely sure it was a rear brake? It is common for the right front to lock since the battery and driver are loading the left side. The rear locking means you had the clutch in? To be sure you might look at the the tire. A vibration is easily felt from a front, less easily on a rear.

Does the parking brake work normally? I have seen the parking brake lever arm shaft (where it passes into the casting) get rusty and return spring is not strong enough to disengage the parking brake. You should be able to move the brake lever by pushing it with your palm. Maybe it's dragging a little.

You don't have to spend big bucks to get over 1.0 G braking and keep your 17" wheels.
40mmBrakes Home

Thats funny. I was just on your website. I am going to take the car out again tomorrow and make absolutely sure it was the rear brake that was locking. I was actually in the passenger seat when this was happening. I was driving with an instructor and he also thought it was the right rear. I`ve read about the front right tire locking up when there is no passenger but of course there was 2 of us in there. I was looking in the side mirror and damn it looked like smoke pouring out the back wheel well but I guess there`s a possibility it was coming from the front. I wish I would have asked one of the corner workers what he saw as we were right in front of him when it happened. The ebrake works prefect. We actually took the rim off and there is no pressure at all on the brake. You can grab the rotor and move it forward and back with no problem.

What is the turn around time for your rear calipers. I am up in Canada so how is shipping done. I am very interested.

[Tom, F&L GoR]

Originally Posted by Rizzo

What is the turn around time for your rear calipers. I am up in Canada so how is shipping done. I am very interested.

Turn around time is zero. All I need to get you started is for you to PM me your address. I ship the new brakes first and expect you to send me a check when you receive the box. Then I ask that you swap brakes within a few weeks and return the cores.

Shipping is normally via US Postal Service flat rate box which costs $26 to Canada plus $8 insurance. Since I insure the box, someone has to be there to sign for it. Typically UPS costs are the same as USPS + insurance (but only get a tracking number and not insurance). Obviously you have to factor in cost of returning the cores. If there is another shipping option, let me know.

[dave6666]

If you have a flat spot then it should be easy to troubleshoot which corner it is. Find the flat spot...

[Rizzo]

Well. We were so sure it was the back that was locking up that we didnt even check the front tire. I just went out and checked and there at the very top of the FRONT right tire, almost lauging at me saying " Look here dumb as$" was a flat spot. It's an ugly one too. So now not only do I need new back brakes to help cure this, I need new tires. This track stuff can get pricey. The tires are 4 years old anyway but I really dont want to test the new tires to make sure the problem is gone. From what I've read the front right will lock if there is no passenger but there were 2 of us in the car? Any insite in to that?

Thanks for all the help guys.

[dave6666]

What tires (size, brand) are you running and what are the condition of the other 3?

[Rizzo]

Originally Posted by dave6666

What tires (size, brand) are you running and what are the condition of the other 3?

Tires are stock sizes. 335/35/17 and 275/40/17. Michelin Pilot Sports. The front tires still look like new. Lots of tread left. The rears are getting worn down. Probably 30 to 40% remaining.

[dave6666]

Ahh. Might have been able to help with an 18... Un flat spotted...

[Tom, F&L GoR]

Ask around your racer friends and see if someone can corner weight your car - just to see what it is, since you can't easily adjust it. You might find that the RF wheel is light, certainly with one driver and maybe also with a passenger. In my experience, a 100lb difference between LF and RF is possible and significant.

If you can get this measurement, you could consider installing one "lowering" spring cap on the RR. This is load up the RF and LR tires more. (In NASCAR, called "wedge") For purely braking performance, you would want the LF and RF (with driver) to weigh the same as the nose gets heavy under deceleration. Only if you are really really good at corners (I am not) you might sense that the car is very slightly different cornering left vs. right.

Instead of a lowering cap, you could also cut one thinner. It's an easy 2 minute job for anyone with a metal lathe. In fact, if Gen 2 and Gen 1 caps are same, I will include one, cut thinner, with the brakes for free as long as you send me back your old one. (I might have a Gen 2 cap, not sure.)

[Burt G]

Toms 40mm rear caliper upgrade was the Best money spent on improved braking for my ACR... Thank you Tom

[sweet gts]

Two things to add...... First off Tom's brake kit is awsum for the money, you can't go wrong! Second, I just changed over my tires and have got a set of frts with some miles on them.....
Just changed over to Kumho's and I'v got a set of 17 in. Mich. Pilots with some miles left on them. Came of my 97, and they are about 4 or 5 years old. I'v seen people looking before so I thought I would offer them up if anybody could use them. send me a PM if you are int. they are located in Natick Ma.

Steve

[DC Performance]

Most likely you have a frozen rear caliper slide.

[Tom, F&L GoR]

Even more most likely is a front tire locked up (see post #7.)

But, a good reminder for brake maintenance is to look at the caliper slide dust boot on the side closer to the rotor. It gets hit with the abraded brake pad material and it looks like a part is sliced off of the rubber material. I see this on about one out of every three caliper cores. The hole allows water and grit to contaminate the grease and can make the slide rough. The smaller slide is not greased, it is lined with a teflon sleeve that seems pretty durable.

[GTS Dean]

Originally Posted by Rizzo

I just went out and checked and there at the very top of the FRONT right tire, almost lauging at me saying " Look here dumb as$" was a flat spot. It's an ugly one too.

You're kidding, right? A right front lockup on a Viper?