('90 F150, 5.0, 180k mi)

I already know that the brake fluid in this truck is beyond nasty and needs to be completely flushed. I am having an issue that's strange though. In normal driving, my pedal sinks way down near the floor before stopping the truck....but it eventually stops. NOW, if I have a load in the bed (firewood, for example), my brake pedal stiffens and the truck stops much better.

As I said, I know the fluid needs changing, and I'm also suspicious of the MC. The part about the braking being better with a load has me puzzled though. It also did better braking back in Dec. when I was pulling a small trailer with a golf cart on it. Could that indicate that it's a vacuum-related issue? Could it just be purely coincidental?


TIA,


Wade

 

That seems pretty strange. I've never heard of a vehicle stopping better with a load in the back.

In any case, I would also check the adjustment on the rear shoes. They should drag lightly all the way around when you spin the tire.

Does the pedal just go all the way to the floor or does it sink slowly?

 

You describe it like you have a load sensitive proportioning valve, which I am pretty sure no F series in that year ever had.

otherwise any chance the master is leaking between the circuits and when loaded you sorta pump the brakes 1-2 times in anticiaption and it swells the pressure seal?

 

The pedal goes pretty freely 75% the floor, and then slows the truck.

The rear brakes need attention as well - When damp out, they grab really hard until they're warmed. I read some time ago that new shoes and/or wheel cylinders would correct that.

The truck is still in great shape. With gas prices though, it's been relegated to trash-hauling duties, and an occasional trip to Lowe's. Lack of use isn't helping it any, but I can hardly afford to drive it either! LOL! I've let these brake issues go on for too long, and I need to make the effort to get them corrected.

/tries to light fire under self



Quad: I don't think I drive it any differently with a load than otherwise. As a matter of fact, I often pump the pedal (when driving unloaded) to try to bring it up, and it actually has little to no effect....which I also find strange.





Wade

 

You definitely need to pull all the wheels off and do a thorough inspection. Make sure to check under the dust boots for the wheel cylinders, if there is fluid in there (a little moisture is ok) then they need to be replaced.

Brakes aren't hard to do yourself at all, but you can drop some serious coin on them at a shop.

 

Yeah, brakes don't scare me too much. While I'm no expert, this is certainly something I will do myself before paying a shop, where it'd cost a ton of money; you're absolutely right about that!!

My initial hunch is that I need new rear shoes, wheel cylinders, possibly a new MC, and definitely have the fluid completely flushed.

I've been looking at maybe buying one of the little Mityvac (6820) gizmos for swapping out all of the fluid......

Wade

 

I suspect your rear brakes need to be adjusted. What's happening is most of your pedal stroke is used just to bring the brake shoes close to the drum, and the last bit is where they touch and then all 4 wheels begin to create breaking force. Drum brakes by design require more fluid to operate than a disk, and the master cylinder is sized to compensate for this some, but if the brakes are way out of adjustment you end up using most of the pedal stroke and/or pumping the brakes just to make up the slack.

 

drum brakes are designed to return to rest when not applied. adjustment due to wear is provided by the star adjusters (you know, those goofy thingies on the bottom that rust up and dont turn)

calipers just simply stop squeezing. the larger reservoir in the master is for the disc side.

a good grab when cold tells me some rust is inside the drum. might not be the worst idea to turn out 10 thou and remove the ridge line. I have seen rusty brakes grab so hard the keepers are sheared off and the lining fractured or otherwise damamged.

the 'when loaded' part even makes me think the spring position and changed axle angle is pulling on partially frozen e-brake lines, semi-applying them.

or rusty wheel cylinders (brake fluid is a wonderful rust solvent)

f150 brakes take about 10-15 minutes from start to finish on each side if you are replacing everything. the wheel cyls are about $11 each, the spring/retainer kit is about $9 for both sides, and the shoes are whatever you can get em for. rebuilding all but the worst basket case adjuster takes 5 additional minutes tops.

with no air in the line, a deep pedal sink points to an internally bleeding master. At todays prices they are not worth rebuilding. chinese slaves have already done that for <$25 each.

should you go that route, pay attention to, and take with you the fitting that is curiously sized. even tho its a 3/16 line, ford used one large fitting. you can find a 3/16-3/8 adaptor in the funny drawers at advance (et al) or cut the 3/16 off a new line and re-flare the line using the old fitting if salvagable. by now, a 1990 needs a lot of brake lines replaced.

 

Thanks guys! Quad, I believe that my plan will include totally rebuilding the rears - they haven't been really right since I've had the truck (6yrs), so this will be a good time to [hopefully] get them right. I'll also plan to replace the MC - I don't trust myself to rebuild one (although I've rebuilt wheel cylinders before) - as you say, for the money, it's not really worth taking the chance.

Thanks again!!


Wade

 

Wheel cylinders, calipers and master cylinders all fall into the same category.. they're so cheap it's not worth your time to rebuild them, just replace them.

The auto adjust thing on the Ford drum brakes is a terrible thing, they often sieze up or just fail to do thier job, so it's pretty common for the rear brakes to get way out of adjustment over time. I have contemplated installing disk brakes on my truck on many occasions just because of this annoyance, but haven't stumbled across the parts needed or had the time to mess with it.

 

Agreed - the auto adjusters bring the suck.

I adjust mine every oil change. Pedal stays nice and high.

 

Auto-adjusters = Something else to be sure to address whilst rebuilding rear brakes.



Thanks guys!!


Wade

 

I had a similar issue with my bronco but not nearly as bad. I had the wheel bearings leaking on both sides that new seals would not fix. Ended up yanking the bearings out and putting all new brake shoes on the truck to fix the rear end. I used a repair bearing for both sides to replace the old bearings. I also found out that a past owner had lost the passenger side bearing, probably due to overloading the truck because even the springs were nearly flat in the back, and had not completely pulled the bearings or worn rubber seals out of the axle tube. After going through the intense labor and installing of new bearings, the brakes were freaking awesome with out the sinking feeling of the pedal.

 

Well, I put the truck up on jackstands today to give things a good looking over. The rears were first, and actually looked pretty good. There was lots of meat on the shoes, and the drums were relatively smooth. The cylinders were a little gunky, but not terrible. I re greased the contact points behind the shoes, adjusted them out a wee bit (auto-adjusters were not rusted up, and actually moved smoothly), and slapped the wheels back on.

I moved to the front. This is where I think the problem was. The Dr-side pads were pretty much gone but not to the rivets yet. The pass-side was bad. The outer pad was close to the rivets, but the inner pad was toast! Unfortunately, it had chewed up the inner rotor surface a little. I opted to take the lazy way out ( I know) and put the pads on without turning the rotors. Pads are cheap, and this was actually a very easy job, so...... I took it for a test drive, and to my surprise, the pedal came up to normal, and was 95-100% better!!

I don't know why, but it never occurred to me that front pads could be causing this. I guess the caliper pistons were pushing as far out as they could, and just couldn't do any more - causing the low, low pedal....? Anyway, there are some other things that I need to do with the brakes, but at least now it's safer until I can get to those other things!



Wade

 

make sure you adjust your front wheel bearings properly, loose wheel bearings can knock the piston back into the caliper and cause a low initial pedal. might as well repack those bearings as well. also make sure the caliper is sliding side to side freely, uneven pad wear points to a bound up caliper slider

good luck

nate