Gear change and High RPM

[blubuckaroo]

Had intended to mention checking the trans ratios by turning the engine over by hand.

With the trans in 3rd gear and the t-case in high-range and wheels up, put a wrench on the crank bolt and turn the engine over 1 turn while either someone counts the rotations of the driveshaft, or you mark it and then verify.
If it's indeed turning over at a 1-to-1 ratio, you'll know it that way.

You can do this at the same time you're checking the rear end ratio.

Paul

Paul, I had no experience with the Tremec T-170 tranny, and so didn't realize it is an overdrive tranny. The top gear is .78 which is the same as the New Venture NV3550.
In this case, the tranny numbers certainly should be checked.

 

[guidoverduci]

According some paperwork, the PO, and some casting numbers, I believe it to be t170.
And I think it’s the one at the bottom of this link.

http://www.f150hub.com/trans/t170-smod-srod-tod.html

 

[SHX669]

Probably not your issue since you've already been driving it with the previous gear setup -but like Tim I'm throwing this out there - I have a friend who was running unusually high RPMs for his gear tire setup - had his tach set for 6 cyl instead or 8cyl .

 

[Broncobowsher]

Probably not your issue since you've already been driving it with the previous gear setup -but like Tim I'm throwing this out there - I have a friend who was running unusually high RPMs for his gear tire setup - had his tach set for 6 cyl instead or 8cyl .

That was why I was asking to verify the tach matched the timing light (sounded like his timing light had a tach on it)

 

[guidoverduci]

Ok- back at it this weekend. I have verified gears are correct, 4.56. I also looked at the back of the tach, the setting is pointing to 8 cyl. I’ll continue to experiment.

 

[guidoverduci]

And... at it’s current state, there’s not front drive shaft in. No matter how I move the j shifter TC, it doesn’t feel like it’s dropping into any gear. It just wiggles around like it’s always in N. I’m a 4wd newb, so keep that in mind.

 

[Broncobowsher]

Since we have not confirmed the transfer case, lets start with that. Since the shifter sounds like it is dead we need to go to what the shifter is controlling.

No front driveshaft, first thing I would do is grab the front output yoke and try to turn it. It will either be free to turn (with normal bearing and seal drag) and that means it is in neutral for the front output, 2WD. If you can't turn it, it is in 4WD.
Next is look between the front output and the transmission. There are 2 shift shafts coming out of the transfer case that go into the shifter. If it is very original there may be a boot over the shifter linkage, but most are gone now. The rail closest to the front output controls the shifting of the front output. The shaft closer to the rear output controls the rear output.
As the shaft is pushed into the transfer case, that is low range. Pull it out, high range. In the middle, neutral.
For normal 2WD operation the upper/inner/rear shaft should be pulled all the way out and the lower/outer/front shaft should be about halfway.

Still not sure? Put the back on jackstands. Put the transmission in top gear. Put a chalk mark on the driveshaft. Put another on the crank pulley. Put a ratchet on the crank and spin the engine 1 full turn. Check the chalk mark on the driveshaft.

Marks are still lined up, 1:1 ratio, high range.
Driveshaft made 1¼ turns, high range and overdrive
Driveshaft only did half a turn, low range in the transfer case.

 

[DirtDonk]

The missing front shaft does not effect anything in this regard, so that's not an issue.
Sounds like your transfer case is in low-range. At 45mph in 3rd gear you should be at 2000rpm and in 4th gear at closer to 1600rpm.
You're not at double that, which would be consistent with the roughly 2:1 low range of your J-shift transfer case (more like 2.2:1 I believe?), but it's nowhere near consistent with just being in a lower transmission gear.

So here are some more tests to perform:

1. Get underneath and figure out your transfer case linkage. Then manually push the rods into the 2wd high range position. Sounds like your shifter is vague at best, and not working at all at worst. So you need to visually confirm where it's sitting.

2. Alternately you could test both the trans and t-case by the previously mentioned turning over of the engine while you watch the output yoke or driveshaft (or tires, if in the air).
You can either remove the shaft, or lift the rear tires off the ground for this.
If you have a helper, have them turn the engine over by hand one full turn of the damper. Mark and count the number of turns the rear output yoke turns. If you're in 3rd gear this should be 1-for-1.
Try again in 4th gear to see how many turns. Should be just under 1 turn of the yoke for a full turn of the engine.
(side note: if your fan makes it awkward to turn the engine over by hand, you could probably put a big ratchet on the output nut of the t-case and have the helper count the turns on the damper while the yoke is turned under the truck)

If you don't have a helper, you can use your camera to video the number of turns of the yoke if you make a clear enough mark.

That's easy enough, but verify the position of the t-case shifter anyway. Lots of people here can tell you how the "flags" and the shafts are supposed to be when in 2wd.
And this way too, you can see what's up with the shifter and maybe give it a quick fix.

Paul

 

[DirtDonk]

There 'ya go. 'bowsher's got you covered.

Paul

 

[guidoverduci]

Ok, for a second I thought we found it! I had to get a screw driver to pop the inner/upper rail out...But I was messing with the shifter rails so much, I can’t remember where they started. Took it for a test drive, and while it felt different... could be in my head... RPMs seemed to be the same. Used 40mph as the measurement. 3rd gear, 1:1, was around 2500 give or take and 4th, .78, was around 1800 give or take. I’ll keep digging and try other tests. Thanks for all the help so far!!

 

[SHX669]

You've verified that you actually have a T170 transmission ? - - NO shift LINKAGE but the shiftier sits in a "tower " directly on top of the tranny .
There is a Ford 4 spd with OD transmission that has linkage on the side . Those often have a modified shift pattern with the floor shifter . The configuration of the linkage makes it necessary to swap gear " locations " in regard to the H Pattern .

 

[guidoverduci]

Well I think you might be on to something. Honestly, that was what I was leaning towards the most. I’ve got a receipt from the PO that is probably 15 years old. It says T-170 (handwritten) on it twice but then at the top it says bronco t-176 which is a different ratio. Although it could just be sloppy writing and the 6 is supposed to be a 0?!..

It’s definitely a top loader. They all look the same. I even selected “ford top loader” from the TREMEC website and the gear ratios were much more accurate with my speeds. And it’s got a casing stamp of C-2605275. I’m still digging, but I feel like it’s probably not a T-170.

 

[guidoverduci]

Found this little blurb on advanced adapters site while googling my casting number...

“This transmission(RTS) commonly was stamped with a casting #2605275. The transmission was manufactured in Mexico by the Tremec Corp under the name “T-170”. The “RTS” was the first predecessor of the successful T-170 series of the transmission that would include the popular Jeep T176.”

So back to being confused... cause the ratios for the above transmission are what I’ve always thought I had...

 

[DirtDonk]

Good to have some confirmation at least. But that still does not matter as much as finding out what's going on.
Your last check showing 2500 rpm when in fact you should be turning over at 1800 is super strange.

So have you measured your tires exactly yet? If not, pleas do so, so we can get the expected rpm down to an accurate number. I'm using 33.5" in the calculator to get the expected speeds, but every tire is different.
I know it's not going to make that much difference being a 1/4" or even a 1/2" off, but it's better to know for sure.
So measure from the center of the hub down to the ground on the rear tire with it on the ground and shout out the numbers.

The problem right now is that this is not enough of a difference to be explained away by the transfer case being in low-range. That 1800rpm when it should be 1400 rpm just can't be explained that way.
You really need to start counting revolutions to know where the variation is.

Paul

 

[guidoverduci]

Ok, next test... tell me if I did it correctly....

Put it in 3rd gear. Jacked the rear. Put tape on rear output of TC. Put tape on bottom of pulley attached to harmonic balancer. Cranked while helper watched for tape on rear output to come back. It took *roughly* 1.5 turns on the pulley for the rear output to do 1 full revolution...

 

[guidoverduci]

And I’m seeing 16 3/4 from center of hub to ground. So 33.5 should be good.

 

[guidoverduci]

And now 4th gear shows 1 full turn on harmonic balancer is 1 full turn on rear output of D20... so, does that mean my 4th gear is 1:1? It would make more sense I suppose... then just need to figure what trans I really have??

 

[guidoverduci]

T-176 gear ratio for 3rd is 1.46:1 and 4th is 1:1....

 

[DirtDonk]

Correct. A one-to-one ratio from the engine to the transfer case output means that not only is the transmission using a 1:1 gear ratio, but your transfer case is in the correct high-range position.
And your rpm is now in exactly the correct range for your setup.

With 33.5" tires, 4.56 gears, 40mph should be almost exactly 1800rpm
Mystery seems solved.

Paul

 

[DirtDonk]

For comparison on your next drive if you can get to 60mph the tach should read near enough to 2700rpm to not matter.
Chart shows 2744rpm @ 60mph.

Let's hope that's consistent too!

Paul