Something wrong at fron passenger axle/caliper. - Impala Tech
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post #1 of 18 (permalink) Old 06-08-2012, 08:08 AM Thread Starter
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Something wrong at fron passenger axle/caliper.

1969 Impala front disc. Just got this car and the prior owner's mechanic just replaced the front master cylinder and calipers due to a sticking caliper. Maybe, but after I drive the car about 10 miles, the front passenger wheel develops a shimmy that feels like a thrown wheel weight and does feels like something is starting to drag. Problem goes away after sitting.
I drove it to work this morning and thought it was just starting this again when I parked. Front wheel on that side definitely smells like something is getting hot.
Any ideas?

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post #2 of 18 (permalink) Old 06-08-2012, 08:55 AM
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The person that converted your drum brakes over to a disc/drum brake system left in the residual valve for the the drum brakes (it is still required for the rear brakes, unless you have converted them to disc brakes as well). The residual valve maintains a constant 3 psi of brake pressure in the system so that water is kept out and so that the reaction time for the brake shoes to react (distance traveled) is reduced.

You need an experienced mechanic (not a brake shop that has high school kids working for minimum wage) that can properly plumb your brake lines so that the rear brakes and your disc brakes work in harmony and safely. Right now the residual valve is pushing the pad up against the rotor very lightly. But as it drags it gets hot and as everything expands it applies more pressure which will burn hot spots (weld harden) your rotor requiring it to be replaced or turned to get rid of them. That is the pulsing feeling you get in the brakes as that hard spot passes under the pad it presses harder because it doesn't wear down as much as the softer base metal.

Big Dave
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post #3 of 18 (permalink) Old 06-08-2012, 10:00 AM Thread Starter
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Car was worked on by Black Widow Garage in Wellington, KS but has had disc brakes at least 28k miles. That being said, the garage did install new lines with the calipers.
Can you be more specific about what needs to be done to correct it? I'm comfortable pulling cars apart down to the bare body but I've never had to work with drum brakes - the old Jags I had in the past were 4 wheel disc.

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post #4 of 18 (permalink) Old 06-08-2012, 12:01 PM Thread Starter
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Brake issues

Figured pictures were worth at least 8 words...
Called the mechanic. He still insists the car had factory front disc and he replaced lines/master cylinder/calipers. The only thing left is the proportioning valve. And here is what's in there:
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post #5 of 18 (permalink) Old 06-08-2012, 01:39 PM
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Did he replace the rubber hoses from the frame to the calipers? Sounds like a hose collapse.
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post #6 of 18 (permalink) Old 06-08-2012, 04:03 PM Thread Starter
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At least one looked new. Still haven't had time to get this thing up on stands and do a thorough check.
One thing I am learning fast is that I could have rebuilt 3 GM's for what it used to cost me in Jag components. Not a big deal to go ahead and replace something if it's in doubt.

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post #7 of 18 (permalink) Old 06-08-2012, 04:07 PM Thread Starter
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Quote:
Originally Posted by Big Dave View Post
The person that converted your drum brakes over to a disc/drum brake system left in the residual valve for the the drum brakes (it is still required for the rear brakes, unless you have converted them to disc brakes as well). The residual valve maintains a constant 3 psi of brake pressure in the system so that water is kept out and so that the reaction time for the brake shoes to react (distance traveled) is reduced.

You need an experienced mechanic (not a brake shop that has high school kids working for minimum wage) that can properly plumb your brake lines so that the rear brakes and your disc brakes work in harmony and safely. Right now the residual valve is pushing the pad up against the rotor very lightly. But as it drags it gets hot and as everything expands it applies more pressure which will burn hot spots (weld harden) your rotor requiring it to be replaced or turned to get rid of them. That is the pulsing feeling you get in the brakes as that hard spot passes under the pad it presses harder because it doesn't wear down as much as the softer base metal.

Big Dave
It is actually a shudder without the brakes applied. Brake modulation is actually very smooth. I don't disagree that something could be causing a dragging pad however. Only on 1 side though?

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post #8 of 18 (permalink) Old 06-08-2012, 04:33 PM Thread Starter
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Hate sitting here at the desk "working" on a Friday but supposing the (mostly Ford) mechanic left off the factory metering valve? Have to look under the hood again.

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post #9 of 18 (permalink) Old 06-08-2012, 04:49 PM Thread Starter
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Yeah, fidgity about it. Walked out just to check. The factory style metering valve is right where it should be. Now I'm back to square one about what's causing this. Just need to park it and look.

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post #10 of 18 (permalink) Old 06-08-2012, 06:21 PM Thread Starter
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forum seagull?

Quote:
Originally Posted by Big Dave View Post
The person that converted your drum brakes over to a disc/drum brake system left in the residual valve for the the drum brakes (it is still required for the rear brakes, unless you have converted them to disc brakes as well). The residual valve maintains a constant 3 psi of brake pressure in the system so that water is kept out and so that the reaction time for the brake shoes to react (distance traveled) is reduced.

You need an experienced mechanic (not a brake shop that has high school kids working for minimum wage) that can properly plumb your brake lines so that the rear brakes and your disc brakes work in harmony and safely. Right now the residual valve is pushing the pad up against the rotor very lightly. But as it drags it gets hot and as everything expands it applies more pressure which will burn hot spots (weld harden) your rotor requiring it to be replaced or turned to get rid of them. That is the pulsing feeling you get in the brakes as that hard spot passes under the pad it presses harder because it doesn't wear down as much as the softer base metal.

Big Dave
You want to maybe re-parse this post to see how it reads? I have to tell you, after working as an automotive engineer for several years, rebuilding a couple of E-types, hot rodding an XJ-S an generally developing some knowledge on mid-80's FI, Stromberg carbs and such, I retire my Whitworth wrenches and got something simple to work on. I'm thrilled with it in fact. I've wanted a 60's B body with a manual since highschool and essentially just found out they existed. Maybe it's not a factory SS with factory discs, maybe it is. (sure seems factory now that I've really dug into it).
So, "Big" Dave, you were my first exposure to the Chevy community and l have to wonder why you're so bitter when all I see is people interested in fixing their cars?
Now you've got pictures of my brakes, the MC, the proportioning valve and the factory style metering valve hanging off the brake booster. Care to trouble shoot again?

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post #11 of 18 (permalink) Old 06-08-2012, 07:25 PM
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Nope. I'm not bitter.

I just use cars as vehicles and drive them 'til the wheels fall off. I don't agree with Chevy's decision on a lot of their design criteria as I desire a car that will go from zero to 100 back to zero as fast as possible so long as it also corners like a slot car. My only concession to creature comfort is A/C but that is only because it is miserably hot and humid where I live. Basically I take an Impala and convert it into a full size Corvette, but only because I can not fit into a Corvette due to my size. But that is just my idea of what cars are for, not shared by others.

Big Dave
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post #12 of 18 (permalink) Old 06-12-2012, 02:16 PM Thread Starter
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Quote:
Originally Posted by Big Dave View Post
Nope. I'm not bitter.

I just use cars as vehicles and drive them 'til the wheels fall off. I don't agree with Chevy's decision on a lot of their design criteria as I desire a car that will go from zero to 100 back to zero as fast as possible so long as it also corners like a slot car. My only concession to creature comfort is A/C but that is only because it is miserably hot and humid where I live. Basically I take an Impala and convert it into a full size Corvette, but only because I can not fit into a Corvette due to my size. But that is just my idea of what cars are for, not shared by others.

Big Dave
Then we share the same problem. Not trying to start up a flame war here - I see enough kids providing "services" that aren't.
But, having to come up to speed quickly because I want to drive this thing, I have a factory disc setup with what looks to be the front passenger caliper dragging. New calipers and M/C, old metering valve and proportioning valve.
Thoughts?

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post #13 of 18 (permalink) Old 06-12-2012, 02:38 PM
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Check the front flexible hoses going to the calipers. I have had them collapse internally and hold pressure on the caliper. Intern overheating the brake pads to the point of causing a fire.
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post #14 of 18 (permalink) Old 06-12-2012, 02:55 PM Thread Starter
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Quote:
Originally Posted by dadstoy View Post
Check the front flexible hoses going to the calipers. I have had them collapse internally and hold pressure on the caliper. Intern overheating the brake pads to the point of causing a fire.
Look to be brand new hoses as well.

Probably going to go ahead and replace most everything in the name of safety.

So...rotors are the expensive piece on 69-70 cars?

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post #15 of 18 (permalink) Old 06-12-2012, 03:04 PM
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I have 69 Impala disc brakes on the front of my 65 Impala. I did not use the factory rotors. I used Corvette rotors on the original 69 impala hubs. Much cheaper and they work great. Here's the link.
http://www.antechlabs.com/Smokey/MJC...Conversion.pdf
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post #16 of 18 (permalink) Old 06-12-2012, 05:08 PM Thread Starter
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Quote:
Originally Posted by dadstoy View Post
I have 69 Impala disc brakes on the front of my 65 Impala. I did not use the factory rotors. I used Corvette rotors on the original 69 impala hubs. Much cheaper and they work great. Here's the link.
http://www.antechlabs.com/Smokey/MJC...Conversion.pdf
Had heard something about this. Thanks. I've been away from home more days than I've had this car and getting eager to tear into it.

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post #17 of 18 (permalink) Old 06-18-2012, 08:58 AM Thread Starter
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So digging a little further into this, I found a poorly repaired master cylinder pushrod. The fork/adjuster union is a gob of weld. No way the travel can be right on this thing. I went ahead and ordered the $20 part.

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post #18 of 18 (permalink) Old 06-27-2012, 11:57 PM Thread Starter
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Finally got to the heart of the problem on this after ordering a couple of brake boosters, buying a spare reman master cylinder, and some misc clevis kit parts.
After finding the botched booster clevis, not a recent botch by any stretch, finding out that 69 car brake parts are readily available but not usually cross referenced right, and a kink in the metering valve line, I finally figured out that the last mechanic stuck in the wrong MC pushrod. There was a long one on a shallow pocket MC.
Just got the pedal/clevis alignment right tonight on the new booster and I'll be keeping the new metering valve as well. Just have to wait out the new pedal bushings and this thing can get back on the road.

1969 Imapala convertible build thread here:
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