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Topic: Transmission Swap C6 to AT545 (Read 2284 times) previous topic - next topic

Transmission Swap C6 to AT545

Has anyone done this swap? The C6 in my 86 Grand Villa is tired, and I was thinking maybe it might be a better idea to put a sturdier transmission. The Allison is also a 4 speed, which couldn't hurt.
I've got the OREG with the V-814 chassis and a Ford 7.3 IDI engine.  I sort of doubt anyone else has such a chimera of a vehicle. I think the only thing left from the original drivetrain on this beast is the C6.  I'm guessing since the 545 was used by international on the 7.3IDI, it would just bolt up?

Or maybe there is a better option? This is the first vehicle I've ever owned with an auto, so I have a lot to learn about them.

Re: Transmission Swap C6 to AT545

Reply #1 –
MT643 is almost identical to the AT-545 but locks up in fourth gear. I believe it is about 1/2"-1" longer.
Might want to check with James Holder the Service Manager at Tennessee RV.

Re: Transmission Swap C6 to AT545

Reply #2 –
I believe the 643 locks the torque converter in both 3rd and 4th.

 Yes, a lot more robust than the 545.

But, I believe their "bolt up pattern" to the engine is different.  Do not know which has same pattern as C6.

Re: Transmission Swap C6 to AT545

Reply #3 –
Here are the two specification sheets for the two trannys.
Brett is correct. The AT545 mounts to a SAE #2 bell housing and the MT643 mounts to a SAE #3 bell housing.
Seems more comparisons are required.+
I got my info/recommendation from James Holder so hopefully someone else can do some more research on this swap.

Re: Transmission Swap C6 to AT545

Reply #4 –
I was worried that the 643 needed a computer, but then I know very little about them.  No Computers on the old 7.3s.

Re: Transmission Swap C6 to AT545

Reply #5 –
Another dumb question- Is there any difference between transmissions for diesel pushers and front engine vehicles? 

Re: Transmission Swap C6 to AT545

Reply #6 –
Quote from: Flopsie –
I was worried that the 643 needed a computer, but then I know very little about them.  No Computers on the old 7.3s.
It is a hydraulic transmission, not electronic.

Re: Transmission Swap C6 to AT545

Reply #8 –
Yup, if it bolts up, the 643 is a much better choice.  Rated for higher HP and Torque and very importantly, torque converter locks up in 3rd and 4th gear.

So, better MPG and less transmission fluid heating.

Re: Transmission Swap C6 to AT545

Reply #9 –
Here's a consideration. The C6 in there now is 175 pounds. The AT542 is 253 pounds. the MT643 is a great big juicy 510 pounds; 638 with the retarder.  This probably isn't a big deal with the 917 chassis, but i have the 814 which already is 200 pounds heavier with the diesel swap.

Re: Transmission Swap C6 to AT545

Reply #10 –
The C 6 is a pretty good trans as is . Does it have a bigfat cooler and  shift kit ?  it should do what you ask of it. 

Re: Transmission Swap C6 to AT545

Reply #11 –
When you say the c-6 is tired, is it slipping or does it just have "morning sickness" when cold doesn't up shift?

Re: Transmission Swap C6 to AT545

Reply #12 –
  What transmission does Ford use in back of the Powerstroke or Binder diesel.? Seems to me that would be the quick fix, maybe with a shorter tail shaft.
  The C-6 is a stout trans. enough to hold on to a Ford big block so rebuild and shift kit ?  ^.^d

Re: Transmission Swap C6 to AT545

Reply #13 –
My C6 slips badly. its fine in reverse, but from a stop its really bad. I wasn't slipping so badly i couldn't drive it, so I thought maybe it was just the burnt looking fluid, but when I changed that it barely moves at all in forward, so I assume the PO dumped a bunch of that stop slip into it.  My assumption with that is that it needs a rebuild, but this is the first vehicle I've owned with an auto, so I am far from an expert.

Then adding to the fact that the C6 is only a 3 speed,  it just seems if i do have to swap it out, I should consider something more robust and with at least 4 speeds.

Re: Transmission Swap C6 to AT545

Reply #14 –
Whenever you put new fluid in an auto trans that has slipping problems, the detergent in the new fluid cleans the remaining clutch material off and they slip worse. I don't believe you were tricked by the seller with a cocktail. If the fluid was brown and smelly it was bad. I agree if you have to rebuild something use the heavier duty one.

Re: Transmission Swap C6 to AT545

Reply #15 –
Quote from: craneman –
Whenever you put new fluid in an auto trans that has slipping problems, the detergent in the new fluid cleans the remaining clutch material off and they slip worse. I don't believe you were tricked by the seller with a cocktail. If the fluid was brown and smelly it was bad. I agree if you have to rebuild something use the heavier duty one.

Ah. I had no idea of that. I had read if a transmission is slipping and the fluid was burnt, changing it out might fix the problem.
I also wouldn't say i was tricked. Its a long story, but I give the PO a pass on a lot of the questionable stuff he did to this coach.

Re: Transmission Swap C6 to AT545

Reply #16 –
Quote from: Olde English –
  What transmission does Ford use in back of the Powerstroke or Binder diesel.? Seems to me that would be the quick fix, maybe with a shorter tail shaft.
  The C-6 is a stout trans. enough to hold on to a Ford big block so rebuild and shift kit ?  ^.^d


I think they moved to the E40D with the Powerstroke. I have heard with the C6, you can beef up some of the parts on rebuild and make it a lot sturdier, so that is an option too.

Re: Transmission Swap C6 to AT545

Reply #17 –
Quote from: Protech Racing –
The C 6 is a pretty good trans as is . Does it have a bigfat cooler and  shift kit ?  it should do what you ask of it. 

I does have a transmission cooler in front of the radiator, and I wouldn't know a shift kit if it came up and bit me.

Re: Transmission Swap C6 to AT545

Reply #18 –
The e4od would be a benefit. They are strong and common. That being said nothing wrong with a good c6

Re: Transmission Swap C6 to AT545

Reply #19 –
What is the final drive ratio? What is  the cruise RPM? If the Cruise RPM is just under max torque,  you may not see any fuel reduction with more overdrive. 
 In your case  with a conversion from gas to diesel, the RPMs may indeed  like to be reduced a little . 22-2400 Is a nice RPM for those  Fords.  If it is under 2500, I would rebuild the C6, if over I would look for the big OD  Ford trans.  Both will be a lot less hassle - money than the heavy Allisons.  The 643 is direct in high gear, not sure on the smaller one.  Plus the rotating stuff weighs a lot more and will result is less performance .