Hesitant brakes

Ok, so here is the situation. A couple of years ago I bought an older used pick up to pull our camper and do any general hauling I might need. It is an '04.5 (they made some changes mid model year) Dodge Ram 2500 turbo diesel. It was high miles when I bought it (hence the reason I could afford it) with upwards of 300k but that is about midlife for this type of truck so I wasn’t worried. It has been a great truck over all with only odds and ends that you would expect from an older high mileage truck.

However, it has one issue that started not long after I bought it and persisted for about the first year I had it. When I apply the brakes the pedal hesitates before moving. The brakes work fine other than this but it is a bit unnerving when you hit the pedal and it doesn’t move for a full second. It is only about a second and then it releases and works fine.

I thought the problem had gone away when it started braking normally for something like six months but lately it has started doing it again. I know it does this and plan accordingly so I have not had any close calls but still, I would like to fix this. I cannot find any data on this problem. Can you help me?

Is it a hydro-boost or vacuum-boost assist brake system?


Good question. Hydro, I think

Hydro-boost brakes should have an actuator that holds an air charge. If the air charge is lost, you will get a delay.

Rock Auto has the Hydro-boost brake boosters for under $200, the accumulator doesn’t seem to be available separately. Replace the master cylinder at the same time.

The other possibility is a weak power steering pump, you would notice a loss of power steering when applying the brake.

Before replacing anything, see if there is a procedure to charge the accumulator. It only needs to be replaced if the bladder is torn or there is no charge port.

This could well be a problem with the accumulator charge/dump valving. Try this when the problem is apparent – run the engine and crank the steering lock to lock a couple of times; shut the engine ‘off’; let the truck rest for 10-15 minutes; and apply the brakes a couple of times (brake pedal will get harder and harder). Is there power boost to the brakes for those applies?

If the accumulator is not holding a charge, it would constantly be dumping the accumulated pressure back into the hydraulic power loop. When you step on the brakes the spindle valve will close off the flow from the pump. As the brake power piston chamber is being pressurized the accumulator is also being pressurized. Once the accumulator gets pressurized to the demanded pressure for braking the booster is as a result also applied. If the accumulator is holding its pressure, the next time the brakes are applied the pump only has to build the pressure in the power cylinder which would be quicker. I suspect that the accumulator is releasing the pressure when you release the brake pedal. This should also be noteable in the power steering as a catch as you start to demand power.

I am thinking that some debris has gotten under the fill check valve or the dump release valve. If I were to service this problem, I would flush the hydraulic power system with special emphasis on the brake power booster i.e. charge the accumulator with the engine ‘on’ then dump it with the engine ‘off’. I would fill the pump reservoir and allow the return to go to waste. Putting a filter in the return line might also help.

Hope this helps.

No experience with this type of braking system, but I do have a comment. Consider parking this truck until the issue is resolved. It seems very unsafe.

Nevada_545, you are correct that I do have a loss of power steering when applying the brakes. I was thinking the two were separate issues but had begun to wonder if there was a connection.

Keith, that seems like a pretty good suggestion.

Researcher, I’ll have to give that a try and see what happens but it seems to fit what I’ve seen recently. I will definitely have to look into clearing any debris and maybe putting a filter in the return line.

GeorgeSanJose, that is a valid concern and an excellent suggestion. I do still drive the truck but only short distances. I live fairly close to work and the speed limits between home and work are low. I do drive careful and with the above problems in mind. Thank you for your concern. I don’t like driving it like this either and plan to fix it as soon as I can

Oh, and I did some research and some looking around under the hood and it does seem to be hydroboosted

Since the hydroboost power brake unit and the power steering are connected in series, this problem could well be the hydraulic pump.

Have you changed and checked the tension on the belt powering the pump? If the belt is fairly fresh, I would have a pressure check done on the pump. I am thinking that either the belt is slipping when the demand is high or the pump itself cannot produce adequate pressure to drive both the brake boost and the power steering.

Having the power brakes depend on a belt seems like a less-than-great design, IMHO.

Not recently, Researcher. That’s an idea. I haven’t heard the usual noises of a slipping belt but that doesn’t necessarily mean anything.