CascadeFirstGen

I'm new here, so let me know if I need to do anything differently in asking this question.

'90 Ram 4x4 Manual regular cab cummins, very few options. Bought the truck 2 1/2 weeks ago.

My ABS computer is disconnected. When I do a long stop or a couple of lesser stops, the brake warning light comes on. Sometimes if I brake particularly long or hard, the pedal feels hard like there is no assist, but I have assist most of the time. I believe the warning is due to a vacuum switch indicating low vacuum - if I disconnect the vacuum line to the booster I get the same warning light all the time (and terribly weak brakes with a hard pedal!).

I've attached a vacuum gauge directly to the vacuum pump and it pulls about 21 inches hg, and I can leave it for 24 hours and it barely loses any vacuum. I thought there might be a leak in the vacuum lines that run from the vacuum pump to the booster and to the back of the timing cover (?) from the pump, so I replaced this whole assembly with fresh lines, tee, and clamps, so lines should be good.

However, I still can't hold a vacuum when I connect to the end that would normally be on the booster. This line assembly has 3 outlets - the booster connection where I'm connecting the vacuum gauge, the vacuum pump, which I know can hold vacuum from testing it directly, and a 3rd connection from a line that goes under the vacuum pump and forward, connecting perhaps to the back of the timing cover? I'm not sure.

By process of elimination, it seems that my leak is coming from the 3rd connection, where it connects to the back of the timing cover or whatever that is? Has anyone dealt with this problem, or at least know what that vacuum line is connecting to? The truck has no cruise or other fancy stuff that vacuum would be connected to.

Thanks in advance,

Andy

NJTman

Is your truck intercooled ? or Non ?

My truck is intercooled, and for the life of me, I don't remember ever seeing the vac lines running to the rear of the TCover. My truck is in the shop right now, otherwise I'd go confirm this.

Again, through process of elimination, can you disconnect that line that goes forwards, and then drive the truck around ? If your brakes remain normal, then you've confirmed your suspicions, otherwise a booster failing would provide the same issues.

Hopefully someone here knows what that forward line goes to.. and can chime in.

dodgenstein

The 90 should have a dual diaphragm vacuum pump. The tee connects the two pots on the pump. One of the diaphragms may be bad or the line may have a leak.

CascadeFirstGen

Truck is stock 90, non intercooled. I was trying to figure out what the heck that pump was about ... I think dodgenstein is right, my lower diaphragm probably has a leak. I'm going to try your idea NJTMan and run the booster off of the top diaphragm only. Might be completely adequate.

fixinrams.com has rebuild kits for the 91.5+ pumps, but I haven't found any for the non-IC pumps, do they exist?

Also, I'm planning to add a powerstroke intercooler to this thing, Did they change the vacuum pump because of intercooler plumbing or was it unrelated? I don't want to invest too much time and energy into this pump if I'm going to have to swap it out anyway.

Thanks so much for the help so far.

Andy

maybe368

No rebuild kits, but you can get reman units at rock auto...Mark

CascadeFirstGen

I wanted to update this thread for the benefit of future readers.

I do have a minor vacuum leak through one of the diaphragms in the dual diaphragm pump, but it is very slow. The real problem is that my booster is bad; When I attached a handheld vacuum pump to the booster and capped the other connections on the booster, I am only able to build a little vacuum by pumping vigorously, and even then it quickly escapes. By contrast, the remanufactured booster I just put in takes a little time to pump vacuum on due to its volume (notably more than the pump end of the vacuum system), but once pulled, it holds steady.

The brakes feel much more power assisted all the time now, and I no longer get the brake warning light after a long stop. Now I need to get rid of a "death wobble" under braking that I believe is due to sloppy steering, but that would be a new thread. Thanks to those who responded on this thread for their help making my truck safer!

Andy

maybe368

My death wobble was caused by bad king pins, see here, it just happens to be right above this thread right now, well below when I post this ...Mark