Cummins 4BT & Diesel Conversions Forums banner

1 - 20 of 64 Posts

·
Registered
Joined
·
219 Posts
Discussion Starter · #1 · (Edited)
I was wondering if anyone has put a 6bt in an M715 and what transmission they used?

I want to retain the stock axle gear ratio, but will change the trans and t-case. The T-case would be a NP205 and the trans I'm not sure, I was thinking about going with a road ranger but not sure what trans is the best with the 5.38 gear ratio. I would like to be able to drive on the highway going about 70-75mph.

Any suggestions on a transmission? :confused:
 

·
Registered
Joined
·
1,203 Posts
you want to keep 5.88's in the axles?

what size tires?

if you ran 56" tall tires you would be right around 2000 rpms at 75 miles an hour with a .75 OD

you will need like a .5 OD to run 38's on the highway with those axle gears.

I'd suggest something a little more managable if you want highway speeds.
 

·
Registered
Joined
·
219 Posts
Discussion Starter · #3 ·
I will run the stock tires. Not 100% on the size tho.

They came stock with the 5.38s and you have to buy a new carrier to install ratios like 4.10s.
 

·
Registered
Joined
·
397 Posts
I will run the stock tires. Not 100% on the size tho.

They came stock with the 5.38s and you have to buy a new carrier to install ratios like 4.10s.
M715 axles came stock with 5.89 r/p ratio. Stock tires are 9.00-16 which measure out to about 36" tall. 11.00-16 Michelins are a popular upsize as they are intended for the stock wheel size and measure about 38" tall.

4.56 r/p sets are available for the stock carriers in the M715 axles(D70 rear, D60 front).

Not to send you away from here but the 'Modified Tech' forum at m715zone has multiple threads specifically on 6bt in M715.

Ken
 

·
Registered
Joined
·
397 Posts
I don't know. I know one doesn't have to swap carriers to install the 4.56 gears that are commonly installed when regearing these particular axles. But I don't know if these gear sets are specifically made for the carriers in the M715. Ie, I don't know if 'off-the-shelf' D70/D60 r/p sets are being used or if the 4.56 sets used in the 715 axles are different from the common D70/D60 parts.

I ended up with a set of these axles(part of a transaction where I was buying something else) but haven't used them under anything. The M715 60 front isn't known for being robust. The housing/spindles will handle typical D60 loads but much power or tire swapped on and it's past the shafts' capability. A later model open knuckle D60 is superior.

Ken
 

·
Registered
Joined
·
219 Posts
Discussion Starter · #7 ·
I don't plan on putting tires bigger than stock.

But what transmission would be a good choice with the set up of a 6bt with 4.88 gears?
 

·
Registered
Joined
·
397 Posts
I don't plan on putting tires bigger than stock.

But what transmission would be a good choice with the set up of a 6bt with 4.88 gears?
Well it is a divorced transfercase so you can choose just about any 2WD trans out there within length considerations. What's the intended use of the vehicle? With 9.00-16 bias plys and without brake upgrades 80 mph highway cruising probably isn't the best idea so I'd assume you're shooting at more of a local area use truck that might see 65 mph top speeds.

I'd look for a 6BT setup with an OD trans out of a Dodge pickup. I'm not versed on what came in the Dodges so I can't point you to specific transmissions there. To keep it manual and 'old school', go the SAE housing route and use the Spicer 3053a, a 5 speed OD that was used in many deuces.

Keep in mind the NP200 is an offset rear output so it's always transmitting the power through gears internally, even in 2H. It makes for a noisy transfercase and thus running a big OD before it to get the speed up also increases the noise and heat. These transfercases can get too hot to touch with stock setups.

There are multiple reasons why many folks swap different axles front and rear into M715s. Stronger front, better brakes, centered rear for use with a different transfercase(like NP205 for example), gearing choices, wheel lug pattern, etc. However, with your plan of using the 9.00-16 tire size and my assumption of occasional 65 mph use vs 80 mph, you should be OK with the re-geared but otherwise stock setup.

36" tire, 4.88 r/p, .82 OD, 65 mph = ~2400 crank rpm
same setup but 80 mph = ~3000 rpm

The transfercase will 'see' higher rpm(~3000 rpm and ~3600 rpm respectively) and it will be very loud.

stock: 36" tire, 5.89 r/p, 65 mph = ~3600 rpm
80 mph = ~4400 rpm

Ken
 

·
Registered
Joined
·
219 Posts
Discussion Starter · #9 · (Edited)
I was thinking about using an NP205 divorced t-case. I would proberly use the truck mostly for around town type driving, may be a little highway but 65 would be fine since that is the posted speed on most highways. I like the idea of using the Spicer 3035a, does anyone have any pics of this swap?
 

·
Premium Member
1989 Jeep Wagoneer, 360v8, 727, stock for now,
Joined
·
2,680 Posts
With a NV4500, your turning about 2225 at 65mph with the 9.00-16's and 4.88's. Well into the power range for more fuel consumption and extra noise. The cruise would be 50 mph at 1700 rpm, not very fast. 4.10 gears would be ideal (IMHO) for the 9.00-16, about 1870 at 65 and you would just be touching 2K at 70.
 

·
Banned
Joined
·
427 Posts
stock r&p ratio is 5.87, stock tire height on 9.00 x 16 is 34", a 6 bt will barely fit and you,ll have to do some cutting to get a big enough rad. to cool it, best bet for tranny is nv4500 with married np205, you,ll definatly need 4.56 r&p gears. they dont make any longer 4.10 and down carriers for the m715,dana 70...... a 4 bt is your best bet for that truck IMO i,ve done several of these swaps and i own 10 m715,s now. if i can help and your serious let me know. cost is 5000.00 to 10,000.00 depending on how much you can do yourself. also if you install a 6 bt you,ll have to get all new yokes ( 1410 ) u-joints, drive shafts etc. to handle the torque of the 6 bt. stock size is 1310. very small.
bob
 

·
Registered
Joined
·
89 Posts
You mean like this one!!

Its a nasty 6bt with a Clark 5 speed overdrive. Its got a/c, powerwindows and locks (doors came of a 70's cherokee) np205, and If im not mistaken its got 4:56 gears. He did a disc brake conversion on the Dana 70 closed knuckle in the front and he runs a Dana 80 in the rear. Super Sweet, I so wish it was mine. I bet LincTex has seen this rig, it was always parked at the RV park where I-35 and 77 split near Elm Mott.
 

Attachments

·
Registered
Joined
·
854 Posts
I bet LincTex has seen this rig, it was always parked at the RV park where I-35 and 77 split near Elm Mott.
I used to pass him every day for several years on my way to work :)

I live 1-1/2 miles from where that picture was taken
 

·
Registered
Joined
·
89 Posts
I know that most will argue BIGGER is better, BUT those trannies are no fun shifting. Ive seen just about every combo that can be put behind a 6b and at the end of the day, an NV or Getrag even can do just the same with less hassle. Doing one off odd configurations just calls for parts headaches and non stop riggin..... Id rather jump behind a synchro 5 speed and slam gears. Just my .02
 

·
Registered
Joined
·
1,366 Posts
I have a 6BT in my M715, but it is somewhat modified :hillbilly: so I'm not sure how much it will help you. Currently in construction - It has a Dodge NV4500 and a Ford NP205. Ford NP205 front axle and modified stock D70's in the rear.
I'm using 1100x16 XL's as well. I'm undecided on the gearing, will probably do 4.56's or 4.10's.
 

·
Banned
Joined
·
427 Posts
cant do 4.10,s in the stock dana 70 rear end unless you can find a used 4.10 & down carrier. good luck.in 16+ yrs. i,ve never seen even 1......
bob
 

·
Registered
Joined
·
179 Posts
Lots of dana 70 carriers around

When i was looking all i could find was the darn 3.54 or 3.73 carriers. You have to watch yourself to . There is a few versions out there. Dana 70 , dana 70 B , dana 70 u and a dana 70 HD and another one if memory is correct.
I have a 4bt , 4.88 gears ,nv4500, 205 and an additional transfercase. Running xzls . Fast enough for me on the highway and slow enough on the nasty stuff.
 

·
Banned
Joined
·
427 Posts
the m715 has the first generation dana 70 in it. its called the .500 or 1/2" offset carrier type and no other dana 70 uses it. thats why its so hard to come by.
 

·
Registered
Joined
·
220 Posts
the m715 has the first generation dana 70 in it. its called the .500 or 1/2" offset carrier type and no other dana 70 uses it. thats why its so hard to come by.
Can you get a spacer for the ring gear so you can use gearsets for the another D70 carrier?
Bob B.
 
1 - 20 of 64 Posts
Top