gearing

[DeepRoots]

just double checking with those in the know.

45mph for me is at 2,000rpms
60 mph is roughly 2,5000rpms
top speed is like 72-73mph or so

235/85/16 tires, c6trans
seems like I would have 4.10gears, ya?
door jam, and tag on the diff says 3.55
previous owner must have changed it.

most of the driving here in southern Ga is highway, where folks are doing 75mph so I was thinking I may change the gears, I'm tired of running the truck at 2,800rpms.
I use this truck for work, rarely hauling a trailer (maybe 1/12 of the time mileage wise) and the load is rarely over 4-5k lbs.
Mostly running empty with my tools, and jobsite supplies. Truck weights 5,900lbs empty (I run it lean) and typically 7,500-8k lbs loaded for a job.

is there anything wrong with using 3.08 gears? It would kill my desire for an overdrive (which I can't afford anyway).
I figure whenever I rebuild the c6 I can use the lower first two gears and make it a 'wide ratio' c6
my old f150 had 2.73 gears and it ran fine, just a lil slow from the start. are these 3.08 gears going to really kill the trucks ability to run?

there are very few hills here, and as I said, I'm not hauling a house, nor am I entering into any races in the near future


thanks in advance,
Drew

 

[aaklingler]

it sounds like you have 4.10s, i wouldn't go any higher then 3.55s, there about bad enough to start out with a load.

 

[towcat]

sounds like 4.10's to me

 

[MIDNIGHT RIDER]

I may be wrong, but I think that 3.08's require a different carrier than 4.10's.

Your RPM sound like 3.55 to me.

Pull the cover and somewhere on the ring-gear will be a set of numbers like

41:10 or something like.

The numbers are the number of teeth on the ring and pinion.

Divide the ring by the pinion and that is ratio.

 

[The Warden]

That definitely sounds like 4.10's to me. When I still had the T-19 in my truck, I hit the governor at 75mph...72mph with a C-6 sounds right on the money to me. My old van (which had a C-6 and 3.54's) could bury the speedo needle (only did that once, but it was for a 4 hour straight run down the I-5, and the engine came back and begged for more )...

BTW, I believe a few people have run 3.08's behind an IDI...it works, and apparently will do pretty well on fuel, but I for one wouldn't do it unless I planned to rum empty 99% of the time. As mentioned, anything higher than 3.54 will make life unpleasant with a load, although there is always the downshift factor Also, in case you're interested, some people with C-6's have installed a planetary out of an E4OD in the course of a rebuild...giving them a lower 1st gear ratio, making for easier starts without changing the top speed. Just an idea, in case you ever rebuild the tranny and decide to put a taller rear end under your truck...

 

[argve]

Easy no mess way of checking the gearing...

Piece of tape on drive shaft (length wise) and piece of tape on tire (cross ways)... Jack up truck so both drive wheels are off the ground - place tranny in neutral - spin tire and count... It's fool proof... If the drive shaft makes a tad more than 4 revs compared to the one turn of the tire then you have 4.10 gears - if 3.5 turns then you have 3.55 - you get the picture...

Tire size will not effect this test because your looking at rotation not distance traveled.

Also just for mentioning it...

If you rotate the tire and the other wheel follows suit as in you rotated the tire like the truck was driving forward and the passengers tire rotates like it's driving forward then you have either a limited slip or locker rear end - if the other tire rotates backwards compared to your hand driven tire then you have an open diff or peg leg kicker as I affectionally call them.

 

[highest_vision]

Randy says 4.10 is too low for the rpms you are running, but 3.55 is too high. They also will only run the numbers with an AOD but I can't imagine slippage would be that different in 1:1. 3:73 matched up pretty nicely though... Maybe your convertor is worn? Whats the tranny temp?
James

 

[Guntherx]

You Have 4.10's no doubt about it. I had the same thing. I installed a US Gear dual Range aux transmission and ove it. It made the truck a new animal. I regualrly pull 20K+ so there is no way I could change the rear. Now when I am empty, I leave the unit in high range and it runs fine.

So you have to ask yourself "do I feel lucky". Actually you have to compare the price of new gears vs. 2 speed tranny. The gears are not cheap, and you better know how to set them up. I found my 2 speed on eBay.

 

[JPR]

My 83 F250 came with 3.08 gears, nice on the highway, but slow to get going when pulling a trailer.

Rather than changing the gearing, have you considered a Gear Vendor overdrive unit. Used ones for C6 transmissions show up regularly at the "other" board for $800 to $1500.

 

[DeepRoots]

warden, thats what I meant when I said using 'lower first two gears'. of course I have no idea when I'll have the time to rebuild my c6... I'd probably have to find an old junkyard one to rebuild so my truck isn't down for long.

yeah, argive, I know that way... I'll probably check tommorow as I have a leaking wheel cylinder I need to replace anyway. and I've got the open differential 10.25

highest vision: I don't know the trans temps, and am uncertain on the convertor, but thats a good idea.

guntherX and jpr, I'd love to find a us gear, but like I said, I doubt I could justify the price. $800 is be doable, but I dunno.... being a contractor I go from rich to poor, poor to rich 2-3times a month

another thought is if the door tag and tag onthe differential say 3.55 and they swapped in 4.10s I wonder if the speedometer is off.
might need to check that too.

I feel REALLY slow with 10 people trying to get past me

drew

 

[troutwest66]

I thought by sometime in '88 they switched from the C6 to the E4OD.?? Getting the overdrive would be the best way to solve the dilemma. I wish I had one and I have the ZF 5 spd. Best mileage comes at 60 MPH in 5th turning 2000 RPM. I got 19.6 MPG or so this summer on our vacation to Montana. With our stuff loaded in the truck it weighed around 6900-7000 pounds. I just set the cruise at 60 and let everyone else go around me. :draw

 

[aaklingler]

89 you could get either

 

[The Warden]

Getting the overdrive would be the best way to solve the dilemma. I wish I had one and I have the ZF 5 spd. Best mileage comes at 60 MPH in 5th turning 2000 RPM. I got 19.6 MPG or so this summer on our vacation to Montana.

That's interesting...my record mileage so far is 20.67, with 4.10's and after the ZF swap. That was on a straight freeway run anally sticking to 55mph and with a load of cannon fodder in the bed, though...I think I'm going to be averaging 17 or so, but I haven't run enough tanks through her yet to tell for sure (my truck doesn't see much road time with fuel the way it is ). After seeing your results, I'll have to try a freeway run at 60 as well as one at 70 (the speed limit on the I-5).

I agree with you, though...even with the ZF, I want an OD unit (decided on a U.S. Gear unit so I can use it in 4 wheel; now I just need the $$). I was thinking about switching to 3.54's, but I'd rather get the aux tranny and keep the low end power I have now...besides, the U.S. Gear unit in OD with 4.10's actually gives a taller ratio than 3.54's without the OD unit (the equivelant of having 3.28 rear end gears; 1900 RPM at 70mph)

 

[Guntherx]

take a look

guntherX and jpr, I'd love to find a us gear, but like I said, I doubt I could justify the price. $800 is be doable, but I dunno.... being a contractor I go from rich to poor, poor to rich 2-3times a month

I feel REALLY slow with 10 people trying to get past me

drew

I bought mine off of eBay for $400. Do a search for us gear and you will get a lot of other junk listed too, but I think that's why no one else saw it. :Sly

 

[DeepRoots]

yeah, been looking for 8months or so.
pretty popular lil units.