700R4 To TH350, speedometer off... also tick/knock sound

[dwatts1984]

So I had a turbo 350 swap done on my truck. I love it. Although I miss the one gear, no more worries of the TV cable. Anyhow, when I noticed that I have to drive the truck at 55mph to get it to go 45 mph. I'm under the impression I can just swap the speedo gear in the trans, however I have no idea what gear to go to.

No idea what the stock rear end in my truck is.
Truck: 1986 GMC 1500 single cab LWB 5.7L 4 Bolt Main V8

Any advice or help would be greatly appreciated.

Also recently noticed a ticking or knocking from under the truck. Truck has always been maintained well. Seems to have happened just after the trans swap. I dont think its the bottom end of the motor... Sounds more like the torque converter or flywheel. To be honest IM curious is anyone else has had this happen. I know the sound is typically a bad bearing in the bottom end. However like I said really sounds to be more on the tranny side.

[MDc10]

Originally Posted by dwatts1984

So I had a turbo 350 swap done on my truck. I love it. Although I miss the one gear, no more worries of the TV cable. Anyhow, when I noticed that I have to drive the truck at 55mph to get it to go 45 mph. I'm under the impression I can just swap the speedo gear in the trans, however I have no idea what gear to go to.

No idea what the stock rear end in my truck is.
Truck: 1986 GMC 1500 single cab LWB 5.7L 4 Bolt Main V8

Any advice or help would be greatly appreciated.

Also recently noticed a ticking or knocking from under the truck. Truck has always been maintained well. Seems to have happened just after the trans swap. I dont think its the bottom end of the motor... Sounds more like the torque converter or flywheel. To be honest IM curious is anyone else has had this happen. I know the sound is typically a bad bearing in the bottom end. However like I said really sounds to be more on the tranny side.

i recently swapped my th350 for a 700r4, since the swap I've noticed the needle bouncing alot. It never did it before. Don't know if the speed is off, guess i should check. When you do a tranny swap are you suppost to change the Speedo gear?
Posted via Mobile Device

[geezer#99]

Lots of info in here.
http://www.transmissioncenter.net/sp...____va.htm#350

[MDc10]

Originally Posted by dwatts1984

So I had a turbo 350 swap done on my truck. I love it. Although I miss the one gear, no more worries of the TV cable. Anyhow, when I noticed that I have to drive the truck at 55mph to get it to go 45 mph. I'm under the impression I can just swap the speedo gear in the trans, however I have no idea what gear to go to.

No idea what the stock rear end in my truck is.
Truck: 1986 GMC 1500 single cab LWB 5.7L 4 Bolt Main V8

Any advice or help would be greatly appreciated.

Also recently noticed a ticking or knocking from under the truck. Truck has always been maintained well. Seems to have happened just after the trans swap. I dont think its the bottom end of the motor... Sounds more like the torque converter or flywheel. To be honest IM curious is anyone else has had this happen. I know the sound is typically a bad bearing in the bottom end. However like I said really sounds to be more on the tranny side.

I actually just left the tranny shop, he said you don't have to change anything in the Speedo for the th350 to 700r4 swap. He said be sure and grease up the end of the cable where it goes into the tranny. Don't kno if this helps you any, but good luck.
Posted via Mobile Device

[Ski-me]

I'm not familiar with the 350 but if the speedo connections are the same:

I'd first start with lubing your speedo cable. There is a lube out there but you will need to pull out your instrument cluster and speedo gauge to get access to lubing it. Once the speedo is removed, the cable will pull out of the sleeve. When you feed it back in, lube it as you go.

Check your speedo cable for any kinks or large bends.

It is possible that the drive or driven gears within the t-case got damages or are worn. One of the gears is pretty easy to change out but the other one requires pulling the tailshaft off of the Tcase.

Basically, in my 89' I had the speedo jumping around. I tried a new cable, tried lubing it, tried swapping one of the gears (the easier on) with no success. Even my cruise control couldn't hold steady because of the jumping around.

I finally went "all in" and converted my cable speedo to a electronic one. Took a LOT of work but really turned out great! Rock solid speedo, cruise rock solid and 6 digit odometer.

[Axle]

Actually you do need to change the gears for the swap unless you get a drive and driven gear from a same axle ratio vehicle. The 700r4 uses a large diameter driven gear, the th350 uses the small diameter driven gear, if you use the th350 speedo adaptor from a junkyard source [and the drive gear from the 700r4], your speedo will more than likely read fast. Mine was exactly 2x actual speed. I had to watch out that I didn't destroy my speedo on the shakedown run.

Do you know how many teeth your driven and drive gear have? Then we can work out what combination to get you close. Actual speed verified with a GPS or roadside radar unit? Or other confirmed CORRECT speedo when following somebody with specific instructions to drive at exactly 60mph? =-)

Alex.

[cory d]

if oyu left the engine in while swapping transmissions the distibutor may have hit the fire wall. that can cause the cap to sit crooked and knock. a cracked flex plat can make noise too

[legendman]

Originally Posted by Axle

Actually you do need to change the gears for the swap unless you get a drive and driven gear from a same axle ratio vehicle. The 700r4 uses a large diameter driven gear, the th350 uses the small diameter driven gear, if you use the th350 speedo adaptor from a junkyard source [and the drive gear from the 700r4], your speedo will more than likely read fast. Mine was exactly 2x actual speed. I had to watch out that I didn't destroy my speedo on the shakedown run.

Do you know how many teeth your driven and drive gear have? Then we can work out what combination to get you close. Actual speed verified with a GPS or roadside radar unit? Or other confirmed CORRECT speedo when following somebody with specific instructions to drive at exactly 60mph? =-)

Alex.

Bumping this up because I have the same question.
I put a 700r4 in place of a th350 and the th350 had a 10 tooth drive gear and a 19 tooth driven gear, the rear end has a 2:56 ratio and a 305 motor.

Not sure how to figure out which gears to use for the 700r4, it was out of 89 pickup so it had a electric speedo.

Thanks

[bnoon]

Originally Posted by legendman

Bumping this up because I have the same question.
I put a 700r4 in place of a th350 and the th350 had a 10 tooth drive gear and a 19 tooth driven gear, the rear end has a 2:56 ratio and a 305 motor.

Not sure how to figure out which gears to use for the 700r4, it was out of 89 pickup so it had a electric speedo.

Thanks

http://www.transmissioncenter.net/sp...n_______va.htm Use the chart or give them the gear and tire height in an email and they'll help you out, or just use their calculation to figure it yourself.

EDIT: Saved and uploaded their calculation for future just in case they every change their site.