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Old 05-20-2005, 03:58 PM
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No brakes

I have a 1969 Dodge Charger, but I can't seem to locate the problem with my brakes. So far, I have put new pads on, machined the drums (all 4 are drum), replaced the pistons on the front drums, replaced all of the rubbers on the brake pistons, replaced the master cylinder, and finally replaced the booster.
I still need a great deal of space to stop. One additional bit of information is that the motor is a 440 (+.030 pistons, oversize valves, 498 lift and 292 duration). Being that the motor is altered, I thought that it may not be producing enough vacuum....but I believe that it is (by feel). I took it to a brake shop and they stated that I need a master cylinder with a larger piston diameter.
I am skeptical of this because I believe that a larger diameter will actually make it worse.
Anyway.. Please give me some ideas...

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Old 05-20-2005, 04:20 PM
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I can only assume the pedal is high and hard, not low and soft, since you made no mention of it. Larger master would push more fluid at a lower line pressure, and make the pedal higher and harder to press.
If you are using all stock sized cylinders, they should be right. Those cars had some big easy drums.

Methodically check booster and check valve operation. Check engine vacuum with a gauge. Check that you are getting brake pressure to all 4 wheels and that it releases immediately when you let off. Check that the primary and secondary shoes are not reversed.

You could be on the right track with thinking not enough boost due to big cam.

If the pedal is low and soft, ignore the above.
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Old 05-23-2005, 01:27 PM
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Well, I did some checking over the weekend. I got the car going pretty good and applied the brakes with the engine idling high. It did brake better... I believe that it is a question of vacuum. I also changed the vacuum source from the manifold to the carburator. It appeared that the carburator had a little more vacuum (still not enough).
With that being said, I need to check out some other things. I either do not have enough oil pressure or the lifters need to be replaced. This could cause some vacuum loss. I also placed a plastic bag near the exhaust and it would push out and suck in... Not good.
I do have another question... How can I determine if the camshaft is properly aligned? I do not have the specs on the cam... I do remember that it has 498 lift and I am pretty sure 292 duration. I believe that I should check these items prior to knowing that the engine will not create the vacuum necessary.
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Old 05-23-2005, 04:06 PM
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A wilder cam profile will definately affect the vacuum.
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Old 05-23-2005, 05:02 PM
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Add a vacuum canister.

As far as your bag sucking in and out, if you have a large cam they are extremely inefficient at idle. Do a compression / leakdown test.

To check your cam you either need to pull it out and find the list numbers or degree it. You can come close by measuring the lifter movement with a dial gauge.
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Old 05-31-2005, 11:55 AM
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OK, its been awhile. My oil pressure is 75-80 psi. Now I believe that I need to replace the hydraulic lifters. I believe that this will increase the vacuum at least a little (and eliminate the noise). If this does not increase the vacuum enough, I have a vacuum canister for the front headlights that I will hook up if need be. This canister is like a coffee can and it will be rather awkard looking. I am sure that racing cars use a vacuum canister that is more apealing to the eyes. Where can I purchase one?
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Old 05-31-2005, 11:59 AM
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Your oil pressure has didly to do with your vacuum..........get that vacuum canister....it should help.
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Old 05-31-2005, 01:48 PM
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If you connect a vacuum canister with a check valve it will hold vacuum at the highest level that your engine produces. Also like someone said earlier 'CHECK YOUR VACUUM WITH A VACUUM GAUGE" then go from there. Do first things first and save yourself a lot of hassel!
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Old 06-01-2005, 12:46 PM
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Ok, I have some questions on the answers. Please have patience with me, I want to better understand.

Poncho62- You state that the oil pressure does not effect vacuum. If the valves are not closing and opening properly doesn't that affect the vacuum?

Lamothe1- I lent my vacuum gage to someone and it hasn't been returned. I can go out and spend the money to buy another one, but my view is that I may get a reading without any reference as to whether it is good or not. I have looked through all of the manuals that I have and I was unable to locate any vacuum readings. Do you have any idea what is an acceptable vacuum?

I really appreciate the assistance and the learning experience.
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Old 06-01-2005, 01:03 PM
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At sea level it should be pretty close to 21 lbs vacuum. You could call some of the brake vendors that advertise in the car mags. and they could tell you how much vacuum the booster needs, 18 lbs seams to ring a bell but I'm not sure.
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Old 06-01-2005, 01:12 PM
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P.S. your oil pressure is more than enough. Stock motors usally run between 40-50 psi at higher RPMS. I think somewhere I read that 10 PSI per thousand rpm was standard and if your lifters are bad they will be clattering REALLY loud.
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Old 06-01-2005, 01:14 PM
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Quote:
Originally Posted by charger69
Poncho62- You state that the oil pressure does not effect vacuum. If the valves are not closing and opening properly doesn't that affect the vacuum?

I really appreciate the assistance and the learning experience.

I see what you are thinking....that extra oil pressure in the lifters would make them open more. As long as you have enough oil pressure so that the lifters don't collapse, they are not going to open any more, or for a different amount of time. 10 lbs of oil pressure per 1000 rpm will do that.
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