Skip to main content ↑ ↓
Topic: Transmission Swap C6 to AT545 (Read 2284 times) previous topic - next topic

Re: Transmission Swap C6 to AT545

Reply #20 –
Quote from: Protech Racing –
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 .

I wish i could answer these questions. I've only had it a few months and I just got it running, and only drove it enough to tell the transmission was bad. Its got a 2 speed Spicer rear end which i also just got working, and have no Idea what the ratios are for either.

The E4OD like It's Toby mentioned is the big OD?  the only real issue I see there is that its electronic, so would I would have to get a transmission controller?

Re: Transmission Swap C6 to AT545

Reply #21 –
The diff may have a tag on it .or you can jack it up and count the turns.  Look at U tube, you only need to spin one side .  My guess is 4.10 But I have no idea what diff your coach came  with .
 Most 2 speed rears are underdrives as installed .  If you have true overdrive and come up with a total gear ratio under 4/1 (3.9, 3.7 etc) than the direct top gear trans should be fine. 
 Figure out how/if the OD /2 speed works .
 Figure the diff gear
 ask around for optimal cruise RPM for your engine.
 Post what you find and I'l be happy to do some math research.

Gear Up!            this shows how to figure gearsets and tire rollout vs speed.
 The easiest way to determine your gear needs is to coax it down the road one more time with a GPS and tack working.
  IMHO  ;Short story and most cost effective is to get the C6 rebuilt with a HD shift kit and clutch packs  and deal with the resulting cruise speed .
 ****Editttt. If the 2 speed is a gear vender aftermarket OD than you  should be good on the overall gear ratio.
  MY racing partner tows with a 7.3and says that 2300  RPM works the best.  He has towed  @ 2800 with his C6 @ 70MPH .
 For the AEOD Ford trans , you need a controller  and some are using a Microsquirt ECU. The same thing that I sell and install  . The parts are about 400$  ECU and Harness.   
 He has the Gear vender for sale at 1000$ with controller .  Corrected, 1500$ sorry.
 The OD Ford can be built for about 1500 $ here inFL/Tampa area.

Re: Transmission Swap C6 to AT545

Reply #22 –
Rebuild the c6 IMO

Re: Transmission Swap C6 to AT545

Reply #23 –
   What Mike is saying makes the most sense to me ........HD rebuild on the C-6 and count the turns on the rear axle.

We had a feed truck on the ranch ( 1981 ) that had the Spicer split shift and it worked as an under drive, but it had a Clark 5 speed stick so split shifts were easy to accomplish, not sure how it works with an automatic, would need the shift kit just to control trans gear selection.

Mick

Re: Transmission Swap C6 to AT545

Reply #24 –
Yeah, keeping the C6 and beefing it up a bit is probably the best answer.  not the most fun one though.

Re: Transmission Swap C6 to AT545

Reply #25 –
Bottom line is the C6 is a 175 lb transmission with no lockup. You can't expect it to have the life of the heavier transmission and without lockup, it's going to get worse fuel mileage plus it's going to produce a lot more heat with the weight of the GV.

Would be a lot better with a HD automatic or 5 speed manual. The manual worked really well behind the 7.3 in our old devil. The 5 speed has an OD fifth too.

Pierce

Re: Transmission Swap C6 to AT545

Reply #26 –
[quote author=Pierce & Gaylie Stewart link=msg=276476 date=1497645226
Would be a lot better with a HD automatic or 5 speed manual. The manual worked really well behind the 7.3 in our old devil. The 5 speed has an OD fifth too.
Pierce
[/quote]

I would love to throw a 5 speed in here. Part of the problem for me with my current transmission is that i just don't have any experience in automatics. Retrofitting a 30 foot run of shifter and clutch cables sounds a  little daunting though.

Re: Transmission Swap C6 to AT545

Reply #27 –
Quote from: Flopsie –
[quote author=Pierce & Gaylie Stewart link=msg=276476 date=1497645226
I would love to throw a 5 speed in here. Part of the problem for me with my current transmission is that i just don't have any experience in automatics. Retrofitting a 30 foot run of shifter and clutch cables sounds a  little daunting though.
Sorry, I was thinking of a front engined Foretravel. Clutch is hydraulic so that would not be a problem. Shift linkage would take a bit of engineering.

If your C6 is a three speed, that's a big gap between gears. Third can't be too tall and first can't be too low. Just guessing but 55-60 would be about it with fairly high RPM on the freeway. Our 7.3 was happy with a lot of torque low down and a good midrange but lost the really smooth feeling at high RPM. It was happy at about 60 in OD fifth.

Must be a forum with experience with a possible auto trans swap. You might try B&M Transmissions. They have been in the business since I was a little kid. 1.707.544.4761

Pierce

Re: Transmission Swap C6 to AT545

Reply #28 –
Quote from: Pierce & Gaylie Stewart –
If your C6 is a three speed, that's a big gap between gears. Third can't be too tall and first can't be too low. Just guessing but 55-60 would be about it with fairly high RPM on the freeway. Our 7.3 was happy with a lot of torque low down and a good midrange but lost the really smooth feeling at high RPM. It was happy at about 60 in OD fifth.
Pierce

One thing the PO did to help out the C6 was add a 2 speed spicer rear end. Before I fixed that, it was stuck in low and 55 was abotu are fast as it wanted to go. The transmission has been acting up since, so i haven't had  a chance to put it through it's paces. No Idea what the gear ratio is... there are no tags on the case at all.

Re: Transmission Swap C6 to AT545

Reply #29 –
I don't think it would be practical to be splitting the gears with the rear end, instead using it as an overdrive. Only having to back out of the throttle one time. All C- 6's were direct in third gear. The 6's are much more common for repairs also.
 

Re: Transmission Swap C6 to AT545

Reply #30 –
The aod is almost more common than the c6 these days.  They were in most ford diesel 7.3 automatics including the ambulances. They were even used on ford lightnings.  Lots of controller kits available it has become a favourite among hot rod guys that want an overdrive.  really no bad choice but the extra gear would be nice.  you can look up your tires and see what the circumference to figure out how far you travel for every turn of the wheel and then use the gear ratio to calculate the shaft rpm at a given speed.  then run it through the trans ratio to figure out what engine speed would be. Bear in mind the math is not finite with a c6 as the torque convertor is not locking up so there is some slip to be accounted for.