The Stovebolt Site Forums The Parking Lot Big Bolts Tranmission and rear axle gearing

Not a big bolt owner, yet, but I am looking to buy a C40, C50, or C60 to convert into a pickup truck (looking at mid 60s to '72). I am hearing some people talk the fact that the top speed is only around 55 or so mph because of the gearing. Is this true?
Seems like I drove a 2 or 2 and a half ton flatbed many years ago for a landscape company and I don't remember it being geared so low.

Can anyone give me more info on this?

Thanks.

What engine and tires are you going to use? That would be a good start as to what diff. ratio might be suitable. V-8's cruise higher RPM, 22.5" tires make for a higher effective ratio, for example.

Ed

I'm hoping to find one with the 292 in it. It is my desire to keep it as stock as possible. I'm just wondering if they are really geared that low.

Yes the big bolts were geared that low. Might get 55 but that would be pushing it pretty hard. They were made for hauling heavy loads not highway cruising. Good luck in your hunt.🛠

My 1958 (I know, older than shat you are looking at) has 9R22.5 tires on the back. All stock drivetrain (SM420, 2 speed rear) will turn 4200RPM at 70 MPH. 3600RPM at 60 MPH. Hope that gives you some idea. I dis put a Ranger overdrive in it, that dropped the RPM on the freeway but also robbed some power (even when not in overdrive). I am not sure how much power loss is from adding the ranger unit or from the condition of it. Mine is an old cast iron one and needs to be gone through.

Did going to the 22.5s seem to help any, before the overdrive unit?
BTW, looking in your gallery, your story of going to look at the 1958 reminds me of the C.W. McCall song called "Classified".

Just so you understand the 22.5 tubeless tires were designed to be direct replacement for the 20" tube type tires. So the same tire diameter advantage can be had by just up sizing bigger tires on your existing rims.

Examples...

8.25x20 is the same diameter as the 9.00x22.5

9.00x20 is the same diameter as the 10.00x22.5

10.00x20 is the same diameter as the 11.00x22.5

Mike B

Thanks, Mike. I did NOT know that. Seems as though the 22.5s would have been quite a bit taller.

Is there a way to easily tell the ratio in a big bolt? From what I’m reading it’s either a 5.43 or 6.17. I found some numbers on top of the axle but have no way to make sense of them.

HI26I30

Couldn’t find any other numbers but there is lots of room under all the crud... just need to know where to look.

Jack up one wheel after you put the two speed in high, count revs. Most truck two speeds are all geared slow or slower, so adding some kind of OD might be the best solution. Also depends on what engine, you have . 69Cuda must have a V-8 judging by his RPM's, so a 292 will cruise at a lower RPM.

Ed

yes Ed, my 58 has a 327 in it. Todd, my 58 had 2 22.5s on it and one rear corner had 20" with Widowmakers. I never drove it like that, but found an almost new set of tires and wheels before it ever went out of my driveway!