Brake issue

lmp9002002 · 11-08-2009, 01:39 PM

I own a 1992 N/a with a 1993 motor/tranny swapped into it, and recently did a brake job on it. Now, i have issues with the brakes locking up when i get on the pedal quickly, but not pushing it down very far. I know they should be able to lock up the tires, but it seems like it is happening very prematurely. My entire brake system is stock, with the exception of ceramic pads. Is there a restrictor in the brake booster vacuum line that could be missing and causing this? If not, what else could be causing it? Thanks in advance.

CJMR2T · 11-08-2009, 05:02 PM

What kind of tires and what sizes are you running?
How old are they and how worn are they?

It could just be the pads being a lot better then what were previously on it.

There is no restrictor. The only thing that should be there is a one way check valve. That only to keep the booster working for a couple of brake attempts should the engine die.

When you did the brake job, what all did you change?

lmp9002002 · 11-08-2009, 07:18 PM

They're Falken 215/40/17's, very good tread, almost like new.
I replaced all the front pads and had the rotors turned.

Are ceramic pads that much more bite-y than stock?

CJMR2T · 11-08-2009, 10:40 PM

Typically no, they are not more aggressive then the stock pad. The question is, what were the pads that were on there up till the change to ceramic.

A lot of pads are avalible in both organic and semi-metalic. If for some reason your old pads were organic compound when they should have been semi-metalic, then I could understand the drastic change.

At that same token, the ceramic compound could have been mixed wrong thus making them more aggressive.

Also, you could have upset the bias by only changing the fronts with the ceramic. It shouldn't have had that much effect, but it is possible.

One other question, your car is not an ABS car is it?
Im guessing not being that you are locking up, but if so and your locking up then there's an issue in the ABS system...

lmp9002002 · 11-09-2009, 01:45 PM

No it's not ABS.
I'm not entirely sure what was on there before, since this is the first brake job i've done since buying the car.
Considering how it's only the fronts locking, i was thinking the same thing, i may have upset the bias. I think i might replace the rears as well, or at least get the rotors turned.

CJMR2T · 11-09-2009, 03:38 PM

I would do the rears (new matching pads too).... Then go from there.

I have noticed that the MR2's brakes are a bit touchy compaired to other vehicles so it might just be that the brake that were on there were very poor quality so it didn't brake like it should.

Remember, because the cars are rear weight biased, they run a lot higher rear brake bias compaired to most cars. Most FF (front engine front drive) run close to 80/20 (front to rear) bias, most FR (front engine, rear drive) are more in the neighborhood of 70/30 and the MR2 being a MR (mid/rear drive) is pretty much dead on 60/40 bias.

Ben · 11-09-2009, 11:53 PM

It could be an issue with the calipers. Does it pull to one side when braking? Did you lube the caliper sliding pins when you did the brake job?

kbrew8991 · 11-10-2009, 09:52 AM

our cars do have a bit of front bias stock, they should lock the fronts first...

though I'd still put in the same brand pads on the rear brakes too just to get the balance better

lmp9002002 · 11-10-2009, 02:16 PM

Quote:

Originally Posted by Ben

It could be an issue with the calipers. Does it pull to one side when braking? Did you lube the caliper sliding pins when you did the brake job?

No, it did before the brake job but that's because the right side caliper was stuck. Yes, i lubed the pins when i did the job, so it's not pulling anymore.
I hadn't really thought about how the brake bias is set on the mr2's, but that makes sense. if the rear end is contributing to 40% of the braking and isn't stopping as well as the front it'd cause my fronts to lock up under hard braking.
Guess its time for a premature rear brake job! lol
Thanks guys

kbrew8991 · 11-10-2009, 05:21 PM

the reason for a split in braking forces is weight transfer btw - under braking weight "shifts" foward - even though at rest our cars are rear-heavy (around 45/55) it gets closer to a 50/50 or maybe even beyond that (ie towards being nose-heavy) depending on tires, brakes, and suspension

lmp9002002 · 11-11-2009, 04:01 PM

i know that, and it was something i thought about and acknowledged in originally analyzing the car (before i bought it) but had forgotten just how much a difference the rear brakes make.

CJMR2T · 11-11-2009, 08:41 PM

Quote:

Originally Posted by kbrew8991

the reason for a split in braking forces is weight transfer btw - under braking weight "shifts" foward - even though at rest our cars are rear-heavy (around 45/55) it gets closer to a 50/50 or maybe even beyond that (ie towards being nose-heavy) depending on tires, brakes, and suspension

Ummm, tires, brakes and suspension have nothing to do with front/rear weight transfer during braking or acceleration. Well let me rephrase that, suspension (and more so shocks) effect how fast (or slow for that matter) but not how much. Ride height is the only thing suspension wise that can effect how much.

The amount of weight transfered is dependent on the wheel base and the center of Cg (center of gravity) height.

Longer wheel base = Less weight transfer
Shorter wheel base = more weight transfer
Lower Cg = less weight transfer
Higher Cg = more weight transfer

Im not trying to start a pissing match or anything and you are right in every sense of the post about why and what not, its just the last part in saying "(ie towards be nose-heavy) depending on.........." which is for the most part false with one exception of the "suspension" if it were lowered lowered thus causing a lower Cg.

11-08-2009, 01:39 PM	#1 (permalink)
lmp9002002 Cage Fighter Join Date: Oct 2009 Location: Spring Hill, FL Posts: 252 Thanks: 6 Thanked 5 Times in 5 Posts iTrader Rating: (1/100% )	Brake issue I own a 1992 N/a with a 1993 motor/tranny swapped into it, and recently did a brake job on it. Now, i have issues with the brakes locking up when i get on the pedal quickly, but not pushing it down very far. I know they should be able to lock up the tires, but it seems like it is happening very prematurely. My entire brake system is stock, with the exception of ceramic pads. Is there a restrictor in the brake booster vacuum line that could be missing and causing this? If not, what else could be causing it? Thanks in advance.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

11-08-2009, 05:02 PM	#2 (permalink)
CJMR2T Fabricator Join Date: Oct 2009 Location: Lakeland, FL Posts: 3,688 Thanks: 3 Thanked 356 Times in 337 Posts iTrader Rating: (4/100% )	What kind of tires and what sizes are you running? How old are they and how worn are they? It could just be the pads being a lot better then what were previously on it. There is no restrictor. The only thing that should be there is a one way check valve. That only to keep the booster working for a couple of brake attempts should the engine die. When you did the brake job, what all did you change?

11-08-2009, 07:18 PM	#3 (permalink)
lmp9002002 Cage Fighter Join Date: Oct 2009 Location: Spring Hill, FL Posts: 252 Thanks: 6 Thanked 5 Times in 5 Posts iTrader Rating: (1/100% )	They're Falken 215/40/17's, very good tread, almost like new. I replaced all the front pads and had the rotors turned. Are ceramic pads that much more bite-y than stock?

11-08-2009, 10:40 PM	#4 (permalink)
CJMR2T Fabricator Join Date: Oct 2009 Location: Lakeland, FL Posts: 3,688 Thanks: 3 Thanked 356 Times in 337 Posts iTrader Rating: (4/100% )	Typically no, they are not more aggressive then the stock pad. The question is, what were the pads that were on there up till the change to ceramic. A lot of pads are avalible in both organic and semi-metalic. If for some reason your old pads were organic compound when they should have been semi-metalic, then I could understand the drastic change. At that same token, the ceramic compound could have been mixed wrong thus making them more aggressive. Also, you could have upset the bias by only changing the fronts with the ceramic. It shouldn't have had that much effect, but it is possible. One other question, your car is not an ABS car is it? Im guessing not being that you are locking up, but if so and your locking up then there's an issue in the ABS system...

11-09-2009, 01:45 PM	#5 (permalink)
lmp9002002 Cage Fighter Join Date: Oct 2009 Location: Spring Hill, FL Posts: 252 Thanks: 6 Thanked 5 Times in 5 Posts iTrader Rating: (1/100% )	No it's not ABS. I'm not entirely sure what was on there before, since this is the first brake job i've done since buying the car. Considering how it's only the fronts locking, i was thinking the same thing, i may have upset the bias. I think i might replace the rears as well, or at least get the rotors turned.

11-09-2009, 03:38 PM	#6 (permalink)
CJMR2T Fabricator Join Date: Oct 2009 Location: Lakeland, FL Posts: 3,688 Thanks: 3 Thanked 356 Times in 337 Posts iTrader Rating: (4/100% )	I would do the rears (new matching pads too).... Then go from there. I have noticed that the MR2's brakes are a bit touchy compaired to other vehicles so it might just be that the brake that were on there were very poor quality so it didn't brake like it should. Remember, because the cars are rear weight biased, they run a lot higher rear brake bias compaired to most cars. Most FF (front engine front drive) run close to 80/20 (front to rear) bias, most FR (front engine, rear drive) are more in the neighborhood of 70/30 and the MR2 being a MR (mid/rear drive) is pretty much dead on 60/40 bias.

11-09-2009, 11:53 PM	#7 (permalink)
Ben Same In The End Join Date: Aug 2006 Location: Oceanside, CA / Reno, NV Posts: 4,274 Thanks: 20 Thanked 309 Times in 284 Posts My Google Map iTrader Rating: (16/100% )	It could be an issue with the calipers. Does it pull to one side when braking? Did you lube the caliper sliding pins when you did the brake job?

11-10-2009, 09:52 AM	#8 (permalink)
kbrew8991 gimme some turns Join Date: Apr 2006 Location: Houston, TX Posts: 1,685 Thanks: 76 Thanked 82 Times in 70 Posts My Google Map iTrader Rating: (5/100% )	our cars do have a bit of front bias stock, they should lock the fronts first... though I'd still put in the same brand pads on the rear brakes too just to get the balance better

11-10-2009, 05:21 PM	#10 (permalink)
kbrew8991 gimme some turns Join Date: Apr 2006 Location: Houston, TX Posts: 1,685 Thanks: 76 Thanked 82 Times in 70 Posts My Google Map iTrader Rating: (5/100% )	the reason for a split in braking forces is weight transfer btw - under braking weight "shifts" foward - even though at rest our cars are rear-heavy (around 45/55) it gets closer to a 50/50 or maybe even beyond that (ie towards being nose-heavy) depending on tires, brakes, and suspension

11-11-2009, 04:01 PM	#11 (permalink)
lmp9002002 Cage Fighter Join Date: Oct 2009 Location: Spring Hill, FL Posts: 252 Thanks: 6 Thanked 5 Times in 5 Posts iTrader Rating: (1/100% )	i know that, and it was something i thought about and acknowledged in originally analyzing the car (before i bought it) but had forgotten just how much a difference the rear brakes make.