Allison Gears -No Forward Gear

[Genevatexan]

Hello Hatteras crew,

I have Detriot Diesel 6-71s fitted with Allison Gears on a Bertram 42 FBMY. 2000 hours on both, port rebuilt before my ownership many years back. I have been away in the OUPV course for a month and just got back up to the boat and was hauling some furniture out and bumped the port gear lever to forward. My bad, out of my normal routine, started the port engine next morning in forward. Boat surged forward at idle and I quickly pulled it out of gear (still had one spring line on). After warmed up, slipped both engines in gear and only had thrust on starboard side. Went below, checked, port linkage, all good. Actuator lever moves forward but shaft does not turn.
Sitting next to gear box with engine running I hear some intermittent hissing noise but an internal hiss more than external up near the pump with oil lines to it which has multi-connection fitting on the back. Those fittings seem slightly loose but don't see a method to firm up. (btw- temperatures are cooler here lately- normally pretty hot in Texas.). Oil shows correct on trans dip stick, and does not show milky or bubbly. Seems correct to the touch as well.
Reverse works fine. Only forward out. Can you guide me? You guys have saved my bacon in the past, really appreciate your feedback. Manuals went home for the winter, did not expect to need them....
Sea Lion

 

[GJH]

The manual and trouble shooting guide are in the first four or five links:

http://www.acadianmarinetransmission.com/site8.php

 

[REBrueckner]

I did not know 6-71's came with Allisons...you sure about the brand?? Just check the picture in the on line and you'll know immediately....

 

[Genevatexan]

Definitely Allisons. I have a full set of manuals at home but am up at the boat. Allison M20's one Left (L) and one right (R). Serial numbers and model numbers clearly visible on the back of the case. Bertram fitted a number of the middle years boats with these. I have photos of the case and pump in question, but no cable to connect the camera to the laptop.
A feel of the starboard pump while running give you a liquid pulsing feel, the port pump feels different. My theory right now is pump failure of some sort. Tightened the pressure switch fittings and opened the top screw on the actuator level in case that had some air or some issue there. nothing but oil there. After tightening everything up, I got a short half turn of the shaft when level moved to forward, but then nothing. I will review the links provided, and check with DieselPro.com for pump cost. I am losing a drip here and there of oil off both the pressure switch assembly base at the pump, and off the main pump housing, although all bolts tight, so I am guessing that I have lost pressure on the forward gear portion of the assembly, since the hard parts actually did give a short turn, even if only for 1 second....this presumes that there is a forward and reverse portion to the pump....

 

[yachtsmanbill]

Theres a forward AND reverse clutch plate. The reverse takes little pressure to engage and the forward takes the brunt. Is pressure on the gage good? ws

 

[MikeP]

If it uses a Hydreco pump, they are pretty easy to rebuild - kits are around 80 bucks. I rebuilt one of mine a few months ago. What you are describing sounds like it could be internal leakage in the pump which a rebuild (new gaskets/seals) would correct.

 

[Pascal]

Just to eliminate one thing, are you checking oil level with the engine running?

Usually if the Allison goes in reverse but not in fwd it is an oil level or oil pressure problem. It takes more pressure to get in fwd than reverse

What reading do you have on the gauge? If you bump RPM a little, up to 800 or 900, does pressure go up? See if fwd engages

Another possible issue is a suction leak at the screen but check level first. It takes very little for pressure to be too low

Also have you been noticing a delay lately when going in fwd? That s a typical symptom of low oil

 

[Nonchalant1]

I had that exact symptom once. One gear ran in reverse but not forward. As mentioned, it takes more pressure to actuate the forward than it does reverse. The problem was simply air getting into the suction side of the pump at the elbow type hose barb fitting on the pump. It was a little loose, but it is a pipe thread fitting and a quarter turn tightened it up and fixed everything. The suction side is the large hose going into a hydreco pump. The pressure side is a small hose.

If it's the pump, you'll be seeing low pressure on the gauge. Hydreco pumps are easy to fix (but sometimes hard to get at to take them off). They're basically bulletproof and what goes wrong is one or both big o-rings wear out and breaks, providing internal pressure loss. You just take them apart and replace the o-rings, which are available from Detroit Diesel.

Doug

 

[Genevatexan]

Great feedback, guys. Unfortunately, I ran out of time and had to come back to town. The pump looks like the pump at dieselprodot com under the Allison M20 pump page- and yachtsmanwilly, this fitment does not have a pressure gauge. May not be a Hydraco pump... Cant find photo cable so cant upload pics, but there are two oil lines: one goes from pump to the oil cooler in the DD engine coolant reservior, and has a diameter a bigger than your thumb. The other is a huge line, and goes down to a three bolt fitting like a salami, that then goes straight into the port side of the gearbox. I drained and opened the filter to see any symptoms there and found it normal. Dirty, but not out of line since it was changed at the beginning of summer. That said, the pump body is clearly leaking (drip, pause 10 seconds, drip)and oil level was probably low from the drip, but did not check level before I drained filter. Pump leak needs to be solved anyway, so I will pull it down tomorrow. Turns out I don't have manuals for the Allisons, so I sure appreciate the link, George. btw, took an engine stethescope to both port and starboard pumps while running, and they sound very different. Port sounded hollow and irregular, starboard strong and whooshy, if there was such a word.
Doug and Pascal, I think you are right-- low oil volume, low pump pressure, bad internal seals. When I get it off, I'll see who makes it. Also like the idea of a pressure gauge. there is a manifold block where the pressure sender switch is mounted that looks like it was blanked where a gauge could be fit...
More later. Can't say how much I appreciate your feedback,
Sea Lion

 

[GJH]

Look at that Acadian page I linked again. They have one link that discusses the different pump types. They are an excellent source of info and parts, and I encourage you to discuss your problem with them. I also strongly encourage you to get gauges, at least a set of mechanicals that you would mount near the engines. Pressure in those transmissions is a critical data point.

 

[rsmith]

If it looks like this its a Eaton.

 

[Trojan]

I WOULD NOT do anything until I had checked the unit for pressure. Get a pressure gauge and check it. Then decide what to do. Make sure its a pump problem before you take that monster apart. Though the guys may be correct. You would sure be upset if after a pump rebuild and all that work, it still had no forward gear. Get a gauge, pick up 2 one for each trans. There cheap and easy to install. I would not leave the dock without them.

BILL

 

[REBrueckner]

Gene, as a matter of interest what HP are those 6-71's?? TI's????

 

[MikeP]

"I WOULD NOT do anything until I had checked the unit for pressure. Get a pressure gauge and check it."

Absolutely right! DO NOT fall into the "throw money at it until it works" scenario that seems all too common. Troubleshoot it and fix what's broken.

 

[Mario Tranquilein]

Hi everyone: My Allison in my 671 non T one always got to 270 as soon I hit the throttle but the other jumps irregularly always from 190 to 270 just jumping!!. But I never feels lost of power at all and in under load I check both shaft and they turn the same way of speed. I checked the oil with the engine running amd are the full level. My DD spend 9 years in a yard without fire in up so could be an electrical problem or I need to afraid of that? I will do a long trip in New Year Eve and want everything perfect so any advice will be appreciate like always!. Temp of motors 145 both thanks a lot! Mario

 

[Genevatexan]

From the picture, not an Eaton pump. I read the link and downloaded information and going back up now. The flow diagram from the transmission web page link you provided is exactly how mine is setup. Great reference. The large line is the suction side and I have not even checked fittings there since the external leaks are both up on the pump away from the connection to the large line. GJH, I will check the threads on the junction block and see if I can find a guage to fit and then also check all the fittings on the suction side as well (have to crawl back along the port outside of engine.) More later. -K

 

[Genevatexan]

Pump IS a Hydraco. Has made quite a mess down back port side of gear housing. Definitely has to be dealt with. Even if I still have a problem in the gear casing, this pump must be fixed. I pulled it off, and now attaching photo shot before removal. Additional housing on back appears to be a tach drive as it has a rotary mechanical device inside attached to an electronic sender.
Found a Hydraulics rebuilder nearby and waiting for feedback. Case is aluminum and does not get good results during rebuild, unlike cast iron original.
Last question: Where would you try to put a pressure gauge, based on this pic? Not sure the fittings out by the tach sender are fully pressurized.
K

 

[MikeP]

The pressure is read from the shift selector housing on the top of the tranny. You probably have an electrical sender there that reads on the helm. Either remove the elec sender temporarily or add a T and install a mechanical sender and gauge in the eng room (I recommend the latter).

I posted some pics a while back re rebuilding my hydreco pump; here's the thread, might be helpful: http://www.samsmarine.com/forums/showthread.php?t=16013&highlight=hydreco

 

[Genevatexan]

Got it. I also talked to Bryan down at Acadian and he sounds like he knows his stuff. I will find a guage and retrofit both shift lever assemblies as you suggest. Local hydraulics shop has pump, and I am waiting on rebuilt price. IF they are out of line, I will send it down to Louisiana and let Acadian handle it. Like George, I saw the big bag of overhaul parts and remembered that I am better with deadblow hammers than with scalpals. Will get the pump fixed ($175 to rebuild yours if you send to Acadian), change the oil, retrofit the gauges on the shifters, refill and test.
Thanks so much to all. I will report success or failure at the end.
K

 

[SKYCHENEY]

Hi everyone: My Allison in my 671 non T one always got to 270 as soon I hit the throttle but the other jumps irregularly always from 190 to 270 just jumping!!. But I never feels lost of power at all and in under load I check both shaft and they turn the same way of speed. I checked the oil with the engine running amd are the full level. My DD spend 9 years in a yard without fire in up so could be an electrical problem or I need to afraid of that? I will do a long trip in New Year Eve and want everything perfect so any advice will be appreciate like always!. Temp of motors 145 both thanks a lot! Mario

Mario,
Based on the pressures, it sounds like you have Twin Disc gears, not Allisons.