1991 dodge dakota 2 wheel drive V6. I have replaced the cliper, master cyl ,rotos and pads. Bled the breaks until I had a hard pedal. All good until I started the truck. Then the pedal when to the floor. Any ideas?

 

Bad booster?

 

Bad booster.

Quick test. Pull the vacuum line from the booster, temporarily plug it, and start the truck.

If the brakes don't drop THEN, it's the booster.

BTW - if the booster's failed, most likely it's because the MC is leaking into it and the brake fluid rotted out the diaphram(s). So plan on a new master cylinder also.

RwP

 

Thank you guys. I will try that. I would think if the booster was bad the brakes would be hard to push all the time. but I'm up for anything to fix the problem.
I also read somewhere that you need to bleed the proportioning valve first. Also read you nee to bleed the hydraulic control unit first. I have never heard of that. And don't know how to do it.
One other person said, drive the truck for a while and re bleed the brakes. Another person said to bypass the anti skid hcu and unplug the wire connector. And I guess re-bleed the brakes.

 

Quit reading everybody on the Internet.

Read this one thing:

Locate the Chrysler Factory Service Manual (printed by Bishko) for your truck.

Open the brakes section.

Follow the troubleshooting there.

End of the one thing.

Now - if you've done that; or even before - try bypassing the booster. If they work fine without the booster boosting, but not when the booster is boosting, then it's the booster.

"When you've eliminated the impossible, what's left, no matter how improbably, is the cause." Sherlock Holmes.

RwP

 

I will try disconnecting the booster. You are right should have the shop manual. I do for all my cars. This truck does not belong to me. it's my wife's granddaughters truck, but registered to her step dad. Ill see if they want to buy it.

Thanks again

 

The CD is less than $23 on Rock Auto plus shipping