M818 5 speed Transmision question

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Olly

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I've read on a lot of different posts here that the gap between 3rd-4th and 4th-5th is pretty bad, also have not found a suitable replacement for the tranny without serious modification to the truck. I am putting a turbo and was wondering if that will take up some of the lag in the shift points? Obviously won't change the shift points in the tranny just was wondering if anyone who has put a turbo on the M800 trucks have noticed a difference when it comes to shifting? Don't really want to switch to an automatic but if the gap is still present with standard 5 speed and can't find a suitable manual replacement without changing over clutch pedal, bell housing etc then that might be my only way to go.... simply because I know the allison mt654 will work. Any input or ideas always welcome. Thanks.
 

Olly

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There is a thread somewhere about a 6 speed manual.

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Every post so far that I have read has given suggestions about 6 speed manuals but never has gone into depth about what parts you need other than having to change over bell housing, clutch pedal etc. etc. however, if you know of the link to it I might have missed it there are a lot of posts on here after all. Because if I have to change over all of the components to the transmission it might be more cost effective to go the automatic. Not really concerned about the PTO and I have already changed over the transfer case so the poppet valve isn't an issue either. Just want to throw my money the right way and get her running again before the snow flies.
 

Lonnie

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Pittsburgh, PA
I can say after adding a turbo, the gear drops are still pretty bad.
The RPM drops off significantly & the turbo loses boost since it drops out of it's preferred RPM range.

The turbo is a big improvement, but it does not make up for the lack of a nicely spaced transmission.
 

Iceman3005

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Jonesville, MI
FSO- 6406A or FSO-8408A. Those are the overdrive versions. The FS model is direct drive in the final gear. You don't want that. One is a 6 sp. Other is an 8. Both have the exact same dimensions as the 5 sp.

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Olly

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I can say after adding a turbo, the gear drops are still pretty bad.
The RPM drops off significantly & the turbo loses boost since it drops out of it's preferred RPM range.

The turbo is a big improvement, but it does not make up for the lack of a nicely spaced transmission.
Thank you for the response and information I wanted first hand knowledge and seeing as my truck isn't running yet I figured someone whose truck was running with a turbo would know.
 

Iceman3005

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I would like to switch the trans also, but one thing at a time. Need to get my 53's finished and mounted on the truck. Hopefully this Sunday it will be done.

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Olly

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I would like to switch the trans also, but one thing at a time. Need to get my 53's finished and mounted on the truck. Hopefully this Sunday it will be done.

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Throw pictures this way when you get them on unfortunately my tires are last on the agenda but going the same way plan to annoy my neighbors :)
 

fasttruck

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Mesa, AZ
The solution to the problem of the big gear jump between 3rd and 4th gear is to learn to split shift the truck with the transfer case. The sequence is 2l, 3l, 4l, 5l, 4h, 5h. The only gears used in high range are 4th and 5th. This will allow you to start in 2nd low even when heavy. You get to use the tight 4-5 shift twice. Whichever box is being upshifted is the one to shift first.
 

Hammer

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Winlock, WA
Using low gear then 4,5 in high is ok, and you are a few MPH faster in low 5th compared to high 3rd. But you have to shift twice from low to high, then from 5th back to 4th, so the time taken, especially when on a hill, means you are dropping speed too fast.
I still do this, but it isn't ideal either.
A 6 or 8 speed transmission would make a world of difference. (well, given the stock HP anyways.)
 

MyothersanM1

19K M1 Armor Crewman
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Culver City, CA
I had been studying the Fuller FSO-6406A and FSO-8406A six-speed OD manual transmissions. I was seriously considering pulling the trigger and installing one. I found a clutch housing that would work with the push type clutch. There would also be modifications necessary to the cab tunnel as the shift lever sits farther back which would not be a difficult job.

Where I ran into issues and confusion was, 1) the proper front bearing cover with the input shaft sleeve that the release bearing yoke slides across, 2) proper input shaft length and the difference between a pull-type and push type (they all seem to look the same), and 3) these gearboxes are NOT compatible with the M809-series OEM PTO's.
 

simp5782

I'm the dude, man!
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Memphis, TN
I have all the steps and parts to put the CAT 7155 in an 809 series truck. Biggest pain is raising the entire front body and cab. Or you have to do a bigger center tunnel and move the transfer case back 8 inches

Cheap way is tunnel enlargement. transfer case back far enough so that you can use the 818/931 transfer to front tandem shafts from the transmission to transfer and from transfer to front tandem. then lengthen the front shaft. Cat has an od of .83 in 16th. It gives the NHC250 gobs of userful power output

With the cat you do not need low range on the transfer case so you do not have to worry about those linkage refabs. PTO for the cat is cheap
 
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