Engine/Transmission (1994 - 1998) Brake booster replacement

[jsjaastad]

Truck is 1995, 5spd with about 95,000 miles



I am going to replace the brake booster (last hope). After new master cylinder and RWAL valve; front pads and rear shoes. Booster check valve checks out okay.

Local ******* (dealer) says brake booster is not available for 95 but if it was we want $240. 00 for it. Money is not a real problem, I just want the brakes to work. Local truck salvage yard says they have a booster that will work.

Question is: my service manual says use only a booster with the same number on the front cover (page # 5-18). I don't know what number the salvage yard has on the booster, (will find out tomorrow) but if they say it fits 95 ???? What difference will it make?

Original problem was/is. Motor off, pump up the brakes and they are solid!

Start the motor (while pushing down on the brake pedal) and the pedal slowly goes nearly to the floor.

My friends 97 does not do that!

Stomp on the brakes in a panic stop and it's Miller time or time to do CPR.

Any suggestions will be helpfull. Thanks, Tom/Idaho

 

[Woodenhead]

Not sure if I really understand what the issue is that you describe. However, have you checked the vac. pump? It's common for the seal in the pump to start leaking and get oil into the vac. lines causing problems with vac. operated accesories. Are you having any problems with your heater controls or egaging. 4x4 (if it's a 4x4)?



Also, your friends '97 will have a different brake booster setup. Up to '96 was vac. assist. '97 and up was hyraboost which works with hyrdralic pressure from the powerstearing pump.



Mike

 

[hsmith]

I would go with an aftermarket unit before using a used unit.

 

[JoeBioDiesel]

I doubt the problem is in the booster. It sounds like you've got a base brake problem. A booster really can't cause low/no pedal condition unless the pushrod is worn out. . which I've never seen.

Now, even though this sounds dumb... you need to try it. Any time I've seen a Dodge 2500 or 3500 with a low pedal complaint, it was because there were bad front wheel bearings. The loose bearings allowed the rotors to cock sideways and push the pads back into the calipers. When you apply the brakes they have to travel too far to apply(low pedal). The reason you have a hard pedal when the truck is off is that you don't have the strength to straighten the rotors without power assist.

So, jack up the front end and give it a shakedown. Let us know how you make out.

Joe

 

[Woodenhead]

I doubt the problem is in the booster. It sounds like you've got a base brake problem. A booster really can't cause low/no pedal condition unless the pushrod is worn out. . which I've never seen.

Now, even though this sounds dumb... you need to try it. Any time I've seen a Dodge 2500 or 3500 with a low pedal complaint, it was because there were bad front wheel bearings. The loose bearings allowed the rotors to cock sideways and push the pads back into the calipers. When you apply the brakes they have to travel too far to apply(low pedal). The reason you have a hard pedal when the truck is off is that you don't have the strength to straighten the rotors without power assist.

So, jack up the front end and give it a shakedown. Let us know how you make out.

Joe

Joe may be on to something here. Now that you mention it, I had a similar issue twice several years ago when I nuked a couple wheel bearings.

 

[jsjaastad]

Thanks to all who replied. As I feared and others had said, the new booster didn't help. I jacked up the front and the wheel bearings are tight. I am to the point that I hoped they were bad.

I went thru the whole check list in my service manual again. Vacuum pump holds 20 at idle and goes up to 24 at 3/4throttle and the check check is also in specs. All the accesories that depend on vacuum are operating including 4 x 4.

New front pads, new rear shoes, new check valve, new vacuum lines from pump to booster, new RWAL valve and remanufactured master cyl. (could that be the problem?) and all air purged & new aftermarket booster. I even disconected the BD exhaust brake without success.

I think I have eliminated everything that has to do with the operation of the brakes. I am at a loss. Any suggestions? Thanks again, Tom/Idaho

 

[JoeBioDiesel]

After you replaced the Master Cylinder, did you bleed the 4WAL ABS Unit? They have an electronic bleed command that you need to do with a scanner. It's not always necessary, but if you get air in there you'll have a low pedal until you get it out.

Do you have a trusted Tech in your area that owns modern diagnostic equipment?

Joe

 

[jsjaastad]

Joe, I bench bled the master cylinder as per the service manual and from numerous suggestions on this forum and then the RWAL valve per the service manual and then the wheel cylinders.

It just feels like you are pushing down on the pedal and brake fluid is bypassing something. Like the brake fluid is being pushed past the valve in the master cylinder. But, why does it only happen when the motor is running creating vacuum? No, I do not have a trusted tech in this area, only the local dealer.

I took it out today and at about 50 mph in a panic stop it will skid the tires (on pavment covered with sand) BUT the pedal goes clear to the floor. . What am I overlooking ? Once again, any help is greatly appreciated. Tom/Idaho

 

[JoeBioDiesel]

If you have RWAL, forget about the 4WAL bleeding procedure. It doesn't apply. If the pedal is slowly creeping to the floor, then it is either leaking or the master cylinder is bad. Try capping the lines on the master cylinder. Make a couple of lines that dead end. Put the lines on the Master Cylinder, Bleed them out, then see of the pedal still sinks. If it does... it's the master cylinder, again.

Joe