th400 tranny HELP

Redog · 02-08-2008, 06:00 AM

As the title says:

I need help figureing out something with my 400 tranny.

The speedo provision hole is CASTED into the block, it's not a freeze plug. I was going to fix up the transmission with a new convertor, flexplate, shift kit etc and add in the speedo gears, but work stop before it started. My mech didn't want to cost me too much cash so he stopped work until I can figure out how to drive the speedo.

I've been searching for 2 days now on the internet and I'm no closer to where I was before I started. I'm spinning my wheels I guess you can say.

The only thing I can think of so far is a 700 r4 or a th350 tail housing but I do not know if they will bolt right up. I think the 4L60 tail housing is the same lenght as my 9" tail I have now.

Any insight, leads, answers will be great help.

Thank you in advance

Olds64 · 02-08-2008, 09:53 AM

Can't you just get a TH 400 tailshaft with the speedo gear attachment? I don't really understand what your problem is. Sorry.

Oldsguy · 02-08-2008, 11:27 AM

There is no hole in the casting because that transmission was originally in a late sixties B body like my '69 Delta 88 I used to own. They drive the speedometer from the driver's front spindle via a cable directly to the speedo, not from the transmission. I think Jesse is correct, changing the tailshaft would allow you to attach the speedo cable to the transmission but you would also have to get the correct ratio drive gear. There may be some internal modifications to the tranmission as well. I know this was mentioned before here at this site. Maybe it was Joe or TexasRed. Not sure.

Redog · 02-08-2008, 08:45 PM

HAven't found anything like that.

Thinking I'm going to have to go with a new case

Olds64 · 02-09-2008, 05:56 AM

If nothing can be done to your existing case then maybe you should look into an aftermarket speedometer with a vehicle speed sensor. I know you can buy them for street rods and such.

2blu442 · 02-09-2008, 07:07 AM

I believe the speedometer attachment is in the side of the main case on these trannies. So if you really want to use this trannie instead of getting a different one then Olds64 has a good idea. The ones I've seen are for electric speedometers and attach a magnetic pickup on the driveline. It will read the electric "pulses" as the driveline rotates and convert that to a signal that gives the speed of your car.

Redog · 02-09-2008, 12:48 PM

My mecan get me a new case for $75 to $100 and then rebuild the tranny (building it up a bit) so I think I'm going that route but after April 14th (Union contract / strike watch) Plus the Alero just cost me $550 for the ign lock cyl and passlock system, and I need a new MAF for it

02-08-2008, 06:00 AM	#1 (permalink)
Redog Alero Chapter Secretary Join Date: Aug 2006 Location: Newtown, PA Posts: 831	th400 tranny HELP As the title says: I need help figureing out something with my 400 tranny. The speedo provision hole is CASTED into the block, it's not a freeze plug. I was going to fix up the transmission with a new convertor, flexplate, shift kit etc and add in the speedo gears, but work stop before it started. My mech didn't want to cost me too much cash so he stopped work until I can figure out how to drive the speedo. I've been searching for 2 days now on the internet and I'm no closer to where I was before I started. I'm spinning my wheels I guess you can say. The only thing I can think of so far is a 700 r4 or a th350 tail housing but I do not know if they will bolt right up. I think the 4L60 tail housing is the same lenght as my 9" tail I have now. Any insight, leads, answers will be great help. Thank you in advance __________________ Me 2000 Alero running 14's 2005 Nissan Altima (her's) 1985 Delta 88 w/1968 350 rocket ( MURDERED )

02-08-2008, 09:53 AM	#2 (permalink)
Olds64 Landyacht Club President Join Date: Jul 2007 Location: Lawton, OK Posts: 1,804	Can't you just get a TH 400 tailshaft with the speedo gear attachment? I don't really understand what your problem is. Sorry. __________________ "Some men are Baptists, others Catholics. My father was an OLDSMOBILE man." Ralphie Billingsley A Christmas Story 1983 "We rei-eign, supreme, ooooh god! Burrito supreme, and a chicken supreme, and a CUTLASS SUPREME!" Tenacious D 2007

02-08-2008, 11:27 AM	#3 (permalink)
Oldsguy Administrator Join Date: May 2004 Location: Lees Summit MO Posts: 3,132	There is no hole in the casting because that transmission was originally in a late sixties B body like my '69 Delta 88 I used to own. They drive the speedometer from the driver's front spindle via a cable directly to the speedo, not from the transmission. I think Jesse is correct, changing the tailshaft would allow you to attach the speedo cable to the transmission but you would also have to get the correct ratio drive gear. There may be some internal modifications to the tranmission as well. I know this was mentioned before here at this site. Maybe it was Joe or TexasRed. Not sure. __________________ Dan '77 Cutlass Supreme '46 2 door

02-08-2008, 08:45 PM	#4 (permalink)
Redog Alero Chapter Secretary Join Date: Aug 2006 Location: Newtown, PA Posts: 831	HAven't found anything like that. Thinking I'm going to have to go with a new case __________________ Me 2000 Alero running 14's 2005 Nissan Altima (her's) 1985 Delta 88 w/1968 350 rocket ( MURDERED )

02-09-2008, 05:56 AM	#5 (permalink)
Olds64 Landyacht Club President Join Date: Jul 2007 Location: Lawton, OK Posts: 1,804	If nothing can be done to your existing case then maybe you should look into an aftermarket speedometer with a vehicle speed sensor. I know you can buy them for street rods and such. __________________ "Some men are Baptists, others Catholics. My father was an OLDSMOBILE man." Ralphie Billingsley A Christmas Story 1983 "We rei-eign, supreme, ooooh god! Burrito supreme, and a chicken supreme, and a CUTLASS SUPREME!" Tenacious D 2007

02-09-2008, 07:07 AM	#6 (permalink)
2blu442 Senior Member Join Date: Sep 2006 Location: Medford, Oregon Posts: 923	I believe the speedometer attachment is in the side of the main case on these trannies. So if you really want to use this trannie instead of getting a different one then Olds64 has a good idea. The ones I've seen are for electric speedometers and attach a magnetic pickup on the driveline. It will read the electric "pulses" as the driveline rotates and convert that to a signal that gives the speed of your car. __________________ 1964 Cutlass Factory 4spd 1965 442 4spd 1967 442 Auto 1967 Cutlass Convertible 1968 442 Auto 1969 442 W30 Auto 1970 442 4spd 1971 Cutlass Flat Top Wagon 1973 Che*vy 3/4 Ton 454/TH400 Tow Vehicle Only the tow vehicle is finished!

02-09-2008, 12:48 PM	#7 (permalink)
Redog Alero Chapter Secretary Join Date: Aug 2006 Location: Newtown, PA Posts: 831	My mecan get me a new case for $75 to $100 and then rebuild the tranny (building it up a bit) so I think I'm going that route but after April 14th (Union contract / strike watch) Plus the Alero just cost me $550 for the ign lock cyl and passlock system, and I need a new MAF for it __________________ Me 2000 Alero running 14's 2005 Nissan Altima (her's) 1985 Delta 88 w/1968 350 rocket ( MURDERED )

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