The Stovebolt Site Forums The Parking Lot Big Bolts 35 mph top highway speed??

After 4 years of work on my '55 2nd series 6500,I am disapointed at the performance of the drive-train. I'm ALMOST positive that I have the rear-end on the "high-side",and I installed taller 9:00x20.00's on the rear axle, to improve gas-mileage,and decrease r.p.m.'s. I previously ran 8.25x20.00's,so there shouldn't be too much more stress loaded on the drive-train. Any suggestions would be greatly appreciated!! Thanks in advance!

I would imagine that your rear is in low range. My '52 3 ton will run 60+ but it has a .83 overdrive on 8.25-20's. The '46, while still not running 100% will do 45 on 7.50-20's with 1:1 rear. You should be able to get 55 with no problem.
Scott

Thanks,Scott! I can live with 55,since most of the roads between my house,and where my truck is stored,are 55 m.p.h.,tops. It's in the exhaust shop,now,being fitted with Fentons,and dual stacks behind the cab.(235 head,261 block). I'll post a video of the finished product later this week,on photobucket.com. As soon as I get it out of the shop,I'll adjust that 2-speed and keep you up-dated. Thanks,again!! I was getting ready to sell her, but NOT YET!! She was fun to drive even at 35!

I am currently building my truck and I knew I would run into this problem so I have done two things. Installed a 4.88 ring and pinion gear set and installed a ranger overdrive in front of my sm-420 transmission. This combination lets me do 65 mph while turning less than 3000 rpm.

The gear sets can be found for about $450, here http://wellertruck.com/lit/Weller_Diff_Catalog_2011.pdf you can find the part numbers for the gear sets. When you find your part number go here and search http://www.truckpartsinventory.com

The overdrive unit was $1400 here http://www.advanceadapters.com/categories/complete-units/91/

Jake, what model year truck and or axle do you have? While you were able to find 4.88 gears they won't be an option for everyone depending on the axle they have.

The axle was a GM T170 it was used up to I think around 85' not sure how old it goes back though.

There are a lot of options for getting more speed, different rear gears, auxiliary units, etc...

You should be getting more than 35mph though...I'm guessing you can fairly accurately judge speed and don't just have a poor speedometer. Remember your speedometer will read slower than actual now. Your 8.25 were 37.6" tall with 536rev/mi and your 9.00 are 39.16" tall with 515rev/mi. It's not much difference though, so I too would believe your rear in actually in low. Have someone pull the switch and listen/feel for if your shifter motor is actually working. You can always unbolt it and visually check if it is moving as well. You should be able to move the rear axle shifter by hand with the motor off to manually shift it to make sure nothing is hanging up. If It's vacuum you can easily visually check if the shift arm is moving or not.

You could also jack up one wheel and spin it to see what ratio you are actually in. If you tape a piece of string to the drive shaft then spin the wheel you will be able to easily count how many revolutions the drive shaft made. I think the drive shaft will spin twice as fast with one wheel on the ground...but that will be easy enough to tell as nothing has a 12 or 18:1 rear

Tad

Thank you all for your responses. Once I get her out of the muffler shop,I'll pull the vacuum pancake,to see if the shaft is free. It should be,since I rebuilt the unit 2-years ago,and used lithium grease on the shaft,prior to re-assembly. But,you never know... I'll keep you posted on the progress. Thanks again!!

You should be able to visually see if the rear is shifted with a vacuum rear w/o pulling anything apart. Unless it is different than the vacuum rear set up my International has.

If it is in fact shifting and you are in high I would be really interested to know what rear ratios you do have.....that would have to be one low-low-low low gear.

Tad

Sounds 'bout like my '57 with the 2 speed stuck in low. It shows about 35 max.,verified by everything including mo-peds passing me.
Speed

Hey Big Bolters! I got my truck back today,and found the shaft on the 2-speed wasn't engaged,so I "flipped" her up on the "high- side",and she's doing 55 M.P.H,just like you guys said it would. I forgot my camera,in my excitement,but I will submit a video sometime next week!! Stovebolt.com ROCKS!! Thanks,everyone!!

LOL, glad things work out that way for people every once in a while.

Tad

Jake!!! Thanks for that link!!!! I have a T170 in my 54'.....my rear is obviously not original...lol....came out of a late 60s/early 70s truck I believe. The 4.88s came in the diesels, I have had a few sightings of them but haven't caught up to a good one recently.....is your rear a single speed? I had hoped to have the 4.88s as a high gear and maintain a the two speed.....lol...Thanks!