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Brake Pedal Sinks After a Few Seconds


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Well, what's a TC without Brake issues? I've got a new problem now, and it's one I haven't read about yet. The brakes on my '89 stop the car just fine with a nice firm pedal and a normal amount of pedal travel.

However, if I'm sitting at a light with my foot on the brake, the pedal will suddenly sink about two inches, after about 10 seconds. This also happens when I'm slowing down to a stop, with light pressure on the brakes.

As the younger generation would say "Wuz up wit dat?"

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As on old geezer, I would say the master cylinder is going bad. Buy a NEW one. Rebuilt units will not give you the warning you are getting right now. They just go to the floor when you need them the most. NEVER use a rebuilt master cylinder. NEVER>>>>>>>>>>>>>>>>NEVER^^^^^^^^^^^^^^^NEVER use a rebuilt master cylinder! NEVER

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As on old geezer, I would say the master cylinder is going bad. Buy a NEW one. Rebuilt units will not give you the warning you are getting right now. They just go to the floor when you need them the most. NEVER use a rebuilt master cylinder. NEVER>>>>>>>>>>>>>>>>NEVER^^^^^^^^^^^^^^^NEVER use a rebuilt master cylinder! NEVER

I'm with Bill on this one all the way and add another reason for new over rebuilt. On this car the price difference between new and rebuilt isn't enough to replace a broken headlight much less the bumper you have to bust to get to the headlights and grill.

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Are new Teves master cylinders available for the TC?

They should be, big question is what the "H" well priced available part number will fit our car. The TC part number is long gone except for used or NOS, We had a great number for a very well priced accumulator and though the part is still available, that best priced part number is now defunct. In the process of chasing down good priced accumulators that will fit and work, I found the rumored $600 Delco pump part number that fits our car, the pump is still available brand new for $1200, the well priced Delco pump part number went defunct with the well priced Delco accumulator part number. I'm with Bill on the get new before rebuilt, even if new is NOS and I suggest checking in with TC and Arizona parts.

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  • 6 months later...

Hello All, 

 

I am having a similar problem to DamnTheTorpedo with a slight twist.  I replaced my accumulator about a year ago and the brakes had been good and then not so good over time.  I recently dusted the car off and followed the directions for bleeding the brakes and all seemed good.  This is what I have started to experience on my '89 TC, if the temperature is cool, I experience exactly what DTT describes.   If the outdoor temp is warm to hot, the brakes work like a champ.   Any idea's why ambient outdoor temperature would affect the braking system.  I will most likely follow up with a new master cylinder, but hard to justify on a car that I paid $900 for to begin with....

 

Thanks in advance!

Mobjak

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As on old geezer, I would say the master cylinder is going bad. Buy a NEW one. Rebuilt units will not give you the warning you are getting right now. They just go to the floor when you need them the most. NEVER use a rebuilt master cylinder. NEVER>>>>>>>>>>>>>>>>NEVER^^^^^^^^^^^^^^^NEVER use a rebuilt master cylinder! NEVER

On a normal, old school, aluminum master cylinder I would agree but NOT on the Teves unit. These cars don't have a master cylinder of that type. The accumulator is the equivalent of the power booster but acts directly on the brake fluid that goes to the brake calipers and if weak can be a major problem. Older iron master cylinders I have no problem with using a properly remanufactured unit, if someone  just put in new cup seals then I wouldn't use it.

 

Check for leaks or ballooning brake hoses, listen to make sure the brake pump is working correctly and not turning on too often (check those underhood electrical connections), replace the accumulator if it requires the pump to run after less than 9 pedal pumps in quick succession or if you feel the rapid pulses in the brake pedal while stopped or at the end of a stop unless you are in stop and go driving.

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Hello All, 

 

I am having a similar problem to DamnTheTorpedo with a slight twist.  I replaced my accumulator about a year ago and the brakes had been good and then not so good over time.  I recently dusted the car off and followed the directions for bleeding the brakes and all seemed good.  This is what I have started to experience on my '89 TC, if the temperature is cool, I experience exactly what DTT describes.   If the outdoor temp is warm to hot, the brakes work like a champ.   Any idea's why ambient outdoor temperature would affect the braking system.  I will most likely follow up with a new master cylinder, but hard to justify on a car that I paid $900 for to begin with....

 

Thanks in advance!

Mobjak

 

After checking everything Ghostly mentioned you might have already found your problem, if not Teves with sinking pedal after replacing accumulator is no great suprise, the restored pressure will exdpose other weaknesses in the system, like fixing an old leaky water pipe and finding leaks in places that didn't leak before.

 

The bypass when cold and not warm sounds a little off, so I have to ask if you used good / new DOT3 when you flushed and refilled the system? if you did, also wondering if the pedal sinks in cool temps when pumped and held without turning the key to on and running up full power pressure?

 

All to often I refer to the actuator as the master; force of habit, but should you need to shop for a replacement, you will need to look for the part by it's proper name.

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"All to often I refer to the actuator as the master; force of habit, but should you need to shop for a replacement, you will need to look for the part by it's proper name."

 

I'm surprise Hemi didn't give me a head slap for saying master cylinder!  Hi Hemi! :)

 

"new Master cylinders" give you a warning in cold weather when they start to fail.  The rubber is stiffer in the cold.  Now a rebuilt will not give you that warning.  There is mention of a couple reliable rebuilders on the forum but I don't know who they are. 

 

You should also replace the flex lines on the brakes!  Our 41,000 mile car cooked both rear tires within a week from flex lines that caused the rear calipers to drag.  By cooked I mean the tires got hot enough to blow out the sidewall.

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You guys all know my remedy for this problem. More and more people are learning that there is only one permanent way to resolve this issue. Need I say it again? Replace the entire system with a standard Vacuum Booster and 4 wheel Disc Brake Master Cylinder.

Instructions found on ALLPAR Forum.

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