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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 

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What all did you have to do to convert to air ride cab? I have a 1988 RD I need to convert, rides like a DM right now.

Where did you get parts, what'd you spend?

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Spent less than 200 in parts I believe. I bought two airbags and two shocks for peterbilt cab air suspension and I bought a leveling valve. All off Amazon. Bolted a piece of channel iron across the bottom of the cab with the original rear cab mount bolts. Then, There is a piece of 2x3 rectangular tubing that clamps across the frame and the original cab mount is factory welded to that. I cut the factory mount off of that 2x3 tubing and used good heavy 5x5 or 6x6 angle iron and welded back in place of the cab mount so that it made a dropped shelf for the air bags to sit on and then the channel iron  on the bottom of the cab sit down on top of the bags. Drilled holes in the angle and channel iron first of course for the air bags to bolt to. Then I bolted the shock tops through that channel iron and the bottom I welded a little bracket on the angle for the bottom to bolt to. Level valve bolted through two existing holes in the right truck frame. Was all a straight forward deal for me because the cab was off the truck. So I was able to mock up and mark holes and then take the pieces to the drill press and welding table. Then of course you have to bracket your radiator down to the frame or front shock mount like factory air cab trucks do. And you need roller type hood rests. I also made most of that myself.  But once you have everything loose, you should be able to Jack the back of the cab up fairly high and get at what you’re doing 

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Cabmate wants @ $850 for a kit for the rear. I almost went that road but I figured it wouldn’t be that hard to do myself surely. And it wasn’t 

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I’m not sure but it seems like I remember that rd might already use a roller type hood rest?

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I'll have to double check the radiator mounts, but I know it has 2 hood rollers. Air was an option in 1988, but this truck didn't have it. Or it didn't get transferred over when H&K  put a new frame in the truck.  Square tube/muffler support is a bit rusty, I may just remake the whole bar. It also sits too close to the back of the cab, H&K took a hammer to the back of the cab to keep the diagonal brace from scuffing the cab....

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I was thinking you might already have the rollers, you should be good to go there. Making radiator supports was easy. I would think remaking that bar behind the cab would be pretty straight forward. My exhaust was bracketed to the cross bar originally at the bottom of the stack and the top stack bracket bolted to the cab. I cut that all off and built a headache rack and bolted the new stacks to that. My fuel tanks also hang off of that cross bar.  None of it was complicated. It took a little time of course but it was pretty straight forward. If I can do it about anyone else can. Lol. Btw, we have an 1981 that’s factory air cab. It’s where I got the notion to convert this one. It always rode much better before. 

I have a new problem now. I hadn’t driven it after dark yet. This morning I realized that the headlight relay gets hot after a few minutes and my headlights go off until the breaker resets. And then go a few minutes again. The park lamps all stay on. The headlights quit. I suppose maybe I have a short to chase. That should suck to find. Lol. I haven’t got another breaker to try, naturally the headlight breaker is different than every other breaker in the panel. 

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My dad has always had to split our headlight switch up on our trucks. Headlights and turn signal clearance lights on one switch, cab roof lights another switch, and rear lights a third switch.

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Good to know thank you 

I did swap the old sealed beams out for some new KC hi-lite replacements with halogens. It might help if I stick some led bulbs in those 

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Turned out nice. I put air ride under the cab of the Superliner I just sold. It did make a difference. I got lucky and found everything I needed off another cab. I still had to fab up some things because nothing ever just bolts on. I had to make the brackets for the firewall that the rollers bolt in. After everything you did to it should last you a long time.

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Thank you I hope so. I haven’t worked on the headlights yet, but I’ll figure it out in a day or two. I put a new foot valve on while the cab was off just because they’re hard to get to and I figured it would be smart. It started leaking yesterday. Lol. Parts are so cheesy these days. 

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That air ride cab, the transmission and all that insulation have made a different truck out of it. So much more comfortable. And I may get flamed for this, but my old steering wheel was in bad shape and I couldn’t find a stocker I could afford so I put an aftermarket 18” wheel on and it also is more comfortable. 

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Yes Rob you’re certainly right. This was a Haldex and I thought it would be ok but not so apparently 

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It’s apparently no good. Lesson learned and it’s frustrating when the whole point of changing it was to avoid changing it after it was all together. Lol I’m fortunate enough to have a/c and I don’t really use the wing glass to hang a finger on. My old steering wheel had cracks in just the right places so as to pinch the piss out of the underside my fingers. Lol

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I can see where you would catch a finger there with those massive steering wheels. Lol. Thank you very much for the compliment but it’s definitely no professional job. I have a really good mechanic and he was a lot of help. He’s also turned out to be a really good friend. I did a lot of it myself but I also had a lot of help from him. He actually sprayed the paint. It’s definitely not a show truck. That said, it’s definitely a different truck and definitely for the better. I appreciate his help very much. I paid him but I feel like I got far more than my money’s worth for his part. I also appreciate the help and advice from all of you guys on this forum. I’m happy with the truck. Like all of you guys and your trucks, it’s not done. It’s nice enough now that I want to do other things to it.  It probably will never be finished. Lol. But I don’t have a hotrod or anything else for a hobby really so this is my hobby that also helps me do my job. 

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Where would a guy start looking for a set of Jacobs brakes for an EM6?

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Jake Brake 675/675A are for the 2 valve Mack engine.

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Thank you sir I just came across that with a google search myself. That’s exactly what engine I have too. 

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I`m sure i`ll get pounced on for saying this but if i were you i would save the 12-1500.00 dollars for something more useful

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I’m here for the info and experience of folks that know. None of our Mack’s ever had jakes so I don’t know. They not work good?

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We have a 475 3406E and the jakes on it make a difference on grades. But if they aren’t effective on the old Mack engines I’d be interested to hear

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Posted (edited)

we have a tandem mack rollback and a 2000 vision .the vision has the 460 eng rollback has e6 350` both are properly tuned  neither is as effective  as a 3406b loaded heavier` and no where near  as effective as a 350 cummins. I should add. that the e6 350 has genuine jacobs  set set up  not positive what the 460 is

Edited by carlotpilot

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It would make sense. More ponies pulling would probably be more ponies braking I suppose 

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to be fair since cummins was the originator of the jacobs eng . brake  their design produces the most usable braking hp of any engine that I know of . supposedly  if you have 500 pulling hp then you have 500 braking . i am told that the 60 series detroits are almost the same . we have one of those to and it works

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I was interested in the Jacobs brand brake. Not the Mack  dynatard. My understanding is that dynatard requires a camshaft change and is also less effective. All things I’ve read as I have no first hand knowledge. But if a jake won’t help any I wouldn’t want to toss away the cash for it. 

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