Jump to content
  • 1
Macktruckman

Eaton behind maxidyne

Question

I have a 1978 R685ST with a 285 maxidyne and the 2 stick 6 speed with 4.17 rears and tall 24.5’s. Truck is getting a new cab this week and paint job. Old cab is rusted out badly. I have an Eaton RTO14909MLL from a wrecked mixer truck with E7, I think has mounts that will work. Now would be the time to swap transmissions if I want. I was thinking it would help lower my rpm at highway speed and give me a little more top end and maybe help me out on hills. I live in an area with lots of hills. Pull a lowboy to move my equipment and pull an end dump. I like the 2 stick but the gap from 4 to 5 is pretty big with all the hills and I can only get about 60 mph or so on flat ground to the floor tached out. Transmissions look to be within 1”-2” of each other in length. U joints different. Would it be worthwhile to swap? Since the cab is off anyway 

thank you 

Share this post


Link to post
Share on other sites

Recommended Posts

  • 0
8 minutes ago, Macktruckman said:

Or anyone who can direct me for that matter and thank all of you guys again 

It will take a fuel shop to work adjustments on the pump. I will say to not touch it yourself as it is a very precise calibration procedure to go through for accurate and balanced delivery. Should you elect to do this, pull both the pump, and fuel injectors after marking which injector is from which cylinder and send them in together. Mack always specified to match the injectors to the pump they were to be used with for proper balance. They are calibrated as per 1000 strokes on a very precise machine, (test stand). I've used Thompson Diesel in both Tulsa, and OKC a few times but that has been a while so don't have any recent history.

Share this post


Link to post
Share on other sites
  • 0

Ok. I have done business with Thompson in Tulsa several times. They would be where I would go. Was a guy there named Paul and he’s sharp. 

Share this post


Link to post
Share on other sites
  • 0

I wish I could stick that 14909 in there and not touch the pump 

Share this post


Link to post
Share on other sites
  • 0

Nothing says you can't. I feel you can do better than that however but it will take a bit of time and unfortunately, $$$. With the "Maxidyne" tuning and gears closely spaced the engine will not perform as designed but will still run well. As mentioned most find the gearing "short". That was the problem I ran across with most conversions is the pump is not worked with.

Share this post


Link to post
Share on other sites
  • 0

I don’t know then. Maybe I should abandon the transmission swap. I’ve spent a small fortune on this already buying a cab and a good hood and then some interior parts from other places, plus paint and all the supplies to ready for paiy. And I’m putting 8 new drives on at the same time. I have the transmission and thought if it didn’t cost me much more to swap it in then it might help me out on the road. But pump work means more money and time. And it’s been down over a week already so it’s getting about time to get it hauling again and get a paycheck. Lol

Share this post


Link to post
Share on other sites
  • 0

I suppose I can try it and see. It wouldn’t be a big deal to pull the pump and injectors later and have them done. After my bank account healed 

Share this post


Link to post
Share on other sites
  • 0

If it were me that truck would need to be earning it's keep before I modified if mechanically sound as it is. Not a lot is saved by converting the transmission and driveline without the cab on the frame over doing it when the truck is all together. That power platform is very robust if taken care of and I'd get some work out of it till the budget allows working with it more.

Share this post


Link to post
Share on other sites
  • 0

You can always ask around here and see if someone has a Jake brake on a spare engine they'd part with. You need all the under valve cover parts including the risers, plus an offset tip turbine adapter/plus offset hose going from intercooler to tip turbine, plus clutch/throttle/dash switches.

Share this post


Link to post
Share on other sites
  • 0

We have a couple old mixers with the 4 valve engine. Mid eighties models they were 250’s with the 2080 transmissions that the dealer upped to 300 and restamped the id plates. Pump and injectors out of one of those work to recalibrate the 285?

Share this post


Link to post
Share on other sites
  • 0

Thank you.  I like the idea of the jakes. But I’m really after that taller top gear. Reduced engine speed in high gear is a big reason for the consideration 

Share this post


Link to post
Share on other sites
  • 0

I do not believe so but am no authority on the four valve head engines so very well could be wrong.

Share this post


Link to post
Share on other sites
  • 0

With my handle of course I'm gonna argue for the Maxidyne. That said, there's applications where a conventional torque rise engine and more gears works better. But first you might want to make sure your engine is putting out the power it should- with the gearing you've got a 285 HP Maxidyne should be good for about 63 MPH on the flat at which point the 2100 RPM governor starts to shut off the fuel flow. If you're running over OK's 85,500# weight limit you might need more power to run 63 MPH, and going up to the 315 HP rating might not be enough.

Share this post


Link to post
Share on other sites
  • 0

Well I’ve used it like this for a few years. I just remembered the Eaton out there and my imagination started churning since it’s in the shop and all apart. Lol. Thought it would be nicer and could pick up a few more hay haul jobs that would be a little further mileage. Would make it a little more comfortable for the longer days

Share this post


Link to post
Share on other sites
  • 0

I really like the maxidyne too. It will pull a full load down the flat road no problem. It’s very sting in the pits and on sites. And it probably runs really close to that 63 at 2100. Running 65 at 1750-1800 would make me happier and Like I said before, in the hills a gear between the last two would help. 

Share this post


Link to post
Share on other sites
  • 0

I’ve heard that the jakes or dynatard is hard on cams...

is that not so?

Share this post


Link to post
Share on other sites
  • 0

By the way this truck doesn’t work solely on its own. It works together with my dozer a backhoe and a 15 ton excavator. 

Share this post


Link to post
Share on other sites
  • 0

The equipment doesn’t tax it. 

That end dump loaded heavy is a little different. 

Share this post


Link to post
Share on other sites
  • 0

sounds like a good truck worthy of refurbishment to me. I've not heard you talk of it being laid up at the dealer for repair work so must be better than something newer?

I too like the "Maxidyne" concept if it is worked and maintained within it's design parameters. One of the best power platforms out there IMO. Just the thought of you still working the truck as it was designed lends credence to the platform as it still gets the job done and I'm hearing reliably.

Share this post


Link to post
Share on other sites
  • 0

Whatever I decide to do, I have a whole lot more information to work with than what I knew and I am very thankful to each of you guys again for your helping me out. I appreciate it more than I can tell ya

Share this post


Link to post
Share on other sites
  • 0

Rob,

The old cab and doors are rusted out severely. It was an oil field tractor that pulled salt water tanks. The engine has about 300,000 miles and does not leak or use oil. It’s rough and it’s loud. But it’s been very trustworthy. Refurbished cab and interior with new dynamat and sound insulation and some interior panels from a wreck. I’m actually going to install a stereo if it works out. Lol.  I’m fabbing up a cab air ride (to help counter those camelbacks, lol) and it’s getting a pair of new used 6” stacks and new rubber. A Lund sunviser off another wreck and new paint. I like the truck. Very simple. It is awful to service... has 3 big oil filters and holds 14.6 gallons of oil. Lol. That hurts. Lol

Share this post


Link to post
Share on other sites
  • 0

I’ve rode many rough miles in r models. Riding along with my dad. The old mixers didn’t have a passenger seat so I sat on a rotella box. 

Share this post


Link to post
Share on other sites
  • 0

You'll love the air ride cab. Nice thing about the big oil pan and 3 filters is 25,000 mile oil change interval. What's hard on the cams is when a tappet lifter face breaks. Wipes the lobe off the cam pretty fast. We just had to replace one for that last year. Good thing we had a spare motor here, Mack can't get the cam anymore. Maybe PAI has them? I've only heard of PAI from guys here, never dealt with them.

Share this post


Link to post
Share on other sites
  • 0

Thank you for the info Joe. We have an 81 model that is spec’d about identical to this one. Difference is it has the charge cooler in front of the radiator and it has air ride on the cab. It’s where I got the idea for that. It is quite a bit better riding. So I agree. I think I’ll love that. 

Share this post


Link to post
Share on other sites
  • 0
Posted (edited)
On 3/3/2019 at 7:05 PM, Macktruckman said:

Rob,

The old cab and doors are rusted out severely. It was an oil field tractor that pulled salt water tanks. The engine has about 300,000 miles and does not leak or use oil. It’s rough and it’s loud. But it’s been very trustworthy. Refurbished cab and interior with new dynamat and sound insulation and some interior panels from a wreck. I’m actually going to install a stereo if it works out. Lol.  I’m fabbing up a cab air ride (to help counter those camelbacks, lol) and it’s getting a pair of new used 6” stacks and new rubber. A Lund sunviser off another wreck and new paint. I like the truck. Very simple. It is awful to service... has 3 big oil filters and holds 14.6 gallons of oil. Lol. That hurts. Lol

I have a couple of cabs out back that I'd wager are just as bad but I've robbed and picked parts from for over 20 years now and they really are getting thin. I'm not picky at all but some little part that cannot be had easily anymore.....

 

Post up some photos when you are done with it for sure. Best way to see if I can make use of what's left.

Thanks,

Rob

Edited by Rob

Share this post


Link to post
Share on other sites
  • 0

If I can figure out how to put up pictures I’ll do that and some before and after pictures when I’m finished. Be a week or two more. I won’t haul anything off so it’ll be here if us Mack guys need something. Lol. Where do you hail from? We got a little snow here today too

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Answer this question...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...