POSSIBLY found my MPG issue

LibertyCRD · **Posted:** Sat Jul 17, 2010 10:38 am

It's going to require more driving and a few tanks of fuel to know for sure...but I might have found my issue.

Last weekend I did some routine maintenance on the Jeep. I changed the t-case fluid, front axle fluid, and inspected/lubed the rear brakes. While inspecting the rear brakes, I noticed that the rotors would not come off. I beat and beat on them with a hammer to hopefully break them free...but no luck. I had to pull the rubber plugs from the back of the drums and used a flat-tipped screwdriver to losen the park brake shoes.

After I losened the park brake shoes up, the rotors finally came off with some force. I cleaned up the shoes and hardware with brake cleaner, and then put the rotors back on. I did NOT retighten the shoes afterward....I just left them in the position they were in at the point that I was able to finally tug the rotors off.

So far this week....according to my EVIC the MPGs are up 2 miles per gallon. My EVIC almost always shows me 26 to 26.5 MPG on my normal driving circuit. This week it's showing me 28.5 or slightly higher so far. It appears that my fuel economy is up significantly since lubing the caliper sliders and adjusting the park brake shoes.

NOW... the question is, will this improvement turn out to be for sure over a few tanks? Or is it just a fluke so far? Time will tell. And more importantly...I have not used the park brake since doing this. Once I do use it, will it automatically tighten the adjustment nut up on the shoes so that they are tight again?? How does the park brake mechanism work on these? I don't want the shoes to tighten up so much like they apparently were from the previous owner. Whoever did them before had them WAY too tight.

RAF 3829 · **Posted:** Sat Jul 17, 2010 3:10 pm

They should be adjusted like any drum brake...adjusted enough till you hear a slight scraping.

ATXKJ · **Posted:** Sat Jul 17, 2010 5:56 pm

it's supposed to auto tighten when you pull the lever - but it doesn't do it well
best bet is pull the lever up 3-4 clicks - and then adjust the brake at the drums.
when you release it has extra clearance, but you can still pull it higher to park.

Big Montana · **Posted:** Sat Jul 17, 2010 6:01 pm

My e brake doesn't work at all. This must be something the brake guy forgot to adjust when he worked on my brakes before.

DieselJeepLuvr · **Posted:** Sun Jul 18, 2010 9:29 pm

I almost never use my ebrake. Only time is when I'm loading my boat on a steep boat ramp.

geordi · **Posted:** Sun Jul 18, 2010 10:05 pm

I adjusted mine when I had the discs off for the rear pads last week... Turned the thing to completely retract the drum pads. The lack of drag is is VERY impressive now, they must have been dragging constantly. I never use the thing at all, so it doesn't really bother me. Maybe someday I will re-adjust it, like when I get new discs in a few months.

LibertyCRD · **Posted:** Wed Jul 21, 2010 11:05 am

Well, apparently that was NOT it. It's just that my EVIC is still useless.

My past 5 tanks hand calculated:

24.2
23.4
23.3
23.4
24.2

I also installed a new thermostat during that time. I am still not budging any by the end of a tank. My MPG on my normal circuit is rock solid at 24 MPG right now. So the brake adjustment and the t-stat didn't do anything at all for economy.

So I'm just going to have to face the fact that the GDE tune isn't helping my MPGs. And I'm going to have to be happy that it IS increasing the fun factor...and I'm still getting several miles per gallon more than our gas KJ ever did no matter how we babied it.

europachris · **Posted:** Wed Jul 21, 2010 1:31 pm

here's what I found happens (especially if you live where they salt the roads): the parking brake is actuated by the cable pulling on the arm at the backing plate. The arm pivots on another arm that in turn pushes on the shoes to engage the drum. The two arms are steel on steel and rust. Even with regular use, ours rusted solid to the point where the right side was always "on" somewhat until the lining material burned right off the shoes and started trying to lock up the wheel while you were driving as the lining wedged itself under the shoe remnants.

I bought the full lining and hardware kit, but had to clean up the lever and pivot arm and grease them. Additionally, the braking surface of the drums was completely rusted over, so I cleaned that up with a flap wheel and die grinder.

Now the parking brake works about as well as I remember, which is still about useless. But definitely better. It's a stupid stupid design from both a corrosion of the mechanism standpoint as well as the fact that since most people who drive slushbox vehicles rarely use the parking brake anyway, and even if they do, it's only a static application, the braking surface never gets polished clean. It's just a dirty pad on a rusty drum - and then we wonder why they don't work worth a darn!!! :banghead:

To keep the braking performance, I recommend using the same procedure as when breaking in the new shoes - coast in neutral at 25mph and then use the parking brake to stop the vehicle. Do that once a week or so and that should keep the shoes and drum somewhat polished and clean.

It definitely makes me appreciate my VW handbrake design where it uses the same rear disc pads for both service and parking even though it then requires a special tool to push the pistons back during a pad change. That's nothing compared to the cussing and swearing I did changing out the CRD parts.

geordi · **Posted:** Wed Jul 21, 2010 5:45 pm

There was a special tool to change the rear brakes? Huh. I know they are supposed to screw-in at the same time the piston is compressed, but I did mine with a standard C-clamp like I do all my brakes. It did rotate, probably b/c the pad on the end of the clamp screw also rotated. I just never thought it was that big a deal to need a special tool. :2cents:

mngoat01 · **Joined:** Wed Aug 06, 2008 11:25 am **Posts:** 67

I got front brakes hanging causing poor MPG and it's starting to piss me off. New caliper/rotors and pads and still the same. Drive for some time jack up front end and wheels are very difficult to turn let them sit for a bit and the free themselves. I'm thinking my problems is somewhere in the abs/master cylinder system. Been battling poor MPG for a while now so i feel your pain

mjk · **Posted:** Wed Jul 21, 2010 6:50 pm

Had the same problem with mine a couple of years ago. The next time you feel them drag, jack it up and crack the master cylinder bleeder. If they release as mine did that eliminates your calipers

geordi · **Posted:** Wed Jul 21, 2010 11:46 pm

Have you flushed the brake system? That sounds like some kind of contamination in the fluid. It isn't releasing the pressure and the heat builds up, making it expand even more, which drags more, making more heat... And the cycle repeats.

bakersoil · **Joined:** Fri Jul 23, 2010 5:43 am **Posts:** 68

geordi wrote:

Have you flushed the brake system? That sounds like some kind of contamination in the fluid. It isn't releasing the pressure and the heat builds up, making it expand even more, which drags more, making more heat... And the cycle repeats.

Check your brake hoses. The mid 90's Chevy trucks were bad about the hoses deteriorating and plugging up. The brakes would still stop but the fluid couldnt return causing excessive drag.

mngoat01 · **Joined:** Wed Aug 06, 2008 11:25 am **Posts:** 67

geordi wrote:

Have you flushed the brake system? That sounds like some kind of contamination in the fluid. It isn't releasing the pressure and the heat builds up, making it expand even more, which drags more, making more heat... And the cycle repeats.

Looking into it to see if i can do it myself or just bring it in b/c of the ABS system. Thanks

mngoat01 · **Joined:** Wed Aug 06, 2008 11:25 am **Posts:** 67

bakersoil wrote:

geordi wrote:

Have you flushed the brake system? That sounds like some kind of contamination in the fluid. It isn't releasing the pressure and the heat builds up, making it expand even more, which drags more, making more heat... And the cycle repeats.

Check your brake hoses. The mid 90's Chevy trucks were bad about the hoses deteriorating and plugging up. The brakes would still stop but the fluid couldnt return causing excessive drag.

Was think the same thing.....Do you think it could be both side at the same time going bad? Seems like maybe that would be one side or the other but i guess if the production of the lines where the same they could go bad at the same time. Thanks.

linewarbr · **Posted:** Fri Jul 23, 2010 11:19 am

I've had something similar for over a year now. I had my rear brakes changed at Midas (I don't mess with brakes) and ever since, when the Jeep is coming from a cold start, the rear brakes drag and squeak for a mile or so. I guess it could be the e-brake doing that; I think I'm going to try europachris's 25 mph neutral suggestion to see if that helps any.

*For the record, I came out of a manual trans into the CRD, so for the first year or so of ownership I always set the e-brake - even on a flat surface. Habit.

Rixram · **Posted:** Fri Jul 23, 2010 5:02 pm

Problem with ANY parking/emergency brake is that the less they are used, the more screwed up they get.

bakersoil · **Joined:** Fri Jul 23, 2010 5:43 am **Posts:** 68

On a 93 chevy truck both front brake hoses were bad at the same time and the same amount. I would have replaced everything before the hoses if not for a good mechanic friend told me to see if I could blow air through the hoses. That was a first for me.

POSSIBLY found my MPG issue

Who is online