Hitting a fork in the road.. The transmission road..

[67chevy_hotrod]

1969 Longhorn, 350 with a 268 cam. 4.10s outback and a th400 in between. Right now I'm turnin 2200 rpm at like 50. (31's for rubber). I know it's not crazy but it feels like it is decelerating way to hard for my liking. Now I understand commpression braking, but i have to keep my foot buried in it even to hold her at 25.. I mean it's crazy once I get to 50 and lift my foot it slows down to like 45 almost instantly that's how wound up it is.. Should I look into gvod's? But I also want a 4 speed.. Should I just do the 4 speed,probably a sm465. I might have a line on a newish gvod for cheap too. Gimme your two cents please!

[WorkinLonghorn]

I'm no expert but when you lift your foot at 50 there should be only a slight deceleration felt unless the sprag clutch is broken in the trans or you have some major drag, but that would show up as heat somewhere.

Even with a 4-spd going 60 (2500 RPM) mine will probably take a good 10 seconds to decal to 50 when foot is lifted staying in gear (5500 lbs. with a low compression engine, 50/80 psi f/r tires).

An automatic has a one-way clutch called a "sprag" that allows you to pretty much free-wheel with not much engine braking if I recall correctly. -BA

[hamjet]

Theres alot of drag on those big tires. next time you're doing 50 slip it in nuetral and see if it acts the same. that will tell you if its transmission drag...

[BugzC10]

Have you checked out your rear brakes adjustment? Emergency brake dragging? Something to rule out....

[A1971Blazer]

Originally Posted by 67chevy_hotrod

1969 Longhorn, 350 with a 268 cam. 4.10s outback and a th400 in between. Right now I'm turnin 2200 rpm at like 50. (31's for rubber). I know it's not crazy but it feels like it is decelerating way to hard for my liking. Now I understand commpression braking, but i have to keep my foot buried in it even to hold her at 25.. I mean it's crazy once I get to 50 and lift my foot it slows down to like 45 almost instantly that's how wound up it is.. Should I look into gvod's? But I also want a 4 speed.. Should I just do the 4 speed,probably a sm465. I might have a line on a newish gvod for cheap too. Gimme your two cents please!

have you had your alignment checked?
I don't think you want a 465 manual....they're bulletproof but have a really useless 1st gear and still 1:1 in high gear.... so you won't realize any difference in rpm/speed.......plus they shift like a goat wagon......they're more for a work truck or 4x4.......in my opinion......(I do have one in my off-road rig and I love it for that!)

You might want to look into a 700R4 OD transmission to drop your highway revs...? just my 2¢.....

[Andy4639]

I would rule out all the other stuff first though before spending any money.

Rear & front brakes dragging are e brake. Make sure all is good inside transmission to. Proper wheel alignment all the easy stuff that want cost you anything unless you find something wrong.
Turning those big tires 31" takes a lot of torque, that is why you feel it slowing down as you say.
Another thing have you had the speedometer calibrated for those 31" tires? If not then at 2200RPM you are not doing 50 MPH!
The link is to figure MPH.

http://www.wallaceracing.com/gear-speed.php

[67chevy_hotrod]

In nuetral it has no drag it will roll down hill at 60 and still try to go faster. Park brake is good and so is the actual brakes no dragging and no smell or heat from anything. I did use that speedo calculator and it said 2000 rpm I'm goin 46mph so it's real close. (Someone can check my calculations) hasn't been aligned but it tracks straight as hell. And it is a work truck so that granny low would come in handy when I pull stuff,I just hate having an auto in a big truck... Thanks for the responses

[WorkinLonghorn]

Nice converter Nick, thanks.

Use a New Process 435 Close Ratio like the one that came in mine and other GMC, Ford and Dodge trucks.
With a 4.56 1st gear you shift at 20-25 MPG and 2nd gear comes on perfectly. It's just as stout as the SM 465 and synchronized in 2,3,4.

"Another thing have you had the speedometer calibrated for those 31" tires?"

Remember Andy, 3/4 ton trucks came stock with 16" or 16 1/2" wheels with 7.50 or larger tires so 31" was the norm as far as I know. Mine came with 750x16 and was 31" (now 235/85/16R which is also 31") -BA

[57taskforce]

Those tires shouldn't cause the kind of speed loss your describing. My trucks (both have od however) both have 35s and I don't have that problem at all. If anything I would think the rolling momentum of them would be more inclined to hold speed than shed it compared to smaller tires. Just my thoughts.

[Shaky]

The SM465 has 1:1 4th so it won't help on the top end. If money is no object, you can put the Gear Vendors behind the SM465 and have an 8-speed with overdrive in "8th".

Personally I won't convert another truck from auto to standard or vice versa, but that's just me. The GV on the TH400 is a nice set-up, but pricey.

I have an SM420 in my '67 C20 and get a kick out of the granny 1st. Will likely add the GV someday.

[jdw]

Does it slow down just as fast at other rpm? 3000, 3500. Does it drop fast if you hold it in second and run it to 2200? Where are you making torque with that cam?

[Mr Handy]

I just finished swapping from a th350 to an sm465 and am very happy. It did not save me more than a few rpm because both are 1 to 1 in top gear. The only thing I saved was converter slip.
I am very happy I did the swap for a number of reasons. cost was one, durability was another, and I wanted to shift gears.

The transmission is slow into 3rd, is a little noisy in the low gears, and on the street is a 3 speed. I don't care about any of those things.
I spent $300 on the trans, bell housing, clutch (that I didn't use) 2 flywheels and a set of heads (that went on a friends engine) locally. I bought everything else to do the swap from board member DLTruck1973 for $500 delivered I believe. That included cross member, driveshaft, steering column, high hump, all clutch linkages... and so on. It turned out very nicely. I also had the driveshaft rebuilt and balanced before install which cost something like $150
When all is said and done I have the trans in the truck at around 1K.
My plan down the road is to save up and put a Gear Vendor unit behind it and then it will be a 7speed. You cannot use granny low/over. That combo should be about as stout as it gets.
for reference I currently have 3.07 rear with 28"tires and turn 2200rpm at 60mph.
when I do the GV i plan to swap to 3.42 which should put me at 1900rpm at 60 and 2200 at 70 in OD. Perfect for runnin down the freeway.

[WorkinLonghorn]

Originally Posted by Mr Handy

for reference I currently have 3.07 rear with 28"tires and turn 2200rpm at 60mph.
when I do the GV i plan to swap to 3.42 which should put me at 1900rpm at 60 and 2200 at 70 in OD. Perfect for runnin down the freeway.

Mr Handy, If you run too low RPMs your mileage might suck.

My first '69 was a GMC 1500, 350 4v, with 3.07 gears and 33" tires (and a SM 465). It turned 1875 at 60 MPH and I never got better than 10 MPG. I believe it is better to run ~2300 or so, at least with a small block. My current GMC 2500 turns 2500 at 60 MPH and returns 15 MPG, but I am comparing 2 different trucks with different carbs and ignition set up.

[stsalvage]

1965 3/4 ton use to do the same thing some how some of those 3/4 ton self adjusters don't work.I had one that would tighten up on the passenger side but loosen up my driver side.Found out later my center spring perch bolt where all your springs hook to was bent.To many heave loads.One other thing your back backing plates are not suppose to have any groves in the metal have them welded up grind the well smooth you brake shoes might be hanging up that why they ask you to put grease on your backing plate where the side of the shoe rubs on.

I live in Calif I was told by a few people that is was Illegal to welled on your backing plates by a few shops i had to replace them a guy at Midas muffler said that was bull crap.He said as long as you are fixxing a wearing problem that is happening as normal use its fine But anything on 2 tons or more he said Check with DOT to know the rules or CHP

[RedRoad]

Ive always voted for manual on a working truck. All of mine in the past have been 420s or 465s with the exception of my current burb which was stock with a th350. I left it stock so the wife would not be scared driving it if needed and the fact it is a survivor but since the trans went out I am swapping in a 465. I love the granny low for the off road we do and I would have been hating life if the auto went out in the middle of no where with the wife and kid on board. Ive killed first gear in a 465 once behind a big block hopping over some boulders 100 miles from the nearest town and was able to drive home and STILL put 20K miles on it once I fished out the broken teeth months later.

Ive thought about NV4500 but the few people I know who actually have done the swap seemed to feel it wasnt worth the money. Expensive gear lube, expensive adapters or weak t case options, noisy rebuilds etc.

Back in the day a buddy had a CR 5 speed out of a GMC and a brownie box with overdrive and that thing was a BEAST. It would haul anything and the brownie helped pull a few more mpg out of the big block. He was into it around $2K but in the mid 80s that was a ton of cash.

My vote is to dump the auto and start rowin'!!!