I have an 88 crewcab 4X4 dually f350. The only thing I don't like is the 70 mph top spd. Is it easier to take out the C6 and install an E4OD or add a gear vendor or add higher rear end gears.

 

Are you red lineing or is the engine just not letting you go over 70? If engine not letting you go over 70 then there is a govenor speed controler been set up on the truck. We have them on our buses and large trucks. Not sure how they would hook one up on a pickup.

 

Gear vendors unless you wanted the E40d with an aftermarket controller like the Bauminator shift deally.............. http://www.baumannengineering.com/e4odcat.htm

 

If it has 4.10 gears 3200 RPM would be 71 MPH with a C 6 tranny.

 

easiest to just put bigger tires on it. effectively the same as installing taller gears.

 

Bigger tires do not change the gearing much unless you go to monster tires.
Also it will still only show 70 MPH on the speedo since it will not be right anymore.
Bigger tires on a dually is an expensive thing to do, because you have to add spacers between the wheels on the rear axle to keep the tires from rubbing between the duals.

235/85-16 tires are 31" tall and would run 71.9 MPH at 3200 RPM with a 4.10 gear
285/75-16 tires are 33" tall and would run 76.6 MPH at 3200 RPM with a 4.10 gear

Spacers would be required to run 285 tires on a dually.

The cost of a gear change on a 4x4, or the cost of a tranny change to an A4OD or 5 speed, the cost of running oversized tires and the cost of an overdrive unit like Gear Vendors or US Gear will all be about the same in the end.

If you like the automatic I think the best option would be the overdrive unit since it coupled with the C 6 will be a much stronger combination than the A4OD will ever be, plus you will have 6 forward gears instead of only 4.

The overdrive unit will make you capable of 92.2 MPH at 3200 RPM or drop your RPM to 2440 at 70 MPH with 4.10 gears and 235/85-16 tires.

I should add that all my tire sizes are for mud tires, because that is all I run on my truck. All terrain or straight tread tire sizes do run a little smaller for diameter so the speeds would be slightly less.

 

AndysFord,

I got an E4OD in my truck and don't like it much. A conversion from a C6 to and E4OD will neither be cheap, nor easy to do because of all the electronics.

The E4OD has a very high OD ratio .71:1 which make it a poor choice for towing. If you want the tranny to live you will be towing in 3rd anyways (1:1)

Early E4OD were not the greatest trannys to start with and had a number of design problems which were to some degree addressed in later years, however the E4OD will always be the weak link in the drive train.

If you got a C6 look into the US Gear Splitter or US Gear Vendor options.

As Dave said you will end up with more gears and a much stronger drive train, the cost will be more or less the same.

 

Mines 72mph at the floor cheyyaa here we come, buy the gear vendor od.

 

andy, i have the same problem with mine. i have 355 gears with a gear vendor behind a c6 tranny and at 65mph i turn 2500rpms. im fixing to put 285/16s on mine just to see if it will help cut down rpms. at 70mph sounds like its gonna come apart and horrible on fuel.

 

j tate,

If you have an overdrive unit behind your C 6 it is not working.

2500 RPM and a C 6 with 3.55 gears will run 64.9 MPH on 235/85-16 tires.

Same setup and RPM with a working gear vendors overdrive the speed will be 83.2 MPH.

Same setup but 1950 RPM will be 64.9 MPH with a Gear Vendors unit.

JMac444, you have a 4.10 rear in yours. The Gear vendors would give you 70 MPH at 2450 RPM, flat on the floor would be in the 92 MPH range.


Going from 235/85-16 tires to 285/75-16 tires makes about a 5 MPH difference at the same RPM.

 

J tate, if i had the c6 with 3.55 and no OD i would be in alot better shape than the 4.10 i got now