Replaced the brake master cylinder and brake booster on my 99 Ford Ranger 2wd with 70k miles because the brakes were so soft that the pedal's about to hit the floor & loud hissing when it was pressed. In addition to that, there seems to be a jerking feeling from accelerating from a stop, but it also happened when reversing so I thought it might be coming from the transmission or maybe the motor mounts. I jacked all four wheels. After reading that the jerking might be caused by u joints, I tried turning the driveshaft & there was a little play so I replaced both front & back, only to find out that the driveshaft still played a little like before, but at least the jerking stopped. I also replaced the rear brake shoes along with the springs when I saw one was broken on the right. I vacuum bled the master cylinder, then all four brakes, but the brakes still felt soft, even though I plastic wrapped the cylinder tubes, I figure it's because air's still in the system (had to wait next day to finish because no stock nearby & cold weather). After vacuum bleeding everything a 2nd time, the brake was still kinda soft but improved a little, but a new problem came up, the rear left side wheel was still spinning even though the brake was almost on the floor (rear right was more responsive to braking). It would only come to a complete stop after a little rumbling from the pedal finally near the floor which felt like the brake was finally biting. It would do it in both drive & reverse, but the brake was somehow more responsive when the truck's warmed up a bit. I also found out that the new (not remanufactured) master cylinder had a leak from the reservoir seal (that's why I wondered where the fluid went after brake testing, it was full before) so I need to exchange it for another one.
The rear wheel still spinning after braking, is that caused by the master cylinder or is it something with the rear axle? The rear differential oil hasn't been replaced as far as I know, but it was almost level when I stuck my finger to check the fill plug. Why is it more responsive when warm instead of cold?
Also, did the jerking stop because the yoke might've been lubricated with fluid from the transfer case? The teeth inside the yoke didn't look broken but it looked dry. Will it come back if I don't grease the yoke with Super Lube with PTFE? Could that have been a slip bump problem instead of u joints since the driveshaft still had a little play?
I do apologize for the length, but giving as much detail as possible prevents just simply guessing & might help others with the same symptoms as mine. Thanks.
You have a lot going on here. If the jerking feeling you're describing feels like it's coming from under the driver's seat area, and it does it when you take off spiritedly, but not flooring it, then that's most likely your slip yoke on the drive shaft lacking lubrication. I have a 1999 Ranger 4x4 Off-Road, and it would do what I'd describe as a thud with slightly aggressive acceleration and deceleration. It's from the slip yoke on the drive shaft binding up as the truck shifts on the suspension. I had this problem looked at by a local transmission shop not long after I bought the truck, and they told me it's a common problem for Rangers, and nothing to be concerned about. Ford actually put out a service bulletin a long time ago specifying a new grease to help fix the issue. The new grease they specified doesn't permanently fix it, either. I solved the problem in my truck by packing the slip yoke boot full of blue Valvoline grease, and synched it shut with a hose clamp so when it acts up again, I can just pack put more in.
For the brakes thing, if I understand your problem correctly, your differential has nothing to do with it the wheel still spinning when you apply the brake. If the master cylinder you bought was leaking fluid after you installed it, that will affect the pressure in the system, because pressing the pedal down forces fluid out, and releasing the pedal draws air back in. Once you replace the master cylinder, you may not be able to get all of the air out of the system if your truck has ABS, Scotty has mentioned before that a mechanic with a scan tool needs to bleed the brakes on an ABS equipped vehicle to get the air out of the internals of the module.
Bench bleed the master cylinder before installing it. Make sure the vehicle is level when bleeding the brakes.
