2004R trans with 3.08 axle

[MikeB]

I'm looking at replacing my 69 C-10's TH350 with a 2004R. A guy at Phoenix Transmission said the highway RPMs would be too low in OD/lock-up with my 3.08 gears. Is anyone here running that combo? The engine is a mild 355. Tire height is 28.5".

I'm in the process of installing an Auburn posi, so now would be a good time to get 3.42 gears if they would work better. Only problem is I'd be committed to buying the OD trans once I installed those gears!

The budget option is to keep the TH350 and go with 2.76 gears. That would drop highway RPMs by 10%, but low gear might be a little too tall for some situations.

[cdowns]

you'd b better with 373 and the overdrive

[Longhorn Man]

3.07 with the overdrive would kill MPG. I would go with the 3.73

[windmill]

i have that setup in my truck so far does good. but just got it going

[wwotr]

Originally Posted by MikeB

I'm looking at replacing my 69 C-10's TH350 with a 2004R. A guy at Phoenix Transmission said the highway RPMs would be too low in OD/lock-up with my 3.08 gears. Is anyone here running that combo? The engine is a mild 355. Tire height is 28.5".

I'm in the process of installing an Auburn posi, so now would be a good time to get 3.42 gears if they would work better. Only problem is I'd be committed to buying the OD trans once I installed those gears!

The budget option is to keep the TH350 and go with 2.76 gears. That would drop highway RPMs by 10%, but low gear might be a little too tall for some situations.

I'll be watching this Thread as I've got a 72 GMC Fleetside with a 350 and a Turbo 350 running (what I believe to be) 3:73 Gears and wanted to switch ovewr to the 2004R. I hear its a direct swap/bolt in?

Roger
"RUDE TOY"

[MikeB]

Roger -- The 2004R is the same length as a TH350 w/ 6" tailshaft, so you don't have to mess with the trans cross member or get the driveshaft shortened. You will need a new TV cable and specific brackets for your carb. I didn't ask about trans cooling lines to the radiator, but I suspect they will be different. Phoenix Transmissions and Bow Tie Overdrives can tell you exactly what you need.

The OD ratio is .67 which will drop your highway RPMs by 33% -- and another 200-300 RPM lower when the T/C locks up.

[Longhorn Man]

you'll have to move the crossmember to the TH400 position
trans cooler lines are in the same location
The yoke is the same as a TH350, as is the shaft length as indicated above.
do some seriouse research on TV cable setup, www.bowtieoverdrive.com is the best place to lean... and they have a great product too.
Don't forget a lockup controler too.

[wwotr]

DAMN GUYS!

Thanks for the detailed info!

Roger
"RATIKLE"

[cparman]

I went to a site that has an RPM calculator, and here is what I did
255/70r15 tire is 29" tall
3.08 gear
.67 OD
should run 1500 at 65 mph.
Now with that said, I would like that number on the highway. BUT, around town you might need to run it in 3rd gear. 3.42 would be my choice for a rear end gear. I have the above with a 3.73 in my truck, and FOR ME it seems the rpms are a bit high at 65-70. My trans is a 700r4

[c10addict]

I am running a 700r4 with a 3:42 and probably a 28" tire.. 1800 at 60/65.. Love it!!!

[chevy_mike]

My '98 C1500 has 3.08 and a 4L60E (same ratios as a 700R4) and on the highway at 65+ it is great. Around town below 55, it sucks to be in 4th gear. Barely off idle but if you want to speed up, you have to get it to kick down to 3rd. I find around town, I just leave it in 3rd and never use overdrive. I save that for the freeway.

3.42's are very ideal, even 3.73's are a good choice. With a 200R4, since the first gear is not as deep as a 700R4 and the overdrive is a little better, I would rather have 4.11's then 3.08's. I think you will find 4.11's would give you better mileage as engines don't like to be lugged.

My .02 worth.

[Truck Dr.]

Originally Posted by cparman

I went to a site that has an RPM calculator, and here is what I did
255/70r15 tire is 29" tall
3.08 gear
.67 OD

around town you might need to run it in 3rd gear. 3.42 would be my choice for a rear end gear.

^X2, this would be the ideal setup with 3.42 and the rest as above, and as mentioned watch the TV setup make absolute that it's correct, otherwise you'll possibly end up with a junk tranny, as for the town driving, just have a lockout or override switch so it won't go into 4th.

Dave



Dave

[wwotr]

Originally Posted by cparman

I went to a site that has an RPM calculator, and here is what I did
255/70r15 tire is 29" tall
3.08 gear
.67 OD
should run 1500 at 65 mph.
Now with that said, I would like that number on the highway. BUT, around town you might need to run it in 3rd gear. 3.42 would be my choice for a rear end gear. I have the above with a 3.73 in my truck, and FOR ME it seems the rpms are a bit high at 65-70. My trans is a 700r4

Yea at 55-60 MPH I'm taching about 2300 RPM's.
I'd LOVE to see it at around 1600 RPM, and I betcha my Gas Mileage would improve too!

Roger
"RATIKLE"

[chevy_mike]

Originally Posted by wwotr

Yea at 55-60 MPH I'm taching about 2300 RPM's.
I'd LOVE to see it at around 1600 RPM, and I betcha my Gas Mileage would improve too!

Roger
"RATIKLE"

Not necessarily. It all depends on your setup, everything from the carb, cam, converter, etc. If you are lugging the engine, you can actually use more fuel because you end up using the throttle more to maintain speed because you are out of the power band. Most engines are most efficient when kept in the power band. Below or above it, you will typically use more fuel.

[69GMCLonghorn]

Originally Posted by Longhorn Man

you'll have to move the crossmember to the TH400 position
trans cooler lines are in the same location
The yoke is the same as a TH350, as is the shaft length as indicated above.
do some seriouse research on TV cable setup, www.bowtieoverdrive.com is the best place to lean... and they have a great product too.
Don't forget a lockup controler too.

A little off subject, but you are right, Bow Tie Overdrives is really great! They are about a 2 hour drive from my place (half way to VEGAS!). They do really clean work and really know their GM automatics. My buddy had them drop a 700R4 in his '65 Nova with a built 383. The install was clean as could be, but the tranny they installed shifted like mush... He found someone else that tweaked it, but for the money he spent, you'd of thought they could have done this for him.

[Wrenchbender Ret]

I run 3.08 gears with a 700-r4. in a 70 stepside with stock 350 engine & 28 in. tires. 235-75.15. Love it. Pulls good & runs quiet. I keep it in 3rd around town to avoid excess shifting. I get 18 MPG in combination city/high.
There is one long hill on the interstate. The only time it will downshift is a strong headwind & the A/C on. Ive driven late model trucks on this hill that downshift every time.

[69GMCLonghorn]

Originally Posted by Wrenchbender Ret

I run 3.08 gears with a 700-r4. in a 70 stepside with stock 350 engine & 28 in. tires. 235-75.15. Love it. Pulls good & runs quiet. I keep it in 3rd around town to avoid excess shifting. I get 18 MPG in combination city/high.
There is one long hill on the interstate. The only time it will downshift is a strong headwind & the A/C on. Ive driven late model trucks on this hill that downshift every time.

I have to agree with you... I can't imagine not being able to pull this gear combo "most" of the time. And as you said, it push comes to shove, pull it down into 3rd, big deal... That's what it's there for. Now if you're going with monster tires, then of course, I'd drop that down a couple notches...

[wwotr]

Originally Posted by chevy_mike

Not necessarily. It all depends on your setup, everything from the carb, cam, converter, etc. If you are lugging the engine, you can actually use more fuel because you end up using the throttle more to maintain speed because you are out of the power band. Most engines are most efficient when kept in the power band. Below or above it, you will typically use more fuel.

BUZZ KILL!

Roger
"RATIKLE"

[MikeB]

I forgot how great this site is. Incredible amount of info!

Some more questions:

Will the T/C lock up in gears other than 4th?

If you're cruising down the highway and step on the throttle a little, will the T/C unlock?

[Wrenchbender Ret]

The TC lockup depends on what system you use. I get the vacuum switch off a late 80's van & hook it to ported vacuum. I use a pressure switch on the 4th gear pressure outlet. It only locks up in 4th gear with cruising throttle.

[leddzepp]

Originally Posted by Wrenchbender Ret

I run 3.08 gears with a 700-r4. in a 70 stepside with stock 350 engine & 28 in. tires. 235-75.15. Love it. Pulls good & runs quiet. I keep it in 3rd around town to avoid excess shifting. I get 18 MPG in combination city/high.
There is one long hill on the interstate. The only time it will downshift is a strong headwind & the A/C on. Ive driven late model trucks on this hill that downshift every time.

This is close to what I have in my SWB. 700R4 trans, 3.07 gears, 275 60 R15 tires, 350 with a Carter 500 CFM carb. 2200 RPM at 70 MPH, get about 17 MPG (freeway) I also keep it in 3rd around town.

[69GMCLonghorn]

I understand the whole deal about keeping it in the torque band. But what you have to realize is there is a torque "curve" associated with the engine. Maybe your peak torque is at 2600 RPM for example. That doesn't mean you have to run it at 2600 on the freeway in order to hold your speed. You just need enough to overcome weight, friction, wind, etc. Maybe there is enough at 1800 RPM in some engines. So why not run it there, and just downshift if it loads up... It's a matter of knowing your engine.

['72customdeluxe]

Well, to use your example as a reference, you won't be running 1800 rpm even, with 3.08's of course. Not at or below 70 atleast. Go 3.42's for mileage, 3.73+ for fun

[MikeB]

Originally Posted by 69GMCLonghorn

I understand the whole deal about keeping it in the torque band. But what you have to realize is there is a torque "curve" associated with the engine. Maybe your peak torque is at 2600 RPM for example. That doesn't mean you have to run it at 2600 on the freeway in order to hold your speed. You just need enough to overcome weight, friction, wind, etc. Maybe there is enough at 1800 RPM in some engines. So why not run it there, and just downshift if it loads up... It's a matter of knowing your engine.

My engine has a small cam with decent heads, so makes enough torque to cruise at 1500-1700 RPM.

In any case, I put it all back together with the 3.08 gears. No immediate pressure to spend the bucks on a 2004R, but will probably do it some day. And if my gearing is too tall, it's only a 10-12 hour job (for me on my back) to install 3.42 gears.

I really appreciate all your comments.

[chevydog66]

I have the 200-4r installed in my 72 GMC longbed, with a 355 sbc, .444 lift cam 1.94 int. valves, 600cfm Holley, nothing great, with the 3.07 rear gear and all is well. I bought all the parts needed from Bowtie Overdrives. I have 20" wheels, probably about 23" tire height. 65 mph is about 1900rpm. Good enough for me. I don't know what kind of mpg I am getting though.