Brake Questions - 1992 Dodge Dakota
Posted October 13, 2008 at 11:32 pm
It looks like the brakes had been neglected for a long time on this truck.
Long story short, we've rebuilt both of the rear brakes, (wheel cylinders, new springs/hardware, new shoes, machined drums)
replaced the front rubber lines, all of the steel brake lines, and the booster unit/master cylinder. The front calipers/rotors/pads were OK
We put the booster unit and master cylinder (purchased as an assembled unit) into the truck tonight and bled the brakes.
right rear - left rear - right front - left front I bled each until the fluid ran clear and no air bubbles visible in the line to the bleeder cup.
The problem is - the brakes are still soft. The pedal travels 2/3 of the way to floor.
The instructions that came with the master cylinder said the brake line fittings should be turned into the cylinder loosely, the pushrod should be depressed
approximately 1" allowing fluid/air to blow out of the loose fitting, then the fittings should be tightened and the pushrod releasedand then repeat until no air is forced out when the pushrod is depressed.
I did as it directed, but I am not confident that it was properly bled.
By bleeding the 4 wheels, did I also purge the master cylinder? If not, what needs to be done to properly bleed the master cylinder?
As always, thanks for your help
Posted October 14, 2008 at 07:25 am
Your bleeding order was correct. I assume you did the master cylinder first, then the wheels. If the master cylinder is not completely bled, it can take a lot of bleeding to get it out via the wheels, and you may not remove all the air.
These trucks have 2-wheel ABS, the unit is on the rear axle. I just blew two leaks in my brake lines on my 92 Dakota, so I'll be doing this soon. I'm wondering if the ABS adds any complexity here. I have the FSM and will review it tonight for any surprises, and let you know.
Posted October 14, 2008 at 08:15 am
Another way is to attach dummy lines and coil them back into the master cylinder. Then before releasing the pushrod, disconnect them and attach the permanent lines.
This is the method I prefer. In the past, rebuilt master cylinders that I purchased have come with plastic fittings and plastic tubing to re-route the fluid from the MC outlet fittings back to the reservoir. I found that it can take up to 20 strokes to get the smallest air bubbles out.
It sounds like the problem is still air in one of the chambers of the master cylinder.
The ABS pump may need to be activiated too in order to push all air out.
Posted October 18, 2008 at 10:52 am
I rigged up the dummy lines using vinyl tubing and the plastic plugs that came with the new master cylinder.
I bled the cylinder until both lines were clear of bubbles and reattached the brake lines.
Bled all 4 wheels again RR-LR-RF-LF
The brakes are rock solid with the engine off.
The pedal sinks through about 2/3 of its travel when the engine is started.
Are boosters supposed to be that mushy?
This is a brand new booster and master cylinder. We bought it as a unit (both parts assembled to each other)
The vacuum line to the booster is in good shape and doesn't leak
What needs to be adjusted (or fixed) to get a firm pedal with the engine running / booster engaged?
John - this truck does have 2 wheel ABS - how would I activate the pump?
Edited by ckrobins, October 18, 2008 at 10:54 am.
Posted October 18, 2008 at 04:26 pm
I just read the FSM while doing my Dakota brakes today. Here's how you bleed them:
Bleed the master cylinder as you did. Top it off. Then open all bleed screws, all four wheels, at the same time. Close each screw as soon as fluid starts to come out (don't press the brake during this step).
Bleed in the following order:
antilock rear brake hydraulic valve (this is what you missed, and why pedal sinks. There is a bleeder screw on it. The unit is just above left rear wheel on the frame.)
right rear wheel
left rear wheel
right front wheel
left front wheel
Bleed the usual way: Run a hose from screw into clean jar of brake fluid. Open screw, hold the brake down, close screw, let pedal up. Repeat til air is gone at each wheel. Make sure the person at the bleeder has goggles on. Brake fluid will blind you.