Author Topic: 84 C10 Brakes  (Read 28393 times)

Offline Irish_Alley

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Re: 84 C10 Brakes
« Reply #15 on: June 12, 2018, 11:45:18 AM »
bd do you think the old MC and new MC could have the same problem? i mean i know stuff can be bad right out of the box but couldnt the problem lay in the brake lines/hoses

I'm not there to make firsthand observations, so must draw from experience with the posted symptoms balanced against how the system functions while doing the best I can to filter out assumptions that have been made.  Based on what has been posted, I suspect an adjustment issue and/or residual air trapped in the system or a simple lack of familiarity with the "feel" of GM power brakes to be the most likely cause(s).  Don't make the mistake of believing that any particular symptom has only one cause.  The original symptom may have been repaired only to be replaced by a similar substitute having a different cause.  Hence, all we can do at a distance is make suggestions for checks to be performed and evaluated in the hope that it is sufficient for the OP to discover the truth and resolve the issue.  Do you disagree?

There are two wrong decisions to make: one is to do nothing, the other is to "overthink" the symptoms rather than just looking.  Filter out that which you can definitively through observation and what remains is probably the cause.

i 100% agree, just was throwing out that idea about the hose and wasnt sure if it was a plausible idea or not.



Checking the hoses while the petal is applies id a good suggestion.
I have noticed that the rear brakes will lock up when sufficient pedal force is applied.
I had not mentioned this earlier because until I replaced the shoes and drums, the shoes and drums had been contaminates with brake fluid or grease, which will cause the drum brakes to grab.
So, new drums and shoes, adjusted (parking brake as well) and rear braking is balanced side to side,
but still will lock up earlier than the discs in front.

Possibly a hose or hoses have some give which they should not.
As the pedal is rock solid without engine vacuum, maybe manual only force is
insufficient to cause a hose to swell, but vacuum assist may provide the force to do so.

On to this step.......

does it pull to one side or the other?
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When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline Ronno6

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Re: 84 C10 Brakes
« Reply #16 on: June 12, 2018, 11:59:43 AM »
does it pull to one side or the other?
[/quote]

No. It stops pretty straight.
But, even if one front hose is weak, wouldn't the equalizing nature of discs prevent one working harder than the other?

And then, there is the proportioning valve..........
« Last Edit: June 12, 2018, 01:25:55 PM by Ronno6 »
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Offline Irish_Alley

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Re: 84 C10 Brakes
« Reply #17 on: June 12, 2018, 02:13:29 PM »
it might reduce the line pressure and it might stop straight but im not sure, never dealt with this issue. im almost on the line of "thats a gm brake system for you" but want to eliminate anything we can. much like my sig says
"When you have eliminated the impossible, whatever remains, however improbable, must be the truth" ~Sherlock Holmes
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline Ronno6

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Re: 84 C10 Brakes
« Reply #18 on: June 12, 2018, 03:48:48 PM »
it might reduce the line pressure and it might stop straight but im not sure, never dealt with this issue. im almost on the line of "thats a gm brake system for you" but want to eliminate anything we can. much like my sig says
"When you have eliminated the impossible, whatever remains, however improbable, must be the truth" ~Sherlock Holmes

It is not usually a good idea to have the rears lock up but not the front....especially on wet roads.
If there is a weak spot in a hose, that would reduce pressure to the calipers and gobble up pedal travel.
Kinda like an aneurysm in the brake system...........

Anyway, as I said, the truck had been sitting for at least 4 years. The MC reservoir was empty, but there was some
fluid still in the lines. Dunno if the proportioning valve went without fluid or not.
« Last Edit: June 12, 2018, 03:57:11 PM by Ronno6 »
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Offline Ronno6

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Re: 84 C10 Brakes
« Reply #19 on: June 26, 2018, 07:29:19 AM »
When I replaced the calipers, I thought that I had the 1" thick discs for the JB3 system.
I based this on the VIN, as I  do not have the RPO sticker.
I was wrong....I have 1.25" thick rotors. JB5?
However, the rear drums are 11" X 2", with 1" bore cylinders. JB3

These 2 do not go together (?)

Am I chasing my tail here?
Do I need to replace front system in order to get balanced braking?
« Last Edit: June 26, 2018, 11:38:20 AM by Ronno6 »
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Offline Irish_Alley

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Re: 84 C10 Brakes
« Reply #20 on: June 26, 2018, 07:58:58 AM »
jb/d 3 and 5 use the same master cylinder so i would assume those are comparable
Brake Tech, what do all the numbers mean..
 
take a read here
Brake System and Diagnosis

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When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline Ronno6

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Re: 84 C10 Brakes
« Reply #21 on: June 26, 2018, 08:21:53 AM »
Thanks.
I have previously read thru those.

I do not know if piston sizes differ between JB3 and JB5 calipers.
I do know that the rear cylinders differ in bore sizes" JB3: 1"; JB5 : 15/16"
Proportioning valve is the same for both systems.
The larger bore size in the rear cylinders would require more fluid to energize?

I have changed every hard part in the system.
Everything but hoses and hard lines.

Braking has improved, but pedal travel is still excessive in my estimation,
and rears still tend to lock up every now and then.
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Offline Irish_Alley

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Re: 84 C10 Brakes
« Reply #22 on: June 26, 2018, 08:33:39 AM »
seams as if your very knowledgeable and know what youre doing but did you bleed your brakes  according to the "Brake system and diag."?
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When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline irk_miller

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Re: 84 C10 Brakes
« Reply #23 on: June 26, 2018, 08:38:22 AM »
I didn't see any comments about the dash light.  If the system is off balance, would the proportioning valve switch not cause the light to come on?  And if it is tripped, it would prevent whatever system is an issue from being bled since the piston in the valve blocks the line between the m/c and that part of the system. 
Only dead fish follow the stream.

Offline Ronno6

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Re: 84 C10 Brakes
« Reply #24 on: June 26, 2018, 08:43:11 AM »
seams as if your very knowledgeable and know what youre doing but did you bleed your brakes  according to the "Brake system and diag."?

Yessiree.
I have bled the master cylinder, both on the bench and in the truck, and have bled each wheel , RR,LR,RF, then LF.
I have adjusted the parking brake.
The brakes all work, just not sure abut the balance.
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Offline Ronno6

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Re: 84 C10 Brakes
« Reply #25 on: June 26, 2018, 08:48:25 AM »
I didn't see any comments about the dash light.  If the system is off balance, would the proportioning valve switch not cause the light to come on?  And if it is tripped, it would prevent whatever system is an issue from being bled since the piston in the valve blocks the line between the m/c and that part of the system.

No dash lite. Though I have not tested to see if bulb in dash is good.........
When bleeding, rear brakes don't seem to put out much volume, but, as they are working, I would have to think the volume is sufficient.
I am still not comfortable with pedal travel.
Without vac assist, the pedal is hard and travel stops higher up than with vac assist.
With engine running the pedal travels way down after first resistance is felt, then firms up near the bottom.
I am still thinking that there may be some internal bypassing going on, but I really don't notice any pedal fade.

When the MC in my F150 was bypassing, I could feel brakes start to engage then release with given pedal travel.
the new MC cured that problem.
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Offline zieg85

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Re: 84 C10 Brakes
« Reply #26 on: June 26, 2018, 08:54:12 AM »
after reading and re-reading this post my thoughts are a bad "new MC"  What you describe about the power booster is how they work with no vacuum to it.
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1986 C10 under construction
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Offline Henry

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Re: 84 C10 Brakes
« Reply #27 on: June 26, 2018, 10:01:15 AM »
Hi Ronno6:
Does your truck have the combo valve (aka proportioning valve)? Some of your symptoms indicate that this valve may be faulty or have residual air in it. My 76 has the combo valve mounted on the drivers side engine frame member down by the steering gear. My combo valve has a button on one end of it that must be held down while bleeding the system in order to make sure you get all the air out of the system.
Regards,
Henry

Offline Ronno6

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Re: 84 C10 Brakes
« Reply #28 on: June 26, 2018, 10:06:33 AM »
I just replaced the prop valve.
The plastic bleeder tool accompanied it, but I did not use it, as I have not really seen a tutorial on how to do that....
(I'm not as smart as I appear to be....)

I just watched a short video on that.
Hope I didn't mess it up...........
I may need to recenter the valve.
But, as I said, the brake light is not illuminated, so hopefully all is good.....
« Last Edit: June 26, 2018, 10:10:35 AM by Ronno6 »
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Offline Irish_Alley

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Re: 84 C10 Brakes
« Reply #29 on: June 26, 2018, 10:26:37 AM »
the brake light should illuminate when you first turn the key "on" or if you ground out the wire that connects to the P valve
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes