But then why would the truck idle at 500rpm? And its barely idling there, not like its revving like crazy and the tach says 500. Also it was 3000rpm at 35 mph not 3500 at 30mph.But I will check to see if there is a switch on the back.
Rear End Gear?
- Thread starter mustang8
- Start date
But then why would the truck idle at 500rpm? And its barely idling there, not like its revving like crazy and the tach says 500. Also it was 3000rpm at 35 mph not 3500 at 30mph.But I will check to see if there is a switch on the back.
George/Maine
Well-known member
I think the best thing is find a 9" 57 to 72 higher gears about 3.50 your bolt pattern and wide enough.
JSeery
Member Emeritus
I agree and none of the "charts" agree with the math! No idea what's up with that, that's why I posted the formulas so anyone could check it for themselves. I would go with the math that's for sure.
I ment to say 3000 rpm, that's the math I used. It's a typo.
What size tyre you got on it? I'm assuming 28" ish high.
Have you done the math? If so you'll see what we're on about.
Martin.
Ross F-1
Well-known member
If your tach is set to 4-cyl, it reads double the true RPM. Which is totally consistent with seeing 3000 RPM at 35 mph. You should be at about 1500. So your idle may be REALLY low.
Sometimes the switch(es) to change # of cylinders is inside the mounting cup, you may need to disassemble somewhat. What make/model is your tach?
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I was going to use a 46 truck rearend in my 41. When I pulled the cover it was stamped 4:27-1 ! I counted the teeth and sure enough it was..
I didn't use it
That would not have been a 46 truck rear end. It would be a Dana 41 or 44 out of a 48 and up F1.
The 46 rear end is a banjo style rear same as 48 And back cars, the only difference beeing the 42-47 pickup rear end is open drive, has a prop shaft not a torque tube. The rear cover and 4.27:1 are the big clues here.
Martin.
I have not resolved the issue yet, going through all the brakes on it currently, then im going to put new rims and tires on it all around and try to get the speedometer to read as accurate as I can with my rear tire size. I have a funny feeling that the tires are taller than the 29"ish that they are suppose to be. I only get one night a week to work on it so it sort of depends on what parts show up and what is ready to get buttoned up.
If your diameter is bigger than 29" this would lower the rpm at any given speed.
I think the tach is telling lies, as Ross said it could be configured for a four cylinder, that would produce the numbers your seeing.
You can easily check the Speedo with a speedometer application on a "smart" phone. The applications are free to download. If you haven't got the clever phone, borrow one off a child.
Martin.
I think the tach is telling lies, as Ross said it could be configured for a four cylinder, that would produce the numbers your seeing.
You can easily check the Speedo with a speedometer application on a "smart" phone. The applications are free to download. If you haven't got the clever phone, borrow one off a child.
Martin.
Yes I checked out the mph with a gps. it showed 39 mph and tach read about 3000rpm. This weekend is the iola old car show in iola Wisconsin. HUGE swap meet etc. hoping to maybe find a gear set that would be a better fit for the truck? anyone going there that might have something that would help out? Or ideas on what to look for? Thanks. Luke
George/Maine
Well-known member
That is way to low.
The best is a 9" out of a 1957-1972 ford pu 3.50 common. 5 on 5 1/2"
Next bolt pattern change is 8" mustang,s10 4x4.
I don,t think you can get a set of gears for that rear end.
The best is a 9" out of a 1957-1972 ford pu 3.50 common. 5 on 5 1/2"
Next bolt pattern change is 8" mustang,s10 4x4.
I don,t think you can get a set of gears for that rear end.
I agree that the best is to do the 9" but im not doing that swap yet. Moved last fall and have to build another shop. I want to do that at the same time I drop a t5 ****** in it. Would putting a 4 speed ****** in it help me out or do you think the final gear ratio would be about the same as my 3 speed?
George/Maine
Well-known member
A stock 4 speed trans wouldn't be any better you need and OD.
If you are able to keep up with traffic go for it.
235/75/15 tire or 650x16 are big tires in dia.
For that truck you also need the width like explorer,s10 4x4 about 60" width.
your tack is way off 4.44 gears at 3k is 58MPH.
If you are able to keep up with traffic go for it.
235/75/15 tire or 650x16 are big tires in dia.
For that truck you also need the width like explorer,s10 4x4 about 60" width.
your tack is way off 4.44 gears at 3k is 58MPH.
Why are you so dead against checking the rpm numbers?
If you don't check them, and they are as off as I/we think they are, you could go through all this rear axle swapping business, say fitting a 3.92 Dana44 and then find the tach gives the same or very close numbers!
Get a tape measure and run the numbers. You can even Jack up one rear wheel and count the turns of it and the prop shaft (drive shaft).
Do a search and you'll find the exact explanation of how too do this.
You've checked the mph against a GPS, now check the rpm against an accurate tool or do the math.
Genuinely trying to help you here, could save you a bunch of work and money and grief.
The four speed (stock type) won't change the final drive ratio as they are both 1:1 in top.
Martin.
If you don't check them, and they are as off as I/we think they are, you could go through all this rear axle swapping business, say fitting a 3.92 Dana44 and then find the tach gives the same or very close numbers!
Get a tape measure and run the numbers. You can even Jack up one rear wheel and count the turns of it and the prop shaft (drive shaft).
Do a search and you'll find the exact explanation of how too do this.
You've checked the mph against a GPS, now check the rpm against an accurate tool or do the math.
Genuinely trying to help you here, could save you a bunch of work and money and grief.
The four speed (stock type) won't change the final drive ratio as they are both 1:1 in top.
Martin.
George/Maine
Well-known member
Checking rearend gears.
If you can push truck one tire revelution mark the tire push forward.
mark at 6 oclock now have someone push the truck backwards one rev.
Now your job is draw line chack line on the drive shaft and count the turns.
If it turns more then 4 times its to low. Now here is a chance to die don,t get run over.
If you can push truck one tire revelution mark the tire push forward.
mark at 6 oclock now have someone push the truck backwards one rev.
Now your job is draw line chack line on the drive shaft and count the turns.
If it turns more then 4 times its to low. Now here is a chance to die don,t get run over.
I did try the gps and compare to the speedo. The speedo jumped a bit but read right in the area of what the gps was telling us for speed. Also I did check the tire size on it and it is right around 28 1/2". I just cant believe the tach says its idling at 500 rpm, if I go any lower it will die. So the check the tach idea is a simple one but I really doubt that's it. No way it is idling at 1000rpm.