First Diesel Braking Issue.

[CrackerJack]

Evening everyone,

I have bought my very first diesel which is a 1987 Ford F250 with a 6.9 diesel in it. I bought pretty dang cheap and was in a no running condition. With a lot of patience a reading I have got this thing running pretty good now. I have this odd issue with the brakes though. I have replaced the rear wheel cylinders, ABS Hydraulic unit, Brake Booster, Master cylinder, and have bleed the system fully several times now. Even bench bleed the Master Cylinder.

So the issue is I feel this thing does not stop well. I went back and adjusted the back brakes to the point where when I slam on the brakes backs would lock up and squeal. Adjusted the back brakes off a tad to make sure I had them adjusted pretty good. I have checked the front pads to make sure that enough pad which I do I compared them to new ones.

I hooked up a vacuum gauge to the the T portion of the vacuum line and was pulling about 24hg at idle. I did noticed when I press and release the pedal it drops to 11-13hg but build back up in a bout 5 to 7 seconds. I also did a semi leak down test and turned the engine off. It dropped about 2hg in about 3 to 4 minutes, so there is some small leak somewhere. I know I do not think I have a leak in the brake booster because It was holding vacuum for a week since I have not started it in a week and sucked air when I pulled it off to test.

I am not sure if I am just not use to this truck at all, or a diesel let alone. I know it is 8800 gvwr so I do know it is pretty heavy. I have honestly been to nervous to drive it far at all because of the brakes. ( I might be just use to new cars since my daily driver is a 2014 Dodge Charger.)

Any advise or things I could be missing or need to check for?

Thanks and have a great day.

 

[riphip]

if you do not have cruise control, probably vacuum pump issue

 

[icanfixall]

WElcome to the forum. Sounds like you have done most of what repairs our sad brake issues. I found the easiest way t find a vacuum leak is use a smoke machine. I just used one on my 98 Accord to find a vacuum leak. The smoke generator makes smoke from baby oil. Then its pumped into the fuel tank. Turns out under my car is a fuel tank vacuum purge module. Because of the fuels today these modules are ruined because the Bio fuel mix is not what these were designed for. So o rings fail and you end up with a vacuum leak. If you can borrow a generator just remove the vacuum line from the vacuum pump and start the smoke from there. Its just that simple and sure beats working on every hose in the vacuum system.

 

[CrackerJack]

if you do not have cruise control, probably vacuum pump issue

I was leaning toward this but first time dealing with a vacuum pump.

 

[CrackerJack]

WElcome to the forum. Sounds like you have done most of what repairs our sad brake issues. I found the easiest way t find a vacuum leak is use a smoke machine. I just used one on my 98 Accord to find a vacuum leak. The smoke generator makes smoke from baby oil. Then its pumped into the fuel tank. Turns out under my car is a fuel tank vacuum purge module. Because of the fuels today these modules are ruined because the Bio fuel mix is not what these were designed for. So o rings fail and you end up with a vacuum leak. If you can borrow a generator just remove the vacuum line from the vacuum pump and start the smoke from there. Its just that simple and sure beats working on every hose in the vacuum system.

Thanks icanfixall. I think I am going to replace all of the vacuum lines since they all appear original. Only looks like 3 of them. One from Pump to T then one to the Brake Booster than one the air intake area (not sure what it is called on diesel) and one that seems to control the AC/Heat controls.

As of replying to this I went out to remove the Vac gauge I had set up and it still had 20hg vacuum on it. So it seems to be holding pretty good but not best imo.

 

[OLDBULL8]

Don't look to me that you have a vacuum problem, vacuum would have nothing to do with the rear brakes locking up, but it's a good thing to replace all vacuum hoses due to age.

On an 88 you might still have the proportioning valve on the rear axle, if you do, it could be adjusted wrong, or someone removed the actuating arm. The valve compensates for bed load, the heavier the load the more braking (sooner/quicker) you have.

By backing off your brake shoes, that is kind of acting like the proportioning valve does.

Locking up brakes is also caused by the backing plate having wallowed out mounting bolt holes or the bolts are not torqued tight enough, which allows the brake shoes to rotate slightly.

If you replaced the brake shoes, I would leave them adjusted up so the wheel just turns, they will wear in pretty quick.

 

[The Warden]

Welcome aboard!

So the issue is I feel this thing does not stop well.

Maybe I should ask first...when you say that you feel like the truck doesn't stop well, can you be more specific?

If it feels like you need a lot of effort to move the pedal even a slight amount, that would indicate a problem with the brake booster, vacuum pump, or vacuum system.

If the pedal moves with "average" effort and it just feels like the truck takes a long time to stop...you mentioned that the rear brakes were adjusted manually and you can lock them up. I know you said that you checked the front pads and rear shoes and there was sufficient material, but what shape was the material in? Any oil or grease contamination? At what point does the pedal stop?

Also, where did you buy the components that you replaced? There's always a possibility that you received a bad brake booster and/or master cylinder and/or ABS unit.

Given that you're unfamiliar with the vehicle, I wonder if it might be worth seeing if there's a member in the area who could take the truck out for a drive and see if maybe it is behaving normally and it's just a matter of getting accustomed to it?

On an 88 you might still have the proportioning valve on the rear axle, if you do, it could be adjusted wrong, or someone removed the actuating arm. The valve compensates for bed load, the heavier the load the more braking (sooner/quicker) you have.

I could be mistaken (I'm still learning the newer vehicles ), but I thought that the ABS valve replaced the proportioning valve? Or are there trucks out there with both valves present?

 

[fsmyth]

Of all the vehicles I have owned, my '91 F350 has absolutely the worst brake FEEL
of any of them. This includes some from the late '40's
Took me a while to get to trust it.
That said, the brakes do work, and mine has stopped some seriously overloaded
trailers with non-functioning brakes.
Stock vacuum system. No maintenance, other than adjusting the rears.
And replacing the booster because the little plastic bushing swelled up and
made it hard to push the pedal.

If you look, you will find quite a few posts on replacing the vacuum system with
a hydraulic system. For some very good reasons.

 

[FORDF250HDXLT]

my f250 never stopped well either and i had the system all replaced.nothing made it stop worth a lick until i swapped to hydroboost.that cured all that ailed it and then some.
the only trucks of this era that had safe brakes where the f150's (due to being light) and the f450's (due to having 4 wheel disc brakes with massive calipers and hydroboost)
we can't lighten up the truck to match an f150,so the most logical choice is to bolt up the f450's hydroboost system.nothing else you do will come close to adding the stopping power.going hydroboost from vacuum,adds more stopping power than any of the turbo kit's add hp to the engine. - that never gets old saying that.


it took me almost getting into a fender bender to wise up and do the swap.use caution because you may not get so lucky if you postpone.any truck hauling heavy should do the swap asap.
i'll never forget it.i was coming down a dual lane hwy in a city to a stop below.loaded with chips/wood and chipper in tow.....was only going like 20mph.pressed and just mush......oh uh here we go.if i didn't crowd the guy beside me and if he wasn't so kind to move over for me,to let me borrow some of his lane, to avoid the car in front of me,id of folded up the little car.i think it was literally that night i ordered parts online lmao.

imo,i think at the very least that all the 7th,8th and 9th gen f250/f350 big blocks and diesels should of just came with hydo.load them up to max capacity and the vac system is just downright dangerous.

 

[snicklas]

imo,i think at the very least that all the 7th,8th and 9th gen f250/f350 big blocks and diesels should of just came with hydo.load them up to max capacity and the vac system is just downright dangerous.

Agreed, and Ford did wise up later on....

I know the 99+ F-250, F-350 and Excursion Diesels (definitely through the 07 6.0's) have hydroboost from the factory (also they have 4 wheel disk brakes). So they do stop very well...... I am almost certain in a panic stop my 8000lb Excursion will stop better than most of my previous cars have.

 

[MTKirk]

Evening everyone,

I have bought my very first diesel which is a 1987 Ford F250 with a 6.9 diesel in it. I bought pretty dang cheap and was in a no running condition. With a lot of patience a reading I have got this thing running pretty good now. I have this odd issue with the brakes though. I have replaced the rear wheel cylinders, ABS Hydraulic unit, Brake Booster, Master cylinder, and have bleed the system fully several times now. Even bench bleed the Master Cylinder.

So the issue is I feel this thing does not stop well. I went back and adjusted the back brakes to the point where when I slam on the brakes backs would lock up and squeal. Adjusted the back brakes off a tad to make sure I had them adjusted pretty good. I have checked the front pads to make sure that enough pad which I do I compared them to new ones.

I hooked up a vacuum gauge to the the T portion of the vacuum line and was pulling about 24hg at idle. I did noticed when I press and release the pedal it drops to 11-13hg but build back up in a bout 5 to 7 seconds. I also did a semi leak down test and turned the engine off. It dropped about 2hg in about 3 to 4 minutes, so there is some small leak somewhere. I know I do not think I have a leak in the brake booster because It was holding vacuum for a week since I have not started it in a week and sucked air when I pulled it off to test.

I am not sure if I am just not use to this truck at all, or a diesel let alone. I know it is 8800 gvwr so I do know it is pretty heavy. I have honestly been to nervous to drive it far at all because of the brakes. ( I might be just use to new cars since my daily driver is a 2014 Dodge Charger.)

Any advise or things I could be missing or need to check for?

Thanks and have a great day.

I have an 87 as well and had problems with the RABS. If you can adjust your year brakes to where they will lock up, your RABS is not working. By backing off the rear adjustment you are just making it so the rears never engage- so of course your braking is weak. In '87 there was no load proportioning on trucks (e series only) so at least you don't have that to deal with.

Check the obvious; make sure the wires are connected & have continuity at the differential, RABS proportioning valve, and master cylinder. If that doesn't work get me your address & I'll send you photocopies of the diagnostics from the factory service manual, I'd post it here but it's 20 some pages long!

When you've got the RABS working right the backs won't lock up, even if you tighten them so you can't turn the wheels by hand. When you are at a stop, the pedal will just mush for the first 2/3rds (thats the RABS recirculating the fluid back to the master because the speed sensor is telling the RABS the wheels aren't moving). The firmness at the bottom is your fronts only.

 

[LCAM-01XA]

I have an 87 as well and had problems with the RABS. If you can adjust your year brakes to where they will lock up, your RABS is not working.

No quite accurate - at low enough speed the ABS shuts off and you can lock the rear wheels up no problem. And if the ABS wasn't doing its thing the light on the dash would be on. Besides, the only way a faulty ABS can cause lousy braking is if the dump valve inside the HCU doesn't close properly and bleeds off line pressure every time you get on the brakes - which is accompanied by a seriously soft and low pedal, and obviously complete inability to lock the rear wheels up. I'd say if he can lock the wheels up without standing up on the pedal while pulling on the steering wheel his rear brakes work just fine. And by extension I'm thinking the entire vacuum/hydraulic system is okay as well.

I'm with Warden on this, why is it that the OP feels the truck doesn't stop well? Also yes, definitely do pull the front pads and inspect the friction surface - I've had mine get glazed to where they wouldn't grab the rotors properly, some 80-grit sandpaper on a wooden block took that layer right off and they were back to working properly. Also there are different materials out there for brake pads, some are more grabby than others - generally speaking anything marketed as low-dust is not going to be as agressive as pads for ambulances and tow trucks and other severe duty applications. So point is, even if it looks fine, it may not be. If the rotors are nice and clean and flat (not grooved), I'd try the sandpaper trick first, and if that doesn't help drop some nice agressive pads in and just deal with the extra dust.