The Money Pit

I had a local builder rework my 700r4 and mentioned the speedometer didn't read correctly.I just took a quick spin to see how it shifted and it still seems off.Is the speedometer supposed to be right in all gears,or only in overdrive?You would think it would read correctly no matter what gear you were in,but I'm not sure.
By the way the tranny guy gutted all the BTO mods,and now it shifts like a stocker.The 1/2 shift is still fairly quick,but the rest is marshmellow smooth.Couldn't cruise too long though,I had 30 sheets of drywall to sand and prime for the boss.(wife) :yesnod:

The Money Pit

Here's the results with the rebuilt 700r4.


And here's what I had before the rebuild.


Both are not correct.Both speedo gearsets were provided by the "Pro's".
How about a hand from the real experts here?I've got 26.7" rear tires,3.70 gears and a 700r4 transmission. What tooth count on the speedo gears do I need so I can fix this?


[Modified by The Money Pit, 9:31 AM 3/22/2004]

Jack71

I don't think it matters what gear you are in because its based on rpms from the tailshaft. I hope it works out for you. The TV cable made a world of difference for me.

gerry72

The speedo cable is driven off the trans output shaft and the speedometer reading will be referenced only to how many revolutions the output shaft is making. It doesn't matter what gear the car is in or what the converter is doing. There will be no correlation between the tach and the speedometer since gears, converter stall and lockup influence the tach.

As to what driven gear you need...that depends on what drive gear you have. You can go here: http://www.tciauto.com/tech_info/speedo_gears.htm to understand what the relationships are.

You're going to have to pull the drive adapter and see what drive and driven gears you have to know where you need to go. Once you have that you can run TCI's calculator to tell you what driven (or drive gear too) you need to use to calibrate your speedometer.

BSeery

Why would you have someone un-do all the Bowtie modifications ?? I have a tranny that was local built and I am thinking of taking the car to Bowtie to have them fix it. Either that or I have to find someone local that knows what the heck they are doing.

SpyderD

You are into my new project. My speedometer with 3.73 gears and the 700R4 is about 20% off. I have to get a new driven gear and also a new gear housing.
Forget about those calculations. Use this website and it will tell you exactly what you need:
http://www.transmissioncenter.net/sp...n_______va.htm

Now with 3.7 gears and 27" tires you need 15 teeth drive gear and 42 teeth driven gear.
Now, the key is to know what drive gear you have, take off the speedometer cable housing that is attached to the transmission and look inside and see what color it is (easy, but prepare for a bunch of fluid to dump out) OR ask your builder what drive gear is in it. Changing the drive gear is difficult, changing the driven gear is easy, so if you have a drive gear that is different from 15 teeth use the above site to match the drive gear to the needed driven gear (i.e. if you have a 17 teeth drive gear you need a 45 tooth driven gear to get you at least close, note that the highest you can get is a 45 tooth gear, if your drive gear match does not match the max number of driven gear teeth you either have to change the drive gear or get some kind of adaptor).
Finally - note that there are two gear housings depending on the number of driven gear teeth - one for 34-39 teeth, one for 40-45 teeth.

The Money Pit

When I ordered the BTO tranny I ordered the 15/42 set and it came fully assembled and I never questioned it.Once on the road it was evident something was wrong.At the time I needed the transmission overhauled I asked the local shop to verify what was installed and make corrections as needed.
Once again if you want something done right you have to do it yourself.

As for removing the BTO mods,I had a heck of a time getting ANY local shop to rebuild my 700r4. All but two shops wanted to replace it with a TH350 or Th400. One of the two said he'd do it,but no warranty,and the guy I had do the work offered only 6 months,but felt with his mods it would last.He did a few things that don't sit well with me,but time will tell if his work will hold up.I'm driving it gently for a while.Once spring really hits and I get the bug,things may be different.

Don't ask me how I feel about BTO. If this fails again I'll be doing the TH400 route in the garage myself. :mad

page62

Is your converter locking up in 4th? Did the tranny guy pull out the Painless Wiring lockup stuff when he was in there? That difference in rpm could be caused by an non-locking converter. Which isn't good. :nonod:

turtlevette

2 votes for a non locking converter or locking converter not locking cause its been given the good ole boy treatment. The way i've heard is a non locking converter is ok but a locking converter thats been disconnected is not good. My 700R4 was converted to a mechanical system of locking in 4th gear.

as far as checking speedo accuracy get a stopwatch and drive 60. Time yourself between mile markers on the hwy. If more than 60 sec you are slower than indicated if less than 60 sec you are faster than indicated. Correction factor is:

actual seconds/60 sec.




[Modified by turtlevette, 7:17 PM 3/22/2004]

redwingvette

There use to be a link on BTO's web site that calculated what gears were needed but I haven't been able to access it for some time. Is there another site some where? Mine is off a little as well but that maybe my fault. I thought I had 27" tires but they are only 26" tall. Its about 3mph@60 slow, shows 0.97 instead of 1.0 mile against the mile markers.

The Money Pit

The lockup converter seems to be working. I tach 2500 in drive and 50 mph is where the speedo reads. When in OD at 2500 the speedo reads 60 mph.Based on a chart I found on the web I'm reading 15 mph slower than I'm actually moving.(Not a good thing where Police are concerned)
Also based on the web the 15/42 gear set I originally ordered with the BTO transmission should be the correct set.I guess the only way to tell now is get greasy.This can wait till the weather breaks,and hopefully the basement project is done.

BSeery

how is this done ??