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Author Topic: Trans swap on 74 kw 900a  (Read 343 times)

Ken Jr

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Trans swap on 74 kw 900a
« on: August 31, 2018, 09:57:56 PM »
Does anyone know if I can swap a RT910 trans out of a 79 western star with a 6-71
In to my 74- KW 900A with a 8v92? My truck has a 6&4 & I would like to have a 10&4
Ken 🤓

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Trans swap on 74 kw 900a
« on: August 31, 2018, 09:57:56 PM »

Wee Willy

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Re: Trans swap on 74 kw 900a
« Reply #1 on: September 01, 2018, 04:47:43 AM »
I don't know if you have much to gain by going to a 10 spd, but an RT 910 probably won't stand up to an 8V92.
 I destroyed an RTO 9513 with a 350 Cummins and replaced it with a RTO 12515, and all of the 8V92's I drove had a lot more snot than my NTC 350 which was putting 350 hp to the ground.
 
If your 8V92 is an old naturally aspirated engine you might get away with it if you baby it, but if it's got a turbo forget about the RT 910.

Just my thoughts.
Good luck.
The first rule of the road is:
"If anything can happen, at any time, it will!"

Ken Jr

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Re: Trans swap on 74 kw 900a
« Reply #2 on: September 01, 2018, 02:54:07 PM »
Thanks Willy, my silver 92 has a turbo & tag says 440 hp, nothing wrong with my 6 speed I just don't like leaning out of my seat to find 5th & 6th.  🤓 I learned on a 5&4 in my dads 50 Pete so 2-sticks
Are not a problem for me but just don't care for the 6 speed ! What about a RTO-12509 a friend just offered  one to me if I want to pull it out in the field
« Last Edit: September 01, 2018, 03:04:56 PM by Ken Jr »
Ken 🤓

Wee Willy

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Re: Trans swap on 74 kw 900a
« Reply #3 on: September 02, 2018, 05:20:31 AM »
Just so you know, an RTO 12509 has a different OD than your 6 spd does, .73 as opposed to .81 or .84, can't remember which.
 This will make your truck faster than it is now.

If you want to keep you top gear close to what it is now, you need to go with an RTX transmission which has a .83 or .80 OD gear.

Here's a list of Roadranger transmissions.
http://www.eaton.com/EN/rr/ProductsServices/ProductsbyCategory/Transmissions/PCT_486870

(for 9 spds)
RT is a direct drive, 1:1 final drive.
RTO means it's an overdrive, has a .73 top gear.
RTX is also an OD, but top gear is .83 or .80, not as fast as an RTO.

The first 3 numbers indicate the torque ratings, the last 2 are the number of gears.

I don't remember the torque of the Silver 92's, but I'm guessing the 1200 to 1400 ft/lb range depending on horsepower ratings.
You need to find the torque rating of your engine before you put a trans in your truck because the wrong choice can cost ya!

 For safety sake, if you're pulling weight, hills, mountains, high winds, you might want look for a 13609 transmission.
 If you choose a 10 spd you have to live with the .73/.74 ratio, which is OK if you think you can benefit from it.

 I drove lots of 92's and pulled big weight with them, (trains at 135,000 lbs), with 435 and 440 hp ratings,had RT12515's in them and no problems.
 If they were OD boxes they might not have done so well.

I'm hoping Troy pops in, he's our resident 2 stick authority and drive's a 6X4, he can  tell you better than I can.
 
« Last Edit: September 02, 2018, 05:24:32 AM by Wee Willy »
The first rule of the road is:
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Ken Jr

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Re: Trans swap on 74 kw 900a
« Reply #4 on: September 02, 2018, 08:49:45 PM »
Thank you Willy, the truck & I are both retired 👴🏻 Heaviest load would be 10 yards of gravel
Or a small dozer on a equipment trailer. My 6-speed is a Spicer 1263-A. I don't believe it has a over drive
Ken 🤓

Wee Willy

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Re: Trans swap on 74 kw 900a
« Reply #5 on: September 05, 2018, 07:49:52 AM »
That RTO12509 should be strong enough for what you intend and can be made into a direct drive.
 Try it as an OD, if it's too fast, or your low gears suffer, change it to DD.

Happy Trails.
The first rule of the road is:
"If anything can happen, at any time, it will!"

Ken Jr

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Re: Trans swap on 74 kw 900a
« Reply #6 on: September 05, 2018, 11:02:41 AM »
Now the big question, the RTO12509 is hooked to a NTC-350 will it bolt up to my silver 92 ?
Ken 🤓

Wee Willy

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Re: Trans swap on 74 kw 900a
« Reply #7 on: September 06, 2018, 06:07:15 AM »
 I suspect it should bolt up, but rather than put your trust in the internet forums at this point, I recommend you seek out a reputable local shop and ask them if there is anything you should know before you start.
 Maybe have them go through it for you and report on their findings, just to be safe.

 There may be nothing to worry about, but sometimes there are little nuances and invisible problems that may occur that guys like you and me won't know about, something as minor as a bolt, plug, pin, washer, shim, etc etc.
 Best to check with the experts before you jump in.
(where's willyboy)

 I'm thinking you're aware that you might have to relocate the A box and mounts, you probably need to have the driveshaft(s) cut and balanced, the linkage altered, driveshaft angle adjusted, maybe different yolks between the trannies, it's not just a drop-in.

 Another thing I'm not sure of is, the diameter of the input shaft on the trans, you may have to change the clutch as well.
« Last Edit: September 06, 2018, 06:13:06 AM by Wee Willy »
The first rule of the road is:
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Ken Jr

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Re: Trans swap on 74 kw 900a
« Reply #8 on: September 06, 2018, 06:46:53 PM »
All good advice, thanks 👴🏻
Ken 🤓

coloradogreen

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Re: Trans swap on 74 kw 900a
« Reply #9 on: September 07, 2018, 01:20:24 PM »
An RT would be a better choice, or a short OD RTO. With an 0.73 OD in the 10spd feeding an 0.81 OD in the aux the compound overdrive will be below 0.6. Bearing speed becomes an issue, loaded or not.

A 1263A is an OD 6spd (0.84) so swapping to an RT would lower top end speed. Direct drive transmissions are also, generally, fairly stout. With a short OD 9 or 10spd, you would have an 0.81 OD in both boxes, a compound OD in the low 0.6x range. Usable, but only when empty, bobtail, or loaded pretty light.
« Last Edit: September 07, 2018, 01:25:27 PM by coloradogreen »
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willyboy

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Re: Trans swap on 74 kw 900a
« Reply #10 on: September 07, 2018, 04:54:22 PM »
The FR or FRO series ( fr 15210b ) is a nice compact strong Transmission, Fleets loved them so there maybe many available at a good price. Second and third users of trucks with fro/fr 's in often swap them out for a 13. The gear spread is better than the rto style, worth checking it out, good luck with the project.

Hank's Truck Forum

Re: Trans swap on 74 kw 900a
« Reply #10 on: September 07, 2018, 04:54:22 PM »