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New to me M35A3, suggestions needed

HDN

HDN

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Falconair07 said:
What kind of coolant are you guys using?
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The coolant in my truck is mostly original. It should probably be flushed, but I plan on doing that whenever I get around to repairing the leaky heater core.

Because of the leaky heater core, the truck lost coolant on the passenger-side floor, so I had to add about two gallons of the red diesel stuff I got from Tractor Supply to get it back up to a good level. Add coolant to the surge tank until you can see it centered in the sight glass.
 
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Falconair07

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GopherHill said:
What is the latest news?
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Last time I was able to work on it, I drained transmission and started cycling Dex3. It only accepted 2 gallons.

This week I dropped the trans pan, cleaned out a bunch of muck, swapped pan and spin on filters and got it to take 5 gallons of Dex3. I did some laps around the barn in high/low all gears. Today, I took it on pavement and it shifted up to 3rd and down again while in drive. Did about 35 MPH. I also washed it for the first time since the flood of ‘19.

Tachometer is dead, so I need to get that cleaned up and figured out. Any tips on things to look at?
 

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HDN

HDN

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The red coolant works better with a diesel engine's vibrations, which are stronger than gas-powered motors - something about bubbles and cavitation with the water pump I think.

You mentioned it got up to 3rd gear - do you have 4th and reverse? The transmission should shift to 4th between 30 and 35 MPH.
 
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Falconair07

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HDN said:
The red coolant works better with a diesel engine's vibrations, which are stronger than gas-powered motors - something about bubbles and cavitation with the water pump I think.

You mentioned it got up to 3rd gear - do you have 4th and reverse? The transmission should shift to 4th between 30 and 35 MPH.
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That’s just as high as I went, sticking very close to home in case I had to tow it back (just the pavement in front of my property). Reverse works great as well, just didn’t get it going fast enough to shift to 4th, maybe closer to 30 MPH for a second or two. I’m having more confidence in it, so next time when I have backup to tow me if needed, I’ll push it faster and into 4th.

1st time out a few months ago, no shifting occurred in drive and then it just quit moving too far from home!
 
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tobyS

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If you are ready to ruin the tranny (as Rusty says), drive it with water damaged clutches. Mine melted the aluminum piston and sent aluminum everywhere. We have rebuilt several 1545 and had the lock up TC rebuilt. Next time I would use the 4L80 (direct clutch) that is made for racing in the 4th clutch pack. It has more surface, better friction and a much better sealing (vulcanized steel) 4th clutch piston (which is the downfall of all A3 1545's).
 
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Falconair07

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I need some help. Good news is that the transmission seems to be working great on the Dex3. Shifts smoothly up and down, reverse. If I melt it, I guess so be it, cross that bridge later.

Problem: under high demand, I lose power. In 3rd for 20+ seconds or up into 4th trying to max speed, just total loss of power. I drove it for quite a bit the other night, when it would lose power, pedal held to the floor during its fit, I would either down shift or shift to neutral and the turbo would spin up again and I could put it in gear and go….until it lost power again. Did this 10+ times on my test drive. Power always came back.

I put on another new fuel filter tonight, and the tank is >1/2 full of fresh fuel. Something about demand is making it quit. What can I check? Thanks
 
glcaines

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Look at the check valve on top of the tank. Be careful with the connections as it is easy to break the fittings. Hold the fittings with a wrench as you loosen so as to not put a lot of torque on the fitting. This is a common problem with M35A3s. Trash from the fuel tank gets caught up in the check valve causing the engine to starve for fuel. Unfortunately, this check valve is before the filter. The usual symptom is loss of power and white smoke from the exhaust. I keep a set of wrenches in my A3 so that if I come to a stop on the road, I can fix it. The check valve is very easy to clean so there is no need to buy a replacement. I've gone through this perhaps 5 or 6 times since I got my A3. If you have any questions about removal, let me know.
 
HDN

HDN

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Falconair07 said:
Thanks for the tip on the check valve. Probably a dumb question but how do I know if the torque converter locks up when it shifts to 4th?
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It'll sound like it's going into a 6th gear. Also check the tach against the speedometer - they should be moving at the same time when the torque converter is locked up. When there's no lock-up the tach needle will move up and down before the speedometer does because of the fluid coupling lag.

The AT1545 locks up only in 3rd and 4th, so you should only see this happening in 1st and 2nd gear.
 
glcaines

glcaines

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HDN said:
It'll sound like it's going into a 6th gear. Also check the tach against the speedometer - they should be moving at the same time when the torque converter is locked up. When there's no lock-up the tach needle will move up and down before the speedometer does because of the fluid coupling lag.

The AT1545 locks up only in 3rd and 4th, so you should only see this happening in 1st and 2nd gear.
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Like HDN said, you can hear and feel it lock up. From a stop, accelerate slowly and count the shifts. Interestingly, the TC sometimes locks up between 3rd and 4th on mine and sometimes waits until it's in 4th gear. It doesn't really matter when it locks up. If you can't really tell, look at the tach as HDN suggested. With the Dexron 3, the shifts are much smoother than with motor oil and less discernible.
 
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