olds68

I am looking at purchasing a '69 Cutlass with an engine rebuild with about 3k miles on it. All other specs are stock other than .030 bore over stock. There is a non original cam with unknown specs in it (possibly W-31 specs?). The vacuum reads 5 lbs. at idle. The car runs great off idle but is a bear at idle. I've asked the current owner to bump the timing and idle to see if the vacuum improves. He has verified that there are no vacuum leaks. Being 600 miles away, I cannot verify this stuff myself.
Question is, will an aftermarket vacuum canister help the idle and/or power brakes? Or will it need a tear down and cam replacement?

joe_padavano

If your primary concern is the power brakes (as opposed to the idle quality) then there are several options. An aux vacuum canister is one option, though it man not be adequate if vacuum is very low. You can step up to auxiliary vacuum pumps, either electric or belt driven. Olds used belt-drive pumps on some early 1980s cars, both gas and diesel. Finally you can use a "sledgehammer" and convert to a hydraulic brake booster like the Bendix Hydroboost. This replaces the vacuum brake booster with one that uses hydraulic pressure from the power steering pump. These boosters are very common on 1 ton and larger trucks, both gas and diesel. The are also used on some newer Mustangs.

olds68

JOE, THANKS for the quick reply! I'm not sure about the booster that you refer to as I've never heard of it. But, I think my issue may be that (according to the current owner), the car will die if the brakes are applied without keeping the other foot on the gas pedal. He says the brakes work okay but I find this hard to believe with vacuum that low. I would also like to keep this car stock appearing if I do purchase it.

joe_padavano

Here's some info on the hydroboost system:

http://www.superchevy.com/technical/...dro/index.html

Of course, I also forgot the most basic possible mod, which is to simply convert to manual brakes. I have manual disk brakes on my 70 W30 and it stops just fine without excessive pedal pressure. That would look stock, also. You need a manual brake master cylinder, which has different diameter pistons, and the correct pushrod to attach to the brake pedal.

f-85

Sounds like a leak to me. 5in of vacuum is crazy low! Most stock cars will get around 20in. I have a good size old school cam in my F-85 and i get 14in. Well if you end up getting the car just fix the leak then worry about the brakes. LOL

P.S. lets see some pics!

Bluevista

If is has a long duration cam nothings going to increase the vacuum. Been there, done that. A pump is the only way to remedy it other than switching the cam. The speed shop pumps are junk, they're so loud you can't hear the engine and vibrate the whole car. If you can find one of these it's the easiest solution IMO, plus it's GM.

http://victorylibrary.com/mopar/pump-tech-c.htm

Olds64

I am with F 85 on this one. It sounds like you might have a vacuum leak. You mentioned that the car doesn't idle well. Does it sputter and spit or does it just idle too low? You might have to adjust the idle mixture screws to get better vacuum.

olds68

Lots of good info here. THANKS! The hydro boost (from Joe) sounds a bit expensive and probably more work than it's worth to me. The GM pump (from Blue vista) sounds almost the same. I tend to agree with Olds64 and F-85 as to the vacuum leak but the current owner insists that this is not the case. As I said, it's 600 miles away so I can't verify it myself.
My own Ram-Rod runs about 8-10 lbs. vacuum but has no power options and it is very difficult to idle below 700 RPM anyway, but who cares?!
Is it worth the risk to buy this animal with the fresh engine and just take on the headache? The car runs well as it is but sight unseen, the vacuum concerns me. Might there be some internal vacuum leak that cannot be determined without a teardown?

Olds64

If the car is 600 miles away then definitely DON'T buy it if you haven't seen it. I suggest telling the owner that you want to do a weekend trip to go and look at the car. Then you can take tools with you and do a thorough check up on it. If the distance is just too far to go unless you are going to buy it then look up a good service shop in the owner's area and tell him to take the car there so a mechanic can look it over for you. You might want to get ahold of the local Olds club and see if there is anyone in it that area that can help you out.

OLD SKL 69

Some points I was thinking of as I read your post:

What has he done to verify vacuum leaks? Has he checked the following:

Determined what the timing set at? If it is set at 2-4 BTDC, he should try to bump it up to 8-12 BTDC especially with the bigger cam. Then recheck the vacuum readings.

Is the vacuum advance working? If the diaphram inside is bad, it can effect idle quality by leaking vacuum past the seal.

Has he sprayed any carb cleaner at the base of carb to check for vacuum leaks? If he has a vacuum gauge hooked up and and the reading improves, it is a leaking carb gasket.

These are the easier items to check 1st. After that, then you have to wonder if the cam was degreed in properly. A vacuum reading of 5 is still definitely low even for a big cam.

Hope that helps.