Hello,

A good friend of mine has a 98 24 valve two wheel drive with an NV 4500. We lost fifth gear the other day while pulling. we got the truck in the shop and popped the tail shaft housing off to expose the fifth gear culprit. both the main shaft and counter shaft gears are ok with no damage. we drained the fluid and found no metal shavings or anything. nothing is broken. However the nut backed off and so did the small gear. we have looked at fixes and we could just put it back on but we thought it might come back off again. However we do not want to change out the mainshaft for the upgraded nut. I was wondering if anyone knew how to fix this permentatly without changing out the whole main shaft. Any info would be greatly appreciated.

Thank Ty

 

If you want a guarrantee of no more 5th gear loss put in the fully splined shaft as the torque produced seems to move anything put there. We have welded the nuts on and then the big thrust washer breaks and goes down into the gears. Eat Beefs is getting done here in the next 2 weeks and the fully splined shaft is on order- spend more, fix once feel good about it. PK

 

P Kennedy, I see you said that you have welded the nut on? I think would this would work, aside for the possible metal fatigue. But why did the thrust break when you did this? What does the fully splined shaft have that wouldnt let this happen?

 

The particular truck that was in had been tuned up (97 12valve) and has 4.10 gears and pulls a tandem dual gooseneck (32000lbs gross) and the young guy that bought it drives it hard. The only thing we could see is that he would power shift it going into 5th which would slack the driveline coming outof 4th and then just dump the clutch in 5th,with all the torque hitting the gear the thrust washer on 5th was taking all the impact. Normally the nut had been coming loose and the extra space would give the gear enough movement to hit the washer hard and it came out in 2 pieces. After we welded the nut on the gear had enough force to break the nut and the washer and it all ended up in the back case. The fully splined shaft would have prevented the gear and its retaining parts from leaving the shaft and falling down into the other gears while they were still turning. I don't think anything would have prevented this guy from breaking the tranny but because 5th gear is outside the actual tranny case only the splined shaft will stop the gear from dropping down. The 6 speed has all the components inside the case with bigger bearings and shafts. It is just an example that if somebody really wants to break something it can be done. PK

 

Wow. Someone who drives that hard is going to break anything. What is the dependablity of the fully splined shaft conversion? How many converted trannys have you seen fail?

 

OK we did Eat Beef's clutch on Thurs/Fri and after 200,000 KM the original nut and gear were real tight and we left it alone, this an example of how driving habits and technique make a difference in longevity. Can't say I have heard too much realated directly to the converted tranny's failing unless of course abuse was directly at fault. The Con OFE definately hooks up better and closer to the floor. PK

 

PK that is a 98 he is talking about. Dodge made an upgrade on the nut to help that situation. I had the info on that but since I went to the 5600 I don't know where it is now. Mine lasted 183,000 pulling heavy and is still good, sitting on the floor.

 

We are very familiar with the nut upgrade but the shaft upgrade is a better dollar value as the nut upgrade has several versions-know what I mean. PK

 

[quote author=P Kennedy link=board=4;threadid=20340;start=0#msg193402 date=1065455700]
We are very familiar with the nut upgrade but the shaft upgrade is a better dollar value as the nut upgrade has several versions-know what I mean. PK
[/quote]

I fully agree PK but he said that he did not want to change the shaft, I was only bringing the info that there was a nut improvement.

 

I have a question ??? I have heard that you are not supposed to haul in fifth gear because of the way that they are set up and I was wondering if it is true. Or is it alright to hual loaded (20,000 lbs) in fifth gear?

 

HEllo,

I just wanted to let you guys know that we went ahead and pulled the tranny and had a shop put the shaft and nutt on for us. Parts were about 300.00 dollars. We thought about welding it on... but decided that would suck if it broke out in the middle of nowwhere with load of horses or cattle. We put it back in last weekend and its all good now, anyways though thanks for all the input. as for me I do not have this problem cuase mine is a 5600. ;D

Thanks Ty

 

Eat Beefs NV4500 had the original punch marked nut at 200,000km=120,000miles and grosses in excess of 20k at times however his driving technique is not overtaxing on the drive train. Rammy gear shifts and excessive low rpm 5th gear lugging are the accredited reasons for the failures, the fact remains the 5th gear is outside the cast iron case and the nut is the only thing holding 5th gear when under heavy load. The nut need only come loose enough to allow the gear to move rearward clearing the short spline and then spins without putting any power the output shaft. The bevel gear design, right hand thread nut, partial spline all work to promote this problem, with the full splined shaft it does not allow the gear to dissengage from the output shaft even if the nut comes loose. Both gear ratios (3.54&4.10) are prone to the problem due to allowing the engine to be pulled down when pulling on the highway attributed to the high torque capacity of the engine and large gap between 4th and 5th gears. Preferably on a hard pull at higher speeds the tranny should be run in 4th which is direct drive where all the load on the shafts is put on the main case, gears and bearings within the confines of the cast iron case. New Venture would have done themselves a favor by using left hand thread on the shaft as under torque this would produce tightening forces on the gear nut instead of what is now happening. PK

 

Incidentally Eat beefs new SBC clutch hooks up like a real truck clutch should even with some fairly healthy power increases, downside would be any lost power due to clutch slippage now goes through the tranny to the driveshaft. These trucks are typically engineered "adequate" to work within the component torque/horsepower/load specifications, abuse and overuse combined with extra power tests the limits of the machine easily despite lower failure rates than the competition. Remember failure appears at the weekest link progressively as one repairs/upgrades each one. PK