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Welcome to the 3500HD.com forum created October 2009

Author Topic: 94 3500HD 4x4 Cummins 6bt conversion  (Read 27337 times)

someotherguy

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Re: 94 3500HD 4x4 Cummins 6bt conversion
« Reply #15 on: March 27, 2011, 01:07:50 PM »
Hey Ed, the pan in the gasoline tank keeps the pump from starving during fuel slosh.  The in-tank gasoline pump is way sensitive to that, not sure why the diesel wouldn't require it but I guess they figured it wasn't necessary.

Richard
06 Silverado ISS / 06 Silverado SS / 06 300C SRT8

ED-NY

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Re: 94 3500HD 4x4 Cummins 6bt conversion
« Reply #16 on: March 27, 2011, 01:46:51 PM »
Hey Ed, the pan in the gasoline tank keeps the pump from starving during fuel slosh.  The in-tank gasoline pump is way sensitive to that, not sure why the diesel wouldn't require it but I guess they figured it wasn't necessary.


10-4..I suspect that because the gasoline pump draws faster and harder they are more likely to burn-up quickly with a dry air pocket. If I not mistaken the diesel fuel pumps runs under 10 lbs of fuel pressure & the diesel fuel itself is more of a lubricant than gasoline :'(

WHOOPS....the diesel has an external pump anyway!
« Last Edit: March 27, 2011, 01:48:43 PM by ED-NY »

someotherguy

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Re: 94 3500HD 4x4 Cummins 6bt conversion
« Reply #17 on: March 27, 2011, 09:29:12 PM »
Yep, lift pump on the frame rail :D doesn't need to stay submerged to survive like the gasoline pump does.  While momentarily losing fuel pressure will cause an EFI engine to cut out like you'd turned the key off, I think the pan/tray is more for keeping the pump surrounded by fuel as much as possible to help keep it cool.

The older pumps (TBI era) are spec'ed at 9~13 psi and tend to deadhead at maybe a max of 14~15; the last 2 years of TBI big block - 1994-1995 - are higher pressure at 26~32 psi.  It's the 1996-up Vortec stuff at 58~62 psi that I'd consider more critical to protect the pump.  Bottom line though it's just more to the point of the good advice to not run the tank low.

Richard
06 Silverado ISS / 06 Silverado SS / 06 300C SRT8

AZTimT

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Re: 94 3500HD 4x4 Cummins 6bt conversion
« Reply #18 on: October 13, 2011, 03:50:20 AM »
I didn't realize how much I missed this site since I have been away a while. I posted some of this reply in another thread about rear ends, but I added some for the update here. It has been on the road since May of last year and worked out pretty well with only a few breakdowns.

I swapped the original 5.12 D80 rear on my 94 4x4 with a 4.63 axle from my 95 2 wheeler that I regeared as an experiment to find the perfect gear for the rear with a stock, if not slightly detuned for economy and limiting egt's ;), 91 cummins after burning up the first 93 cummins that was turned up way too high by the previous owner. :o :'(  The upside was that I learned how to tune the VE pumps on my own to get the results I needed.



The solution was the 3.73 thin gear set for the low ratio carrier that already came in it, except I also had a lightly used 37 spline low ratio detroit so I used that in place of the open carrier. I run the stock 225/70/19.5's on it.

First there was the temporary flex pipe exhaust to get the cab quiet after losing a muffler that was apparently not clamped well enough. The flexpipe moved and wound up lining itself up with the drivers side of the rear pumpkin which was too much heat for that side gear of the detroit locker so it sheared all of it's teeth in the middle of a left turn. This forced me to get a front driveshaft made for the 5.12 geared front so I could limp home to where all of my spare parts were.

On the way home, then there was the frame mounted fuel filter which was overlooked during the conversion. It plugged up 600 miles from home and led myself and the more than willing mechanic shop to believe the injection pump had crapped out on me. After a tow, 3 days downtime, and a new IP the problem persisted when pulling out of the garage I had just paid way too much money!  >:( The fix was drilling the baffle out of the center of the fuel filter since I had no way to replace it with anything else at the time.

The only other real problem I had was the snap ring on the hydraulic clutch kept popping off at random times over the last year. Out of sheer stubborn refusal to throw more senseless money at this truck I was able to put it back together each time. Then after about the 5th time, it dawned on me to use some fine baling wire to twist tie the ends of the snap ring together so it could no longer pop off and the problem was solved.

Needless to say, there were a lot of expensive lessons learned in this project that should help me save a lot more down the road.

For reference, while I was researching the axle upgrade options I was informed by several different guys that work on lots of axles from class 4 to class 8 trucks and they said that the most common thing that will kill the Dana 80 HD (37 spline with huges tubes like we have) is heat, so I put a temp gauge and a mag hy-tec cover on it to help. I believe they are right as even with the upgrades, I have seen 250 degrees several times when pulling heavy loads. It is one tough axle though!

With the 3.73 rear and granny gear in the NV4500HD to start out with, I have pulled just over 30,000 gross several on several 1250 mile trips and averaged 8 MPG but I got rid of the 40 ft gooseneck after I finished moving with it so it would be harder to get that heavy in the future.

I get 15-16 empty with the truck is 8500 lbs and cruise as follows:
75 MPH @ 2250 rpm,
65 MPH @ 1950 rpm,
55 MPH @ 1650 then I grab a gear between 55 down to 50 if the need arises to keep her climbing the plentiful 6-7% grades in the Rockies.

I get 12-13 MPG pulling a 4,000-8,000 lb load all day long, and I am a stickler for tracking mileage. I have verified all of my numbers via multiple gps units and I correct for the 37% difference on the speedometer/odometer. It makes me realize how slow I would really be driving with the old gears which are only an axle swap away.

This setup got me 11 MPG with a 5680 lb trailer loaded with 6 x 1050 lb large round bales and a stock 78 f250 4x4 on a 200 mile haul at 65 mph. I did not scale that load so the fuzzy math puts me a little over 24k gross.


As long as the trailer brakes are working before I leave I have no hesitations running this rig up to 26k gross that I have the truck permanently registered for, but it starts feeling a little bit overworked beyond that despite being more than willing.

This load scaled at over 27,000 and got close to 9 MPG on the first 1250 mile haul last year after the cummins went in. I did not load the trailer as it was a favor for a relative that needed help moving so it was way overloaded and permanently tweaked the bumper (see angle of hitch on above pic) where the receiver is mounted on L shaped angle 1/2" plate, but it settled there and never broke.


I still haven't regeared the front as I haven't really had the need for it to justify the cost yet and I still have the original matching rear, but with the detroit I find the low range transfer case with the hubs unlocked very useful for pulling a 24' flatbed up steep forest service grades to go get firewood 3-5 cords at a time.

With the heaviest loads I was wondering if I shouldn't have gone with 4.10's, but with those being way less frequent than empty or under 15k gross I am very glad I went with the 3.73. Anything lower would be less than ideal for me on the highway 75% of the time I drive it.

I hope some of this may have been helpful and good luck to anyone else who attempts this!
94 K3500HD (factory Monroe 4wd upfit) short wheel base 9' bed 454 no more/NV4500HD/NP261HD/D70 frt/D80 rear 5.13's Cummins powered with 3.73's.
93 C3500HD long wheel base parts truck 14' bed 6.5(gone)/NV4500HD/D80 4.63
95 C3500HD medium wheel base 11' bed 6.5/4L80E/D80 4.63
2000 C3500HD Monroe extended cab 9' bed, 6.5/4l80E/D80HD 4.63 will become 4wd with D70 front and repowered some day...

KODIAK

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Re: 94 3500HD 4x4 Cummins 6bt conversion
« Reply #19 on: October 18, 2011, 12:45:16 AM »
Have you seen any HD with a Duramax diesel conversion ? ?

AZTimT

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Re: 94 3500HD 4x4 Cummins 6bt conversion
« Reply #20 on: October 19, 2011, 01:33:49 AM »
No I have not, but I prefer having the simplicity of no computers in my rig so I haven't looked for any. However if a guy likes his whole powertrain computerized then it would be a nice setup with a Duramax/Allison combo... kinda like the newer 4500's you can buy factory built that way.   ;)
94 K3500HD (factory Monroe 4wd upfit) short wheel base 9' bed 454 no more/NV4500HD/NP261HD/D70 frt/D80 rear 5.13's Cummins powered with 3.73's.
93 C3500HD long wheel base parts truck 14' bed 6.5(gone)/NV4500HD/D80 4.63
95 C3500HD medium wheel base 11' bed 6.5/4L80E/D80 4.63
2000 C3500HD Monroe extended cab 9' bed, 6.5/4l80E/D80HD 4.63 will become 4wd with D70 front and repowered some day...

1995-3500HD4X4

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Re: 94 3500HD 4x4 Cummins 6bt conversion
« Reply #21 on: August 02, 2012, 05:00:18 PM »
I am getting ready to atempt putting in a Cummins out of a 93 Dodge in to my 94 4x4 35000HD. Do u have any important advice for me before I get started?

 


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