4g61t.org

Hey all,

I have been having this problem since I got my 89 GT. I thought the problem may have just been my really old brakes, but Chris (89MirageMan) just did my front and rear brakes, and the issue is still there. Basically sometimes my brake pedal feels like it has brake boost, while other times it doesn't. The pedal never goes to the floor or feels squishy, so I don't think it's a problem with a leak. I will be driving and apply the brakes and sometimes the pedal will feel as if it has brake boost, giving me the ease of lightly applying the pedal with stopping. And then the pedal will suddenly become stiffer, sometimes right around the time I hear a "click" sound. It seems reasonable to think it would be the brake booster, but I have no earthly clue how often those things go bad on these cars. I'll check to make sure the vacuum line to the booster is fine, too. Any thoughts?

thanks!

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89 Colt GT Turbo - Durham, NC

You can check the vacuum line that goes to the booster also.

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Thom
1991 GVR4 1025/2000 (PTE 1200's, 16g, DSMLink v3, gm-maf, eagle/ross, .020 over, 272's, EVO VIII Wheels)
1992 GVR4 866/1000 (getting everything from above)

There is a check valve in the vacuum line coming from the brake booster. Make sure it's still working properly.

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91 GSX - 511fwhp and 352 lb/ft 25psi 110 octane, 7.68 @ 95.9mph 1/8th 21psi 91 octane, 11.93 @ 112.9mph, 117.7mph best trap speed, 20psi 91 octane
98 Volvo S70 T5 - DD

http://www.facebook.com/captaintonus

I did notice this when the car was over here. All calipers are in good shape, the pistons went in easy just like they're supposed to. One of the pins on the rear was a little sticky but I cleaned it up really good and lubed it with caliper grease but that wasn't the problem. I don't think it could be the master cylinder since it's not leaking so I'm thinking maybe its the booster, or the line/check valve like mentioned above.

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93 Mitsubishi Expo LRV 1.8/manual
95 Eagle Summit DL Coupe 1.5/manual
01 Mitsubishi Mirage ES Sedan 1.8/manual

Good deal, thanks Chris!
Any way to test the valve hooked to the booster?

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89 Colt GT Turbo - Durham, NC

As far as I know it's just a check valve, meaning you can blow through it in one direction but not the other.

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93 Mitsubishi Expo LRV 1.8/manual
95 Eagle Summit DL Coupe 1.5/manual
01 Mitsubishi Mirage ES Sedan 1.8/manual

^^^ Should work.

Also, try this test.

Engine off.
Press and hold brake pedal.
Start engine.
Brake pedal should fall slightly.

Continue holding brake pedal.
Turn engine off.
Release and apply brake pedal in slow succession, until it loses vacuum assist.
Should be a couple of pumps.

This is the basic vacuum booster test.

Some pics.
So here is the vac line coming off the booster. I don't see any valve, and feeling around after didn't seem to have a valve either. Where is the valve usually?


Here is the vac line going to the manifold from the booster.


What is this plug for? The master cylinder has a plug going to it already for the level.

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89 Colt GT Turbo - Durham, NC

its inside that hose...or at least it should be... probably under the section that has the covering on it.. just pinch the line until u find a hard spot.



Steve

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Steve 89 colt 2.3 stroker stock top end. evo3@20 psi 13.489@99.30mph 3/10 2012
On drag radials.auto trans.launching @ 5 psi and no traction thru 2nd.

Will do, thanks!
Anyone know what that plug goes to?

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89 Colt GT Turbo - Durham, NC

Cruise.

Your booster is on the right?

Ahh, great, thanks!
Yes, the booster is on the passenger side (right).

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89 Colt GT Turbo - Durham, NC