I have a 85 4X4 B-2 with a 2.8 V6, manual locking hubs, manual 5 speed transmission, 3.45 gears and 235 60/R15 tires. Don't know if it's the Mitsubishi or the M5OD. My question is 45 mph is the top speed I can go in 4th gear before I get in to 5th. Then 55 it my top speed in 5th without really turning up the RPMs. I'm afraid to go past 60 mph because the engine is really screaming. I know this can't be right. 1st through 4th may be right but shouldn't 5th be an overdrive gear for highway use? Thought maybe it might be stuck in 4 wheel hi but checked the front drive shaft and it does seem to disengage when I put in in 2 wheel drive hi. Maybe I lost 5th? Don't seem to be much of an RPM drop when I go into 5th. Any ideas?

 

Your stock tire would have been 27.10 inches tall, your current tire is 26.10 inches tall. That has effectively lowered your gear ratio.

IF your 5th gear is .79 or .80 then your RPMs at 55 would be 2150. If your 5th gear is actually a 1:1 then it would be 3200 rpms. You might have had someone switch in lower gears or your transmission might not really be an overdrive. You really need to pull the model number on the transmission and the cover off your rear diff. before solving the problem.

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Sounds like you are in low range.

What rpm do you see at 55 in 4th and 5th? Got a tach?

 

Well, I just checked my 1984 B2, the stock tire is a P195/75r15. Yours might be too. I guess you really need to find out what is what with your vehicle, anything could have been done over the last 25 years.

 

My old 2.8v6 84 4x4 Ranger does about 2150 rpms at 60mph in 5th with 3.73 gears and 31 x 10.50s tires...........just a reference point for you to work with.

 

Thanks for the responses. Was able to check to see if the front drive shaft turns when I drive forward and it doesn't so I know it's not the front wheels being lock or the transfor case. The only thing left is the gears and or the transmission. Both diff. have the ID tag still in place and both say it should have 3.45 gears. I know they could have been changed so is there anyway to find out if they are 3.45s? As for the trans where is the ID tag? Looked last night couldn't find it. Don't have a tach on the truck but having owned many cars and trucks with a tach's I would have to say it's well over 3000 rpms in 5th gear at 60 mph.