1994 dodge 2500 diesel. Put remanfactored calipers and new hoses on the front of this truck. Now I have a soft pedal that if held fades to the floor. Thought the master cyl must have a leak in it. Replaced...
sound as if you really do have a problem!
From your description I presume that you are confident in doing your own work?
The quickest way to check your system is to use brake hose clamps to isolate each section of the braking system. I would suggest that you rent or buy a set of the clamps.
Put the truck on axle stands and make sure it's safely secured. ]
If possible have an assistant to sit in the cab and depress the brake pedal on your instructions.
Place a brake hose clamp on both front brake hoses and the rear axle hose.
Depress the brake pedal firmly.
The pedal should have minimum movement, and be rock-solid and you should not be able to depress it further.
If the pedal does go down when you apply it, the likely reason is that the Brake Master Cyl is by-passing internally, ie, only one section is active.
You stated that the M/C had been replaced. so we shall presume that the brake pedal is rock hard.
Go to the rear brake hose clamp and release it. Instruct your assistant to depress the brake pedal. If the brake pedal moves a significant distance, then (a) your rear brake shoes require adjustment (b) rhere is a leaking brake cyl, (check for brake fluid in the drum) or (c) you have a "lazy' or a piston (s) which have siezed during a brake actuation. That problem will require removing the rear brake drums for further inspection. Not the problem? Then adjust the rear brakes if required, then depress the brake pedal again. The downward travel should now be noticeably reduced.
If all is well at the rear brakes. refit the brake hose clamp. Go to the passengers side front brake and have your assistant apply the footbrake. Pedal rockhard/minimun movement? Release the brake hose clamp whilst your assist has pressure on the pedal. spin the front wheel by hand, and note if (a) the brake pedal has excessive downward travel. (b) the brake pads are contacting the brake disc, (the wheel will cease rotating and you will hear the pads contact the disc.)
Pedal displays limited downward travel and pads contact disc? Refit the brake hose clamp and go to drivers side brake and follow the same procedure. If the pedal has excessive downward travel then you have found your inital problem.
If releasing both front brake hose clamps results in excessive brake pedal travel, then the problem will be easier to address if you deal with one side first, complete the resolution, test by using the brake hose clamps, then start / complete the other faulty brake.
Whichever side you start to work on, be methodical, boring as it sounds.
remove the road wheel, but before doing so, place a hand on the top and bottom of the tyre and rock the wheel away from you and check the bearing play. If memory serves me correctly, that year Dodge has the discs in one piece with the hub.
You have removed the wheel. Now, have your assistant turn the steering onto full right lock. Before continuing, I would like to remind you that the vehicle is up on axle stands and you have secured it safely, in order to conform with accepted safety parameters, correct?
The steering is now on full right lock and you can see both disc pads. Now, very carefully check the position of the caliper in relation to the disc pads. Is there and equal spacing on each side? Now, have your assistant release the brake pedal and very carefully observe the travel of the disc pad pistons. They should retract and the hub should turn freely by hand. A very light drag is allowed between disc pad and disc, but it should NOT be discernible when you rotate the hub by hand.
With no pressure on the brake pedal, and using an appropriate tool, attempt to have the caliper pistons retract into their cylinders / bores. Completed? Use caution as it is very easy to break / damage a disc by using undue force when retracting the pistons.
There is now an obvious gap between disc pads and disc (or rotor..sorry) Now, carefully check that the pad guide pins are not deformed and that the pads ride easily on them. if a pad jams when the brakes are applied, then, when the piston retracts, when force is removed from the brake pedal. There is an appreciable gap to close, upon the next application of the brakes!
Some types of disc pad retaining /guide pins are a tight fit, and it is very easy to tilt a pad when fitting the pins, causing the disc pad to fail to retract fully, and again, displayed by a brake pedal with excessive travel.
When the brake pedal is applied, the brake fluid has to fill the caliper piston bores, then exert pressure on the piston to force it against the disc pads, and they in turn are forced into contact with the disc. If the piston has to move an appreciable distance before contacting the disc pad, that takes more brake fluid to fill the bore of the piston, and the master cylinder piston has to travel further,resulting in a brake pedal that displays excessive travel .
I notice that you did not mention the type of effort or number of applications of the brake pedal which resulted in a firm pedal.
If you fitted replacement calipers, can I presume that you fitted new guide pins to the calipers?
Last but not least, (a) are they the correct calipers for the vehicle as regards piston bore size? The brake Master cyl will not be able to fill the bores of the calipers with enough fluid to drive the pistons out to apply the disc pads, if the bores are oversized. The pedal will also display excessive travel.
(b) If the brake master cyl is overfilled, when the brakes are applied, the master cyl will force fluid to the calipers, expand the caliper pistons, but will be unable to release the application to the pistons due to the fluid being unable to return to the master cyl as the allotted reservoir space has been filled with static fluid. When the brake pedal is depressed again, the Master cyl cannot service the caliper pistons on the first stroke as the pistons are locked at full stroke / travel in the bores, resulting in the brake pedal going to the floor, or giving that impression.
HOWEVER, that condition, if the vehicle is driven any distance, will result in the obvious odor of overheated disc brake pads, and the vehicle struggling to display any state of acceleration.
(c) Are they in fact the correct disc brake pads? It would be wise to remove a guide / retainer pin and check for free movement of the pad on the remaining pin. All ok, then refit the pin which you removed and test again. The pads have to be free to move on the pins, and thus align themselves with the face of the disc / rotor when the brakes are applied. Some people coat the pins with never-seeze or hi-temp grease when fitting them, others prefer them to be dry.
In closing, I would recommend that you check the full travel AND RETRACTION of the caliper pistons in their respective bores. It is not unknown for re-built / new parts to be defective.
It would be interesting to hear if any of the above proved to be beneficial in resolving your problem.
Jan 27, 2011 |
1994 Dodge Ram