What transmissions do I have? 1974 48YF with 8V71TI's

[silverpaul]

Working my way through my new to me 1974 Hatteras 48YF and learning. The survey says the gears are marked: AS 5-72C 1.291:1 (ratio can't be right?). I have not confirmed this information as I haven't yet found the data plate!. Dipstick is showing low and I need to know what oil to add and where to add it.

Any help appreciated,

Paul
Oxnard CA

 

[Genevatexan]

Borg Warner built a V drive labeled the 72C, but I don't know enough about Hatteras to comment if they were fitted or not. I run Allison gears. Here's a diagram and a sales link:

http://www.kdtrading.no/tradingshop/tekniskinfo/borg_warner_71&72_v-gear.pdf

https://marineandrvpartssupply.com/velvetDrive_parts_List.html

 

[Genevatexan]

And apparently an inline version as well:

http://www.harbormarine.net/transmission_service.php?page=71c-72c-inline-tech-specs

 

[captddis]

Should be Allisons. The BW 72 series would never hold up to the 8V71 torque.

 

[silverpaul]

Thank you. My feelings exactly - I had a Velvet Drive on my last boat (71C) so I was suspicious of the data also the ratio makes no sense for the props fitted.
I still have the problem of where to add oil as there is no transmission manual on the boat. Any general advice? Does the oil go in through the breather on top or is there a plug somewhere?

Any help appreciated.

Paul

 

[Genevatexan]

Here is a photo of Allison M20 Gear box. I add oil at the breather. If you notice the gear selection lever at top, there are two brass plugs in the top of the selection lever unit. the bright brass cap is low pressure and the lower one (less visible) is high pressure. This forum recommended adding a pressure guage there to keep up with the transmission pump (external) pressure. I have done so, and its a super modification. I run around 120 lbs of pressure on each transmission. I have also attached a picture of the hydraco pump for the Allison M20.

 

[Genevatexan]

Note also: my ID plate for the gearbox is right behind the gear selector lever housing, partially covered in paint.

 

[lumina]

Hi All,

Paul,

My 48YF came from the factory with Allison M20-R (2 : 1) transmissions.

 

[silverpaul]

Thank you both, very much.
Kent, excuse my ignorance but what is a Hydraco pump? I have pressure gauges on the console that read around 100 psi, are the gauges you mention additional?
Gene, I figured out that the only viable ratio with my props is around 2:1.

Back to the engine room this weekend with a gallon of oil and a camera!

Paul
'Freeway'
Oxnard CA

 

[saltshaker]

I would expect they are Allisons but you need to confirm that before adding any oil. Take a picture and post it here. Call Hatteras and they can tell you what engines and gears she left the factory with. Allisons use the same motor oil that you use in the engines, either straight 40W or 30W depending on climate.

 

[silverpaul]

Thanks all. They look like all the pix I have seen of Allisons. The good folks at Hatteras have now fixed their microfiche printer and I have my original 'Vitals'. They confirm the transmissions are Allison M-20's with a 2:1 ratio.

Paul
'Freeway'
Oxnard CA

 

[REBrueckner]

You should adjust your pressure so you run 120 psi in forward gear at moderate, cruise, RPM.
I measured operating temperature at about 185 degrees with 170 coolant thermostats. Maximum allowed temperature for the transmission is 200 degrees per the manual. Straight 40 weight heavy duty diesel lube oil, same as for your TI, is recommended.

I added temperature gauges to be sure the oil cooler was doing it's job and strongly recommend
that change. I had some Borg Warners overheat years ago...those were easy to fix, not so the large and heavy Allison M20's.

 

[Genevatexan]

The Allison M20 uses an external pump to drive the tranmission. Mine is made by Hydraco and the second picture posted. I believe my transmissions use 3.5 gallons of motor oil each. The large Hex adjuster on the top is the pressure adjustment. The guages you have on your console are reading the pump pressure. Falling pressure will first show up by losing the ability to go into forward, which takes more pressure. This forum has suggested 120 to 130 psi as standard. My boat did not come with onboard guages so I fitted mechanical guages to the gear selector lever housing in the engine room. At that time I had one pump rebuilt by a company down in Louisiana that specializes in rebuilting these and all is well.