Manual Trans question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Slater383 · 08-25-2009, 06:35 PM

I just bought a 69 3/4 ton 4X4 Chevy pickup with a 327 and a 4 speed with granny gear. I drove it up and down the road and running about 3000 rpms at 40 mph. Clearly this is not a useful driving range. I am wondering if i bought a 5 speed manual out of a early to late 90's gm would it bolt up to and work with my 327. Also the numbers off the 327 came back that its a 350hp 327 out of a 1965 corvette. Anyone have any thoughts??

Thanks
Ryan

68lwb292 · 08-25-2009, 06:50 PM

fourth gear should be 1:1 like every other non-overdrive transmission I would blame the differential gearing. 3/4 ton is probably geared for pulling more than going fast. (Its just a 3 speed tranny with a granny low)

unclewatts · 08-25-2009, 09:31 PM

Quote:

Originally Posted by 68lwb292

fourth gear should be 1:1 like every other non-overdrive transmission I would blame the differential gearing. 3/4 ton is probably geared for pulling more than going fast. (Its just a 3 speed tranny with a granny low)

68lwb292 is right. I have the Muncie M20 which is the same trans that you have. If your doing that high RPM at fourty it sounds like you have 4:88 or even higher rear end gears. I would change out the ring and pinion or get a new rear end at a wreckers before changing out the tranny. Just MHO.

OOPS! Just noticed that you said you have a 4X4 so you'll have to change the ratio of the front end too. Bummer...

**Palf70Step** · 08-25-2009, 09:33 PM

There is also a good possibility if it is a stock tach, that your tach readings are off a fair amount. These tachs are not known for being real accurate.

BAGNDRAGIT · 08-25-2009, 09:59 PM

does it sound like 3000 RPM??

sorry had to ask..

Longhorn Man · 08-25-2009, 11:11 PM

do you have a tach, or are you just guessing at the RPMs?
you should have a 4.10 or 4.56. which would but yout 3000 RPMs closer to 70, or 60 prospectivly.

BarryB · 08-25-2009, 11:19 PM

I would definitely check the diff gear ratio's. I pulled a 5:13 out of a 3/4 and replaced it with a 4:56 gear . Then at least I could get it up to speed.

*2tons of fun* · 08-25-2009, 11:54 PM

also depends on tire size, 4.88 and 39"s are perfect for a healthy small block.

4.88 and 29" are perfect for a briggs horizontal crank 5hp.

dan42 · 08-26-2009, 12:15 AM

...but to answer your original question, you can put a later model tranny in there, but you will have clutch linkage issues, and speedo issues to work out.

Jacfourteen · 08-26-2009, 12:34 AM

wow, someone with lower gears than me! LOL. I have 4.56 and 31 inch tire in mine and it does about 3000 at 60 mph (this is a guess because I have no tach, but the math says I'm about right). I plan on going to a 3.73 gear and changing to a 5 speed like you mentioned. Sorry that I don't have an answer on your original question, but I know that others have done the swap. hopefully they will chime in. Good luck!

Blazer1970 · 08-26-2009, 06:42 AM

As stated above, if you are looking at a factory tach, there is a 99% chance that it reads at least several hundred rpm high at higher rpms.

69GMCLonghorn · 08-26-2009, 09:26 AM

Quote:

Originally Posted by Palf70Step

There is also a good possibility if it is a stock tach, that your tach readings are off a fair amount. These tachs are not known for being real accurate.

This was my first thought, too! When I bought my truck I thought I had 10:1 gears in it!! The dang thing was SCREAMING on the freeway, according to the tach. I hooked up a secondary tach and realized the factory unit was off by as much as 800 RPM!! Of course, I was still doing 3000 at 70, but it's better than 3800!

OrangeCrush1970 · 08-26-2009, 09:51 AM

GM ran the SM420 till '67 and in '68 started running the Muncie 465 4-speed (also a New Process NP435)....all are granny four speeds. Either way they are both pretty much unbreakable units, and if you are planning on using the truck for towing, etc. I (if it were me) would not replace them. This is information I found before we swapped a 5.14 rear to a 4.10 in 72Freaks '68 dually and he's getting about 10 mph...with the Muncie 465. I think there are also 2 different SM420 and one of them is geared even lower. Check you SPID or try to ID what you have before changing it out, maybe a different rear end is what you are looking for?

martindc1 · 08-26-2009, 01:37 PM

I would determine your gear ratios and calculate your rpms off that, your tire size and what mph you want to drive. It would be even better if you could determine how close your speedo is off of a hand held GPS. I felt the same as you when I first got my 67. It has 4.57 gears and a 250 straight 6 and I thought I needed a NV4500. The first thing I did was add a muffler and that made me feel alot better. Then I just got used to it. The 33" tires help some too.

My 67 has a factory tach and I am sure it is a good bit off. For one thing it seems to read differently if the lights are on. My speed is probably off too.

A while back we calculated the fuel economy off the odometer and how many gallons of fuel we put in and it was hair over 14 mpg. Now understand that the speedo could be off and also it was my dad driving and he takes her pretty easy. But I do know my 67 K20 with 4.57s and a 250 gets better fuel economy than my 72 C10 with 3.73s and a 350.

Slater383 · 08-29-2009, 08:22 AM

Quote:

Originally Posted by BAGNDRAGIT

does it sound like 3000 RPM??

sorry had to ask..

OH YEA! It def sounds like 3000 rpms

08-25-2009, 06:35 PM	#1
Slater383 Registered User Join Date: Aug 2009 Location: Penn Yan, NY Posts: 2	Manual Trans question I just bought a 69 3/4 ton 4X4 Chevy pickup with a 327 and a 4 speed with granny gear. I drove it up and down the road and running about 3000 rpms at 40 mph. Clearly this is not a useful driving range. I am wondering if i bought a 5 speed manual out of a early to late 90's gm would it bolt up to and work with my 327. Also the numbers off the 327 came back that its a 350hp 327 out of a 1965 corvette. Anyone have any thoughts?? Thanks Ryan

08-25-2009, 06:50 PM	#2
68lwb292 Ex-Minitrucker Join Date: Apr 2009 Location: Bushnell, FL Posts: 301	Re: Manual Trans question fourth gear should be 1:1 like every other non-overdrive transmission I would blame the differential gearing. 3/4 ton is probably geared for pulling more than going fast. (Its just a 3 speed tranny with a granny low) Last edited by 68lwb292; 08-25-2009 at 06:51 PM.

08-25-2009, 09:33 PM	#4
Palf70Step State of Confusion! Join Date: Jul 2002 Location: Gulfport, MS USA Posts: 47,249	Re: Manual Trans question There is also a good possibility if it is a stock tach, that your tach readings are off a fair amount. These tachs are not known for being real accurate. __________________ Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God!

08-25-2009, 09:59 PM	#5
BAGNDRAGIT Just Not Low Enough! Join Date: Mar 2009 Location: Phoenix, AZ Posts: 525	Re: Manual Trans question does it sound like 3000 RPM?? sorry had to ask.. __________________ NEED ELECTRICAL HELP? ASK ME! 67-72 Full Wiring Diagrams Lots Of Info, TAKE A LOOK 1967 Chevy C-10 Shortbox Bagged 327 4spd Previous: 1971 Chevy C-10 Short Sep I6 Auto (Traded) 1973 Chevy C-20 THE REDNECK BATTLE TRUCK 2001 Chevy Silverado 2Dr 5.3L Shortbox. R.I.P. 1969 Volkswagen Bug This is my first meeting, I have a horsepower problem.

08-25-2009, 11:11 PM	#6
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Manual Trans question do you have a tach, or are you just guessing at the RPMs? you should have a 4.10 or 4.56. which would but yout 3000 RPMs closer to 70, or 60 prospectivly.

08-25-2009, 11:19 PM	#7
BarryB Senior Member Join Date: Jul 2006 Location: Blountville, Tn. Posts: 3,904	Re: Manual Trans question I would definitely check the diff gear ratio's. I pulled a 5:13 out of a 3/4 and replaced it with a 4:56 gear . Then at least I could get it up to speed. __________________ We could learn a lot from crayons... Some are sharp; some are pretty;and some are dull. Some have weird names; and all are different colours;but they all have to live in the same box. You may be only one person in the world, But you may also be the world to one person. * Some mistakes are too much fun to only make once. Two rules in life. 1. Never sweat the small stuff! 2. Everything is small stuff!

08-25-2009, 11:54 PM	#8
2tons of fun Account Suspended Join Date: Jan 2009 Location: galt ca, Posts: 749	Re: Manual Trans question also depends on tire size, 4.88 and 39"s are perfect for a healthy small block. 4.88 and 29" are perfect for a briggs horizontal crank 5hp.

08-26-2009, 12:15 AM	#9
dan42 Registered User Join Date: Feb 2007 Location: Cali Central Coast Posts: 5,191	Re: Manual Trans question ...but to answer your original question, you can put a later model tranny in there, but you will have clutch linkage issues, and speedo issues to work out. __________________ '67 SWB Fleetside ZZ4/350/Tremec 5-speed/4link/Scott's IFS - and fun as heck! SOLD Click here to support the board Philippians 4: 6-7

08-26-2009, 12:34 AM	#10
Jacfourteen Big Red - Now its a SWB! Join Date: Jun 2009 Location: Oroville, Ca Posts: 1,624	Re: Manual Trans question wow, someone with lower gears than me! LOL. I have 4.56 and 31 inch tire in mine and it does about 3000 at 60 mph (this is a guess because I have no tach, but the math says I'm about right). I plan on going to a 3.73 gear and changing to a 5 speed like you mentioned. Sorry that I don't have an answer on your original question, but I know that others have done the swap. hopefully they will chime in. Good luck! __________________ 68 3/4 ton (Project)-350 Small Block, .030 over, 10:1 comp, 3998993 heads, C3BX edelbrock intake, comp cams XE268, Holley 670 SA, long tube headers, dual flow 40's, E-fan, Alum rad, currently under the knife getting shortened and bagged build thread 41 3/4 ton (wife's)-flatbed, fully restored to original 01 Tahoe LT 4WD (my daily driver)-Magnaflow Muffler, Rollin on 22's 02 Ford Mustang Convertable (Wife's Car)-Flowmaster 50, Clear corners, Intake, sittin on 18's

08-26-2009, 06:42 AM	#11
Blazer1970 Registered User Join Date: Dec 1999 Location: Old Mission, MI, USA Posts: 2,507	Re: Manual Trans question As stated above, if you are looking at a factory tach, there is a 99% chance that it reads at least several hundred rpm high at higher rpms. __________________ Tim

08-26-2009, 09:51 AM	#13
OrangeCrush1970 Registered User Join Date: Jun 2007 Location: Smyrna, GA Posts: 709	Re: Manual Trans question GM ran the SM420 till '67 and in '68 started running the Muncie 465 4-speed (also a New Process NP435)....all are granny four speeds. Either way they are both pretty much unbreakable units, and if you are planning on using the truck for towing, etc. I (if it were me) would not replace them. This is information I found before we swapped a 5.14 rear to a 4.10 in 72Freaks '68 dually and he's getting about 10 mph...with the Muncie 465. I think there are also 2 different SM420 and one of them is geared even lower. Check you SPID or try to ID what you have before changing it out, maybe a different rear end is what you are looking for? __________________ *Rottenwood Garage* 1970...71...72 C1500 aka Orange aka Sideshow Bob 540 BB Straub Roller Cam, AFR Magnums, XP 950, TKO 600 2 Tons of Fun Last edited by OrangeCrush1970; 08-26-2009 at 09:53 AM.

08-26-2009, 01:37 PM	#14
martindc1 Registered User Join Date: Jul 2009 Location: La Crosse, WI Posts: 218	Re: Manual Trans question I would determine your gear ratios and calculate your rpms off that, your tire size and what mph you want to drive. It would be even better if you could determine how close your speedo is off of a hand held GPS. I felt the same as you when I first got my 67. It has 4.57 gears and a 250 straight 6 and I thought I needed a NV4500. The first thing I did was add a muffler and that made me feel alot better. Then I just got used to it. The 33" tires help some too. My 67 has a factory tach and I am sure it is a good bit off. For one thing it seems to read differently if the lights are on. My speed is probably off too. A while back we calculated the fuel economy off the odometer and how many gallons of fuel we put in and it was hair over 14 mpg. Now understand that the speedo could be off and also it was my dad driving and he takes her pretty easy. But I do know my 67 K20 with 4.57s and a 250 gets better fuel economy than my 72 C10 with 3.73s and a 350. __________________ Currently truckless, previous trucks: 67 K20, 87 K10 aka V10 & 72 C10



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