I have a 2008 T&C Limited (4.0L) with braking issues. I could just replace a lot of parts but I'm trying to keep my costs under control by getting just the needed parts.

My symptoms are: Under gentle braking the pedal will sink much further than before but before bottoming out give reasonable breaking performance. With the power off the pedal is properly firm on pressing. If while breaking press the pedal down and quickly double pump, I will have a very normal feeling pedal and very solid breaking performance for any speed. If I double pump too slowly, the pedal will feel somewhat firmer for a moment and then slowly sink back to a low level near the end of the travel. Also, after some heavy quick use of the brakes, the pedal will feel slightly firmer for a little while, but eventually go back to being too soft until it almost bottoms out.

I have thoroughly flushed and bled the entire braking system. The old fluid did appear a bit darker than I would like to have seen.

This van has always had excellent braking performance for pedal feel and stopping distance. I feeling that the evidence points to the ABS pump unit and that there may be either seal wear or dirt on a seal somewhere in the pump unit, but could it be somewhere else? I have no leaks whatsoever and the pads and rotors are all in good shape.

I can't seem to find master cylinder rebuild kits for this unit; i only find refurbished units (big cost difference - kits are a few dollars). I also don't find a lot of pump modules that aren't used (I find plenty of the used ones for about $150 and up). I don't want to go through the hassle of replacing a pump module if it really isn't the problem and I would rather rebuild a unit, if it can be done. Not afraid of serious car work as I have rebuilt transmissions and engines in the past.

What direction is the evidence pointing and what are my options?
Thanks.

 

Your assumption sounds about right, master cylinder seals. It's either seals or you have a scratch/grove/wear area on the cylinder walls causing it to sometimes sink the pedal depending on where piston is in bore.

 

I was thinking that it may not be the mater cylinder but the ABS pump unit that is located on the firewall below the brake booster and master cylinder.

My thinking is that if I can do a quick double pump and get a firm brake pedal, does that rule it out or not? The double pump doesn't work if it is too slow. Feels like I can build on existing fluid that has not has fluid flow/pressure relief. This started after the van had sat for about 6 weeks not being used.

By the way the van doesn't have any codes being thrown on any issues.

I am familiar with master cylinders, but don't know the inner construction of the ABS pump unit that the master cylinder connects to. I am assuming that there is a moderate speed gear pump and some solenoid valves in the unit, but don't really know. I have never taken one out or played with one. Are they rebuildable?

I also don't know why I can't seem to find a master cylinder rebuild kit for the vehicle. I am used to just pulling them apart and putting new seals for the ~$6-$10 for the parts (compared to ~$130-$170 for a rebuilt master cylinder).

 

I did contact my local garage with the question (a major Chrysler dealership) and was met with "don't know."

 

when you call any shop or dealer you are talking to the sales people not teh techs they are never really any help. The service writers sell teh work the techs ask to fix the cars.

 

I would doubt that it's the ABS pump. That shouldn't come in to play at all in normal braking.

 

Are there bypass circuits in the ABS unit that could leak but if you pump enough fluid into the unit they all fill and allow a good pedal feel? I just have a hard time feeling its the master cylinder if I can get a very firm normal pedal with double pumping. If there was seal damage in the master wouldn't I always have the sinking pedal? The double pump gives a rock hard pedal.

 

As you are an impecunious fellow like myself, why not remove the master cylinder, strip down and remove the piston seals (presumably O-ring type) and take them to a really good accessory shop (we have such in Leeds) and ask if they have any that size or slightly smaller, of course mentioning Jeep as a possible.
You never know until you try...
Leedsman

 

the ABS pump and module is only used when an ABS situation is needed. like a wheel or 2 is spinning faster or slower them the others. The abs pump is not used when you press on the brake pedal at all.

 

It isn't the Master Cylinder! I replaced the master cylinder and flushed the system again, bled the brakes and the problem is the same.

Who has real knowledge of this system?

Again here are the "symptoms":
1) Fading pedal on normal braking,but ending in almost normal braking when at the bottom of the travel,
2) If quickly double pumped during braking, you get an almost rock hard normal pedal,
3) No codes thrown by the vehicle, no known vacuum leaks,
4) No leaks to the exterior of the car and no drop in the level of the brake fluid with use,
5) The brake pedal's sinking is made very much more apparent when the engine is running,
6) I have verified that all four pistons are operating.
7) I did notice a small gap between the rear pistons and the pads when the brakes were not applied. Is this supposed to be this way?

What is would cause this?