just lookin for confirmation

[K5dreamer]

Fuel mileage question, my TH400 is starting to act up, i believe from the way its acting, its a bad pump, which would need a rebuild to address. Ive got the TDI jetta to drive daily so ive kinda back burnered the truck and its issues for now. But i just checked my fuel mileage on a long highway trek, and was a bit confused. My best highway mileage (too and from school for instance) was around 22-23 mpg, but this last go around it was about 19. both numbers corrected for larger than stock tires.

So my question is, could this be another symptom of a failing transmission pump? if the pump isnt creating enough line pressure, could the clutches be slippnig and loosing my high mileage?? Im not a tranny guy, so im just kinda guessing here.

 

[toomany]

If the transmission were slipping, the RPMs of the motor would be higher for a given road speed. You would know if it were slipping. Pressing on the accelerator harder wouldn't gain any more speed. 19mpg is great for one of these trucks, especially if you have bigger tires. I average around 9mpg with my K5.

 

[K5dreamer]

oh no, youre right, and i hate to sound like a complainer, the lack of mileage more concerns me because its a drop from the norm, and that indicates a problem, and i dont like having problems with my truck. also to preface, it is a diesel, M1009, 3.08 axles, so its hard to feel when its accelerating even slower than normal and i dont have a tach, so i cant see if there has been a change. slipping trans happens over a long time so im sure ive acclimated to the change in pitch of the engine, and couldnt tell if its higher than it was when i first got it.

But it has long since had no responce to more throttle, i just assumed it was a lack of power. im tryin to remember if the rpms went up at the same time...i think i would have noticed that.

 

[imiceman44]

oh no, youre right, and i hate to sound like a complainer, the lack of mileage more concerns me because its a drop from the norm, and that indicates a problem, and i dont like having problems with my truck. also to preface, it is a diesel, M1009, 3.08 axles, so its hard to feel when its accelerating even slower than normal and i dont have a tach, so i cant see if there has been a change. slipping trans happens over a long time so im sure ive acclimated to the change in pitch of the engine, and couldnt tell if its higher than it was when i first got it.

But it has long since had no responce to more throttle, i just assumed it was a lack of power. im tryin to remember if the rpms went up at the same time...i think i would have noticed that.

I was gonna say it must be a diesel to get those numbers, especially with a th400.
If it is slipping and is going to need a rebuild, it will let you know soon enough, your last trip back home will be a little stressfull but should get you home.
Untill then i wouldn't touch it since you have a daily driver, unless you have the money and would like to have it ready as a backup vehicle, the go ahead and rebuild it and put in a stage 1 shift kit, it will make it stronger and last longer too and get a bit more mileage.

 

[K5dreamer]

the other rub is that if the th400 is going, i had been planning on a 4L80-E swap at some point. but the question is, realistically how far down the road is that swap gonna be. Realistically i should rebuild this tranny, and then once i have the other upgrades (turbo, 1ton axles, bigger tires, etc.) ill do the 4l80-e tranny last, and that could be a few years out. ah hell, i suppose i could always sell the th400 as a rebuilt one if worst comes to worst.

anyone know how hard it is to rebuild a TH400 in your garage????