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,
Rocket99 is online now Report Post

 

Wonder if there is a restriction somewhere between the pump, and the rest.....

If that is 'normal', then I would be at least giving the brake booster a bigger reservoir. Or, you could convert to hydra-boost..... uses the power steering pump instead.

 

Reasonable thought, that hose is new now, the previous one was leaky with no apparent defect until I used a hand vacuum pump to bench test it. The hose came new with the check valve at the vacuum pump. Refer to safety recall 720 from Dodge. After replacing it the braking did improve moderately, boost recharge a little quicker …. but …. still sloowww vac recharge.

I've done a little searching for a great summary of that conversion ie soup to nuts recipe for switching over to power steering pump brake boost.

Got any ideas or links?

Thanks heyyou

 

As some of these trucks actually came from the factory with hydra-boost (notably, the v-10 fellers apparently) I would just go to the yard, find the parts you need, and yank 'em off an existing truck. Barring that, you could just go to the parts store, and order the unit, m/c, and all the lines. That would prolly be a fat bill though.... I would suspect that it would be a direct bolt-on conversion.