700R4 Experts/down shift kit ?s And speedo gears?s - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Reumster · 09-19-2002, 01:21 AM

Ok I'm wanting to take my Blazer into a Tranny shop and get the down shift valve put in. Summit May-June issue page 159. How much should I expect to pay to get it put in, and can it be installed with the tranny in the Blazer?

Next ?s is how do I find the right tranny speedo gears to use? I have 3:73 gears, and 295/50/15 tires. I really want to get that electric speedometer from Autometer, and eliminate the problem, but for now, I just need a working speedo! LOL

Project1970 · 09-19-2002, 01:34 AM

http://www.bgsoflex.com/speedo1.html

This is what I used...I'm not 100% sure it's accurate, though.

With your setup: 295/50-15 tires are 26.6" tall...

Hopefully you've got a 15 tooth drive gear on the tailshaft, in which case you'll need a 42 tooth driven gear. The next smallest drive gear has 17 teeth (no 16 tooth gear, oddly) which would require a 48 tooth driven gear - which GM doesn't make. Largest for the 700R4 is 45 teeth. I had to swap mine out to a 15/40 setup to go with my 3.73s and 28" tall 275/60-15 tires.

68 with 350 TPI · 09-19-2002, 02:00 AM

Should only be about 100$ to get the valve put in and yes it can be put in with the trans still in.

On the speedo gear there are a few places to get them and you may want to ask your local trans shop or trans parts supply house if they can get you one cheap.

Most of the time trans shops can get that cheaper than most speed shops.

Reumster · 09-20-2002, 11:15 AM

Thanks for the info. Do you know what color the 15 tooth drive gear is? I'll tell them to throw in a 42 tooth. They go by colors right?

68 with 350 TPI · 09-20-2002, 11:20 AM

yes they go by color.
I dont have my book handy and I dont want to tell you the wrong one.
The trans shop should have a book on it there to tell them color/tooth count.

I would just ask them to make sure they get the right one.

Project1970 · 09-20-2002, 12:57 PM

The 15 tooth drive gear is grey.

One other thing...you will need to change the sleeve if you're going from a 34-39 tooth driven gear to a 40-45 tooth. I bought mine new, but it's not cheap - almost $60.

And finally, buy the clip for the drive gear as well. I broke mine when I was getting the old drive gear off.

gabet40 · 09-20-2002, 01:41 PM

is there any diagram or help anywhere on how to install that clip? i couldnt figure it out and got so impatient i just threw the gear on and it was so snug it didnt need the clip.
but then i broke my driveline and my tail shaft busted and everything is gone, so now when i get a hold of a new gear ill know how to get that clip on.

Project1970 · 09-20-2002, 05:47 PM

There's a notch on the inside of the gear that fits over the clip; place the clip in the notch so that the rounded part goes forward, the end opposite that points up, and the tab sticks down. Then, just slide the whole mess forward. A local speedo shop I called told me I needed to heat the gear up in a microwave first to expand it (nylon will do that) but I didn't have to after all.

Also, there's two holes on the tailshaft, at least there were on mine. I believe the front one is for mechanical speedos, but not sure. Look it up on Google, it's in there somewhere (that's how I found out).

09-19-2002, 01:21 AM	#1
Reumster L.E.D. Freak Join Date: Jan 2002 Location: Polson MT Posts: 1,358	700R4 Experts/down shift kit ?s And speedo gears?s Ok I'm wanting to take my Blazer into a Tranny shop and get the down shift valve put in. Summit May-June issue page 159. How much should I expect to pay to get it put in, and can it be installed with the tranny in the Blazer? Next ?s is how do I find the right tranny speedo gears to use? I have 3:73 gears, and 295/50/15 tires. I really want to get that electric speedometer from Autometer, and eliminate the problem, but for now, I just need a working speedo! LOL __________________ Specializing in Custom L.E.D. inserts. http://www.ccled.com/ Contact me @ blazer2wd1972@hotmail.com (406)675-8082 or Joel @ jmcwaters@eps-corp.net 1972 2wd Blazer, 350/700R4/3:73 posi, err & Custom L.E.D. inserts! LOL

09-19-2002, 01:34 AM	#2
Project1970 14.1 @ 96MPH Join Date: Jul 2001 Location: Mesa, AZ Posts: 2,811	http://www.bgsoflex.com/speedo1.html This is what I used...I'm not 100% sure it's accurate, though. With your setup: 295/50-15 tires are 26.6" tall... Hopefully you've got a 15 tooth drive gear on the tailshaft, in which case you'll need a 42 tooth driven gear. The next smallest drive gear has 17 teeth (no 16 tooth gear, oddly) which would require a 48 tooth driven gear - which GM doesn't make. Largest for the 700R4 is 45 teeth. I had to swap mine out to a 15/40 setup to go with my 3.73s and 28" tall 275/60-15 tires. __________________ Project1970 - LS1 Swap Complete!

09-19-2002, 02:00 AM	#3
68 with 350 TPI Registered User Join Date: May 2002 Location: Wingate NC Posts: 456	Should only be about 100$ to get the valve put in and yes it can be put in with the trans still in. On the speedo gear there are a few places to get them and you may want to ask your local trans shop or trans parts supply house if they can get you one cheap. Most of the time trans shops can get that cheaper than most speed shops. __________________ Life is good with a 6-71 supercharged 355 in a 72 camaro

09-20-2002, 11:15 AM	#4
Reumster L.E.D. Freak Join Date: Jan 2002 Location: Polson MT Posts: 1,358	Thanks for the info. Do you know what color the 15 tooth drive gear is? I'll tell them to throw in a 42 tooth. They go by colors right? __________________ Specializing in Custom L.E.D. inserts. http://www.ccled.com/ Contact me @ blazer2wd1972@hotmail.com (406)675-8082 or Joel @ jmcwaters@eps-corp.net 1972 2wd Blazer, 350/700R4/3:73 posi, err & Custom L.E.D. inserts! LOL

09-20-2002, 11:20 AM	#5
68 with 350 TPI Registered User Join Date: May 2002 Location: Wingate NC Posts: 456	yes they go by color. I dont have my book handy and I dont want to tell you the wrong one. The trans shop should have a book on it there to tell them color/tooth count. I would just ask them to make sure they get the right one. __________________ Life is good with a 6-71 supercharged 355 in a 72 camaro

09-20-2002, 12:57 PM	#6
Project1970 14.1 @ 96MPH Join Date: Jul 2001 Location: Mesa, AZ Posts: 2,811	The 15 tooth drive gear is grey. One other thing...you will need to change the sleeve if you're going from a 34-39 tooth driven gear to a 40-45 tooth. I bought mine new, but it's not cheap - almost $60. And finally, buy the clip for the drive gear as well. I broke mine when I was getting the old drive gear off. __________________ Project1970 - LS1 Swap Complete!

09-20-2002, 01:41 PM	#7
gabet40 Registered User Join Date: Dec 1999 Location: Modesto, CA Posts: 565	is there any diagram or help anywhere on how to install that clip? i couldnt figure it out and got so impatient i just threw the gear on and it was so snug it didnt need the clip. but then i broke my driveline and my tail shaft busted and everything is gone, so now when i get a hold of a new gear ill know how to get that clip on. __________________ Current owner of 2016 2500 Silverado Midnight Edition. Former owner of: 69 1/2 ton, change from long/fleet to short/fleet, shaved door handles, shaved tailgate, 4/6 drop, power windows, 700r4 72 blazer, 350 with Holley Commander 950 DFI, crane energizer cam, 350 tranny, dual sanderson blockhuggers/magnaflow exhaust

09-20-2002, 05:47 PM	#8
Project1970 14.1 @ 96MPH Join Date: Jul 2001 Location: Mesa, AZ Posts: 2,811	There's a notch on the inside of the gear that fits over the clip; place the clip in the notch so that the rounded part goes forward, the end opposite that points up, and the tab sticks down. Then, just slide the whole mess forward. A local speedo shop I called told me I needed to heat the gear up in a microwave first to expand it (nylon will do that) but I didn't have to after all. Also, there's two holes on the tailshaft, at least there were on mine. I believe the front one is for mechanical speedos, but not sure. Look it up on Google, it's in there somewhere (that's how I found out). __________________ Project1970 - LS1 Swap Complete!



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.