I6-289 Transmission?

Braden65 · Jan 14, 2014

Me and my dad are working on an automatic 1965. we pulled the i6 out of it and planned on bolting a 289 out of our parts car right in and driving..ha it's never that easy. The parts car we bought is another 65 with with a 289 and a 3 speed. Well we bolted the engine in and two cylinders weren't firing so off to the machine shop where they bored it .040 over, put in a mild cam and cleaned it up, and now we gotta hook it all back up. Once we get it hooked up the issue of a transmission comes into play. The c4 (i6) auto doesn't bolt up to the 289 and my dad doesn't want to use the 3 speed for fear of all the work the conversion is going to need. He got a c5 where where we ran into more issues of everything matching up.what should we do? my dad had the idea of drilling our own holes to use the bigger torque converter on the smaller c4 so so it will work with with the 289. can the c4(i6) handle the somewhat beefed up 289 If we can rig it Up? Or should we explore explore other options? picture of the car if anybody is interested and thanks

rbohm · Jan 14, 2014

you need a flexplate for the 289, the six cylinder one wont bolt up, and has the wrong balance factor. the torque converter and transmission will work, but you need a C4 bell housing for the 289. as for how much power the six cylinder C4 can handle, as long as you are not making more than about 300hp, the trans should hold up fine for NORMAL DAY TO DAY driving. it wont hold up though for racing.

my advice would be to get a rebuilt V8 C4 or rebuild and upgrade teh six cylinder C4 you currently have.

Braden65 · Jan 14, 2014

Thanks!! Good to know. Is there an actual difference between the i6 c4 and the v8 c4?

Braden65 · Jan 14, 2014

And we got a c5 transmission. We tried the bell housing and torque converter from the c5 on that C4 but the input shaft was too small for the c5 torque converter. So we need a torque converter that will fit the c4 input shaft but will also bolt up to the c5 flywheel. Or should we just rebuild the c5 and use that?

rbohm · Jan 15, 2014

Braden65 said:
Thanks!! Good to know. Is there an actual difference between the i6 c4 and the v8 c4?

yes and no. the transmissions are the same basic unit, but the six cylinder trans got fewer clutch plates and lighter duty bands. what many guys do is when they rebuild the six cylinder unit, they add the extra clutches the V8 versions get, and they upgrade to the heavier duty bands. they also instal a good shift kit, trans go make a good one.

rbohm · Jan 15, 2014

Braden65 said:
And we got a c5 transmission. We tried the bell housing and torque converter from the c5 on that C4 but the input shaft was too small for the c5 torque converter. So we need a torque converter that will fit the c4 input shaft but will also bolt up to the c5 flywheel. Or should we just rebuild the c5 and use that?

you can use the C5 flexplate with the C4 converter. but you need a C4 bell housing also, the C5 bell is a bit deeper than the C4 bell.

Braden65 · Jan 15, 2014

rbohm said:
you can use the C5 flexplate with the C4 converter. but you need a C4 bell housing also, the C5 bell is a bit deeper than the C4 bell.

Wow that information is so helpful. I did not know that. Thanks so much

Braden65 · Jan 15, 2014

rbohm said:
you can use the C5 flexplate with the C4 converter. but you need a C4 bell housing also, the C5 bell is a bit deeper than the C4 bell.

If I Remember right (it's been half a year) the C4 torque wouldn't bolt up to the c5 flywheel. Does that sound wrong?

rbohm · Jan 15, 2014

Braden65 said:
If I Remember right (it's been half a year) the C4 torque wouldn't bolt up to the c5 flywheel. Does that sound wrong?

it should, depending on the bolt pattern of the flexplate. there are detail differences between the C4 and the C5, mostly dealing with the lock up torque converter on the C5, a change in the bell housing to trans bolt pattern, the depth of the bell housing to allow for the lock up converter, etc.and yes input shafts between early and later transmissions are different. as i recall up to 1969 ford used a 24 spline input shaft on the C4, and in 1970 they switched to a 26 spline input shaft, which i believe they carried forward through the C5, but thats of the top of my head, its been a while since i last investigated this(about two years or so). but it would be easy enough to check, take the flexplate and the torque converter and match them up, if the converter bolts to the flexplate, you are good to go there, if not then you need another solution.

Braden65 · Jan 15, 2014

rbohm said:
it should, depending on the bolt pattern of the flexplate. there are detail differences between the C4 and the C5, mostly dealing with the lock up torque converter on the C5, a change in the bell housing to trans bolt pattern, the depth of the bell housing to allow for the lock up converter, etc.and yes input shafts between early and later transmissions are different. as i recall up to 1969 ford used a 24 spline input shaft on the C4, and in 1970 they switched to a 26 spline input shaft, which i believe they carried forward through the C5, but thats of the top of my head, its been a while since i last investigated this(about two years or so). but it would be easy enough to check, take the flexplate and the torque converter and match them up, if the converter bolts to the flexplate, you are good to go there, if not then you need another solution.

I'm somewhat inexperienced. My first time tearing an engine down but I tried the c4 converter but the converter doesn't directly bolt to the flex plate. There's a kind of a spacer that keeps the converter from touching the flex plate I took a picture of the stock c4 setup with c4 flex and flywheel

rbohm · Jan 15, 2014

i think you are confusing the block plate with the flexplate. the on you show is the six cylinder flexplate, which has no ring gear as it is on the converter. the block plate helps prevent damage to the block should the converter or in the case of a manual trans the clutch, comes apart. by the way that flexplate cannot be used on the 289.

Braden65 · Jan 15, 2014

I tried the i6 c4 converter into the c5 flywheel, the converter was too small the bolt holes didnt line up. We had the idea of drilling holes into the c5 flywheel so the c4 converter will bolt up. Or trying to find a 24 spline converter that would bolt into the c5 flywheel. Do you think either option will work? What would you recommend? You have been extremely helpful. Thanks so much. We've been at a standstill and we're slowly getting back on track.

rbohm · Jan 16, 2014

get the right converter. drilling the flexplate really isnt an option as you cant guarantee to get the bolt holes drilled on a proper concentric circle which would create an imbalance in your motor that would drive you nuts trying to find.measure the bolt circle on the C5 flexplate, it should be 10.5" as i recall.

Braden65 · Jan 16, 2014

I was confusing the flex plate and block plate. Thanks for clearing that up for me. Yes the c5 flexplate is 10.5" while the c4 converter is 9.5" so I need to find a 24 spline converter (which I believe the c4 input shaft also has a smaller diameter) that will bolt up to the c5 flexplate?

rbohm · Jan 16, 2014

try getting a torque converter from a 68 or 69 mustang with the 302 V8.

Braden65 · Jan 16, 2014

What about another 66? My buddies got one, but he knows what hes got.

rbohm · Jan 16, 2014

Braden65 said:
What about another 66? My buddies got one, but he knows what hes got.

that works too as long as it is the V8 one.

Braden65 · Jan 16, 2014

Alright I'll do that. Thanks for everything!

Woten67 · Jan 20, 2014

Well, since you got a good portion of the power set up, I hope you are transferring the rear end and the front spindles. The I6 rear end will not last long behind that modified engine. Also, you are going to want to upgrade your brakes. Don't forget that if you upgrade your "go" power, you want to upgrade your "stop" power as well.

Braden65 · Jan 20, 2014

Alright.ya we definitely should. Thanks

I6-289 Transmission?

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