vacuum question

[fng]

I was talking to an engine tech today and the topic of vacuum came up.
In particular, I asked him if it was possible to tap into the intake vacuum tee next to the carb mount (SBC) to operate the vacuum wipers on the truck. He said it may be possible to do that but he wasn't really sure how much negative pressure was required to run the wiper motors.
You guys have any input on this? I don't see why it wouldn't work unless it made my engine run rough somehow. Any ideas would be of interest.

[brute4c]

It would work at low throttle settings, high engine vacuum, much much better than it would at high throttle settings, low engine vacuum...where the wipers would stop altogether....

This is the reason the M715 has a vacuum pump on the motor....a constant amount of vacuum to run the wipers at an even speed regardlss of throttle setting/engine vacuum levels.

Just running off engine vacuum is a pain in the butt...the faster you go, the less wipers you have...accelerate and they slow down..stomp on it, they stop.

Many older vehicles had that setup...it was a poor solution to keeping the windshield clean and thankfully died out along time ago.

[jfnemt1ff1]

You could get a vac tank with a one way valve that would store vac would help some. They also used a vac pump on GM cars and trucks that runs off the engine belts. Should not be that hard to hook up.
John

[redneck1]

I run my wipers off of the intake.
No biggie really I just tapped in on the drivers side of the intake.If you load the motor up too bad just reach up and grab the wiper lever to get you by til the motors RPM's get up.
Redneck1

[fng]

Okay, the power steering pump that I have is from a chevy van that used a vacuum line to provide power to a brake hydroboost. I was planning on plugging it off but if IT provides negative pressure would that work?

[tacoma]

In a word, NO. That is not quite how Hydroboost works.

[Barrman]

Yes, you can run the wipers off engine vacuum. They aren't constant and as pointed out above, will slow down up hill and speed up down hill.

Hydoboost brake boosters worked off of pressurized power steering fluid. Do not try and rig anything with the power steering lines. You will make a huge mess and probably hurt yourself in the process.

[Doug]

Do you mean brake power booster instead of hydraboost? Big diaphram mounted on the firewall?

[Swampthang]

I don't know of a G.M. p/s pump with a vacuum port. I think what you are seeing is two fluid return lines for the steering gear and brake hydroboost unit. They both carry p/s fluid. A vacuum can would be your best bet. Lots of cars with lopey cams and vacuum brakes use them because the engine doesn't create enough vacuum.

[fasteddie]

Agree to all of the above . Went through this issue on a 725 , SBC with manifold vacuum , they slow down to nothing on acceleration , went to electrics because of this.A vacuum resevoir would have to be large for a good supply . The dedicated GM vacumm that runs off belt for the diesels that I've delt with do not supply a large amount of volumn , don't think it would run the wipers.