you know how the speedometer always goes to and hits the little stop at 85 mph??? well, i fixed that roblem yesterday, i just took the dash panel off, then took the front clear instrument anel cover off and yanked the little stop pin out of the hole. i didn't like the way the hole looked that it left in the guage cluster, so i bent the little lastic stop pin over and it just snapped right off, then pluged the little hole back up with it so it isn't even noticeable. now the speedo doesn't stop any more and i'm happy with it!

 

Must have 3:55's. I am hard pressed to get mine to go fast enough to hit the little stopper with 4:10's I do know that 3000 rpm is 100mph, had a buddy follow me one day. but as the egt's were slowly climbing past 1200* I let off. and the wind was about to rip off my visor.


Diesel Rod

 

3,000 rpm's is 100 with 3.55's, i have a i.d.i. with 4.10's and it's running 75-80 at 3,000. that's in overdrive on a 5-speed standard. but i don't think the auto trannie's are too much different in the final gear ratios. i own 2 identicle trucks 1 with 3.55's and the other with 4.10's. i have gotten into a pretty heated argument over what gear ratio runs what rpm's at a given speed M.P.H and don't wish to start another argument.

 

I'm not gunna try and argue either, just saying that mine with an auto and 4:10's 75, which i go quite often is 2500, the ZF5 will have a slightly slower O/D ratio, which will result in a higher engine rpm. my buddy has a truck the exact same as mine, its like 2 months new, and he has 3:55's and 75 in his is only like 2150, I dont know what his does at 3000rpm, but its hauling *ss i know that. Check this out from a thread that is a couple of days old.

Quoted from SOCALRACER
Axle codes:

39 = 3.55 open diff
C9 = 3.55 limited slip
35 = 4.10 open
C5 = 4.10 ltd slip

Engine speed per vehicle speed depends on 3 things: axle ratio, trans ratio, and tire diameter. The ZF 5-speed has a 0.76 5th gear ratio. The E4OD's 4th gear ratio is 0.71, which partly accounts for the differences you guys are seeing with the same axle ratio. Tire diameter, even on 2 tires with the same size marked on the sidewall is not consistent with all tires. They are usually close enough though.

Rough math, using the formula:

RPM = (MPH x AxleRatio x TransRatio x 336) / TireDiameter.

For ZF trans in 5th gear and 4.10 axle ratio with 235/85-16's or 265/75-16's (roughly the same diameter):

(65 x 4.10 x 0.76 x 336) / 31.5 = ~2160 rpm.

For E4OD in 4th gear with same tires and axle ratio:

(65 x 4.10 x 0.71 x 336) / 31.5 = ~2018 rpm.

E4OD with 3.55's: ~1748 rpm.

ZF & 3.55's: ~1870 rpm.

mostly look at the difference between the ZF5 and the auto. I think that is where alot of arguments could stem from, same rear end, different tranny, different rpm's


Diesel Rod

 

i can't get anywhere close to those numbers with either of my trucks....

 

You will have to do the math to see if its right, he was just using numbers for examples.

I havent tried it but I have done many calculation that are like that to find out speed, from all the motor/tranny/ rearend swaps We do the speedo is the first to get disconnected. the latest swap as a "theoretical" speed of 195, but the car will never go that fast in O/D, the rest of the numbers where right so I dont doubt the formula he gave. you will have to do the math, see if anything matches your truck. its bed time so till tomorrow.


Diesel Rod