vacuum check valve question - AUSJEEPOFFROAD.COM Jeep News Australia and New Zealand

BwanaBob · #1 09-08-2013

Greetings from Africa. On my 98 diesel XJ the brakes are good for one or
maybe two pumps, then the pedal is very hard. I suspect the vaccum
check valve is not holding long enough.

The Chrysler P/Ns for the valve for the diesel and petrol models are
different. Can't find a valve for a diesel anywhere here so I wonder if I
could get by using the valve from the petrol model. Anyone ever put a
vacuum check valve from a 4.0 petrol on a diesel XJ?

layback40 · #2 09-08-2013

What you are seeing is normal for a diesel with a vac pump. it takes a while to build vac after you use the brakes. If your booster diaphragm is no good it will have low vac & a hard peddle all the time. IIRC the non return valve is near the vac pump.
It is more likely that you have a vac leak some where else in the vac system.

BwanaBob · #3 21-08-2013

Thanks for the reply. My Jeep was been converted to a Toy 2L diesel.
After 48,000 km it is doing well.

Except the power brakes. When the conversion was done, the original
vacuum lines were discarded and the vacuum pump was routed
directly to the brake booster. The problem is when rpms drop to near
idle the power brakes are only good for one braking. Usually I just
drive in the bush and get by ok since rpms are up most of the time,
but I recently took it to the city and in heavy traffic I had to put a lot
of weight on the brakes from time to time. So I have been wanting to
improve the power assist.

There don't seem to be any leaks in the simple line to the booster.
Yesterday my shadetree mechanic put a vacuum reservoir from a Toy
Corolla in the line but the braking is no better, maybe even worse.
Today he is going to try another booster he found on a junk 97+ VM
XJ somewhere.

I wonder if the vacuum pump on the Toy is just a lot weaker than the
VM's was. The pump seems physically smaller. The pump has been
rebuilt six months ago but really doesn't pull much at idle as
compared to when the rpms rise. Is that normal?

Or, I'm wondering if the booster's check valve is bad. Anyone have
any ideas?