AA engine

[John Walters]

Looking in various publications I have seen AA trucks pulling heavy loads. What was the engine in the AA? A heavier duty 4 cylinder?

[Chris Haynes]

Exactly the same engine that cars had. Just lower gearing.

[columbiA]

NO.The only difference is that the "AA" engine used a larger clutch & the rear ends were much lower geared & often used an aux trans for more pulling power but at reduced speeds.The "AA",s are not very practical for touring due to slow speeds & poor gas mileage.

[329s]

Originally Posted by John Walters

Looking in various publications I have seen AA trucks pulling heavy loads. What was the engine in the AA? A heavier duty 4 cylinder?

As Chris says...it is the same engine;

HOWEVER...the difference was that the clutch in the "AA" was equiped with heavier springs and had a slightly wider disc than that used with the "A" (Refer to page 351 of the Ford Service Bulletin).

There was a short time in early 1928 I think that FORD dropped the "AA" designation for the trucks because they went back to using the same clutch spring as the "A" but found out that they needed to revert back to the heavier clutch so the "AA" was reinstated.

Pluck

[329s]

Originally Posted by fordgarage

A "wider disc"? What do you mean? Bigger diameter or thicker?
Early 1928 were multi disc clutches and all the same.

Refer to page 351 of the Ford Service Bulletin...you be the judge!


The engine could have had an “A”

(Fig. 5) or “AA” (Fig. 4) associated with the

number and the engine itself. An “A” usually meant that the engine was for a car
or a light commercial vehicle. The “AA” usually meant that the engine was
associated with the heavy duty trucks. This concept remained the same
throughout the production of the Model A/AA Ford except from starting with
engine number A26268, a February 16, 1928 engine, the “AA” prefix was
dropped due to the fact that all truck clutch springs were the same weight as the
car and commercial vehicles.

On May 15, 1928, the Indianapolis Ford Service Letter indicated that all the truck
engines were now being equipped with a 455 pound spring and that the engine
numbers on such motors were being prefixed with the letters “AA” again. The
cars and commercial vehicles retained the 420 pound clutch spring and the prefix
“A”. These heavier truck clutch springs were painted “red” to distinguish between

the two. Not sure of the engine number that this change occurred with.

Pluck

[329s]

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Originally Posted by fordgarage

I was asking what you were referring to by a "wider disc".
I am still wondering.

Me to...maybe the next time you go to the FORD Archives, you can research it out and report back! That would be the best place to find out your question.

In the mean time read what it says in the Ford Service Bulletins.

Pluck

[James Rogers]

Vince, I have tried to find verification of a wider disk and only could find some flywheels that had a marking of wear the disk made that is 9 1/4" instead of 9". I have also found a couple of pressure plates with the same wear pattern. This would indicate, the AA disk was 9 1/4" diameter instead of 9" but, I have no real proof.

[Bob C]

Does anybody have a drawing of BB-7550?

Bob

[Kurt in NJ]

I have a28-37 parts book, it lists "AA", and "BB" clutch disc as being 9-3/4 " outside diameter ----and in my used clutch disc pile I have at least one non spring hub 9-3/4 disc---it is also listed for "Taxi" use
2 different pressure plates--A,B,18,40,46 and AA/BB
In the service bulletins it says the truck clutch can be easily identified by the red paint mark and the grey enamel springs--page 351

all the multi disc parts have "A" except the spring which has "AA" and is listed for A also (AA truck with 3 speed trans)is in all the listings

[Bob C]

Kurt,
What month is your 28-37 parts book? I have a June 1937 and it doesn't list a size for BB-7550 but
my green book shows 9.75".

Bob

[Tom Wesenberg]

I always thought of the A and AA discs as 9" and 10", as that's what I read years ago. I guess the measurment could have just been rounded off to the nearest inch. Anyway I bought an NOS 10" disc at a swap meet for the 1930 AA I worked on, and recently I found an excellent slightly used 10" that I'll use sometime. The 10" does overlap the square openings in the pressure plate, but that doesn't matter.

[Rowdy]

Mine is a June of 1941 Reprint and it does not show the size. Rod

[Rowdy]

The NOS disc I have I thought measured 9 1/2" I may want to measure it again. No part numbers on the box or the disc. Rod

[Kurt in NJ]

The book I was looking in was published july 1945 --it is interesting to look at the differences in the same year span book published different times---and how it changes in the green book

[Chris Haynes]

I prefer to use the later disk with the shock absorbing springs in the center.

[Rowdy]

I remeasured the NOS disc and it is 9 3/4". Also I dug out some of my other origianls including 2 relined ones (upper left) and one AA BB (upper right) the AA BB is 9 3/4" also. Rod

[Kohnke Rebabbitting]

Originally Posted by Tom Wesenberg

I always thought of the A and AA discs as 9" and 10", as that's what I read years ago. I guess the measurment could have just been rounded off to the nearest inch. Anyway I bought an NOS 10" disc at a swap meet for the 1930 AA I worked on, and recently I found an excellent slightly used 10" that I'll use sometime. The 10" does overlap the square openings in the pressure plate, but that doesn't matter.

If your disk is 10 inches Tom, it won,t do you any good, as the flywheel surface is only 9-3/4's, all my pressure plate cores are in the warehouse, so I can't tell what they are now.

We have always used the 9-3/4, in cars, and trucks.