tpchmara@wateng.UUCP (Tom Chmara) (10/09/84)
I've got a 1979 Chrysler Newport (we're talking Detroit coffin here...) in
beautiful condition...I just took ownership, and the fellow at the garage was
quite impressed with the shape it is in. A minor point, though, has been
bothering me...there's a very faint hissing sound coming from somewhere in
the dash, on the driver's side. I haven't been able to localize it, but
here's a bit of what I've found out about it: the sound quietens under
acceleration, almost dying when you tromp on the accelerator; it also disappears
when you hit the brakes (regardless of pressure). This second part sounds like
something to do with the brakes, but they're doing fine: passed the safety
inspection and a 300-mile trip with nonstop traffic jam last night with no
troubles. The hissing fades slowly when the engine is turned off.
Equipment: 360 cid V8, `lean-burn' engine
ps,pb
automatic
The sound doesn't seem to affect performance nor handling nor braking, and if
I turn up the stereo, it even goes away :-)...but I'm still curious...
I never did learn to let well alone...
---tpc---
(Tom Chmara EE @ University of Waterloo)
--
...!{allegra | decvax | clyde | ihnp4 }!watmath!wateng!tpchmarapwv@fluke.UUCP (Pat Vilbrandt) (10/15/84)
> I've got a 1979 Chrysler Newport (we're talking Detroit coffin here...) in > beautiful condition...I just took ownership, and the fellow at the garage was > quite impressed with the shape it is in. A minor point, though, has been > bothering me...there's a very faint hissing sound coming from somewhere in > the dash, on the driver's side. ... Big pig iron sleds of the vintage you describe have a "finger tip touch" climate control system that uses engine vacuum to operate valves and open / close dampers for the defroster, heater and air conditioning. (Some GM iron had this feature back in the 60's as well.) Your problem sounds very suspiciously like a vacuum servo / valve / line / other leaking under the dash. Since engine vacuum drops under acceleration and is almost non-existent with an open throttle, it is definitely vacuum related. I don't think it has anything to do with the brakes (Careful Here! I'm just guessing.) The amount of vacuum allowed to be "drawn off" the engine manifold for accessories must be limited for performance reasons, so the hissing could stop just because all vacuum is going to recharge the power brake booster (tho I doubt it, now that I've thought about it more). If it is brake related, it probably is the power brake vacuum booster leaking (this is the big, round canister mounted on the firewall under the hood right in front of the driver). The brakes will work just fine with the booster leaking, it would just require more brake pedal pressure to stop the car, depending on the volume of the leak. This would be the easiest to check for, just remove the vacuum line from the booster, PLUG IT, and start the engine. If the hissing is gone, you've found your problem. I wouldn't recommend driving the car like this, for it will take *a lot* more brake pedal pressure to stop the car. Good Luck! -- Pat Vilbrandt John Fluke Mfg. Co., Inc. Everett, Washington USA { uw-beaver, decvax!microsoft, ucbvax!lbl-csam, allegra, ssc-vax }!fluke!pwv
chim@ncsu.UUCP (Bill Chimiak) (10/15/84)
Could be a vacuum leak. I saw a Mercury station wagon that suffered the hissing sound. It was definitely a vacuum leak for the system that opened and closed the cars hide-away headlights.