M62 Wrecker - Question about brake system

[vnwrecker]

Hi,

According to TM 9-2320-211-34P (1972 and 1985), there are two part numbers listed for the wheel brake cylinders (one for the front - FSN 2530-421-9687/MFR 8758255, one for the rear - FSN 2530-920-7568/MFR 8758259). However, I can't find any detail on why there is a different part number. None of the other manuals mention this difference (ie none of them say that there is a difference between the front/rear wheel cylinders, nor to take care in assembly to ensure that they don't get mixed up).

Does anyone know what the difference is (I'm guessing maybe the bore size)? The reason for asking is that one of the cylinders is leaking (damaged bore), and none of the cylinders I have will fit. If it is a difference in bore size, does anyone know what the bore size is?

Thanks.

Colin.

 

[DDoyle]

Per ORD9 SNL G-744 January 1954 the 6 wheel cylinders could be Lockheed FD682 or FC1012 (the later being the bare wheel cylinder). Ordnance part number was B184346. The change in sie of rear wheel cylinders was made per TB9-837-10 in October 1955. The larger cylinders were for use on the rear wheels and are ordnance part number 8333648. These have a two-inch diameter (the originals were 1 3/4 inches.) The purpose of the increased size was to decrease the amount of pressure required on the brake pedal. Do not mix wheel cylinder sizes on any given axle. There is not enough capacity in the master cylinder to accomodate the use of the large wheel cylinders on the front wheels as well - so do not attempt that. The Wagner part number for the large (rear) wheel cylinders is F6630.

Hope this helps,
David Doyle

 

[vnwrecker]

Thanks David - that was very useful.

 

[acetomatoco]

Hey, have you been looking in my book??? Isn't the Ord 9 a wonderful unit. By the way , even the 800 series 34P1 shows the two different cylinders... The MC and the Air Pak remain the same too...

 

[5_TON_TOMATOE]

Wheel Cylinder Size

Per ORD9 SNL G-744 January 1954 the 6 wheel cylinders could be Lockheed FD682 or FC1012 (the later being the bare wheel cylinder). Ordnance part number was B184346. The change in sie of rear wheel cylinders was made per TB9-837-10 in October 1955. The larger cylinders were for use on the rear wheels and are ordnance part number 8333648. These have a two-inch diameter (the originals were 1 3/4 inches.) The purpose of the increased size was to decrease the amount of pressure required on the brake pedal. Do not mix wheel cylinder sizes on any given axle. There is not enough capacity in the master cylinder to accomodate the use of the large wheel cylinders on the front wheels as well - so do not attempt that. The Wagner part number for the large (rear) wheel cylinders is F6630.

Hope this helps,
David Doyle

Is this recomendation based on maintenance quotes in the TM's, personal experience, None or both, ?? Curious about the source of your statement

 

[73m819]

what about a extended m/c reservoir and the 2" cyl.

 

[jasonjc]

Unless you pump the brakes the M/C only moves so much fuild at a time. It's not the reservoir, it's the bore of the M/C.

 

[5_TON_TOMATOE]

Well, this is my deal- The brakes on the truck have never worked right for me, as the truck sat for 30+ years, and I'm surprised I got them to work at all. Someone has changed this cylinder out, either in the motor pool, or the state agency that used the truck to tow school buses. I asume they must have worked alright, but who knows. I'm going to use them and see what happens. Maybe some more info will come up in the meantime.