GHOSTOWLGRID

Having a bit of trouble finding this. I see mostly VSS and front wheel sensor as replies.

I'm removing my 200-R4 and installing a TH400 because I am swapping my 307 for a 455.

I understand the driveshaft will be shortened, and I already verified my mounts will work.

What about the speedometer cable? Will it unplug from the 200-R4 and plug into the TH400?

Will my speed be different? And if so, can I swap reluctor wheels or whatever it is between the transmissions to fix that?

Its an 87 Cadillac Brougham.

svnt442

If it is a cable there is no reluctor wheel, but plastic gears in the transmission that spin the cable. The ratio of those gears must be correct for your rear end ratio and tire diameter to make the speedometer to read correctly.
Most likely you will need to swap those gears to correct it for your car. You need to know what the rear end gear ratio is and the tire diameter and you can get everything close.

GHOSTOWLGRID

Thats good.
I see a lot of gears on summits web site as well as other places.
I found the site for finding the ratios:
http://www.tciauto.com/tc/speedometer-gear-calculator/

So I can't just use the plastic speedometer gears from the factory 200-R4 transmission, I have to buy different ones for the TH400?

I attached a photo of my factory service manual page that says what the drive gears have now with my factory setup.

Fatory settings:
My rear gears are 2.73:1
My tire size is 225-75-15

Accordign to my chart, my 200-R4 trans has:
Drive: WHITE / 13T
Driven: BLACK / 27T

Does this mean I buy the same gear teeth count for the TH400 for each gear?
(Unless these 2 gears from the 200-R4 will work in the TH400, then I just swap em right?)

GHOSTOWLGRID

I found this web page:
http://www.performanceautomatic.com/...ter-gears.html

I used their excel file to calculate my TH400 gear ratio using the above info I found about my car.

I got two options

Option 1:
Drive: 18
Driven: 35.0908

Option 2:
Drive: 19
Driven: 37.0403

What selection of gears would be best for me to use?
Is there better?

I want to make sure I'm doing this right and I also want to make sure I found the best option for my car.

joe_padavano

1) The TH400 and 200-4R use the same speedo cable. Your old one will screw directly the new trans.

2) Figure out which drive gear is currently in the TH400 that you have and pick the driven gear to match. That way you don't have to buy two gears.

3) What did your TH400 come out of? Be aware that the 1970-earlier full size cars did not have a speedo drive feature on the trans - the cable was driven from the LF wheel. A trans from one of these cars won't have the case machined for a speedo drive adapter.

4) Every different GM trans uses different drive and driven gears. You need the ones for your specific trans.

GHOSTOWLGRID

I numbered my replies to match.

1) Awesome, I been looking online for this and now its verified.

2) Ok, I will count the teeth on the drive gear then select the driven gear to match.

3) The guy who had it got it from someone else for his built 455 and he didn't need it anymore because he sold his 455 and is going with something else. Came with a new chrome pan and the torque converter.
He said he never had trouble with it and it always worked, seemed trust worth as we were talking to him for a long time when we visited.
I think he said its a 72 TH400 long tail transmission, does have the drive gear, see attached photo.

4) Ok, I was hoping the drive gears were similar at least for this, but I'll do like you said, see what I have and just buy the one gear.

It will be a bit before I can get the transmission apart to replace the gears.
I see 1 bolt with a bracket holding it on, Do I also need to disasemble the tail shaft to get it out?

joe_padavano

No, but unfortunately you do need to pull the tailhousing to count the teeth on the drive gear.

svnt442

The tail housing uses an O-ring to seal it, not a gasket so as long as it's in good shape you shouldn't need to replace it. Just make sure not to tear it when you install it back on the trans or you will end up with a leak that you weren't planning on.
When I swapped mine with the trans in the car it wasn't a big deal. I actually was able to get the gears I needed from a local trans shop for a straight swap...gear for gear. Not saying that you can do this, but you never know.

svnt442

Oh...also. Look at the housing for the driven gear and you can see numbers on it. That denotes what driven gears can be used with that housing. If for some reason you need to go beyond a 39 tooth driven gear, then you will need to get the housing for the higher toothed gears. (again, I got lucky at my local shop...YMMV)

65vistacruiser

19 and 37 will probably be easier to find. Pretty common gears for 400 speedo. But its nice to have the option just in case.