O.D. vs. O.D.

[SCOTI]

OK. I'm tired of screwing around w/the mickey mouse 3spd stuff. One of the things I hate about my 68 is the fact that I'm spinning 3000rpms @ 65mph, so I'm thinking about an O.D. tranmission.

Since the truck has a 6cyl., I think the automatics parasitic (sp?) drivetrain loss would really kill what little power it has (compared to a standard). It's current 6cyl/3spd has no problems pulling my 18ft trailer..... but what will an automatic be like??

I was thinking a T350 was the easy way out. But, if I'm going to swap to an automatic, I figure it's about the same amount of work so I might as well spend more up front & get a 700R4.

The other side of the coin is once I start swapping to an auto, I have other things that need to be considered, like: locating the correct flexplate, starter (if necessary), trans crossmember & mount, re-routing the exhaust, column related linkage (I already have a van tilt), lose the extra pedal, possible driveshaft mods, + other stuff I'm probably forgetting.

Orrr...... the alternative is an aftermarket 5/6spd. I would have to update the clutch/p.plate to fine spline & poke a hole in the floor & possibly contend w/the same d.shaft mods as the automatic, but what else am I not considering???

I must admit my fondness for banging gears & that's affecting my decisions...... what would you do??

[bigvinnie]

I'd live with the current engine/trans combo til I had the funds to convert to a smallblock/700r4 combo.... it's so easy in these trucks, and not overly expensive if you take your time and look around...

I was at the same crossroads when I had a 6 cyl and manual column shift trans...bought an entire parts truck for $300 that had everything I needed (except the 700r4), swapped it all over and never looked back....

[70short/step]

Another thing to consider if going with an automatic is your rear end gearing. Mine has a 4:11 posi with a 327/350 setup. While it is a blast around tound it sucks on the freeway turning about 4000 rpm at 75 mph.

[SCOTI]

Bigvinnie, although I agree that the small block upgrade is the way to go eventually, right now, my 6cyl leaks some oil but runs just fine & pulls the trailer w/no probs so it's hard to spend for another powerplant.

The biggest problem is the 3spd (linkage) & high freeway rpms killing the milage, not to mention the extra noise. The small block swap means even more parts needed vs. just swapping the current trans.

BTW, it's got a 29" tire & 3.73's.

[bigvinnie]

I hear ya, money is always a consideration, but if you want an overdrive trans to bring your hiway rpms down, I'm not sure the 6 cyl is up to the task... is it a 250 or a 292...???

A stock 250 will be a dog with an auto, so looks like you would be looking at a 5 speed manual gearbox from a camaro, I think that's what some guys are running, and since it's a six, the trans should be able to handle it, although I'm not sure about towing...

check out this recent thread on the 5 speed...
http://67-72chevytrucks.com/vboard/s...threadid=85865

a 6 with a 5 speed would be cool and unique, and when you swap in a smallblock, you could put it in the 6 cyl position and not have too many headaches getting it to work.

[SCOTI]

It's a 250 that's been upgraded w/HEI. It's not just the $$, because I'll spend $$ if it's going to go far, but right now I have no place to perform a motor & tranny swap (nor do I have the time required to do a complete swap working 60hr weeks). A trans is a little less complicated @ this time.

I've been looking @ a tremec style 5spd that has a forward mount for the shifter & works w/the existing clutch set-up (not hydraulics).

[jjk3]

Stay with the straight sixe, and swap to a T-5 tranny. You can go to www.inliners.org and we have tons of threads and articles on this swap. I'm in the EXACT same boat you are in. I wanted a T-5 from a mid to late '80s Camaro or Firebird with a 305. Those trannies have a 0.63 overdrive with a 2.95 first gear. They really seem to be the best swap. The only problem is the shifter is further back than the truck or van T-5s. You can actually swap the tailshaft from a truck T-5 onto a Camaro T-5, which will give you the right shifter location. The only problem being you will have to modify the tranny for the difference in speedo gear placement. Right now I'm thinking about a T-5 from a '85-'86 Minivan with a 4.3 V6. Their gears are (1-5) 3.50, 2.14, 1.39, 1.00. 0.72 Also, the Camaro/Firebird T-5s will usually be higher in price. Hope this helps. John

Go to www.inliners.org, look on the bar at the left. Go to "Tech tips" the click on the "T-5 tranny page". That will give you some good links. Also do some searches on that board for previous threads on the topic.

[stelth2002]

Im in love with my 6. It willtake me anywhere i want to go. As far as the cruisin issue. Ive been there. I recently aquirced an overdrive manual. Its out of a early 80 chevy with a diesel. It shoudl handle the torque and it looks almost exactly like a 3 speed.

[SCOTI]

I'm a V8 guy, but if it works.... hey, it works. I'm suprised how 'peppy' my 6cyl/3spd & 3.73's feels vs. my 74's 350/350 & 3.42's.

[1969 GMC]

you could always locate a 3.08 geared rearend, that would be an easier swap than a tranny. it wouldn't eliminate the linkage slop, though.

[SCOTI]

I would bet 3.08's would kill the towing ability of the 6cyl as well.... but, still a good idea.

[73stepside]

you wouldn't want to tow really heavy items with an auto overdrive tranny unless you build it for hauling really heavy loads in overdrive, which means money. towing is the worst enemy of overdrive trannies

[SWINGSAX68]

I6 are good little motors.....if this v8 I got goes out I'm thinking 292 I6 as a replacement....I hope I don't have to worry about that for a good while though.

[SCOTI]

In my research I've learned that when towing w/an automatic O.D. tranny you simply leave it in drive & it's just like any other auto trans. When your not towing, take advantage of the O.D.

[N2TRUX]

Originally posted by SCOTI
In my research I've learned that when towing w/an automatic O.D. tranny you simply leave it in drive & it's just like any other auto trans. When your not towing, take advantage of the O.D.

Scoti took the words out of my mouth. You can tow with a 700r4 all day long if you drop in into drive.

I was told by a couple of "supposed" transmission experts that you could shift to OD while towing once you got up to a steady cruise speed. WRONG!

After burning up a 700r4 I invested in a temp gauge. It was amazing how quick the temp would climb when I shifted to OD. When I left it in drive the temp stayed normal all day long. I towed my 84 Z-28 from Houston, TX to Springfield, MO. and back without any trouble at all...

BTW- Scoti I think you need a long stick four speed. That would work perfect with your farm truck theme...:p

[Huck]

My 72 has a 5 speed out of a 96 1/2 ton truck. 5th gives me 65mph @2200rpm. 307 rear. Crate 350, HEI, Hookers, Edelbrock carb and intake.

Issues for install:
1- convert to hydralic clutch-add pedal-cut firewall
2- modify drive shaft length
3- convert to high hump and cut hole for shifter
4- use auto crossmember for rear trans support
5- shim pdb bkt for hyd master cylinder placement
6- no speedo due to electronic pickup on newer trans - can buy converter for like $300.+ but not willing--drive by tach
7- need to downshift for hauling up hills

Was getting 20-21mpg till I converted to edelbrock 2101 intake and headers---mpg dropped 3mpg due to loss of low end torque. Will switch back to stock intake to see what happens.
Huck

[SCOTI]

Well I had a chance to inspect everything & the trans is indeed wasted: The output shaft bearing 'race' is completely worn through, there were several broken 'small' needle bearings (from somewhere around the input shaft area) & there was alot of excess shavings/scrap metal floating around (most likely the remains of the cage/collar that held the rear bearings).

Weird thing is, I 'wiggled' the output shaft before while checking for play & it wasn't as bad as what I found last night .

[gmtruck71]

355 c.i. 700r4 3.73 posi. sweet for all around streetability highway crusing, and occasionial trips down the ol 1320. Mandatory trans cooler and no tow in OD


I have had all combinations I6s to 502s, powerglides to 700r4s and 2:70s to 5:13s

[FRENCHBLUE72]

What about useing a gear vendor's overdrive unit I know they are $$$$ but would pay off in the long run and you could still bang gear's and transfer it over when /if you ever wanted to put in a small block...

[SCOTI]

I considered a GV unit but the price is scary for a beater. Since the 3spd is trash, I'll swap to a 700R4. The 3.06 1st gear should help get it going vs. a 2.52 in a T350 & the O.D will come in handy when not pulling a loaded trailer.

Thanks for all the responses!