installing factory 4 speed manual in 3 on the tree truck

[no_rice]

so...

i have the opportunity to to get a factory 4 speed for a very good price. with everything i need to put it in my truck (70 gmc 2wd currently with 350th auto, but originally 3 on the tree truck)

the clutch pedal and the main rod connected to that are still in my truck, and the way this came about is i just picked up a matching green smooth, manual on the floor column for my truck. a friend saw that and asked if i need the a trans as well... i was intending to just put a ratchet shifter on the floor for now until(already bought the thing a couple months ago damnit!) i decided what trans to put in(6 speed was eventual hope, but money will keep that at bay for some time) the reason i was going to put the manual column in now, was because im installing my power steering hopefully soon and figured i may as well get the column i want in at the same time and get rid of the random automatic blue one installed now.

all that being said. has anyone ACTUALLY tried to install a manual 4 speed in a low hump floor without changing to a high hump?

i may be able to get my hands on this high hump(out of the truck i just took this column out of). small hole chopped for a auto on the floor ratchet shifter but patchable.


is the spot where that shift boot is up front, where a factory 4 speed would come out(i think so)? i have yet to see this trans that i may get, and havent been in a factory 4 speed truck of this body style.

with what i assume is some pretty long legged gears in the rear of my truck, and 22's on the back. it cruises pretty decent down the interstate even at 80mph. no tach currently so i dont know what rpms im running, but it is not screaming and has throttle left. the 4 speed would have even a bit longer legs normally then an old 3 speed auto.

the woman and i just put about 150 miles on it yesterday with alot at 70-80 mph and also plenty of downtown traffic driving, and got 16.4 mpg(with an old leaky out of whack in need of rebuild quadrajet!)

also, i think the cross member should work...?! but are the driveshafts usually different? (its a 2 piece)

thanks for any info.

[no_rice]

Ooookay...
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[SS Tim]

There are a number of variables at play here.
To start:
Was you truck originally a V-8 or an I-6?
Is the original manual transmission crossmember still there or did it get cut out?
The high hump pictured looks to be the factory location for a V-8/four-speed. On an I-6 it sits about 3 1/2" further back with the boot sitting flat on the hump.
The automatic rear crossmember would not be used with the four-speed in a stock installation IIRC only the car four-speeds have a rear mount that can be adapted to an auto crossmember.

[rsavage]

The truck 4 speed's final drive ratio is 1:1 just like your 3 speed so it will not reduce your rpms. It is basically a 3 speed with a granny gear 1st that is rarely used in normal driving. It does not have a crossmember that nounts to the trasmission. There is a crossmember for the bell housing with a mount on each side of the housing to the crossmember. The trans hangs off the cast iron bellhousing.

[no_rice]

ill have to look at the spid again(been awhile) but im fairly sure it started as v8 3 on the tree... it doesnt look like to me that the trans cross member has ever been messed with from what i remember. i think it still had what looked like the original rivets in it.

ive been trying to find some pics of the 4 speed mounting to no avail so far. and i do not currently know if this 4 speed im looking into is out of a v8 or I6 motor... so the shifter could be either place.

i suppose if i do this i will have to find a different cross member then also... ugh...

[no_rice]

by the way, i appreciate the input!

[SS Tim]

It pretty easy to determine if a truck is V-8 or I-6 originally.
A V-8 VIN will start CE and an I-6 will start CS.

The manual trans crossmember is pretty easy to spot.
It is mounted at the rear of the engine and supports the bellhousing on two mounts. The trans is bolt to the bellhousing without additional support to the rear. There is no rear trans crossmember on a manual truck. See picture below.

The transmission shifter is due to the I-6 bellousing being mounted about 3 1/2 inches further back on the frame than the V-8 is. So the shifter position is due to driveline relative to the cab not a different transmission.

If you are having trouble a good place to start is with the factory service and overhaul manuals. They can be downloaded at this link.
http://67-72chevytrucks.com/vboard/s...d.php?t=558016

[WIDESIDE72]

IMO I see nothing to gain by swapping a 4 spd into an auto trans truck, unless you need the granny low 1st gear for towing. save your time and money toward an overdrive of some sort, auto or manual.
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[no_rice]

the only thing to gain, would be the manual trans... which i prefer over auto's. hell i probably would have left the 3 on the tree for awhile if it had still been in the truck when i got it! although ive never driven one...

honestly my gearing is fine. actually i could gear the rear lower a bit for some more oomph.

but yes, the long term(read years) hope was to put a 5 or 6 speed in it... and steeper rear gears, that being said, is there a 5 speed(mechanical clutch?) that swaps in reasonably well into our trucks? it seems that most use hydraulic. i roughly know what it takes to swap in a 6 speed. a friend swapped one into his 66 caprice, and the basic dilemmas would be similar.

[Shyguy]

Many people seem to not like the SM-420s or SM-465s, but I for one like them better than a standard 3 speed because they are heavier duty and have the super low 1st gear.

Either of the transmissions with the right gearing in the rearend and tire size will give as good economy as an automatic without over drive.

I like to be able to use the low gear when I am using my trucks around the farm or pulling boats out of the water.

The latest truck I have bought is a '75 C-30 with a NP-435 with the low first gear.

However I do like an automatic for long trips and heavy traffic driving.

[SS Tim]

Really need to know where you are starting from. Is the manual crossmember still there? If not are you willing to reinstall one and all the related parts? If not then you need to look to a rear support type that will adapt to your auto trans crossmember. If you have a working auto just leave it in until you decide on a final trans and do it once. The auto column can easily be painted to make it less offensive to you.

[no_rice]

im sure there is no crossmember up front on my truck. just what i assumed was the original rear mounted crossmember on the tail of the current automatic(that i thought was leftover from the previously removed 3 on the tree trans since the cross member appears to have been a factory part...?!)

i wouldnt have a problem installing the forward crossmember and parts to put the 4 speed in, or changing the hump. none of it would be to difficult. maybe getting some of the small linkage pieces mounted up right, but that just takes some thought and searching.

most of our cars are manuals, makes them more fun to drive and in the case of these cars(saturn sl1's) also much more fuel efficient. id also prefer if my duramax had a manual in it, but apparently in 08 that was not an available option anyway.

but normally we arent in our cars. most days rain/snow/or shine, we ride some of our motorcycles, way more fun and much more mpg, so shifting is second nature to me. autos are the abnormal anymore.

as for waiting to do it once, that is normally my style. but that may also be YEARS before i manage to swap in a 5 or 6 speed and new rear gears. atleast a factory 4 speed for the most part is a bolt in process and fairly inexpensive. i mean, i'll be into the trans, clutch, bellhousing(possiably all or most of the linkage) and all for less then a couple hundred. so id still need a trans mount and some small miscellaneous things.

regardless i will swap out the column when i swap in the powersteering, and if an auto stays for awhile i will just bolt in the floor shifter i already bought and run that!

[FL71C10]

I don't think the automatic would have fit if the old manual trans cross member was in there. Not positive though.

I know you already have the 4 speed lined up, but you can also put a five speed from an older s-10 in there using the manual trans bellhousing and a input shaft spacer. There are some threads on here about that.

That would give you the overdrive.

Looks like a nice truck either way.

[no_rice]

Originally Posted by FL71C10

I don't think the automatic would have fit if the old manual trans cross member was in there. Not positive though.

I know you already have the 4 speed lined up, but you can also put a five speed from an older s-10 in there using the manual trans bellhousing and a input shaft spacer. There are some threads on here about that.

That would give you the overdrive.

Looks like a nice truck either way.

really? heck older s10's are a dime a dozen, that wouldnt be to bad at all. i do wonder about them holding up to much of a motor though? would be alot less expensive then the 6spd thats for sure. but with the 5spd overdrive i could lower the gearing in the rear to get some more oomp.

ill have to try my luck and do some searching and see if i can find a thread on it.

thanks