T-5 or T-56 Manual Trans swap

[Ronno6]

I have already replaced the TH350 with a Muncie M21 4-speed in my '84 C10.
But, I fear that mileage is gonna suck with 3.73 rear ratio.
I have always wanted a 5 or 6 speed with OD, but they are not cheap these days.
Gonna have to handle about 400HP

What recommendations do y'all have?
Is the shifter location going to be a problem?

Any other thoughts, please.

 

[mcarlo86]

What gas mileage would you be expecting to "suck?" My '68 C10 with a mild 327 and SM465 4 speed with 3.73's probably gets 12-14 on the highway, but I'm not daily driving it, so the fun factor out weighs gas mileage. I quit worrying about it and just drive it. It's more enjoyable to mash the pedal when you aren't thinking about gas mileage. haha

You could consider swapping to 3.42's and that would help a little bit without loosing too much fun factor.

 

[Bextreme04]

I would think if you are not going to be doing "truck" things with it like towing and hauling tons of rock in the bed, you can probably get away with something like an NV3500 5-speed. Guys that do heavy towing and pull lots of weight go to the NV4500 and they are getting expensive and hard to find.

 

[mcarlo86]

What do you have for a clutch setup currently? One thing to consider with the NV3500 is that you will need to have a hydraulic clutch. I think Advance Adapters sells a mechanical clutch bellhousing for NV4500's.

 

[Slybeanx]

I have already replaced the TH350 with a Muncie M21 4-speed in my '84 C10.
But, I fear that mileage is gonna suck with 3.73 rear ratio.
I have always wanted a 5 or 6 speed with OD, but they are not cheap these days.
Gonna have to handle about 400HP

What recommendations do y'all have?
Is the shifter location going to be a problem?

Any other thoughts, please.

Just another thought, the AR5 can handle the hp and I bought one for 250$ at my junkyard.

 

[Ronno6]

What gas mileage would you be expecting to "suck?" My '68 C10 with a mild 327 and SM465 4 speed with 3.73's probably gets 12-14 on the highway, but I'm not daily driving it, so the fun factor out weighs gas mileage. I quit worrying about it and just drive it. It's more enjoyable to mash the pedal when you aren't thinking about gas mileage. haha

You could consider swapping to 3.42's and that would help a little bit without loosing too much fun factor.

That has been my philosophy. I'm afraid I'll see sub 10mpg, but really have no basis for that.
Truck originally has 3.08 open diff, and I installed 3.73 posi

 

[Ronno6]

I would think if you are not going to be doing "truck" things with it like towing and hauling tons of rock in the bed, you can probably get away with something like an NV3500 5-speed. Guys that do heavy towing and pull lots of weight go to the NV4500 and they are getting expensive and hard to find.

Nope. No "truck" things,,,just toolin' around, but may need to do some highway driving....
I had heard thet NV trannys are not too good for quick shifts.....

 

[Ronno6]

What do you have for a clutch setup currently? One thing to consider with the NV3500 is that you will need to have a hydraulic clutch. I think Advance Adapters sells a mechanical clutch bellhousing for NV4500's.

Clutch is mechanical linkage, but converting to hyd would not be all that difficult....

 

[Ronno6]

Just another thought, the AR5 can handle the hp and I bought one for 250$ at my junkyard.

Not up on the AR5. Will need to research......Thanks.

AR5 has way too deep 1st gear, at 3.75 or 3.95. Makes 1st gear useless....and turns
it onto a wide ratio 4 speed.........

Tremec TKX may be the ticket, but probably gonna be pricey....

 

[bucket]

T56. Hands down.

 

[AuroraGirl]

That has been my philosophy. I'm afraid I'll see sub 10mpg, but really have no basis for that.
Truck originally has 3.08 open diff, and I installed 3.73 posi

How exactly did you put a m21 in a truck? I have one laying on a shelf from a nova I thought it was worthless for anything I can do with it. What’s the benefits of it

 

[Ronno6]

How exactly did you put a m21 in a truck? I have one laying on a shelf from a nova I thought it was worthless for anything I can do with it. What’s the benefits of it

I was in my heyday in the 60's and 70's, when the close range 4 speed was the way to go fast....
Never really left that behind. Benefits are purely subjective.
Poppin' an M21 into the C10 was no biggie...remove the TH350, change flywheel, install pilot bearing, clutch & PP, bell housing, and fork/TO bearing, then bolt up the tranny, cut holes in the floor for the shifter (and clutch rod) and install the Hurst. that was the easy part....then remove the steering column to remove the auto pedal assy and install the clutch and brake pedals.....a real pain in the butt....not to mention that the pedal assy was not plentiful and was pretty expensive. Add the bell crank. ball stud and mounting tab, return spring. and connect linkage and adjust. I haven't worked on the correct speedo gear yet.... Driveshaft had to be a tad longer as I recall.

 

[Ronno6]

T56. Hands down.

I had one years ago which I had planned to install into a '79 Z28, but other stuff got in the way and I sold it.

It seemed like a good idea at the time........

 

[AuroraGirl]

So is an m21 more “street able” than a sm465 and obviously an extra gear than the trans the lighter manuals came ?

Ehat kind of mpg ? Is it stil able to do lighter duty truck stuff or too anemic?

 

[Ronno6]

So is an m21 more “street able” than a sm465 and obviously an extra gear than the trans the lighter manuals came ?

Ehat kind of mpg ? Is it stil able to do lighter duty truck stuff or too anemic?

I would say the M-21 could handle everything except heavy towing.
The 3.73 will ease the strain on the tranny anyway.
they were in Verres et al back in the day and can handle the HP and torque, and, as the C10 is much lighter in the rear, I would have no problem with hauling a bedful...... but, no sand and gravel, cus that would mess up the paint and wood floor.....