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Strange brakes in the morning...

4speedfunk

Well-Known Member
Messages
4,212
Location
Tardville
After logging 5000 miles or so on the SAS, I've noticed something weird happening after sitting over night.

In the mornings, I can start my truck...take off down the road...everything's normal. Then when I hit exactly 40mph...the truck will suddenly dart to the right, and slow down. Clearly the right-front caliper is being activated. The RF caliper remains clamping for 5-seconds before releasing itself. After the release, there is a 3-second pause...then the truck darts to the left, slows down again...clearly the LF caliper is being activated. After 5-seconds of clamping the LF caliper, it releases. Everything re-sets and its good the rest of the day. This only happens after sitting overnight...and only happens the first time I hit 40mph. It occurs when driving normally...without a foot anywhere near the brake pedal. No dash-lights whatsoever. No ABS pulsing. Everything works and feels exactly as it should. My brakes are awesome, and I have no other issues. Strange.

I have pulled my front rotors, calipers, and such...to have a look. I've also checked my home-made ABS rings and sensors. Everything looks 100% perfect. TCS, ABS, and VSS all work great, and the only possible thing I can think of, might be some air in the brake lines. I get the feeling this might be tied to the electric brake booster, and the H3 might be performing a "self-check" every time I reach 40mph. I'm guessing it does it every time...but its only noticeable when the truck has sat overnight and somehow lost pressure from the PB booster. After it does it once...I'm good the rest of the day. I'm going to try pumping the pedal 5 or 6 times before I leave the driveway each morning to see if it has any effect on the issue. Of course I'm highly modified...but I'm using all stock brake components. Anybody else experienced this?
 

f5moab

Mr. Beretta
Messages
1,986
Location
Hiding in a potato patch in Idaho
ABS self-diagnostic checks are performed when the vehicle is first moved after startup. Most will never realize it, but if you ride the brake pedal when you first pull out in the day, you can feel the slight pulsations in the brake pedal.
The brake booster motor is part of the hydraulics, not the ABS system. It's job is to keep the accumulator pressurized with fluid for the system. Not sure of the spec, but the accumulator should be able to hold pressure longer than overnight. Are those hyd connections tight at the motor?

I have no idea, but it is really strange it hits at the same mph, and after sitting a while. Sitting here it almost sounds like stab control or TCS is trying to do something for no reason.
 

4speedfunk

Well-Known Member
Messages
4,212
Location
Tardville
Ahh...that's sort of what I deduced. Its definitely a self-check thing, I have learned to know when its coming. Its predictable and repeatable...although some days it seems more drastic than others. Due to the 37" tires and pitman/box steering...you had better have a good grip on the wheel first thing in the morning! Everything is more noticeable with the box (instead of R&P). MkMcgreg drove it a couple weeks ago, and he can vouch for me...it damn near shot off into the ditch! (he wasn't expecting it).

Hyd. connections tight at the motor??? Hmmm. I'm not sure where you mean but, I'll check all of my connections and fluid level. I can say for sure that I had the entire brake system drained for the SOA & SAS. I actually removed 3-feet of solid brake line and a T-block up by the radiator. I had all of the brake lines loose from the master cylinder (motor?), at one time or another. When it was all done...I used a reverse-bleeder and filled the system from the calipers-up to the master cylinder. I think this problem has just recently started, and I don't think its due to any of the SAS work. Perhaps I'm low on fluid or have a leak somewhere. I'll check that.

I agree its very strange. My first thoughts were the same...it had to be TCS or ABS trying to do something. But I do not get any TCS, ABS, or VSS lights when this occurs. Nor do I have any codes...active or stored. Also, it happens while I'm accelerating...NOT while I'm braking. (even more strange). The brakes work great with EBC-Greenies and PowerSlot rotors (better than stock), and all systems seem to work perfectly. This blizzard that hit recently was the test weather I had been looking for. I took my H3 out and intentionally flogged it, trying to induce all of the electronics. Believe me...they were working overtime! I got TCS lights when I was supposed to. I got VSS lights when I was supposed to. I got ABS lights when I was supposed to. So I feel pretty confident that the computer side of things is working correctly. This has to be something mechanical (or hydraulic). I need to check for leaks, air, or low fluid. Thanks for your input...I'll post up what I find out.

P.s. The H3's electronic systems work so good...that's its actually quite difficult to get the H3 sideways. No more donuts in the Wal-Mart parking lot! :sigh:
 
Last edited:

Scarsman

Sponsor
Messages
1,561
Location
Monroe, WA
Can't wait to hear what you figure out. Strange problem indeed!

You are correct about the GM stabilitrac system, it is very effective. My '06 Envoy had it, and it was a real buzz kill! I was always turning it off so that "I" could drive the vehicle!

Sent from my C771 using Tapatalk
 

08H3

Well-Known Member
Messages
1,314
Location
United States
Just take it in to Lockhart. They'll be all over that in a jiffy! Ha!

Hope you figure it out soon.

BTW, I'm jealous Matt got to drive that thing before me. We need to get a Redbird run scheduled.
 

mkmcgreg

Well-Known Member
Messages
196
Location
Carmel
Yea I can vouch for it.. It would have been nice had someone informed me prior to the ditch/ on coming traffic dance I did once we hit forty lol
 

3Hummers

Super Moderator
Staff member
Messages
10,398
Location
Central Texas
That would have taken all of the fun out of it. besides this shows he had absolute confidence in your driving skills. :)
 

4speedfunk

Well-Known Member
Messages
4,212
Location
Tardville
Great advice 08H3. Lockhart should just give up and close for good! I've been seeing this new Cadillac commercial where two guys are flogging one all over Monaco. I don't get it. Cadillacs are for blue-hairs in Florida, and GM should quit trying to make them sporty and go back to what made Caddy a legend....big, floaty, cruisers, with zero road feel and AC so cold it makes you car-sick. I would gladly take a Saturn, a Pontiac, or a Hummer over a Caddy. Oh wait...they got rid of those. Duh!

MK, sorry I didn't say something ahead of time. Actually...I was jibber-jabbing on the cell phone. I knew it was coming and I tried to warn him...but, I couldn't relay the upcoming dart in time. When it happened he shot me a "WTF?" look...and I knew right then that it wasn't just me imagining it. The surprising part is after it does the RH purge (and you get it back on the pavement)...there is a pause and the truck goes back to normal and tracks straight down the road. At that time you assume the weirdness is over, and relax. Right about then...the LH caliper does the same thing, and the truck wants to dart across the centerline! I'm fairly certain this is something that probably happens to other H3's but, it's amplified on mine because of the crossover steering, and lack of sway bars. Anyway...thanks for keeping it up-right Mk. Hopefully the romp thru the river-bottoms made up for the this.

I'll get to the bottom of it.
 

mkmcgreg

Well-Known Member
Messages
196
Location
Carmel
I wonder if you could somehow "reset" the truck by taking the battery out to replicate the issue on command.

And yes the river run more than made up for it. You have built a very nice rig!

08 I am up for a Redbird run but I don't know if we should bring 4speed and alpha along. Apparently they found some pretty intense trails we missed ;). If CJ had butt pucker I probably would have had a heart attack
 

cgalpha08

"Like Nothing Else"
Messages
3,584
Location
Indianapolis, IN
I wonder if you could somehow "reset" the truck by taking the battery out to replicate the issue on command.

And yes the river run more than made up for it. You have built a very nice rig!

08 I am up for a Redbird run but I don't know if we should bring 4speed and alpha along. Apparently they found some pretty intense trails we missed ;). If CJ had butt pucker I probably would have had a heart attack

As long as its not muddy i think that trail will be fine, but if its muddy, well then we are all doomed. Ill come so you all can have someone to pull out when i get stuck :)
 

4speedfunk

Well-Known Member
Messages
4,212
Location
Tardville
Guys...I was wheeling in Freedom (about 15 miles north of Redbird) on Christmas Day. That night we got 12" of snow, and its just now starting to melt along with another inch of rain. So, I can promise you...ITS BEYOND MUDDY at Redbird right now. It would difficult to walk on some of those trails.
 

4speedfunk

Well-Known Member
Messages
4,212
Location
Tardville
Sorry...I've been goofing off (sailing). I did notice that if I pump the brakes four or five times before I leave my driveway...it doesn't do it. That tells me its most likely some air still trapped in the lines. I'll re-bleed them this weekend and see what that does.
 

alrock

El Diablo
Staff member
Messages
10,442
Location
Scottsdale
Isn't this similar to what Steve #1 used to talk about with his 5 speed? He (or someone else) talked about soft brakes in the morning when heading out of the driveway. I believe the thinking was that in a manual he wasn't pressing the brakes before rolling out and that the booster wasn't fully pressurized
 

4speedfunk

Well-Known Member
Messages
4,212
Location
Tardville
Could be. Its very strange but, then again...so is an electric motor that generates brake vacuum. I've never felt anything like it, and I can only assume that it is caused by the system sensing low brake line pressure and "pumping it up". I am still using 100% stock brakes, and the only thing I did with the solid axle swap was install longer flexible lines at the front calipers & rear diff. Seems like air in the lines could cause it. In fact...its the only thing I can come up with. I still have no dash lights, and it occurs without touching the brake pedal at all. The darting is probably amplified by my steering system, as the box generates more "feel" than the rack & pinion did.

I would be interested to know if Steve #1 did a caliper replacement or some other work that allowed air into his system.
 

4speedfunk

Well-Known Member
Messages
4,212
Location
Tardville
UPDATE: After trying every brake-bleeding trick I know...I bought a vacuum bleeder. This little guy plugs on the bleeder valve, and it has a reservoir that captures the brake fluid as you use it. It's basically a hand vacuum pump, and you connect it to the bleeder valve...pump it down to 30lbs or so...then open the bleeder. It sucks the air bubbles out (instead of pushing them out)...along with some fluid, which gets captured in the small reservoir. I was very surprised at the amount of air trapped in the rear brake lines...and I knew immediately this was the problem. Even though the symptoms seemed related to the front brakes...the air in the rear brake lines must have been the problem.

I did all four calipers, and when I got done, the feel at the pedal was much firmer...no sponginess at all. So far so good...and the strange darting that happened in the mornings is all gone. The truck stops much better too.
 

mkmcgreg

Well-Known Member
Messages
196
Location
Carmel
Glad to hear the problem is fixed... Any ideas why that would cause the issue?? Seemed weird that it always cycled right side then left side as if the air was amplifying a normal start up procedure you normally can't feel

Any way glad its fixed
 

4speedfunk

Well-Known Member
Messages
4,212
Location
Tardville
Mk...it was definitely related to some sort of "start-up & purge" test that occurs as soon as you hit 30mph. It would do it everyday without question. Only when I pumped the brake pedal 4 or 5 times before leaving the driveway...would it not do it. I think the puter was sensing pressure in each brake line and making adjustments in pressure with the motorized booster. And just like a normal brake system...once you had it pumped up, there was no problem. Thats all I can come up with. Strange.

Alrock...here it is...

http://www.ebay.com/itm/Brake-Bleed...t=Motors_Automotive_Tools&hash=item2328541fee
 
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