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Markf
09-11-2005, 10:55 PM
Gentlemen,
We went ahead a purchased a 1989 F350 auto, 4x4, 7.3l, dumper, 9' fisher plow with 134,000 miles on it. (This stems from my thread of V10 versus PSD). Man, I do not wish to visit that thread again. The immaturity knocked me over. Enough said.

The problem here is that the brake pedal will travel to the floor but the truck will stop. The vacuum booster was replaced by the previous owner. If I rapidly pump the pedal, the pedal resistance will increase, however, the pedal will continue to the near the floor. My best guess is that the master cylinder is shot. We did bleed all four brake lines. Is there another vacuum pump that is tied into the brakes?
Thanks for the help.
Mark

Green Grass
09-11-2005, 11:13 PM
was there any air in the brake system? Make sure that you bleed the brakes intill there is new fresh fluid comming out. Also make sure that you start with the rear brakes.

lawnmaniac883
09-11-2005, 11:47 PM
Sounds sorta like what happens when the engine is off with transmission in neutral and brake pedal on floor right? If so then either air or master cylinder.

Markf
09-12-2005, 12:39 AM
Some air came out. However, I started with the front then moved to the back brakes. Lets say for arguments sake that the fluid is somewhat new, how will I know when the fresh fluid is coming out?

The truck was running and moving when I tested the brakes on the driveway.
Mark

Gravel Rat
09-12-2005, 01:02 AM
It sounds like the master cylinder is shot if the the pedal has very little resistance. A rebuilt master cylinder isn't that expensive so I would replace that. When you bleed the brakes you start with the passenger side rear-drivers side rear-passenger side front and last drivers side front. You always start with the furthest away wheel from the M/C.

The other thing you should check is the rear brakes if they are way out of adjustment or just plain worn out the wheel cylinders travel so far and the brake pedal keeps dropping.

You should whip the rear wheels off and pull the drums off to see whats left for shoes. If the shoes are worn out then do a complete brake job on the rear and I mean complete Change wheel cylinders-shoes-return springs and brake drums. Replace the parts with Raybestos they seem to be the best out there. When you change the brake drums really consider changing all 16 wheelstuds those older Fords have a nasty habit of snapping off wheelstuds.

The reason why I say change all those parts is the F-350s seriously lack brakes they don't stop worth a damn its pretty much flintstone brakes. You need the rear brakes working in perfect order or the truck won't stop. Its the biggest problem with F-350s is they just don't have any braking power you put 2-3 ton on the truck no way its going to stop safely.

You also have to keep on top of the rear brake adjustment don't rely on the automatic adjusters they don't work you have to manually adjust the brakes by turning the star wheel. On my previous F-350s it was a job that I did every week to 2 weeks depending on how many heavy loads I hauled. All it takes is a bottle jack lift up the one side remove the rubber plug and take a blade screw driver and turn the star wheel.

I really could tell if the rear brakes were out of adjustment the pedal would drop plus she didn't want to stop.

While your doing the rear brakes better do the front too then you shouldn't have to worry too much about stopping.

If you do replace the M/C yourself make sure you bench bleed the M/C thoroughly it prevents you from getting alot of air into the system.

xcopterdoc
09-12-2005, 07:29 PM
I've done quite a few early F-350's with this concern. Its usually the RABS valve. Rear Antilock Brake Sytem. The RABS valve is located on the drivers side frame rail, under the firewall. It has brake lines running to it, along with an electrical harness. It usually fails due to a piece of crap keeping the valve slightly open.
Now that being said... there is also a concern with the diesel and vacumn boosted brakes... no workie so good. Ford says the sinking, annoying, low pedal is OK... so anyway they have a new and improved brake booster that specifically addresses this concern, Contact yur dealer parts dept to check it out, thats if the RABS valve checks out OK.
If needed I can e-mail you the procedure for the RABS valve test.

Markf
09-12-2005, 09:47 PM
xcopterdoc,
That would be greatly appreciated. Also, we are in the process of removing the drums. I cannot locate the the mechanism that holds the star wheel in place so that I can loosen the drum brakes. I turn the star wheel to the outside of the truck to loosen, I hope.
Mark

xcopterdoc
09-12-2005, 10:05 PM
Attached you'll find the parts brk down for the rear wheels. Hope that helps.

Also here is the procedure for the RABS valve testing... If everything else is in order, I'd do this test and see what it reveals.


90ford24
WAGNER BRAKE CENTER

BRAKE FAX

TECHNICAL TIPS

Bulletin No. 24

Date November, 1989

Vehicle Make/Model

DODGE FORD and GENERAL MOTORS TRUCKS 87-90 BRONCO BRONCO II/RANGER F,E Equipped with Rear Anti-Lock Brake SystemFord: RABS (Rear Anti-Lock Brake System) GM & Dodge: RWAL (Rear Wheel Anti-Lock) Topic

False or Dropping Pedal

Some of the above-mentioned vehicles may experience a "false" or dropping pedal condition that may feel very similer to a master cylinder with an excessive amount of by-pass. Upon installation of the replacement master cylinder, there is little or no improvement in pedal feel or height. This condition may be caused by the dump valve in the E-H (Electro Hydraulic) valve being held slightly open by a small particle of foreign material. This allows fluid to flow into the accumulator and create the low or dropping brake pedal.
To determine if this is the cause of the dropping pedal, begin by disconnecting the steal line at the master cylinder that serves the rear brakes. Install a solid tubing plug into the outlet that serves the rear brakes. Note: When installing the plug, have an assistant depress the pedal about one inch to purge any air from this outlet. Tighten the plug while the assistant holds the pedal in this position. After, tightening the plug, continue to apply pressure to the pedal. This will prevent damage to the primary cup in the master cylinder as the cup moves across the vent port. If the pedal no longer drops as it did with the rear brakes connected, this would indicate that the problem is in the rear brakes and not the master cylinder.
The next step would be to block off the outlet port of the E-H valve and retest the brake pedal as done previously. If the dropping pedal reappears, the problem is in the E-H valve and most likely caused by fluid leaking into the accumulator of the E-H valve. If this is the case, it will be necessary to change the valve. The E-H valve, including the accumulator and valving, is not serviceable.

Note that brake fluid over a period of time absorbs contaminants, therefore, annual flushing and replacement with clean, fresh brake fluid will help to prevent this condition from occurring.

xcopterdoc
09-12-2005, 10:16 PM
To get the star wheel to turn the correct way to loosen the shoes, you will more than likely have to push the adjustment lever out of the way. Its part of the self adjusting system. See diagram.

Gravel Rat
09-13-2005, 12:57 AM
When your doing the brakes do one side at a time so you have a reference on what goes where. With the brake adjusters pull them apart and wire brush the threads up and clean the things up really well then lube them up with brake caliper lube. You can use Neversneeze it may get hot and start running into the drum. The adjusters have to spin really easy for that little arm to turn the star wheel.

To get he drums off you will have to back the brake shoes off as far as they can go the drums prolly have a good rust ridge. Like I said if you are going to do the rear brakes change the drums they are cheap. Usually brake drums are egg shaped and thin so replace them with new. The thicker the drums more heat they absorb and less brake fade you get.

Markf
09-13-2005, 12:09 PM
Gentlemen,
I appreciate the feed back. I will try this information tomorrow. I have night school tonight.

I learned my lesson in my teens by not leaving the other side as a guide.

Thanks again. I will let you know how it worked out.
Mark

Markf
09-21-2005, 03:31 PM
Gentlemen,
I thought you would like to know how your advice has worked out for us. Beautifully. After getting the drums off, (guy who had it before me had several things put together incorrectly) we decided to put in new wheel cylinders, spring kit, self adjusting lever cable, brake lines etc. We did the brake bleeding, and to test the RABS (per repair manual) had the all four tires off the ground. Placed the truck into 4x4H, trans into D, let the tires rotate and applied the brakes. The idea is that if the rear tires continue to rotate after the application of the brake, then the RABS in bad. Well everything went according to plan and the pedal no longer is spongy or continues to sink. However, I will be the first to admit that the brake stopping could be better. Thank you all for your help. :waving:
Mark

Gravel Rat
09-21-2005, 04:17 PM
I would have gone back to a F-350 because I would have liked to have 4wheeldrive again but the lack of braking power the F-350s really concerned me. I have been there with F-350s and I went to the F-Superduty (F-450) and wow these trucks can stop good I just can't deny that they are a better truck but they are 2wd.

Does your truck have that thing on the rear brakes with the arm and valve if so you can remove that and just run a hard line to the rubber line and eliminate the valve. It will get the rear brakes working more as right now its mostly the front brakes doing all the work.

I looked into every way of trying to increase the braking power of a F-350 and the only way is to get a rear axle out of a E-450 Ford cube van it is a Dana 80 with disk brakes and standard 8 bolt wheels. Then you convert to hydroboost to make the rear disk brakes work the best. When I totaled up the cost to do all that its a little pricey.

Anyhow its good to hear you found the problem :)