2004r Tranny

[daveo68]

Anyone know how much would be involved in changing a Saginaw three speed to a TH2004r transmission? I injured my leg last year and had surgery and it looks like no more clutches. I've searched everywhere for this topic, but mainly found TH350 swaps. Also my truck is LWB,with 3.73 gears. I also plan on using floor shift. Any answers would be truly appreciated.
Thanks,
Dave

[hugger6933]

The 200r4 is the same lenght as the th350 . It will also carry the smae driveshft yoke. the difference comes into play at the crossmember. It is on the very rear of the case as the th350 has the crossmember 6to 9 inches from the end of the tailshft. You will need to slide back the crossmember and drill new holes into the frame to bolt up . Also the 200R4 does not have a removeable rear housing so you need to make sure before installation that everything is there to make the speedo read correctly. Don't get me wrong you can change that stuff with it installed ,it would be easier with it on the bench so you can look in to the speedo hole so as to see the color of the speedo drive gear. Also , you will need some kind of lockup switch for the converter. Summit and Jeg's both carry those as well as any trans shop. It is very similar to the set up used on early s-10's with a vaccum switch that mounted on the fender and a switch the goes next to the brake lamp switch. Jim

[stich626]

the 200r4 bolts in place of a th350..
so the install that you've read on th350 will be mostly the same..
the 200r4 uses a t.v cable and a lock up converter.
the t.v. cable is what controls the trans. I'd get a throttle mount that bolts to the engine off a 200r4 doner car (monty carlo 85-88) or aftermarket..
the lock up is a few wires and painless, mad engineering,b&m,tci make kits.
floor shifter, any g.m. shift from a g body (monty and clones) or 85-92 f body (camaro/ta) or aftermarket, plan on having to make the handle longer..
or lockar might have one with a long handle..

[VetteVet]

There is plenty of information on converting to an automatic usually a th350 from a standard shift but if you substitute the 2004r for the th350 and use the information in this link I think you will find it valuable.
http://67-72chevytrucks.com/vboard/s...d.php?t=232486

here is a link for the swap from standard to auto.

http://67-72chevytrucks.com/vboard/s...d.php?t=414133

copy and paste the link into google if it doesn't link directly.

[daveo68]

Thanks for your input

[Twisted78SS]

Since I just picked up a 2004r at the swap meet this weekend, I was researching some info and found the speedo chart below. As mentioned, you will want to verify what your speedo gear is and change as needed. This chart is from http://www.montess.org/index.html.

Another site with Speedo info - http://www.tciauto.com/Products/Tech...eedo_gears.asp


Speedometer Gear Chart 200-4R

After changing rear end gears or tire diameter you will likely need to swap one or both speedometer gears to keep the speedometer reading correct. To determine which speedometer gears are needed, you need to know two things, tire diameter and rear end gear ratio. If you plug those numbers in below and click the Calculate button, it will calculate the the ratio the speedometer gears need to be for the speedometer to read correct:

Rear end gear ratio (ex: 3.73 or 4.10)
Tire diameter in inches:

Once you know the ratio you need, look through the chart below to see which combination of speedometer gears is the closest match. The chart is arranged by ratio from low to high.

The second row (in bold) is the stock gear combination for a 85-88 Monte Carlo SS with stock 3.73 rear gears and stock tires, which are approx 26" diameter. If you plug those numbers in the calculator, it says a .345 ratio is needed. However, I confirmed with several other 1985-88 Monte SS owners that the 10/30 speedo gears are stock. If you know why GM chose to use the 10/30 gears instead of the 10/29 combination, let me know!

OE GM# Drive Gear Driven Gear OE GM# Ratio
8639906 10 31 403417 0.323
8639906 10 30 561035 0.333
8639906 10 29 403999 0.345
8634965 11 31 403417 0.355
8639906 10 28 416765 0.357
8634965 11 30 561035 0.367
8639906 10 27 410731 0.370
8634965 11 29 403999 0.379
8639906 10 26 25502669 0.385
8634935 12 31 403417 0.387
8634965 11 28 416765 0.393
8634935 12 30 561035 0.400
8634965 11 27 410731 0.407
8634935 12 29 403999 0.414
8634934 13 31 403417 0.419
8634965 11 26 25502669 0.423
8634935 12 28 416765 0.429
8634934 13 30 561035 0.433
8634935 12 27 410731 0.444
8634934 13 29 403999 0.448
8634935 12 26 25502669 0.462
8634934 13 28 416765 0.464
8634934 13 27 410731 0.481
8634934 13 26 25502669 0.500
Each .007 of ratio equals about 1 mph of error at 60 mph. If you choose with a lower ratio (numerically) pair of speedometer gears than required, the speedometer will read less than actual speed, and vice-versa.

Since the ratio you need will likely fall between two of the available gear combos, most people choose the higher ratio combo, so the speedometer reads a little faster than actual speed.