Defects in NV4500 Cast Iron Tailhousings

Documenting Defects in Imported NV4500 Cast Iron Tailshaft Housings

By Dan Guarino

It all started with a phone call from a customer who was stranded 400 miles from home with a blown 5th gear in an NV4500 transmission we had sent him about 6 months back. From his description of what happened, I knew it had to be either a countershaft clutch failure or fifth gear tooth breakage. The customer also mentioned the transmission had been unduly noisy since day one. Now some gear noise especially in 5th gear at low rpm's is not unusual with NV4500 transmissions, but the customer stated this transmission was definitely a bit on the loud side.

Well, when you are in the business of fixing things and selling parts, you know sooner or later something is going to come back at you. Still, out of all the hundreds of NV4500 transmissions we had worked on or sold since our first one 1996, our NV4500 comebacks totaled one brand new transmission in 1997 with a cracked case, and 5 rebuilt transmissions in 2001 that had to have the reverse shift fork pads replaced when a supplier had sneaked some counterfeit pads into an order of genuine New Venture parts.

About 4 days later the transmission showed up at our door. From the moment I got my hands on it and turned the shafts, I knew we had a case of 5th gear tooth breakage, but why? Actual gear breakage in NV4500 transmissions is rare and fifth gear tooth breakage is almost unheard of.

A few weeks prior to this incident, we had learned our supplier of these cast iron bellhousings knew of an interference problem with certain NV241 transfer cases but was not telling anyone about it.. We had one of those problems with a 1996 Dodge so I called them up and spoke to our about-to-retire salesman. He told me they knew of some problems but not many. OK that gave us a clue, so before pulling the tailshaft housing, we looked for evidence the transfer case bearing retainer was hitting the tailshaft housing, and sure enough, three marks were visible back of the cast iron housing. These dents were caused by the transfer case bearing retainer bottoming out against the tailshaft housing. We then pulled the tailshaft housing and looked at what was left of the fifth gears. Yep you guessed it, an uneven wear pattern was present confirming the failure was a case of mis-alginment. We checked the tooth angle on the gears, it was perfect. Next, we checked the gear bores and shafts for trueness, again right on the money. So, at that point, the cast iron tailshaft housing was suspect #1.



Areas where NV241 Transfer Case Bearing Retainers hit imported cast iron tailshaft housings before transfer case mating flange is tight against cast iron output housing. This problem seems to occur primarily on 1997 and older Dodge 2500 and 3500 trucks with the wide input bearing. This can caue the transfer case to be cocked or mis-aligned Excessive gear noise, bearing failures, transfer case breakage, transmission gear failure, and propeller shaft vibrations are all possible. This interference problem can be corrected by modifying either or both the tailshaft housing and transfer case bearing retainer.

Believing we had found the cause of the failure, we bored out the tailshaft housing to provide clearance. To be on the safe side, we also decided to check the bores on the cast iron housing. We couldn't believe the results so we checked 3 more cast iron housings and 3 original equipment housings. To verify the results we had a machine shop perform the same tests. What follows is from the documentation we sent the supplier:

To check the run-out:

1. Brand new NV4500 transmission case were securely mounted on a vertical mill with the rear output bearing bore up (two cases were used, results the same on either case). A indicator reading was taken off the rear face to check for parallelism to the mill table and front face. The rear case faces are square within .001 .
2. A co-axial indicator was attached to the spindle
3. The mill table was adjusted so the output bearing bore was perfectly concentric to the mill spindle. (x=.000, y=.000 )
4. Each tailshaft housing was bolted to the transmission case. Two NVG factory supplied dowel pins were used to align the tailshaft housing to the case.
5. On 4x4 housings, Indicator readings were taken off the seal bore, transfer case pilot bore, and rear face. The 4x2 housing was checked in bushing bore and seal bore.


Yellow Lines indicate x and y axis for run-out measurement

4x4 Housing #1: x .005, y .015
4x4 Housing #2: x .0095, y .023
4x4 Housing x-.007, y-.019
4x2 Housing x-.006, y-.017

All 3 OE Housings had maximum runout of between .0005 and .0015

The rear faces on all 4x4 tailshaft housings both OE and cast iron are parallel to within .001 to the case.

Then seal bore is concentric within .001 to the mounting pilot bore or bushing bores on all housings.


Since the cast iron housings tested were purchased over the span of nearly one year, and all four have been found to be machined significantly off center in relation to the centerline of the mainshaft, it is my conclusion that a very significant percentage of all cast iron housings are defective and need to be recalled for replacement or correction. The 4x4 housings are also not suited for use with many 1994-1997 transfer cases without modifying the tailshaft housing and/or transfer case input bearing retainer.

Furthermore, one of the 4x4 housings also showed evidence of the 5th gear synchronizer sleeve rubbing against it (this customer complained of a faint rubbing sound)

My gut feeling is 99.9% of all cast iron housings are defective and would greatly exceed the .002 run-out which would seem the maximum allowable for this application.

Dan Guarino

Well, as I write this article in March of 2006, we are working on contacting all our customers who may have purchased a cast iron tailshaft housing from us. We are also waiting for the supplier to "Do the Right Thing" and issue a recall. I think they will, but if they don't you can be sure I will put their name in this article!

This type of problem was reported with another cast iron housing sold by different outfit several years ago. Before we ever purchased these things and several times over the next few years, we asked our salesman if their housings ran true. The answer was always yes. I wish we would have checked a housing ourselves years ago, but we didn't. So if you have a cast iron tailshaft housing from us and we have not yet contacted you, CALL US!

UPDATE January, 2008

The company that imported and distributed the bellhousings described above was Blumenthal Mfg. of Tulsa, Oklahoma. When we first informed Blumenthal's about the problems we found with their cast-iron NV4500 tailshaft housings we expected a speedy resolution to the problem and we anticipated, from past experiences with Mr. Kevin Blumenthal, that Blumenthal Mfg. would do the "right thing" and stand behind their product. Blumenthal Mfg. has never denied the housings were defective in any of the correspondence exchanged between myself and Blumenthal's General Manger, Phil Warren, who described the housings to me with the words "They are all jacked up". Now, 22 months later and after more reminders, we are still waiting for Blumenthal Mfg. to "Do the Right Thing" ........

Update February, 2017

After years of searching and spending thousands of dollars testing imported housings, we FINALLY found a supplier that makes an accurate, quality checked 4x4 tailhousing for 1994-2005 Dodge Ram 4x4s. See QU10060.