Engine/Transmission (1998.5 - 2002) 5 speed versus 6 speed

[SAvery]

Hey everyone, I am building a project vehicle and I want to use either the NV 4500 or NV 5600. I would prefer to use the NV 4500 because it is lighter and not as massive. The engine will be a 4BT (mini me cummins), so the NV 4500 will handle the power. My concern is that I hear that the NV 4500 synchros are very susceptible to failure. I was wondering if this is the case for the NV 5600 as well? Any input is greatly appreciated.

 

[Joseph Donnelly]

The synchros work well and last well unless you believe in shifting without the clutch. I'd call 800-std-tran for info.

 

[Texas Diesel]

Originally posted by SAvery

My concern is that I hear that the NV 4500 synchros are very susceptible to failure. I was wondering if this is the case for the NV 5600 as well?

It's the NV-5600 synchros that like to quit. I've had two 5600's replaced due to multiple grinds. The present 5600 is doing fine @45K miles. I've never heard of a synchro problem with the 4500's. Bluementhals or Standard Transmission &Gear make a set of solid brass (?) synchros for the 4500's. My 98 has 150k hard miles on the 4500 and shifts perfect.

 

[SAvery]

So Joseph, do you think that it is safe to get a used NV 4500, depending on miles, or is it likely that the thing is eaten up? That's kind of really my question. If I get a used NV 4500, is it likely to fail. If the NV 5600 has the same synchro problem, due to bad maintenance, then should I just buy a new NV 4500?

 

[SAvery]

Sounds like the NV 4500 with lower miles is the way to go. Just switch the the Royal purple as you said Tejas. Thanks.

 

[Ol'TrailDog]

My two cents.



I did not like the five speed gear ratios. Second and Reverse are two high. This means premature clutch wear. Backing up was particularly problematic especially trying to back a trailer.



Of course this will also be affected by your axles and tire size.



I definately prefer my six speeds. Even more so with the 3. 73 Gen3 axles.