high rpm's at 55mph

[MiniMe]

I thought my transmission wasnt shifting into OD but last time i drove it i counted. It shifted to all 4 gears but im running around 4000 rpms at 55 mph and as far as i know the gearing is all stock. is this normal? 89 b2 automatic. Also wheres the best and cheapest place to buy a CV driveshaft?

 

[wildbill23c]

Something isn't stock, or something in the transmission isn't right. I believe you should be running around 2k in overdrive or slightly higher but no where near 4k.

 

[GentleRF]

Four wheel low range maybe.

 

[Gilbee01]

For the cv go to Amazon . But for the rpms at 55 you should be at 2500 ish mine is the same as your and that's what I get. I also on my recently replaced wheel bearings and gushed and changed filter on trany . Also check to see if the hubs are locked . Or if someone ran with them locked you could have done damage. First thing I would check is to make sure your not stuck in 4 low/high.


-gil-

 

[RonD]

You should have an A4LD trans in an '89 BII, OD gearing is .75 ratio

So about 1,800rpm at 55mph, really depends on the rear axle gearing and tire height, even with a 4.10 rear end you would only be up at 2,100rpm at 55mph

4 wheel low is often 2.3:1 ratio, so you would easily get to 4,000rpm at 50mph

 

[SenorNoob]

Just another possibility: Are sure the tach (I'm guessing that's what you're basing this on.) is accurate?

 

[wildbill23c]

At 55mph if the t-case was in fact in low range he would have done blown the t-case by now with the gear reduction its just not built to go that fast in low range whether or not the front hubs are engaged or not, its not made to go that fast. Does sound something of that nature though just don't see the truck staying in one piece at that rate of speed if it was in fact in low.

 

[PetesPonies]

The best scenario is something is ready wrong. If your tach is accurate, you don't have it in low 4wd . . . then you are up the creek without a paddle and you have a TC or more likely an A4LD problem.

 

[MiniMe]

Im sure it is not in 4 hi or 4 lo.. is there any adjustments to this tranny?

 

[PetesPonies]

SEarch A4LD problems. It is a weak transmission unfortunately.

 

[Gilbee01]

I'm guessing like mine you have the button on the dash for the 4x4 drive. I have heard about the engagement mechanism getting stuck. Just a thought .


-gil-

 

[MiniMe]

Yes i have heard all about the A4LD problems. I bought this from my uncle who said the tranny was rebuilt about 10,000 miles ago and only driven only drive 2000 miles in the past eleven years according to the oil changes sticker on the window.


Again im sure its not stuck in 4wd

It just seems this bronco runs and shifts too good to have a major tranny issues. I was leaning toward a simple fix or at least hoping for a simple fix

 

[RonD]

Not stuck in 4 Wheel Drive, stuck in Low which is a problem in the transfer case which may or may not engage the front drive line, so not a problem in the transmission.
Transmission is probably fine if it is shifting OK.

The transfer case has another set of gears that transfers power from the transmission to the front and read drive lines.
"Regular" transfer case gears are 1:1 so no change in speed or RPM when front axle is engaged, "Low" has a 2.2:1 to 2.6:1 depending on the model, so it would more than Double the RPM vs speed, which is what you describe.

It could be a simple fix by removing the shift motor and manually resetting the shift location so you are back to "regular" 1:1 gears.

 

[PetesPonies]

Really? The trans already had to be rebuilt ( no promise it was done like new ) . .then it sat
for 11 years with almost no use and you don't think it could be the trans????

 

[kimcrwbr1]

If it dont sound like its revving real high I bet it is just the tach going goofy. Maybe ypou can borrow a timing light tach at the part store to compare it to?