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Vladislav

TM308 8-speed transmission - basic info needed

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I am offered to buy such unit locally. The price tag is reasonable but I have no idea on the ratios, body length etc.

It was removed from (as they said) 2004 DM dump truck with some kind of E7 engine.

IMG-20190205-WA0017.jpg

IMG-20190207-WA0000.jpg

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I'd check the bellhousing to make sure the mount flange still has some taper--hasn't been run loose. Also looks like it may need an input shaft by the looks of the throw-out bearing area. If the bellhousing is in bad shape then the only good thing its good for is parts.

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Good point on the bell housing, thank you.

Actually the potential use is in a hobby truck. So not many miles are planned. This doesn't bring much worries on the input shaft cond too. As long as I know the engine was taken off just a week back. The matter of the rust seems the truck was parked with another issue (rears) for nealy 5 years as I was told.

My main question at the moment is the ratios. Originally I had T2090 with 40% steps between the shifts and now T2070 installed with about 70% which is not what I like. So that unit with 6 speeds in the main box might be a compromize. Depending on the step lenthes and the top gear ratio.

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Thanks the great Jim, that's what I was looking for.

Interesting that the overall length of the transmission (798mm) is almost similar to T2090. The overgear ratio is also similar - 0.71. Definitely looks like T200 and T300 series have a lot of things in common. But too probably many parts of the content could be found different.

Ok, my engeneering addiction gets my thoughts in direction of taking apart and combining/modifying everything I find on my way. This time its possible to install the unit as is since no modifications required to. The last point - I should find the reason :)

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Macks version of a 8ll but only to be used behind a maxidyne motor due to large gear spacing compared to 9spd mack  or fuller trans

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Here is the MACK Tech Bulletin on the trans series  T2060A, TM309, TM308, T306G upgrades just in case it has a manufacture date earlier then 04.

http://hr.mckenzietank.com/maint/Bulletins/26-sb323006.pdf

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On 2/8/2019 at 10:34 PM, bts-4120 said:

Macks version of a 8ll but only to be used behind a maxidyne motor due to large gear spacing compared to 9spd mack  or fuller trans

That's what i keep in my mind. Originally my truck had T2090 and I would keep it but the sliding clutched got worn during the years of unexperienced driving. Locally I could find T2070 with 0.60 overdrive and put in the truck. Affordable but the gear spacing is up to 70% what is too much for Econodyne E6-350. Fast overdrive is good but one more gear between the direct and the over is required. My current idea is to try fixing the 9-speed using parts off the 7-speed but that newer 8-speed unit could make the deal too having the steps of nearly 60%.

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On 2/8/2019 at 11:54 PM, 41chevy said:

Here is the MACK Tech Bulletin on the trans series  T2060A, TM309, TM308, T306G upgrades just in case it has a manufacture date earlier then 04.

http://hr.mckenzietank.com/maint/Bulletins/26-sb323006.pdf

Paul, those are very interesting files, put alot of light on the matter. Thanks.

I see they note T2060A transmission in the list. Seems like it was done the same way (or even the same design?) as later T308 tranny. 6 speeds on the main stick require different top cover with one additional shift fork and a rail. All that seems done on T2060A. Wonder how the engeneers could put additional gear set into the main housing of the same size as a 5-speed unit had. And sure I wonder how the gear wheels are similar of the seating sizes to the shafts so I could take everything off two or three transmissions and play with until get dirty and upset. Let's see :)

tra0371_1-vi.jpg

tra0371_2-vi.jpg

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The best fuel mileage I have recorded on a Mack truck came out of a fleet of those Maxicruise w/T-2060 hauling lowboys of lumber over flat earth. When you take the synchro out of a Mack transmission you have a bulletproof unit. 

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On 2/11/2019 at 2:35 AM, Mack Technician said:

The best fuel mileage I have recorded on a Mack truck came out of a fleet of those Maxicruise w/T-2060 hauling lowboys of lumber over flat earth. When you take the synchro out of a Mack transmission you have a bulletproof unit. 

Ha-ha-ha! If you take that synchro out just send it my way :)

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