1998 Intrepid 2.7 non-ABS brake issues - DodgeIntrepid.Net Forums - Dodge Intrepid, Concorde, 300m and Eagle Vision chat
 
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post #1 of 5 (permalink) Old 09-27-2019, 04:37 AM Thread Starter
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1998 Intrepid 2.7 non-ABS brake issues

Does anyone know what the compression should test at the power brake booster vacuum hose (at idle)?
I changed the booster and master cylinder a year ago (10k miles) and the braking improved but was never crisp. Recently, after a lot of rain, the brake pedal became hard and the brakes barely work. What should take three feet to stop then took twenty feet.
So I changed the Proportioning Valve (block) and that improved the problem barely. Now what should take three feet takes ten feet. I bled all four wheels but my experience is that air in the system causes a soft pedal. Could the booster have gone bad again? When I changed it the first time (a year ago), the car stopped better then it does now before the replacement. When I remove the grommet with engine off, there is a rush of air, which normally indicates that the booster is OK. Thanks.
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post #2 of 5 (permalink) Old 09-27-2019, 06:57 AM
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Do you get the impression that the booster is not using the vacuum that it has? The push rod on the nose of the booster that pushes the master cylinder has an adjustment that determines the point at which the booster’s internal valving applies the vacuum boost. Maybe it needs adjusting. Although both boosters I put in my two Concordes needed no adjusting when installed, some people have reported that theirs did need it. You say yours was never great right after replacing it. Maybe it’s adjustment was marginal and something has shifted further in the bad direction so that it’s not just marginal anymore, but never activates.

Not saying that that is definitely the problem, but there are instructions on how to test and make that adjustment. I don’t believe the FSM goes into that, but I think I scanned the instruction slip that came with an aftermarket booster and may have even posted it. I’ll try to find it.

You have to remove the booster to make the adjustment. Since you have to remove it anyway, you could consider buying another booster and trying it to see if that fixes it whether the problem is the rod length adjustment or an internal mechanism problem. Worst case, you’ll have a spare booster and be out $100 (or whatever they sell for these days) if that doesn’t fix it. (It’s a long shot, but you may find that the rod adjustment lock nut is loose so it has changed length - not likely, but check.)

Since it appears that vacuum is getting to the booster, from your description, it would appear that one way or another the booster is the problem. (Check that the vacuum hose connection is tight at the plenum. I was loosing boost, and discovered that the vacuum hose was swelled up like it had been exposed to oil and was loose on the plenum nipple - leaking like a sieve at that connection. Probably not the case since you detected that the booster is getting vacuum - but as you suggested, is it enough vacuum?)

If someone else has other ideas, please post.


'98 LXi - Later Concorde gages (black w/ chrome rings)/'99 LX - LHS gages (white) - HIR bulbs

Last edited by peva; 09-27-2019 at 08:03 AM.
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post #3 of 5 (permalink) Old 09-27-2019, 07:06 AM
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This info. from the ‘02 FSM may be helpful:

Quote:
BASIC TEST
(1) With engine off, depress and release the brake pedal several times to purge all vacuum from the power brake booster.
(2) Depress and hold the pedal with light effort (15 to 25 lbs. pressure), then start the engine.
The pedal should fall slightly, then hold. Less effort should be needed to apply the pedal at this time. If the pedal fell as indicated, perform the VACUUM LEAK TEST listed after the BASIC TEST. If the pedal did not fall, continue on with this BASIC TEST.
(3) Disconnect the vacuum hose on the side of the vacuum check valve that leads to the speed control then connect a vacuum gauge to the open vacuum port on the valve.
(4) Start the engine.
(5) When the engine is at warm operating temperature, allow it to idle and check the vacuum at the gauge.
If the vacuum supply is 12 inches Hg (40.5 kPa) or more, the power brake booster is defective and must be replaced. If the vacuum supply is below 12 inches, continue on with this BASIC TEST.
(6) Shut off the engine.
(7) Connect the vacuum gauge to the vacuum reference port on the engine intake manifold.
(8) Start the engine and observe the vacuum gauge.
If the vacuum is still low, check the engine tune and repair as necessary. If the vacuum is above 12 inches, the hose or check to the booster has a restric or leak.
Once an adequate vacuum supply is obtained, repeat the BASIC TEST.

VACUUM LEAK TEST
(1) Disconnect the vacuum hose on the side of the power brake booster vacuum check valve that leads to the speed control, then connect a vacuum gauge to the open vacuum port on the valve.
(2) Remove the remaining hose on the vacuum check valve that is not the vacuum supply hose coming from the intake manifold. Cap off the open port on the check valve.
(3) Start the engine.
(4) Allow the engine to warm up to normal operating temperature and engine idle.
(5) Using vacuum line pliers, close off the vacuum supply hose near the booster and observe the vacuum gauge.
If the vacuum drop exceeds 1.0 inch Hg (3.3 kPa) in one minute, repeat the above steps to confirm the reading. The vacuum loss should be less than 1.0 inch Hg in one minute time span. If the loss is more than 1.0 inch Hg, replace the power brake booster. If it is not, continue on with this test.
(6) Remove the pliers from the hose temporarily.
(7) Apply light effort (approximately 15 lbs. of force) to the brake pedal and hold the pedal steady. Do not move the pedal once the pressure is applied or the test results may vary.
(8) Have an assistant reattach the pliers to the vacuum supply hose.
(9) Allow 5 seconds for stabilization, then observe the vacuum gauge.
If the vacuum drop exceeds 3.0 inches Hg (10 kPa) in 15 seconds, repeat the above steps to confirm the reading. The vacuum loss should be less than 3.0 inches Hg in 15 seconds time span. If the loss is more than 3.0 inches Hg, replace the power brake booster. If it is not, the booster is not defective.
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post #4 of 5 (permalink) Old 09-27-2019, 08:23 AM
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I havenít found my scanned aftermarket instructions on adjusting the booster rod, but did come across a discussion in which someone described the instructions like this:

Quote:
Turn the screw until you can get the fluid in the brake fluid resevoir to erupt when the pedal is depressed a 1/2 inch.Ē
Sounds straight forward, but trial-and-error with putting the booster on and pulling it back off for each adjustment iteration is needed, but investing an hour or so should be plenty of time to get it done if thatís the solution.
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post #5 of 5 (permalink) Old 10-09-2019, 02:03 PM Thread Starter
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Thanks Peva. Been out of town. Will try your recommendations this weekend.
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