NSW Corvettes

Technical Tips => Pre 84 => Topic started by: Dale on November 03, 2014, 12:51:26 PM

Title: Lack of vacuum
Post by: Dale on November 03, 2014, 12:51:26 PM

My 80 model with a 350 has been modified, part of that was a lumpier cam. Works well but it appears to have an issue in reducing the available vacuum.
For example, when I accelerate hard the lights pop up, it is also causing a problem with the heater in that there does not appear to be enough vacuum to open the valve when required.
I saw a video from the states where they installed an auxiliary vacuum pump to fix similar problems created by a big cam, but there were no technical details.
Anyone had  similar issues and found a cure?

Title: Re: Lack of vacuum
Post by: bfit on November 03, 2014, 04:02:41 PM

Sounds fishy to me. sounds like something is not hooked you correctly.
first 
Is there a one way valve in your vacuum  line  from the engine

Bfit

Title: Re: Lack of vacuum
Post by: Dale on November 03, 2014, 04:06:23 PM

Yes there is, I bought a new one and a new filter a while ago as I thought that was the problem but to be honest I am not positive the mechanic has it hooked up properly.
How can you tell?

Title: Re: Lack of vacuum
Post by: bfit on November 03, 2014, 04:26:41 PM

Dale
the guru on this is sirfixalot ( Geoff )
I've seen the headlight going up  when the relay valve  between the headlight  is hosed incorrectly and or hoses are not on  enough to seal

Geoff is bound to see  post in due course
Bfit

Title: Re: Lack of vacuum
Post by: sabre on November 03, 2014, 05:34:18 PM

Hi Dale,
Come across this before but usually only with cam with huge overlap and big bore carb????
Solution is fitting a diesel alternator with vac pump on the rear. I understand the old 2H / 12H Toyota alternator is a popular choice.

I'd check the vacuum with the vac lines removed (and blocked) first. Usually low vacuum will stop lights lifting, not make them lift.
Also agree with Bfit. You should check the hoses and function of the actuator relays for leaks. These die with age.

Title: Re: Lack of vacuum
Post by: bfit on November 03, 2014, 08:05:29 PM

Dale
Why not get a gauge an measure just what vacumn your engine is developing .
My guess is your brakes are working and a 80 modle would have a booster in most cases.
So try a gauge and you will know where you are at .
Then you can start to eliminate the posibilities .
Oh it's not unusual to find the vacumn tank has a hole  or two in it
Bfit 
Ps as a Matter of interest Dale 
What colour is the inside of you're exhaust
It's a bit of an indicator of how your engine is running

Title: Re: Lack of vacuum
Post by: sirfixalot on November 05, 2014, 08:42:33 AM

For the headlites to pop up tells me you are loosing vacuum to the control valve diaphragm. There is obviously vacuum at the bellows to make the lites go up. my guess would be the vacuum feed for control valve diaphragm is connected between  the non return valve & engine

Title: Re: Lack of vacuum
Post by: Dale on November 10, 2014, 04:27:29 PM

Thanks guys for all the input, I am printing this out and taking the car to an excellent auto electrician and A/C guy, he teaches at Tech.
I will let you know what the outcome was for future reference and anyone else having similar issues.