M35A3 Transmision question.

[mktopside]

I believe you got your A3 at the same sale I did and many of the A3s at Sparta during that sale had low mileage like mine. I find it too much of a coincidence that the clutches went out on your Allison at the very instant you changed out your fluid. I'm wondering if there is not an air pocket someplace inside the transmission causing your problem. If it was me, I would make certain the fluid level was correct after it is hot. If the transmission is not slipping in the working gears, I would drive the truck, slowing down and speeding up, making it shift up and down for maybe 10 miles or so, and see what happens. There also might be some Allison forums that you could post on asking for help with the problem. Another thought is to visit a transmission shop that rebuilds Allisons and try to talk to the mechanic about what might cause the problem. You could also try e-mailing Allison directly and ask for assistance. Good luck solving your problem.

+1

Things just don't break like that. I've never ever ever ever in my life seen a transmission take a dump immediately after changing the fluid; and I've seen a whole lot of transmissions.

 

[Rustygears]

Agree with mktopside

Very unusual and there is either something simple being overlooked, like fluid level or there were problems before draining. Something doesn't add up.

BTW - I really enjoyed the Tokyo quake. The Narita Rollercoaster!
Aftershocks every couple of minutes in the magnitude 6 & 7 range all night and today. I want to go home to California where the quakes are wimpy.

 

[glcaines]

Well. I'm ****ed. pulled the tranny pan, changed the internal filter, and still no love.

Any update on the transmission problem? I'm hoping it's something simple.

 

[motomacguyver]

OK, the truck was bought in the same auction as glcaines, it has about 2500 mi and 300 hours on it. I think it's in pretty good shape. The next step is to do a psi check on the transmission. There is a 1/8 npt port above the shift cable, the allison tech says I should have 125 psi at idle and a little more in reverse. Then I also need to make sure the transmission and the shift tower are timed correctly. (they both have detents, and both need to click in at the same time)

However, both allison guys I talked to said that it sounds like the fourth gear clutch is going out.

I asked what would cause this and they stated "pulling a heavy load"

 

[mktopside]

Agree with mktopside

Very unusual and there is either something simple being overlooked, like fluid level or there were problems before draining. Something doesn't add up.

BTW - I really enjoyed the Tokyo quake. The Narita Rollercoaster!
Aftershocks every couple of minutes in the magnitude 6 & 7 range all night and today. I want to go home to California where the quakes are wimpy.

Glad you're ok! I'm watching the news and the damage looks mind boggling. I hope we are helping them work through their reactor situation, I get the feeling they are nearing the point of desperation trying to avert another disaster.

 

[glcaines]

OK, the truck was bought in the same auction as glcaines, it has about 2500 mi and 300 hours on it. I think it's in pretty good shape. The next step is to do a psi check on the transmission. There is a 1/8 npt port above the shift cable, the allison tech says I should have 125 psi at idle and a little more in reverse. Then I also need to make sure the transmission and the shift tower are timed correctly. (they both have detents, and both need to click in at the same time)

However, both allison guys I talked to said that it sounds like the fourth gear clutch is going out.

I asked what would cause this and they stated "pulling a heavy load"

I would check the pressure as the Allison tech recommended. I still find it hard to believe that the transmission failed at the same instant that you changed the fluid out, or that the timing of the shift tower and transmission detents got out of sync at the same time. Also, if the 4th gear clutch was going out I would suspect that the first symptom would be slipping, not a total failure to engage. I'm assuming here that the transmission completely fails to engage in reverse or 4th?

 

[motomacguyver]

I would check the pressure as the Allison tech recommended. I still find it hard to believe that the transmission failed at the same instant that you changed the fluid out, or that the timing of the shift tower and transmission detents got out of sync at the same time. Also, if the 4th gear clutch was going out I would suspect that the first symptom would be slipping, not a total failure to engage. I'm assuming here that the transmission completely fails to engage in reverse or 4th?

It is slipping, when it tries to shift to fourth it revs up and never really "locks in". Reverse doesn't drop the engine RPM like putting it in drive does. It will back up but engine RPM has to be double what it used to be.

 

[ApopkaFL]

Allison Model AT-1545P Website says only 5,602 ever made.

Type Constant Mesh ( what ever that means )

Speeds four foward one reverse

Gear Ratios

first gear 3.45 to 1
second gear 2.25 to 1
third gear 1.41 to 1
fourth gear 1.10 to 1
reverse gear 502. to 1


Says it holds

DRY 21qts
Drain and Refill 10qts
After Rebuild 16qts

It does not say what type of tranny fuild to use. Do you think you have the right type of fuild? in it?

 

[mktopside]

Allison Model AT-1545P Website says only 5,602 ever made.

Type Constant Mesh ( what ever that means )

Speeds four foward one reverse

Gear Ratios

first gear 3.45 to 1
second gear 2.25 to 1
third gear 1.41 to 1
fourth gear 1.10 to 1
reverse gear 502. to 1


Says it holds

DRY 21qts
Drain and Refill 10qts
After Rebuild 16qts

It does not say what type of tranny fuild to use. Do you think you have the right type of fuild? in it?

That popped into my head as well.

Maybe try one of those fluids that is DEXIII approved, but works with transmissions that require friction modified fluid. It's a bit stickier and might help. That is an idea for later, not a suggestion for now though. I still think that your issue is something dumb you have overlooked (I do this all the time) or the shifter adjustment.

 

[glcaines]

According to Allison, the transmission was designed to use Dexron III. The Army switched to motor oil to eliminate one extra fluid. Subsequently, TranSynd was developed by Castrol and Allison recommends that fluid over Dexron III. However, according to Allison, TranSynd will not perform any better than Dexron III. Only the frequency of ATF fluid changes is extended if you switch to TranSynd. However, the newer Dexron VI is ABSOLUTELY NOT compatible with the Allison 1545 transmission. It will eat up the seals if used. This is straight from Allison. Dexron is a trademark of General Motors. GM has now withdrawn certification of Dexron III ATF. A lot of companies are producing ATF and calling it Dexron III or Dexron III compatible, but GM is no longer approving these fluids. When I changed out my 1545 to Dexron III, I used NAPA Premium Performance Automatic Transmission Fluid, P/N NP75203, in five gallon pails and manufactured by Ashland Oil (Valvoline). The label specifically states to use it where Dexron III is recommended and it also specifically states to use it in Allison transmissions. I have had zero problems since switching to the ATF. The only change I've seen is a major improvement in the smoothness of shifting.

 

[ApopkaFL]

you never said if you had any metal in the pan once you change the filter? Also what was your reason to change the fluid anyway?

 

[motomacguyver]

you never said if you had any metal in the pan once you change the filter? Also what was your reason to change the fluid anyway?

Their was a small amount of black dirt in the bottom of the pan. I could have/did wiped it out with 2-3 paper towels. I changed the fluid because allison recommends dexron III as do several members here.

I went for a drive today after verifying that the linkage is timed correctly and the fluid is at the correct hot run level. The symptoms are the same. Fourth gear doesn't fully engage at full throttle, and reverse requires 2x the RPM to back up than before the change.

I will be checking the PSI, but I have to obtain the tools first.

 

[Rustygears]

I switched to Napa NHF 85-405 Premium Heavy Duty Tractor Hydraulic & Transmission Fluid GL-4. This fluid (in 5 Gal pail also) carries GM Dex-III, Allison C-4 and Caterpillar ATF ratings. It is cost effective and made a world of difference in my truck, both in shift performance and in much reduced operating temperatures. This is HD, professional fluid meant for these types of applications.

 

[mktopside]

Their was a small amount of black dirt in the bottom of the pan. I could have/did wiped it out with 2-3 paper towels. I changed the fluid because allison recommends dexron III as do several members here.

I went for a drive today after verifying that the linkage is timed correctly and the fluid is at the correct hot run level. The symptoms are the same. Fourth gear doesn't fully engage at full throttle, and reverse requires 2x the RPM to back up than before the change.

I will be checking the PSI, but I have to obtain the tools first.

****.


Well........ Dope it up with some Lucas or BG and see what happens. Maybe you can upgrade to an MD3060 if you have to replace it.

 

[glcaines]

I went for a drive today after verifying that the linkage is timed correctly and the fluid is at the correct hot run level. The symptoms are the same. Fourth gear doesn't fully engage at full throttle, and reverse requires 2x the RPM to back up than before the change..

I just went for a ride in my A3 after reading your last post. I believe I am seeing a slight increase in RPM when I'm in reverse, but it doesn't appear to be slipping. I don't really remember what the RPM was before the change in fluid, but it solidly went into reverse with a clunk before change in fluid and does the same now. The transmission shifts fine, including 4th and the lock-up feature is working fine also. However, my 1545 transmission doesn't shift into 4th until I hit about 2300 RPM and it locks up almost immediately after. This is the same behavior I had before I changed to ATF. The transmission is so smooth now, I almost can't tell when it goes into 4th, only the RPM drops.

Do you have a 545 or 1545 transmission? If you have a 1545, does it lock up? You mentioned that it doesn't 'fully engage' into 4th. Does the RPM drop when it tries to go into 4th? With the reduced viscosity of the Dexron III over motor oil, there is likely more slip in the TC after the change in fluid. Can this account for what you are seeing?

You have been driving your truck after changing to ATF. It won't take long for the fluid to turn dark if the transmission is slipping, although with such a large capacity it might take longer. Have you seen any change in fluid color?

 

[motomacguyver]

I just went for a ride in my A3 after reading your last post. I believe I am seeing a slight increase in RPM when I'm in reverse, but it doesn't appear to be slipping. I don't really remember what the RPM was before the change in fluid, but it solidly went into reverse with a clunk before change in fluid and does the same now. The transmission shifts fine, including 4th and the lock-up feature is working fine also. However, my 1545 transmission doesn't shift into 4th until I hit about 2300 RPM and it locks up almost immediately after. This is the same behavior I had before I changed to ATF. The transmission is so smooth now, I almost can't tell when it goes into 4th, only the RPM drops.

Do you have a 545 or 1545 transmission? If you have a 1545, does it lock up? You mentioned that it doesn't 'fully engage' into 4th. Does the RPM drop when it tries to go into 4th? With the reduced viscosity of the Dexron III over motor oil, there is likely more slip in the TC after the change in fluid. Can this account for what you are seeing?

You have been driving your truck after changing to ATF. It won't take long for the fluid to turn dark if the transmission is slipping, although with such a large capacity it might take longer. Have you seen any change in fluid color?

Before the change in fluid, the engine RPM's would drop the same amount in drive or reverse. At Idle. (apx 100 rpm with a defenite "Clunk"). Now when going into reverse there is no "clunk" and very little, if any RPM drop.

I have a 1545 transmission.

Before the change, first to second gear change was smooth, no hesitation, just rpm drop, then second to third, their would be an upsurge of rpm for about 1-2 seconds and then the rpm drop into 3rd. then the exact same upsurge for the shift to fourth.

When down-shifting the 4-3 drop was smooth, almost not noticable, then I would slow to about 15 MPH and it would drop two shifts hard enough to skid the rear wheels for an instant.

After the change, every shift is the same except for the 3-4 upshift. It starts to shift with the "upsurge" and just doesn't stop the "overrev" portion of shifting. If I hold the throttle to the floor it will just hit the governer and not really accelerate. When I let off the throttle, the RPM's drop to a normal amout for the upshift, but if I get back into the throttle it sure seems like it is slipping.

I haven't driven it far enough to see if the fluid changes color.

 

[glcaines]

When down-shifting the 4-3 drop was smooth, almost not noticable, then I would slow to about 15 MPH and it would drop two shifts hard enough to skid the rear wheels for an instant.

I don't think your experience during downshifting was normal behavior, or at least my A3 never behaved like that, either before or after the change to ATF. When I slowed down with motor oil in the transmission, there were two distinctive clunks as it downshifted to 2 and then 1. Both were delayed more than I thought they should be. However, it never skidded the rear wheels, even on gravel, when downshifting. With the ATF, I almost don't notice the downshift when slowing down unless I slow down very fast. My A3 is the only one I've ever been in, so I don't know which behavior is more common. Maybe some other A3 owners can chime in.

 

[ApopkaFL]

I can tell you this much I will not be changing my fluid anytime soon......

 

[glcaines]

I can tell you this much I will not be changing my fluid anytime soon......

A lot of people have done it without issues, and Allison recommends the change as long as the old motor oil is significantly purged.

 

[motomacguyver]

I did the pressure test today, Bought some compression fittings, a 0-300 psi gauge and some 1/8 dia. copper tubing. Hooked it all up and... 150 psi at idle in neutral, 150 psi in drive, 40 psi in reverse, apx 135 psi when it tries to go to fourth. If I rev the engine in reverse, the PSI goes up, at around 90 psi it starts to move. I have a call in to the Allison guy and will update here when I find out what he says.