I have an '87 F-350 6.9 NA with 4.10 gears and a C6. At 55 I'm turning 2550 RPM. I am seriously considering changing to a ZF5 5 speed manual. I know that these come in two types, close ratio and wide ratio.
My questions are these. Will I need to change the flywheel ? Looking at a used or rebuilt transmission how can I tell between a close and wide ratio ?
I have not yet decided which way to go with the ratio. I am looking to improve my fuel mileage and extend engine life. I'm hoping to get 55 at about 1900 RPM with the new setup. At present it turns about 3000+ at 65 and eats fuel like a beast. I'd like to be able to get on the interstate without either getting run over or going broke.
I know I'll need a pedal, clutch and pressure plate, slave cylinder, throw out bearing, and fork. I don't yet know if the shaft would have to be doctored or not. It has a two piece shaft. The truck is a crew cab SRW.
I have a 3 row radiator and with this setup in cold weather the engine doesn't work hard enough to put out good heat as evidenced by the gauge and my freezing. In the low 40's or around freezing the guage stays below the NORMAL brackets on the guage. Warmer weather it runs warmer. It stays about the N in normal on the guage in the heat of a Texas summer. Creeps up a little then the fan clutch kicks in and back to N.
I am presently getting between 11.5 and 14.5 MPG The OD should improve this considerably at highway speeds. Any help would be appreciated. I do know that I need a trans from a diesel application, gas won't match.

Thanks in advance.

 

go for a t19 and 355 rear gears a clutch and a zf5 is 1000 bucks

 

I'm looking at the cost to be between $1000 and $1500. I plan on doing the change myself. The truck is worth the expense if it gets me the desired result. Great body and int. just needs a paint job to be a very fine specimen. It's an XLT and everything in it works. A/C, cruise, all lights and guages all work fine, I love the truck.

 

my truck geats around 20 mpg unload with 37 and i have a t19 with 3.55 gear

 

How many miles have you actually driven to get those figures? It seems like your truck would be more likely to get around 17 MPG or less with those tires the lift and a T19 transmission.

 

Joe I bet with your 37's, it knocks your 3.55's down to a 3.08 or so.

 

could be i went about 500 miles

 

Just a couple days ago, this was the mileage you claimed you were getting...


I'm sure your speedo is accurate too...

 

i depent how fast i go 20 at 65 70 i get 17 and lower

 

Well I hope somehow my truck can do that well. I have 4.10 gears with a ZF5 and 36x 12.50's . I figured mine would only get 16 or 17mpg at best . And if you have 3.55s and 37s I am suprised you can pull much of anything with that truck, it would be loaded all the time. Has someone put 3.55s in that truck? Seems that a ton truck would have lower gears.

 

In the 86 and earlier trucks, you could only get 4.10 or 3.55 gears with either a C 6 or T 19.

With 3.55's wide open high gear was 85 MPH, 4.10's put you at 75 MPH.

 

According to the old calculator, with 37" tires he is running an effective gear ratio of 3.07 :1. I went with a stock tire diameter of 32" for 235/85 16's. That must suck for towing.

 

Dang 91, you beat my to it, I just remebered where the calculators were on this forum.

 

it ok i just not in a rush

 

Yeah I am pretty bored tonight and not all that tired yet. This post sure has gotten off topic though.

As far as the gearing goes, there are times I wish my 04 6.0L had lower gears after I went to 315's. It has 3.73s and I wouldn't mind if it had 4.10s sometimes, but that would probably kill the mileage. I really wish reverse was geared lower when trying to back a loaded trailer up a grade, it really sucks when it is too fast even at idle.