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

Hugh Mongus · 02-06-2014, 02:50 PM

I was going to change the fluid and filter in my TH350 a couple of nights ago, but noticed that I cannot get the two back bolts out of the pan. The cross member is in the way. I thought about removing the cross member but there are two bolts on each side of the frame that would require lifting the cab to get them out. My truck also has a new drive shaft from the PO.

My question is, what transmission do you think would have came with it originally? I am assuming the ability to remove the transmission pan without removing the cross member would have been possible with the original configuration.

**jocko** · 02-06-2014, 03:08 PM

just loosen the trans-to-crossmember mount bolts at the isolator so the trans is just resting on the crossmember - then gently jack up the tailshaft just enough to get to the last bolts and slide the pan out. Don't jack it up too much - and monitor fan-to-radiator clearance as you do so. Motor should rock fwd on the front mounts and the jack will hold the tail. Also monitor the slip yoke of the driveshaft, you should have several inches of travel for the d/s to slip out before you run into a problem, so the fan-radiator interface is probably most important. The furthest it can drop (off the jack) is back onto the crossmember, but watch your fingers. No telling what your truck should have come with without additional info. M49 on the SPID? Most of the automatic trucks came with TH350s. All 4x4s had TH350s I believe. TH400s more reserved for big block or special order on a small block.

Hugh Mongus · 02-06-2014, 04:21 PM

PO scraped off the SPID.

Thanks for the help. I was afraid I might break something if I jacked up the back of the transmission. I'll try that.

MagmaJct · 02-07-2014, 02:49 PM

Please let us know how it went. I'm about to do the same due to a leaking gasket. Pictures would be appreciated, but it's okay if you can't get any.

I go into many repairs intending to document them. I'll start out with "before" pics, only remembering the "during" and "after" pics hours after I've finished. Oops!

BTW, I have a 71 with a 350engine and 350thm transmission, and I've wondered about that frame too.

D13 · 02-08-2014, 11:13 AM

Same problem and same solution on my 87 700R4. What I did was jack it up and slip a small wooden block under the trans mount ot hold it up, allows swivel socket and long extension to get to it from the side. Also a good time to replace that mount, which makes the whole thing easier. Do watch your fan clearance.

**bigmac73** · 02-08-2014, 04:03 PM

i use a 1/4 drive socket and a universal a little tedous but it works with out jacking the tail shaft up

1968SWBBigBlock · 02-08-2014, 04:36 PM

If you take the time to pull the cross member cut a couple of notch's in the cross member with your dremel tool or some other grinder and you will have access forever.
It can be done on the truck just more tedious

**bigmac73** · 02-08-2014, 08:28 PM

also once you do get it out take the time to install a drain plug if there is not one already saves you from a nasty mess

Hugh Mongus · 02-09-2014, 07:00 AM

I have not had a chance to tackle this chore yet. I was trying to figure out why my truck seemed to like to leave me stranded on the side of the road. After installing a new fuel pump, vacuum advance, re-timing it, and exchanging my new carb for another, I finally realized it was the coil. It only took all day to figure this out.

02-06-2014, 02:50 PM	#1
Hugh Mongus Registered User Join Date: Jan 2014 Location: Tulsa, OK Posts: 360	Transmission question I was going to change the fluid and filter in my TH350 a couple of nights ago, but noticed that I cannot get the two back bolts out of the pan. The cross member is in the way. I thought about removing the cross member but there are two bolts on each side of the frame that would require lifting the cab to get them out. My truck also has a new drive shaft from the PO. My question is, what transmission do you think would have came with it originally? I am assuming the ability to remove the transmission pan without removing the cross member would have been possible with the original configuration.

02-06-2014, 03:08 PM	#2
jocko Senior Member Join Date: Oct 2009 Location: Godley, TX Posts: 17,985	Re: Transmission question just loosen the trans-to-crossmember mount bolts at the isolator so the trans is just resting on the crossmember - then gently jack up the tailshaft just enough to get to the last bolts and slide the pan out. Don't jack it up too much - and monitor fan-to-radiator clearance as you do so. Motor should rock fwd on the front mounts and the jack will hold the tail. Also monitor the slip yoke of the driveshaft, you should have several inches of travel for the d/s to slip out before you run into a problem, so the fan-radiator interface is probably most important. The furthest it can drop (off the jack) is back onto the crossmember, but watch your fingers. No telling what your truck should have come with without additional info. M49 on the SPID? Most of the automatic trucks came with TH350s. All 4x4s had TH350s I believe. TH400s more reserved for big block or special order on a small block.

02-06-2014, 04:21 PM	#3
Hugh Mongus Registered User Join Date: Jan 2014 Location: Tulsa, OK Posts: 360	Re: Transmission question PO scraped off the SPID. Thanks for the help. I was afraid I might break something if I jacked up the back of the transmission. I'll try that.

02-07-2014, 02:49 PM	#4
MagmaJct Registered User Join Date: May 2008 Location: Mesa, AZ Posts: 281	Re: Transmission question Please let us know how it went. I'm about to do the same due to a leaking gasket. Pictures would be appreciated, but it's okay if you can't get any. I go into many repairs intending to document them. I'll start out with "before" pics, only remembering the "during" and "after" pics hours after I've finished. Oops! BTW, I have a 71 with a 350engine and 350thm transmission, and I've wondered about that frame too. __________________ I own 3 classic vehicles. 1971 LWB C10 Deluxe. 1974 VW Super Beetle. 1971 VW Fastback. The C10 and the Super Beetle run, the Fastback is just not there yet! Please visit my Super Beetle and Fastback profile on TheSamba.

02-08-2014, 11:13 AM	#5
D13 Registered User Join Date: Feb 2007 Location: Memphis MI Posts: 1,851	Re: Transmission question Same problem and same solution on my 87 700R4. What I did was jack it up and slip a small wooden block under the trans mount ot hold it up, allows swivel socket and long extension to get to it from the side. Also a good time to replace that mount, which makes the whole thing easier. Do watch your fan clearance. __________________ 1987 2 ton 1982 250/TH350 beater in progress Dad's 1981 3/4 L6 3 on tree posi and no options, awaiting restoration or scrapping Plus a mess o' tractors

02-08-2014, 04:03 PM	#6
bigmac73 Senior Member Join Date: Mar 2012 Location: Chesapeake, Va Posts: 1,275	Re: Transmission question i use a 1/4 drive socket and a universal a little tedous but it works with out jacking the tail shaft up __________________ Mike 72 C-10 Cheyenne off frame resto and Upgraded to 4 wheel disk, Tilt, Dakota Digital Dash / Rear slider. 421 SBC / TH350 3000RPM Stall Progression Ignition /Holley 750 DP/3:73 gear Eaton Limited Slip unit / 2 1/2 exhaust glasspacks

02-08-2014, 04:36 PM	#7
1968SWBBigBlock Active Member Join Date: Oct 2006 Location: Ohio Posts: 1,643	Re: Transmission question If you take the time to pull the cross member cut a couple of notch's in the cross member with your dremel tool or some other grinder and you will have access forever. It can be done on the truck just more tedious __________________ 1968 SWB 454 + .040, 490HP x 540 FT pounds of Torque 10-1 Kb Forged pistons, recon rods w/ ARP wave loc bolts 781 heads Ported with 2.19/1.88 SSTvalves Lunati 60204 cam, Micro Trol lifters, Ported Edelbrock Performer Rpm manifold armor coated, Pertronix Triple Strike Ignition Holley 770 Street Avenger carb,Headers armor coated Built by Watson Ruppel Performance in Sarahsville Ohio. Hardshift Tranny Built Turbo 350,TSI 10" 3000 stall 12 Bolt Eaton Posi 4.10 Richmond Gears moser axles 18.5" x 31" Hoosier Pro Street Radials ET Classic 5 Wheels - polished Power Steering, Power Brakes,Disc Brakes,Tach & Gauge Dash, Tilt,Factory Air (gone) Custom Paint & Body Work Special thanks to my wife, my son and my money tree

02-08-2014, 08:28 PM	#8
bigmac73 Senior Member Join Date: Mar 2012 Location: Chesapeake, Va Posts: 1,275	Re: Transmission question also once you do get it out take the time to install a drain plug if there is not one already saves you from a nasty mess __________________ Mike 72 C-10 Cheyenne off frame resto and Upgraded to 4 wheel disk, Tilt, Dakota Digital Dash / Rear slider. 421 SBC / TH350 3000RPM Stall Progression Ignition /Holley 750 DP/3:73 gear Eaton Limited Slip unit / 2 1/2 exhaust glasspacks

02-09-2014, 07:00 AM	#9
Hugh Mongus Registered User Join Date: Jan 2014 Location: Tulsa, OK Posts: 360	Re: Transmission question I have not had a chance to tackle this chore yet. I was trying to figure out why my truck seemed to like to leave me stranded on the side of the road. After installing a new fuel pump, vacuum advance, re-timing it, and exchanging my new carb for another, I finally realized it was the coil. It only took all day to figure this out.



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