[GMCnet] Brake Project - advice needed

[Jim Curran via Gmclist]

Hi Folks,
I replaced my brake lines last year and have bled the system at least 3 different times and adjusted the rear brakes over and over. I just don't have
the same braking that I did before replacing the lines.

Today, right after taking the coach for a spin, I measured temperatures of the disks and drums all around and I have some strange results but maybe
there is a clue in here?

Front driver & passenger: 185 , 186 (degrees F)
Driver mid & rear: 220, 172
Passenger mid & rear: 95, 95 (drums just warm to the touch)

Air temp was about 65 F today.

Do I still have air in the system?
Could the passenger side calipers be frozen?
Do I have the driver side drum brakes adjusted too tight?
And by the way, should I fiddle with the combination valve while bleeding? (I have not)

Thanks in advance for any insight.

Jim






--
Jim Curran
1976 Palm Beach
Alexandria, OH

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[Jim Kanomata via Gmclist]

Are both side of rear warm, not hot.
Rear lines are long so you need to consider that.

--
Jim Kanomata
Applied/GMC, Newark,CA
ji...@appliedairfilters.com
http://www.gmcrvparts.com
1-800-752-7502

[Terry via Gmclist]

The hot brakes are adjusted too tight or the wheel cylinders are frozen, or just stuck enough in corrosion (that they just got pushed into when you
bled them and got any air out) to be able to overcome the return springs.
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.

[6cuda6--- via Gmclist]

My first thought as well....sometimes doing a good thing makes other stuff worse

Bullitthead wrote on Sun, 14 June 2020 00:27

> The hot brakes are adjusted too tight or the wheel cylinders are frozen, or just stuck enough in corrosion (that they just got pushed into when
> you bled them and got any air out) to be able to overcome the return springs.


--

Rich Mondor,

Brockville, ON

77 Hughes 2600

[Tyler via Gmclist]

I see in your data a big difference between sides - which leads me to think passenger rear line still has air, and both rear sets may not be adjusted
properly.

When I replaced my metal lines, I tried my usual gravity bleed and it did not work AT ALL to the rear. I had to use my Harbor Freight vacuum bleeder
to get the lines to wet. One line (I don't remember which one) I had to undo at the master and use the vacuum sucker at the wheel end to draw a little
bit of fluid that had started from gravity and vacuum previous attempts. Once this mostly air attempt had moved some fluid through, I reattached and
used vacuum to draw fluid from master cylinder until some consistent flow appears at caliper.

Once the lines got wet, I returned to gravity bleed process. Put clear hose on one nipple, loop it up and over something higher than nipple to watch
flow of any bubbles, and down into a container/catchment. Open the nipple and wait. It might take an hour per caliper, sometimes longer, to move a few
master cylinders worth of fluid through each rear caliper. I do all six wheels this way, and then re-do the four rears. If you let the master cylinder
got too low on fluid, you have to start over. Just because it flows fluid with no bubbles, you are not done until you know a perfect column of fluid
from MC to caliper is present... my estimation is that you have to refill MC at least twice when draining the first passenger side caliper, and then
another full MC to second passenger caliper to even have a reasonable expectation of a complete hydraulic column. Then another full MC to driver rear,
another full to driver front. It takes less to fill front lines because shorter.

As for adjustments, search this forum and re-read manual for those rear drums. Looking for initial settings and parking brake settings. You say you
replaced lines, but you did not mention replacing shoes/pads or hardware - anything or everything new in there?

Keep in mind running temp of fronts and rear won't be comparable because fronts do more work than rear, and discs drag different than drum. More
informative is side to side in this case.

And, just for kicks, you can repeat your experiment after you re-bleed and check hardware on everything by finding a good long (like 5 miles or more)
stretch where you need no brakes and can come to stop using very little brake and then take all six wheel temps. Take as many points per wheel as you
can to compare (laser gun access is different with different style wheels) such as actual front rotor, front center bearing nut, rear drum, rear
center, etc. This test gives you an idea if anything is dragging. Repeat again with driving and stopping hard for 10-15 minutes a few times (stop and
go) and see what you get then to see if temps are even when working hard. The first unloaded run can be complicated by bearing heat if there is
problem, but that is information you need also, so go for it. Write your temps down for the experimental runs. I repeat this temp walk around on trips
for a health checkup - stop to get gas I head first to an empty area and test wheel/tire/bearing/brake temps. Stretch, hit the john, and then get gas.
Takes 3 minutes to check temps once you have a laser temp gun and a routine.

JWIWD
--
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC

[Jim Curran via Gmclist]

Thanks for the great advice. I'll get more brake fluid and a lot more patience.

You didn't mention the combination valve so I assume I can leave it alone.

Thanks!

Jim


--
Jim Curran
1976 Palm Beach
Alexandria, OH

[James Hupy via Gmclist]

The distribution valve is a separation device between the front disc brake
system, and the rear drum brake system. Another of it's functions is to
serve as a warning device should there be a great difference in pressure
between those two systems.
Sounds to me like you still have air in the rear s and stem. They can
be a real bit## to expel all the air due to the siamese lines between the
rear/rear and the intermediate/rear brakes. Often, all you accomplish by
most pump n hold attempts is to chase the air bubbles back and forth in
those siamese lines. Takes quite a bit of fluid sometimes, especially when
lines have been open for a while, or have been replaced like yours were.
Keep on bleeding them. I prefer pressure bleeding, but you use whatever
floats yer boat. Be patient.
Jim Hupy
Salem, Oregon

[Tyler via Gmclist]

I have seen mixed reviews on replacing the combo valve as an OEM quality is not widely available...my solution has been to follow the very important
but often overlooked process in the factory manual that you have to recess the pin to properly bleed the system. I use a zip tie and click it down to
depress the little button. In fact, once set, I leave the zip tie hanging there permanently and just slip it on and off as needed.

If you are not familiar with the process, a pressure bleeder seems to be the favorite on the forums, but I don't have one.

--
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC

[6cuda6--- via Gmclist]

When i run into possible brake bleeding issues or i think the pedal just isn't right i will bleed the brakes in different patterns, i use a catch
bottle and i'm careful as to how much i open the bleeder [open it to much and you can suck air back in during pumping]......i always start with the
furthest away from the master cylinder.....so right rear, then left rear, right center, left center, right front, left front with catch bottle on and
pumping by hand.

Then i will go back to the rear but this time center right, center left, right rear, left rear, right front, left front....again pumping by hand with
a catch bottle.

Then left rear, left center, right rear, right center, right front, left front...this time gravity bleed but with catch bottle.

I have learnt over the years that a catch bottle makes it easier if you keep the hose elevated above the drum height that way air bubbles rise out of
the fluid.....if you bleed by hand with a helper pumping from the cockpit always keep your a finger or thumb on the bleeder opening anytime the
bleeder is open, yes it can make the fluid spray a bit but it keeps air from being sucked in on the return stroke of the pedal.

A bleeder ball, vacuum bleeder or manual all work you just need to use what you have and you may have to repeat it several times and its always a good
idea, in my opinion to make sure the brakes actually apply/release by turning the drum/rotor by hand with brakes applied and then released to make
sure the cylinders/calipers actually work. JMHO.

--
Rich Mondor,

Brockville, ON

77 Hughes 2600

[Emery Stora via Gmclist]

If you really want to go from the farthest first you should go right rear, right center, left rear, left center, right front, left front.
The two right rear brakes are fed from the same line going across the frame.

Emery Stora
77 Kingsley
Frederick CO

> On Jun 15, 2020, at 5:00 AM, 6cuda6--- via Gmclist <gmc...@list.gmcnet.org> wrote:
>
> When i run into possible brake bleeding issues or i think the pedal just isn't right i will bleed the brakes in different patterns, i use a catch

[6cuda6--- via Gmclist]

Yup agreed...thats why i always start with that as stated...then from their i'll modify it a bit just in case any air gets trapped in different places
in the rear T lines, cylinders etc....

Emery Stora wrote on Mon, 15 June 2020 09:22

> If you really want to go from the farthest first you should go right rear, right center, left rear, left center, right front, left front.
> The two right rear brakes are fed from the same line going across the frame.
>
> Emery Stora
> 77 Kingsley
> Frederick CO
>

[Jon Roche via Gmclist]

Jim-

These GMC's will stop. I know this because of all the stuff I had fly forward when I slammed the brakes on yesterday when I thought I was missing a
turn....


I have to admit- I now use Jim Hupy's brake bleeder: http://www.gmcmotorhomemarketplace.com/jhupy/

it has never failed me yet... if it does not easily bleed the brakes quickly, you have other issued to deal with, such as bad lines, bad master
cylinder or calipers or cylinders. I just recently had a coach that would see no fluid flow from the hupy pressure bleeder, but easily bled when you
did the old school 2 person step on the brake and time the bleeding. a few hours of pissing around with that, it just would not want to stop.

tosses a new set of hoses/calipers and a proportioning valve, a 10 minutes brake bleed with the bleeder told me things were improved as fluid was
flowing as it should. 5 minutes of that is hooking up and removing the brake bleeding plate.

I have done this well over a dozen times now, and that pressure bleeding method has been fool proof in making sure you are not dealing with air in
the system.


With that said, I also never do anything with the valve other then replace it when it is questionable. on my coach, the questionable valve for
sure was a fix of having bad brakes after all other parts were new. did not have a soft pedal, just took way too much effort to stop once the
peddle bottomed out.


and also for adjusting the brakes, it really needs to be done with wheel removed. I have had good success in adjusting them up to point of stopping
the drums, then backing off so you can spin them. I like to do that as a last step, because I will also press the pedal a little bit as to make sure
the brake pads seat/center a bit. Trying to adjust the brakes up with the tires on, works, but the leverage the tire has on the drum can really
throw you off on where they need to be set at when you spin them.

left compared to right side should be near the same temps after dropping. I will see varied temps a little mid axle as compared to rear axle, with
my mid reading a little higher.




--
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/

[Richard H Staples via Gmclist]

Jim,
Are you SURE the rear brakes are adjusted properly? Before redoing the bleeding process, I would carefully adjust the rear brakes. STEP ONE is to
be certain the parking brake cables are completely slack and the parking brake lever at each wheel is at rest back against the shoe. (It appears from
your description that you have drum brakes. No problem with that.)

STEP TWO is to adjust the shoes, snugging up until you cannot turn the drum in either direction. Turn it both ways as you tighten the brakes to be
sure everything is centered. Then back off until the drum turns more or less freely, again turning it both ways. (If your drums are not perfectly
round and concentric with the hub, and your shoes either worn in or arc ground, you may not be able to eliminate all drag. My NEW drums weren't
perfectly round/concentric.)

STEP THREE: Only now should you try and adjust the parking brakes. Again, the cables must move freely and release ALL tension when off. If this is
not possible, leave 'em loose for now and proceed with bleeding as others have described. Replace cables as soon as you can. (I believe Jim K
carries them.)

STEP FOUR: After bleeding each wheel, have your helper (or a big screwdriver against the driver's seat) apply the brakes, and be sure that wheel
locks up. Then release the brakes and be sure that wheel again turns freely. If either test fails, you probably have a sticking wheel cylinder,
caliper piston, or caliper bushings/pins.

If all else fails and the pedal is still spongy or low, I'd try tightening all 4 rear brake adjusters until the wheels lock up, and then try the
pedal. If it is STILL spongy, then you have more air OR possibly bad flex hoses. (They CAN get soft and swell under pressure.)

My .02. , HTH
Rick Staples
--
Rick Staples, '75 Eleganza, Johnstown, CO

"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien

[James Hupy via Gmclist]

Got to have concentric brake drums, good return springs, and wheel
cylinders that work as they should. No drag. E brake cables must release
completely. Then, jack up the rear of the coach and remove the wheels and
tires.
Then, and only then can you proceed with brake adjustment. Adjust the
star wheels until the drums will no longer turn, AND the star wheels will
turn no further. Then, back off the star wheels 5 clicks at a time until
the drum will turn. Then, back off 5 clicks until slight drag can be felt
on the drum. If it free spins, that is too loose. Do all 4 drums this way.
Then check your pedal with engine running. You should have a firm pedal. If
it is spongy, go back and bleed the lines until this procedure gives you a
firm pedal. Remember, the brake drums expand away from the shoes when at
operating temperatures.
These coaches will stop well if the brakes work properly. OP

[Johnny Bridges via Gmclist]

I get slow flow when I bleed the back. Gushes out of the calipers in front. The back brakes are all new, as is the (chinese) valve. Maybe the valve
is the problem? Back brakes behave like there's still air in them...

--johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell

[Dolph Santorine via Gmclist]

If you have time when bleeding the brakes, there is this thing called “gravity”

It’s not just a good idea - - - it’ the law!

Seriously, with a gravity the challenge is keeping the master cylinder reservoir full.

Dolph

DE AD0LF

Wheeling, West Virginia

1977 26’ ex-PalmBeach
Howell EFI & EBL, Reaction Arms, Manny Transmission

“The Aluminum and Fiberglass Mistress”

|[ ]~~~[][ ][] \
"--OO--[]---O-"

[John Wright via Gmclist]

If you have drums in the back then forget what I said, but for those of you that do it is relevant.

JR Wright