Speedometer error and related issues !

[87BlazeLS]

I know about the speedometer calibrator section in the faqs. But, I do not know what my current gears are.
I figured since many of you guys probably have done the same swap I did it has been figured out already....

OK so I had a 305 / 200R4 combo with 2.41 rear gears 205/70 R/ 14
Now I have a 350 / TH350 combo with same 2.41 rear gears and 255/ 60 R /15 27" tall

OK some back ground - The transmission was out of an 85 Chevy pickup just for reference..
When driving the car the error is around 25 MPH on the slow side. (reading 25 mph at 45 to 50 actual)...

I need to know what drive gear color and driven gear color to get it in the correct ball park.

Suggestions anyone ?

NEXT, Due to the swap of said transmissions above my shift indicator (column shift LS ) is mounted in the speedometer
housing. However the red needle is stuck at Park. And does not move.... I no longer need the P-R-N-OD-2-1 from the
200R4 transmission. I need to replace it with the P-R-N-D-2-1 common with the 3 speed automatic.
Can I get just the replacement indicator and swap it out ? Or does this require a different speedometer all together?

Any help with this issue would be super... Thanks in advance jake 87BlazeLS

 

[stuckincincy]

this page will tell you what drive and driven gears are available. TH350 is about 1/3 of the way down.
http://www.transmissioncenter.net/speed ... ____va.htm

Then you can go here to calculate which gears you need.
http://www.bgsoflex.com/speedo1.html

As for the gear position indicator, you didn't indicate what kind of car. Most of the overdrives are just an overlay. If you remove the bezel there should be two screws at the bottom of the indicator. If you remove those you should be able to remove the OD plate the standard three speed markings should be underneath.

 

[87BlazeLS]

Thanks for the links. MY stage name here should have been a give away for the type car I have, As in 87 monte carlo LS
It has been rebadged with Blazer emblems with the "R " cut off And a Flame in chrome.

As I stated I do not know what gears are inside the speedometer connection at the TH 350. Can these be pulled out easily ?

Fluid loss ???? I know the speedometer cable can be unscrewed from the case easy enough.

I've never done a speedo re gear... Sorry for numbness....

And how do I fix the broken red needle movement ???? A wire ? A spring ?

jake 87BlazeLS

 

[stuckincincy]

The driven gear is fairly easy to replace. Just remove the cable and then the retaining bolt and you should be able to pull out the sleeve and driven gear as a unit. (you will lose a little fluid) Gears are color coded so when you pull out the unit just look up the color and that will tell you how many teeth you have. To find the number of teeth on the drive gear just look inside the hole where the driven gear assembly was to find the color. It's easiest to try to find the correct driven gear for your setup, but depending on final gear and tire size you may have to change both gears. If you have to change the drive gear you need to remove the tail shaft housing to get at the gear.

There are two possibilities for you gear indicator depending on if you have a column or floor shift. If you have a column shifter, the gearshift needle is attached to the steering column behind the bezel by a small cable a U-clip. You can usually reach it by removing the trim piece below the column and reaching up from the bottom. Just pull the cable until it indicates what gear you are in and push it back onto the column. I like to put it in neutral or drive since that is about in the middle.

If you are using a floor shifter and the linkage from the trans to the column has been removed you will need to replace the linkage to get it to work. Either way the needle attaches to the column the same way.

 

[87BlazeLS]

Hey thanks for the extra effort, I guess that means there is a point of no return on selection.

Meaning unless the drive gear fits within the driven gears range you need to pull the tail shaft.

This requires removal of transmission ... I wont go there for the sake of speedometer Error.
I may look at alternate methods of correcting the speed.

If another less expensive alternate exist I would go there. Trans was just pulled for a B&M torque
converter swap 9/02/2012 $400

87BlazeLS jake

 

[455'ed80Regal]

No need to pull the trans again. Just drop the driveshaft and pull the extension housing off the trans. To get your speedo close you will need a 10T drive gear and 18T driven gear. Swapping the gears out is pretty straightforward after you get the extension housing off. Fluid loss will be little to none if you raise the rear of the car to change to gears out.

 

[dogsht]

He asked specific questions and got good specific answers. Great. But he still seems a bit green with building what sounds like a performance street car. So here is my thoughts or questions; if performance is the objective the 2.41s need to go. Assuming you want to get the most out of your gear swap (such as the best quartermile gear for the power he has) and that gas isn't free out there and that he wants to protect or get the most out of his engine investment ie rebuilds & parts are not free either.

Why not rebuild if it needs it or add a shift kit etc if not to his 200-4R? Especially since he already has it. Maybe it FUBAR but nobody likes going backward and he made no mention of this being a drag or roundy round car. Just thinking we should ask as many newbs to building hot driver.project cars way under estimate the value of an OD vs an older non OD trans. Anyway so say a 4.10 gear would get him a lot better acceleration than a 2.74 (same final drive ratio) and still get the same or better mileage as well the same or less engine wear. He may also not know the benefits of a lock up converter especially for a well cammed motor or than the trans weighs less and has less parasitic loss. Some people know that a lock up converter saves gas but don't realize it also especially on a higher stall keeps a lot of heat out of the cooling system. Maybe he has thought of this or not or maybe as mentioned the 200-4R is FUBAR and he is just trying to get it up and usable as quick and cheap as possible for now. Anyway food for thought.

 

[84clonewars]

Like Vern I'd also consider using the 200-4R trans it will bolt right up to the sbc.

 

[87BlazeLS]

Had a 200R4 now have a TH 350. This is a Ratrod project car. I know full well the 2.41 gears need to go.

This was not the question. It was correcting speedo error. Yes I'm green on this car but have been building hot rods
for years just not with a TH 350 and a chevy v8. The TH 350 is perfect. Gone thru and good to go. Just not with
the speedo gear in mind.

Since there is considerable error I thought I would ask what you think. I'm here to get info. I have the ability to do
damn near anything. Just though a little extra from the ones who know would be better than blindly attacking something
that I have not dealt with before.

jake

 

[87BlazeLS]

On second thought I did not consider the fact that it is possible the speedo gears need to be selected
AFTER the rear gear ratio is changed out.... No doubt 2.41 is not where I want to be.

I think it would be best to concentrate on the gear swap in the 10 bolt first and then re-gear the speedometer.

I would like to get gears around 3.23 to 3.40

I'll be shopping for these parts in the next few weeks.

thanks for all the comments.

jake