Did a Trans swap in my 82 GMC now have way to many RPMS

[harvnut]

I have a 82 GMC with 37 inch tires on it and had a 700r4 in it with 456 gears I redone the truck and while doing so decided to put a manual trans in the trans I put in had the low gear then 1-3 gears.with the 700r4 gears were fine cause the trans had a overdrive now its turning way to many RPMS and I might could run 40-45 if I am lucky I dont want to run my truck like that So I am trying to see what can be done .I have had people tale me to get a 5 spd for it but were could a person get 1 and what year modles would work if any?I found a guy that was running 38 inch tires and he was saying that his gears were 3.05 in his truck and they did good with the trans like I have I read that Online Dont know him other than what he wrote.Any info on this would be Greatly Apprciated.Thanks

 

[bucket]

My crew cab doesn't have OD, has 4.56 gears, and only has 35's on it. It runs down the highway as fast as you want without any trouble... sure it winds out a bit, but it doesn't run hot or anything. The 4.56 gears are factory installed BTW, so it ran a much higher RPM when it was stock.

 

[crazy4offroad]

Welcome to the forum! Sounds like you need taller tires or taller gears. 4.11s might help a little, just depends on what your max speed is gonna be and what target rpm you want to have. You can use a gear ratio calculator to figure out what speed/rpm to expect out of your transmission/t-case/axle gears/tire size combo...
http://www.grimmjeeper.com/gears.html

 

[bucket]

Sorry, I just kinda rambled and didn't state my point. If you just want to lower the rpms the save the motor, don't worry about it. As long as your motor is not on it's last leg, it'll be fine. The only thing that will suffer is fuel mileage.

 

[harvnut]

The gears that are in it now worked fine with The auto trans in it Rpms was not a issue but it had a overdrive so now its like I am driving in 3rd gear all the time cause I really am as for driving like it is now I dont think I would want to do that to much I was hoping to atleast to be able to go the speed limit .

 

[Swims350]

you should have no problems going the speed limit. you change gear ratios and it's not gonna get up and go very good at all. I think something is wrong if you can't go part 50 or so, either motor or trans aint working right. maybe even t-case or rear end. if anything you should be able to smoke tires easy and take off quicker then before.

Gear swap, or trans swap unless you got big bucks for an OD unit to bolt on the back is about all you can do to lower rpm's.

Honeslty though unless you drovve in od alot, you aint seeing no difference, just less gear, final drive is the same like 1 to 1, no matter if it's 20 speed.

 

[harvnut]

I have asked around at graugues and even called local trans shop and most have told me that if I have all my things that I should put back to a auto bascily telling me I need a overdrive.I work with some guys that have the same trans in ther truck and they say its geard low but they can go at least a high way speed theres is stock.I am having a problem figuring out what can be done to solve my issue.My motor is stock other than I put a comp off road cam in it and some roller rockers.I can say this the transfercase is one that I bought with the trans and I was assuming that It was good All I done to check it was to see if it went in and out of 4 wheel drive which it done so I took it to be ok.I dont know if somthing could be wrong there and I am unaware of it.I have had people to tale me to check and make sure the transfer case was not locked.

I have plenty of take of and get up is good.I just need to get someway figured out to were I can drop some Rpms on the top end to were I can run my engine and not worry about being to hard on it.with me going around 40MPH my rpms are about 4000-4200

I see were some was talking aboout a overdrive unit were can you look in on that and about what do they run price wise?

 

[bucket]

I have plenty of take of and get up is good.I just need to get someway figured out to were I can drop some Rpms on the top end to were I can run my engine and not worry about being to hard on it.with me going around 40MPH my rpms are about 4000-4200

I don't have a tach in mine for comparison, but that doesn't sound right at all. Sounds like you're driving in second gear? Or the t-case in low range? I dunno.

 

[bucket]

Or your speedo is now WAY off and 40mph is actually 65mph?

 

[Swims350]

agreed even with 5.13's for gears and them big tires it'll bring it down to a lower numbered ratio and lower rpm's. Something is wrong I too was thinking t case in low or something and the timing is off. I would bet some else going on though.

As for overdrive units bowtie overdrives and gear vendors overdrive, search em. They aint cheap, be alot cheaper to swap in a 5 speed or auto with od.

 

[crazy4offroad]

I have 38" TSL's, SM465 (which I guess that's what you have now), NP205 t-case and recent 5.13 gears and it looks like mine will be running about 3,000 rpms at around 65 mph, so either you're stuck in 4-Lo, your speedometer is off, or something else going on. If you have a GPS or someone to follow you at different speeds and find out how fast you're really going at different rpms it would help figure out what's really going on.

 

[crazy4offroad]

I'm leaning more and more towards "stuck in 4-Lo" and here's why. Using that gear ratio calculator I posted earlier in this thread, it has a way to figure low range speed, but in feet per minute. Assuming you have an NP205 t-case, in 4th gear low range you're running about 4337 feet per minute at 4,000 rpms.

4337 fpm x 60 minutes = 260,220 feet per hour / 5,280 (feet in a mile) = 49.284 miles per hour.

In comparison, my truck with 5.13 gears/38" tires, 4th gear low range at 4,000 rpms would run 44.989 mph. 4-Hi at the same rpms would be 88 mph in my truck so I really think you need to figure out how to get it in 2-Hi because obviously you're in 4-Lo. Hope this helps get you going in the right direction. Also knowing exactly what we're talking about, is it an SM465 transmission? Is it an NP205 t-case?? Things like that are very important details for helping figure out what's wrong.

 

[GreaseDog]

Sorry, I just kinda rambled and didn't state my point. If you just want to lower the rpms the save the motor, don't worry about it. As long as your motor is not on it's last leg, it'll be fine. The only thing that will suffer is fuel mileage.

just because the RPMs are lower does not mean that fuel economy is better. if that were true, we'd all be running around in trucks powered by 4 cylinders with 2.56 gears and 44" tires.

 

[GreaseDog]

I have plenty of take of and get up is good.I just need to get someway figured out to were I can drop some Rpms on the top end to were I can run my engine and not worry about being to hard on it.with me going around 40MPH my rpms are about 4000-4200

your tach is broken. at 4200 RPMs with 4.56 gears, 37" tires, in direct drive, you're traveling 100mph.

 

[GreaseDog]

I have 38" TSL's, SM465 (which I guess that's what you have now), NP205 t-case and recent 5.13 gears and it looks like mine will be running about 3,000 rpms at around 65 mph, so either you're stuck in 4-Lo, your speedometer is off, or something else going on. If you have a GPS or someone to follow you at different speeds and find out how fast you're really going at different rpms it would help figure out what's really going on.

the math works out for an NP208 or NP241 in 4 Lo... dumb question for the OP... did you adjust the transfercase shifter at all?