M35A3 Transmision question.

[Scar59]

WB,
I had 10 gallons of new Shell Dex III on hand and was prepared to drain and flush the system several times. When I discovered the trans already contained ATF direct from the Air Force I simply performed the task mentioned in post # 98. I was going to drain the pan again at the end of the summer (parade & ice cream season), this truck has been handled with kid gloves since I got it, compared to my M813 doing chores on the farm. The truck just turned 4k miles and 300 hrs.
Had I any idea this would happen I would have left it alone. Who knows, something dislodge; scale, varnish,etc and compromised the seals in the high press. pump. The same pump operates 4th gear and reverse. Side note; there was no stencil/placard at the trans fill port stating "10w40" that I have seen on most A3s. Another note, I cleared the vent tube of dirt/ (insect debris) and got it clear when I serviced the truck. Some nasty smelly straw colored fluid vented when the trans made a loud squeal noise, it was not red fluid. I 'm thinking this stuff was up in the top of the unit clogged up some how. I just got some metal to fab up the trans lifting fixture per the drawing in the -24-1-2 TM. Going to do it by the book.
Hope this helps
JC

 

[glcaines]

There may be another possibility going on here. When I talked to the engineer at the Allison factory, he highly recommended replacing the motor oil with Dexron III. However, he was careful to make sure I knew that motor oil and Dexron III were not compatible and to make certain that I got all of the motor oil out of the system via repetitive drain and fills and driving between each. If the military had already changed out your A3 fluid to Dexron III, you have no idea whether or not they did it properly. Also, you have no proof that they used Dexron III. Dexron IV and certain other fluids will deteriorate the seals in the transmission and cause failure. The only fluid recommended besides Dexron III is TranSynd fluid, which is very expensive.

 

[motomacguyver]

We will all be interested in hearing if the transmission shop finds a torn "O" ring on the 4th gear piston. It could be as simple as a burr that was left on a 2.79$ part. See post #69.

 

[Scar59]

Gary,
My thoughts are the same, something changed quickly in the trans. I have a sample of the gunk that came out the vent and it is not ATF. Hopefully the tear down report will ID the root cause. It will be a couple of weeks before I get it to the shop, hay season and other chores are on the list first. What's really got me is the truck didn't get a half mile down the road, never shifted to fourth.

 

[cattlerepairman]

Disclaimer: I do not own an A3.
I think it would be helpful if members posted not only the (often very good and detailed) descriptions of how the failure occurred, but also what the teardown of the tranny by a repair shop actually revealed, and what the $$$ damage turned out to be.


This would aid others in their decision making, should they find themselves in a similar situation.

 

[wb9btz]

Scar59...

Any status update on your trans repairs? Hopefully you got 'er fixed by now. What did they find? Inquiring minds need to know!

I'm in the process of converting mine to C4-rated Dexron III. Currently ready to do the 3rd drain & refill, then change both filters and refill for the last time. So far so good... Results are pretty much as Gary (glcaines) and others previously stated... smoother upshifting and downshifting... Thank God... No more "clunky" downshifts. Maybe my rear end won't try to swap ends with the front end when it downshifts in the snow this winter!

 

[ducer]

I'm just throwing this out there but when I worked for Buick when we did a trans service we ran the transmission through all the gears including reverse for a few minutes before the tires ever touched the ground. The reason is when you drain the fluid and filter residual fluid trapped in the passages of the valve body and clutchpacks has a tendancy to drain out also so you will end up with trapped air in the circuit. It takes time for that air to work it's way out. Say if the transmission is calling for 4th gear and the circuit is full of air until all the air is purged from the circuit it will only halfass apply the clutches letting them slip until all the air gets purged. Air compresses fluid does not. Only then will the 4th gear clutchpack fully apply. If that is truly whats happening that means 4th is slipping it's but off and will fry within seconds under load. In the Hydromatic transmissions we had 4th gear had the longest circuit which is why you would loose it before you lost any other gear. Does this make any sense? If it were me servicing the transmission I would jack up and block up securely the rear tires off the ground and run the transmission through all the gears including reverse before I ever thought of driving it down the road. Then make sure my fluid level was just a little low to allow for expansion during my first test drive so as to make sure not to over fill it which will cause airation and foaming which is just as bad as not having enough. Believe it or not it is better to slightly underfill than overfill due to possible foaming issues.

The reason some of you are puking fluid I feel is due to the superheating of the 4th gear clutchpack under load. I hope this makes sense to you all and it helps avoid further transmissions from being dammaged.
Good Luck,

Denny

 

[Scar59]

Hey fellas,
Trans is still in the truck, I have recieved the service manuals, sling assemble, and fabricated the lifting adapter called out in the TM. (one big hunk of metal) waiting for the temps to drop here in KY, I hate sweating over my work. Denny has some good points, not sure of the failure mode yet. Just make sure the vent attached to the top of the trans housing (left top) is CLEAR of obstructions. I ran my truck stationary, and then idled around the farm, backed up several times. However never got it through all the gears until I headed down the county road. (slow) . It never did shift into fourth. I'll keep you guys updated.
JC

 

[wb9btz]

JC... Trans vent was the first thing I looked for based on numerous people's experience. Well, I found it, but it wasn't where it was supposed to be (behind the cab on passenger's side) according to the TMs and other peoples descriptions. There are only two hoses there on my truck- one large one and one smaller one.

The hose from my vent went forward into the engine compartment and was looped into a cable clamp on the front side of the firewall. It was the larger size hose also. Anyway, I found it to be clear of any obstructions.

 

[ducer]

One other thing I would like to add is you probably will not feel the transmission shift through the gears while the tires are in the air. We used to just run them up to highway speed for a quick blast through the gears (10 or 15 seconds at 55 mph on the speedometer) a couple of times to work the fluid through the circuits and servos.

Denny

 

[Scar59]

I bought another set of HD jack stands. Going to put it in the air and run it when completed. I thought about that the first time, had visions of the truck vibrating off the stands and driving through the shop wall, down the hill and into the pond.

 

[cattlerepairman]

I bought another set of HD jack stands. Going to put it in the air and run it when completed. I thought about that the first time, had visions of the truck vibrating off the stands and driving through the shop wall, down the hill and into the pond.

Yes, that is not unreasonable. A precaution (aside from sitting in the cab, anticipating that it MIGHT happen and hovering with the foot over the brake) would be to chain a second truck to the truck on the stands, as an anchor.

There is at least one video on youtube where a truck takes off from a dyno, as you describe.

 

[Scar59]

I'll have to look for that video. 99% of the time I'm solo in my shop. Always planning for the "what if"?

 

[ducer]

Yea, even the cars jumped around a little bit on the rack. If you took the tires off it would probably shake less.
Speaking of coming off a dyno, here is what happened to me. About 13 or so years ago I top to bottom rebuilt my chevy c30 flat bed it has a 15' x 8' bed with a hoist the bed alone weighs about 1800 lbs. I built a really healthy 4 bolt 350 engine. I happened to be at an old family friends shop in it he had an old Bear dyno he put in in 1962. Well after hearing my truck running when I pulled in he got the idea we should put it on the old chassis dyno. I thought the truck was too big and heavy to do it but he said he had not used the dyno in years and if it broke who cares he was just going to rip it out any way. It only went to 500 horsepower and 500 pounds foot of torque. So I drive it up on the roller he chained the truck in the rear with 3 chains and 2 more from in front of the axle and then I got out of the truck and looked it over. I told him I did not think the 3 chains in the back would hold the truck if the dyno roller should lock up and he agreed so being that there were only 3 pots in the floor he pulled over his 79 ford f350 wrecker and parked it sideways with the mico brake lock on where I ran 3 more chains from the rear hitch this time from my truck to the rear, frame center and front of his truck. The dyno was in a concrete block room of it's own about 30'x12'. The truck twisted the dyno needles to 468 horsepower and 460 pounds foot of torque at about 6000 rpm and all were still climbing when it happened. Don't know if the old bearings in the rollers let go or the shaft for the drum but without warning it locked up fast and hard when the drum hit the ground in the pit. the truck went into about a 6' wheel stand immediatly then the 3 tops of the floor pots ripped off. After that it drug his wrecker side ways on the concrete for about 6' or so and snapped one of my new 3/8" hi test chains before I got it stopped. When the truck came to rest I had only gone into his concrete block wall about an inch and bent up my new nice chrome GM front bumper. It was definatly a hold my beer and watch this moment except for 1 thing, we were stone cold sober. Coulden't say that 5 minutes later. Total dammage to my truck, front bumper, rear axle brake lines and one seriously wrung out rear half of my drive shaft and my 1 snapped and stretched chain.
Dammage to his equiptment, 1 seriously totaled out dyno, 3 floor anchor pots destroyed, bent frame on his wrecker and bent front push bumper. When I went back there 2 weeks later he had a nice new shinney Hunter 4 wheel alignment rack in it's place.

Denny

 

[wb9btz]

Yea, even the cars jumped around a little bit on the rack. If you took the tires off it would probably shake less.
Speaking of coming off a dyno, here is what happened to me. About 13 or so years ago I top to bottom rebuilt my chevy c30 flat bed it has a 15' x 8' bed with a hoist the bed alone weighs about 1800 lbs. I built a really healthy 4 bolt 350 engine. I happened to be at an old family friends shop in it he had an old Bear dyno he put in in 1962. Well after hearing my truck running when I pulled in he got the idea we should put it on the old chassis dyno. I thought the truck was too big and heavy to do it but he said he had not used the dyno in years and if it broke who cares he was just going to rip it out any way. It only went to 500 horsepower and 500 pounds foot of torque. So I drive it up on the roller he chained the truck in the rear with 3 chains and 2 more from in front of the axle and then I got out of the truck and looked it over. I told him I did not think the 3 chains in the back would hold the truck if the dyno roller should lock up and he agreed so being that there were only 3 pots in the floor he pulled over his 79 ford f350 wrecker and parked it sideways with the mico brake lock on where I ran 3 more chains from the rear hitch this time from my truck to the rear, frame center and front of his truck. The dyno was in a concrete block room of it's own about 30'x12'. The truck twisted the dyno needles to 468 horsepower and 460 pounds foot of torque at about 6000 rpm and all were still climbing when it happened. Don't know if the old bearings in the rollers let go or the shaft for the drum but without warning it locked up fast and hard when the drum hit the ground in the pit. the truck went into about a 6' wheel stand immediatly then the 3 tops of the floor pots ripped off. After that it drug his wrecker side ways on the concrete for about 6' or so and snapped one of my new 3/8" hi test chains before I got it stopped. When the truck came to rest I had only gone into his concrete block wall about an inch and bent up my new nice chrome GM front bumper. It was definatly a hold my beer and watch this moment except for 1 thing, we were stone cold sober. Coulden't say that 5 minutes later. Total dammage to my truck, front bumper, rear axle brake lines and one seriously wrung out rear half of my drive shaft and my 1 snapped and stretched chain.
Dammage to his equiptment, 1 seriously totaled out dyno, 3 floor anchor pots destroyed, bent frame on his wrecker and bent front push bumper. When I went back there 2 weeks later he had a nice new shinney Hunter 4 wheel alignment rack in it's place.

Denny

You forgot to mention that you both were now major shareholders in the CLOROX bleach company ! Sure glad no one was hurt! Sometimes the best laid plans.....

 

[ducer]

No one pooped themselvs but, I did feel a few drops of pee. Seriously, the only reason we chanced doing this was because he did have plans on tearing out the old dyno and putting in the alignment rack. Not much call for dyno tuning any more with the modern fuel injection and it only went to 500 hp and torque. The truck was way over weight for the dyno, we risked it anyway and lost. Larry was sure if we could have kept going I could have burried the needles on it.

Denny