Vacuum pump question

[Nelsoncat]

I am swapping a 6.2 into a 1977 Ford F250 Highboy 4X4 using a 700R4 2wd trans coupled to the 205 devorced transfer case. I am wondering if the gear drive vacuum pump will be suficient for the fords brakes booster? I had thought about swapping in the hydraulic assist system from the donor truck but this would be much easier. I also have some cooling questions. I'll start another thread.
Thanks
Craig

[diesel65]

Ford used the vacuum pump on their mid 90's F350 with the 7.3 diesel, but the vac booster was BIG.
I think the vacuum pump will not supply enough volumn with the original booster.

[DmaxMaverick]

With few exceptions (D65 mentioned one), Ford used Bendix hydroboost, just like GM in most LT Diesel applications. You can either transfer the booster from the donor truck with some modifications, or find a Ford replacement.

DO NOT try to operate the vacuum brake booster with the engine driven vacuum pump on the 6.2. It will work, until you really need it! The volume is much too low.

[BobND]

I'm not advocating this, or saying that it is safe, but most of the 6.9's and earlier 7.3's used a belt-driven vacuum pump to operate a conventional vacuum brake booster.

If you look at the 6.2 gear driven vacuum pump, and the Ford belt driven vacuum pump, you will see that the diaphragm pump umits are identical in appearance, and likely interchangeable.

Ford did, however, use a "tomato juice can" vacuum reserve tank with their system.

I just worked on one of the Ford systems a month ago, in a 1993 F-250. The owner complained of weak brakes. "Tomato juice can" reservoir and loss of brake boost vacuum switch are both thoughtfully located under the LH battery, and were corroded out. Bad can caused no vacuum, bad switch caused no warning!

Here's a link to a Ford unit on ebay... note the similarity to the 6.2 diaphragm unit...

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=7952985868

[arveetek]

The big difference between the Ford pumps and the early Chevy pumps is that the Ford units are belt driven directly off the crankshaft while the Chevy units are driven off the camshaft. This means the Ford pumps are turning twice as fast, with the ability to quickly pull down a vacuum.

Having said that, I have driven my '81 Chevy diesel conversion for over 9 years with vacuum assisted brakes. Having a really healthy vacuum pump, vacuum assist booster, and an auxillary vacuum tank makes all the difference. The only real problem is that you have to wait a few seconds after startup in order for the vacuum to pull down enough to have power assist. Also, if you step on the brakes several times in a row in quick fashion, you'll run out of power assist.

I initially installed the engine without a vacuum tank, and it didn't work very well at all. After installing an auxillary tank, it improved greatly to the point that I have no desire to swap in the hydroboost any time soon.

Perhaps a belt-driven vacuum pump off a later model Chevy or Ford would be an easier swap.

Most of the later model diesel pickups, including Ford and Dodge, use vacuum assisted brakes.

Casey

[SimonUK]

Most Ford diesels over here have the vacuum pumps bolted to the back of the alternator. I don't know if they are available over there.

[Nelsoncat]

I suppose another option would be to add an electric vacuum pump like the ones they sell in the street rod magazines for motors with radical cams and little manifold vacuum. Anything would be easier than swapping the hydraulic boost, or am I wrong?
Craig

[BobND]

[QUOTE]Originally posted by arveetek:
[QB] The big difference between the Ford pumps and the early Chevy pumps is that the Ford units are belt driven directly off the crankshaft while the Chevy units are driven off the camshaft. This means the Ford pumps are turning twice as fast, with the ability to quickly pull down a vacuum.

[BobND]

[QB] [QUOTE]Originally posted by arveetek:
[QB] "The big difference between the Ford pumps and the early Chevy pumps is that the Ford units are belt driven directly off the crankshaft while the Chevy units are driven off the camshaft. This means the Ford pumps are turning twice as fast, with the ability to quickly pull down a vacuum."

ARVEETEK... Do you know if the gear ratio in the 6.2 vacuum pump drive is actually 1:1 from the camshaft to the vacuum pump?

Not only are the Ford units driven off of the crankshaft, but there is quite a small pulley on the pump, compared to the crankshaft, so the pump is actually OVERDRIVEN by quite a bit, so I guess I'll have to agree with you!

[arveetek]

Originally posted by BobND:


ARVEETEK... Do you know if the gear ratio in the 6.2 vacuum pump drive is actually 1:1 from the camshaft to the vacuum pump?
I would assume that it's 1:1 for the following reason: the vacuum pumps are mounted in the same place as a distributor on a gas engine, using nearly the same identical shaft and gearing as the distributors. I'm sure GM did this to cut costs and use an existing design. The distributors must use 1:1 gearing or the engine wouldn't run. Therefore, I would make a safe assumption and say the vacuum pump is turning the esact same speed as the camshaft.

Casey

[arveetek]

Originally posted by Nelsoncat:
I suppose another option would be to add an electric vacuum pump like the ones they sell in the street rod magazines for motors with radical cams and little manifold vacuum. Anything would be easier than swapping the hydraulic boost, or am I wrong?
Craig If I remember right, Randy, aka 78Chev, used an electric vacuum pump in his conversion. I'd do a search in this 6.2L furm and also in the 'members' forum on 'electric vacuum pump' and see what you come up with.

Casey

[Fumes]

I have an electric vacuum pump in my van, it came off a newer Ford diesel. But I wouldn't think this would work for vacuum brake booster though.