1996 Ram 2500 Cummins

When I tap on the brake pedal a few times the vacuum assist depletes and recharges slowwwwly. Too slow.

Things already done:
new brake master
new power assist boost
rebuilt RWAL valve
repair all vacuum leaks
replace check valve on vacuum pump, plus vacuum hose

It generates 25 in Hg solid
It holds 20 in Hg overnite
vacuum gauge direct on vacuum pump shoots to 25 in hg immediately

on cold start with zero vacuum: the vacuum gauge sits flat on zero for 3 to 5 seconds then rises slooowwwwly to 25 in hg. 20 to 30 seconds to get up to 25 in Hg.

It stops like crazy reallly good, super good with tiny pedal pressure, but, do that twice and there is not more power assist for 15 to 20 seconds.

Some say this is normal

Some add a pressure vessel from 6" diameter plastic pipe. Then it takes much longer still to charge up but there is lots more vacuum reserve.

Is this a failing vacuum pump, or,

 

Totally normal, the vacuum pump just can't keep up with repeated braking when the engine is idling.
Be aware of it and avoid repeated braking at idle, install a vacuum reserve tank or turn the idle way up.
Dodge was fully aware of this problem and offered a vacuum reserve tank setup at the rip-off price of $125.
Doubt if it's still available.

 

Or you could always step up to a Hydraboost system........

 

Finally. Someone who sounds well informed.

Thx

 

Yes, after some searching around I found Speed Manufacturing in S. Calif.

New Bosch units with hoses seems to be about $1K.

Does sound like "the" solution especially if doing towing in mountains.

The cost of add on home made vacuum tank would be close to zero and may be an interesting experiment, as would a permanent vacuum gauge on the dash….

thx

 

I hate that sense of avoiding uncontrollable circumstances.

Mine rechages too slowly even above idle, with revving too….

The home made version sounds fine: 18" plus or minus of 6" PVC with rubber vac hose to a T fitting in the vac hose from the pump to brake booster unit.

Repair manual spec for vacuum says minumum 9 in. Hg to 25 in. Hg. That nine sounds way too low,

 

Egads, just give member here Redlinear a PM, he can hook you up with good used WAY cheaper........

But yea, a tank and a gauge would be preferable in terms of cost.

You know, another possible assist would be to put a tank and a gauge, and then add a Ford Powerstroke electric vacuum pump, I believe it is automatic operation, I think they are still under a hundred bucks new.

 

Ditto on Redlinear. He runs a salvage yard in Arkansas that specializes in parting out Dodge/Cummins trucks. I've bought several things from him, on ebay, and he's a good guy.

 

This was my solution.
Not the greatest, but it worked for me.

 

If the problem is running out of vacuum while towing get an exhaust brake.
The vacuum assist and an exhaust brake compliment each other since the exhaust brake only works at idle.