When i hit rear break i get a pulsating in the front break

Question edited for clarity.
Question moved to model category.

It could be a few things, none of them good and all dangerous. Have it checked out by a mechanic. A few of the reasons in the link, disc brakes and suspension are the most likely.

https://www.google.com/search?q=2004+Dodge+Dakota.+I+hit+the+brake+pedal+and+the+whole+truck+vibrated+in+the+front+end

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Can you also you feel the pulsation in the steering wheel or the body of the car? If it is in the steering wheel then recheck the work that you did. Make sure that the hubs are clear of rust and torque the wheel nuts when putting the tires on.
To check if the rear are bad you can while driving down the road, lightly apply the emergency brake. If you feel the pulsation in the body then it is the rear brakes.
One last test that I have done is clamp off one brake caliper at a time using a clamp on the rubber line and seeing where the pulsation is coming from. Also if the antilock system is engauging there will be a pulsation in the pedal.

Usually a sign one of the front brake rotors is out of round. It could also be something wrong with the abs but I doubt it.

Did you replace the front and rear or just the front? Rear brakes can make the pulsation as well. Also if your ABS system is activating that could be described as a "pulsation". The ABS problem is usually caused by a bad wheel speed sensor or ABS module failure. ABS modules can be rebuilt (see ebay BBA-Reman) Wheel speed sensors are available at most auto parts stores. Some Saabs require the replacement of the whole hub assembly.

if it is in the brake peadle only you need to replace the rear drums/ rotors if you feel it in the streeing wheel it will be the front rotors

your problem is not in the rear drums, you need to replace the front pads and rotors. you have excessive run out on the front rotors. replace and let me know

saif.

warped brake rotors. don't resurface just replace them. if the steering wheel shakes its the front, if the seat of your pants shakes its the rear. in most cases the front will warp first

If the wheel nuts cannot be tightened properly, then yes, this could result in pulsating at the rear end. Tighten lug nuts and recheck.
Also this may be caused by an abnormal spare tyre. Many spare tyres are not put into use and can become distorted or hardened over time. There is a date on the sidewall of all tyres, and no tyres are recommended for use by vehicle manufacturers over six years.
http://www.lets-getaway.com/tyre-markings.htm

That sounds like a bad brake rotor or drum. If the brake rotor or drum is thick in one spot and normal on the rest that will cause the pedal to pulsate every time the the rotor or drum reaches that part of its rotation. The solution to this problem is to remove the front and rear rotors or drums and take them to a machine shop so they can be smoothed out, bear in mind you may need to replace them if the thick spot is too great.

wheel bearing needs changing