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

rhamlin · 06-09-2010, 04:26 PM

On a 68 C-10:

I learned from a post here that I have a un-synchronized transmission.

Was there ever a 4 speed (floor shifted) transmission that bolted to the same clutch assembly that is installed now with the 3 speed I have ?

Is there one I can bold in without having to modify the clutch system ?

How hard it is to convert to Automatic ?

Thanks
Rob

Wrenchbender Ret · 06-09-2010, 06:21 PM

The 3 speed trans. in a 68 should be syncronized in all forward gears. The earlier ones were suncro. in 2nd & 3rd gears. If it grinds when you shift there is something wrong with it. If someone has put an older trans. in it it still should shift to 23 without clashing. You can put a 4 speed in it. If you use the truck 4 speed it will still not be syncro. in the granny gear. A car 4 speed works but a good shifter is expensive & sets way back against the seat. A t-5 5 speed o-drive is good if you don't have a real powerful engine or hot rod it. An automatic takes a lot more modification.

Shyguy · 06-09-2010, 06:28 PM

It is not real hard to convert to an automatic, but it can be a little pricey.

Some things you will need are flex plate, torque converter, automatic cross member, shift linkage, automatic transmission and maybe modify the drive shaft.

I am sure there are more things, but off the top of my head that is what I can think of now. I am sure others will chime in.

The least expensive way would to find a good three speed.

Danny

raycow · 06-09-2010, 11:09 PM

Any 68-up 3 or 4 speed TRUCK transmission will bolt up to your bellhousing and fit your clutch without modification. If you use a car transmission or a 67-earlier truck transmission you will need a spacer ring to take up the difference in bearing retainer diameter. These rings are avaialable from Novak, Advance Adapters, and others. You could also have one made at any machine shop.

Some Muncie 4 speed CAR transmissions will require you to replace the clutch disc only. These are easy to spot because the input shaft will have 26 splines instead of 10.

Installing any automatic will take a lot more work and money. In addition to the parts Shyguy listed, you will also need an automatic radiator, oil cooling lines, kickdown linkage or cable, and a block-mounted starter that matches your flexplate size. You will also have to remove the existing bellhousing crossmember, and those are usually riveted in place.

Ray

06-09-2010, 04:26 PM	#1
rhamlin Registered User Join Date: Feb 2010 Location: Allen Texas Posts: 40	Transmission On a 68 C-10: I learned from a post here that I have a un-synchronized transmission. Was there ever a 4 speed (floor shifted) transmission that bolted to the same clutch assembly that is installed now with the 3 speed I have ? Is there one I can bold in without having to modify the clutch system ? How hard it is to convert to Automatic ? Thanks Rob __________________ Rob Hamlin Last edited by rhamlin; 06-09-2010 at 04:27 PM.

06-09-2010, 06:21 PM	#2
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,204	Re: Transmission The 3 speed trans. in a 68 should be syncronized in all forward gears. The earlier ones were suncro. in 2nd & 3rd gears. If it grinds when you shift there is something wrong with it. If someone has put an older trans. in it it still should shift to 23 without clashing. You can put a 4 speed in it. If you use the truck 4 speed it will still not be syncro. in the granny gear. A car 4 speed works but a good shifter is expensive & sets way back against the seat. A t-5 5 speed o-drive is good if you don't have a real powerful engine or hot rod it. An automatic takes a lot more modification.

06-09-2010, 06:28 PM	#3
Shyguy Junior Member Join Date: Dec 2006 Location: Southeast Missouri Posts: 2,436	Re: Transmission It is not real hard to convert to an automatic, but it can be a little pricey. Some things you will need are flex plate, torque converter, automatic cross member, shift linkage, automatic transmission and maybe modify the drive shaft. I am sure there are more things, but off the top of my head that is what I can think of now. I am sure others will chime in. The least expensive way would to find a good three speed. Danny __________________ '67 Chevy C-20 short stepper - build complete, 454/SM-465. '75 C-30 Single Cab DRW-350 small block/NP-435. '77 GMC-6500 Dump Truck, 427 Tall Deck. '92 GMC K-3500 Duallie, 454/4L80E.

06-09-2010, 11:09 PM	#4
raycow Registered User Join Date: Mar 2003 Location: San Francisco, CA USA Posts: 2,454	Re: Transmission Any 68-up 3 or 4 speed TRUCK transmission will bolt up to your bellhousing and fit your clutch without modification. If you use a car transmission or a 67-earlier truck transmission you will need a spacer ring to take up the difference in bearing retainer diameter. These rings are avaialable from Novak, Advance Adapters, and others. You could also have one made at any machine shop. Some Muncie 4 speed CAR transmissions will require you to replace the clutch disc only. These are easy to spot because the input shaft will have 26 splines instead of 10. Installing any automatic will take a lot more work and money. In addition to the parts Shyguy listed, you will also need an automatic radiator, oil cooling lines, kickdown linkage or cable, and a block-mounted starter that matches your flexplate size. You will also have to remove the existing bellhousing crossmember, and those are usually riveted in place. Ray



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