Transmission Code / SPID - The 1947 - Present Chevrolet & GMC Truck Message Board Network

harrydunn · 12-09-2010, 09:56 AM

Morning Guys--

Will the transmission code on the SPID tell me whether I've got a TH350 or TH400? I need to take a photo and post that up I suppose.

Also, I've not been around old transmissions since the days of my '68 Cutlass (2-speed Jetaway) and '74 Camaro (3-spd manual) many moons ago. Would you advise to at least change the fluid/filter or should I leave things alone? I've got some engine oil records but nothing on when the transmission may have been serviced. Shifts very smoothly.

Thanks,

Mark

slategrove · 12-09-2010, 10:22 AM

Here's what you need to identify your tranny...I had to figure out what I had, too.

http://www.maliburacing.com/auto_tranny_id.htm

**special-K** · 12-09-2010, 10:26 AM

No,both will have the M49 code.Weird,but how it was done.Makes no sense.It's like using the same option code for a 350 and a 400.

It wouldn't hurt to change out the fluid and filter,but probably fine as is.Is the color still nice and red?Heat will make it dark and could be a sign the trans has been slipping

harrydunn · 12-09-2010, 10:31 PM

It's a 350. Thanks for that link.

harrydunn · 12-10-2010, 12:13 PM

Should have asked this in my initial post. Where can I find the rear-end ratio?

Thanks,

Mark

Longhorn Man · 12-10-2010, 06:26 PM

Some trucks got the car option number (M38) for the TH350, but generally they were all M49 in trucks.
The rear gear, if not listed on the SPID would be the standard ratio for the series/eng/trans.
Assuming we are talking about the 72 GMC in your signiture, we now know it has a TH350... what motor does it have?

ChevLoRay · 12-10-2010, 06:54 PM

Had a pair of '69's. One had a TH350, and it also had M38 on the SPID. Mine has a TH400 and says M49 on the SPID.

sameyrasmea72 · 12-10-2010, 07:39 PM

Most spid use M49 for both,but the firewall will use M38 for the 350 and M49 for 400

**DANTIP** · 12-10-2010, 08:14 PM

Nice catch Jason! I hadn't noticed that.

harrydunn · 12-11-2010, 12:35 AM

Quote:

Originally Posted by Longhorn Man

Some trucks got the car option number (M38) for the TH350, but generally they were all M49 in trucks.
The rear gear, if not listed on the SPID would be the standard ratio for the series/eng/trans.
Assuming we are talking about the 72 GMC in your signiture, we now know it has a TH350... what motor does it have?

Engine is a 350.

harrydunn · 12-11-2010, 05:24 PM

Metal tab on the bottom left of the diff has a 4.10 stamped on it. I'm assuming this is my ratio? It does scream on the highway at 60 mph so I would not be surprised.

Longhorn Man · 12-11-2010, 07:50 PM

you got it, a 350/auto in a 3/4 ton would get a 4.10 ratio standard.
It's MUCH better than the 4.57

12-09-2010, 09:56 AM	#1
harrydunn Registered User Join Date: Dec 2010 Location: Columbia, MO Posts: 256	Transmission Code / SPID Morning Guys-- Will the transmission code on the SPID tell me whether I've got a TH350 or TH400? I need to take a photo and post that up I suppose. Also, I've not been around old transmissions since the days of my '68 Cutlass (2-speed Jetaway) and '74 Camaro (3-spd manual) many moons ago. Would you advise to at least change the fluid/filter or should I leave things alone? I've got some engine oil records but nothing on when the transmission may have been serviced. Shifts very smoothly. Thanks, Mark __________________ 1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport

12-09-2010, 10:22 AM	#2
slategrove Registered User Join Date: Apr 2009 Location: Normal, IL Posts: 138	Re: Transmission Code / SPID Here's what you need to identify your tranny...I had to figure out what I had, too. http://www.maliburacing.com/auto_tranny_id.htm

12-09-2010, 10:26 AM	#3
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: Transmission Code / SPID No,both will have the M49 code.Weird,but how it was done.Makes no sense.It's like using the same option code for a 350 and a 400. It wouldn't hurt to change out the fluid and filter,but probably fine as is.Is the color still nice and red?Heat will make it dark and could be a sign the trans has been slipping __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~ Last edited by special-K; 12-09-2010 at 10:27 AM.

12-09-2010, 10:31 PM	#4
harrydunn Registered User Join Date: Dec 2010 Location: Columbia, MO Posts: 256	Re: Transmission Code / SPID It's a 350. Thanks for that link. __________________ 1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport

12-10-2010, 12:13 PM	#5
harrydunn Registered User Join Date: Dec 2010 Location: Columbia, MO Posts: 256	Re: Transmission Code / SPID Should have asked this in my initial post. Where can I find the rear-end ratio? Thanks, Mark __________________ 1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport

12-10-2010, 06:26 PM	#6
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Transmission Code / SPID Some trucks got the car option number (M38) for the TH350, but generally they were all M49 in trucks. The rear gear, if not listed on the SPID would be the standard ratio for the series/eng/trans. Assuming we are talking about the 72 GMC in your signiture, we now know it has a TH350... what motor does it have?

12-10-2010, 06:54 PM	#7
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Transmission Code / SPID Had a pair of '69's. One had a TH350, and it also had M38 on the SPID. Mine has a TH400 and says M49 on the SPID. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

12-10-2010, 07:39 PM	#8
sameyrasmea72 Senior Member Join Date: Aug 2003 Location: Lubbock, Texas Posts: 2,443	Re: Transmission Code / SPID Most spid use M49 for both,but the firewall will use M38 for the 350 and M49 for 400 Attached Images __________________ 72 Cheyenne Super 80 Silverado Blazer 2wd

12-10-2010, 08:14 PM	#9
DANTIP Registered User Join Date: Sep 2001 Location: Fort Wayne, Indiana, USA Posts: 1,888	Re: Transmission Code / SPID Nice catch Jason! I hadn't noticed that.

12-11-2010, 05:24 PM	#11
harrydunn Registered User Join Date: Dec 2010 Location: Columbia, MO Posts: 256	Re: Transmission Code / SPID Metal tab on the bottom left of the diff has a 4.10 stamped on it. I'm assuming this is my ratio? It does scream on the highway at 60 mph so I would not be surprised. __________________ 1972 GMC 2500 Custom, 96K miles, Purchased New By My Grandparents 2016 Toyota Tundra TRD Off-Road SR5 1993/2003/2005 Toyota Land Cruisers 2004 Corvette Z06 / 2000 Covette Coupe 2006 Ducati Multistrada 2014 BMW X3 XDrive35i M Sport

12-11-2010, 07:50 PM	#12
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Transmission Code / SPID you got it, a 350/auto in a 3/4 ton would get a 4.10 ratio standard. It's MUCH better than the 4.57



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