904 lockup info

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cheech14

cheech14

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I am trying to make a decision on which transmission to swap into my early A body. Ihave a 904 lock up (core) and like the idea of having the bigger clutch pack and other more heavy duty bits and the idea of having an extra "gear" when the converter is locked does have appeal.
My questions ; just what kind of RPM drop do you get when the lockup engages?
With the lower gear ratios of the lockup trans, I would imagine you could get away with running a taller (numerically lower) set of gears, what would be a good starting point?
I was thinking of perhaps 3.23 instead of 3.55 or 3.7. My rear tires are 27.5"
Is there a reputable lockup converter builder that I could get a unit from with a good stall speed? (2400-2600rpm would be my guess with the lower gear ratios in the transmission - the cam is 231/236dur @ .050, .525lift - approx HP 400)
I take my car to local events, but plan on a few road trips in the future - freeway drivability is a concern. (I could just change diffs, not a big deal, but a PITA)
 
I can only answer that a LU converter drops the rpm’s down approximately 500 rpm. I would not change a gear ratio to work with or without a LU converter. I had my non lock up converter done by Pro Torque. IDK if they work on LU converters. 631-218-8700 to talk to them.

The more information you can give them the better the converter will turn out.
 
Aside from your question, be aware that the "lockup 904" (AKA the A999, 32RH) does not fit well in the very restrictive early A transmission tunnel. It has reinforcing ribs on the tail housing that are not present on other 904s, and these require extensive grinding (almost to the point of removal) in order to clear the upper crossmember.
upload_2021-10-28_16-42-34.png

The lockup also dictates the use of 3/8" cooler lines instead of the normal 5/16". They're a bear to bend and fit into the cramped early A tunnel... just so you know ahead of time.
 
Professor Fate said:
Aside from your question, be aware that the "lockup 904" (AKA the A999, 32RH) does not fit well in the very restrictive early A transmission tunnel. It has reinforcing ribs on the tail housing that are not present on other 904s, and these require extensive grinding (almost to the point of removal) in order to clear the upper crossmember.
View attachment 1715811898
The lockup also dictates the use of 3/8" cooler lines instead of the normal 5/16". They're a bear to bend and fit into the cramped early A tunnel... just so you know ahead of time.
Click to expand...

Professor, where can I find the proper attaching hardware? I figure, fuel line can be used and bent up to route the fluid. But the attaching ends and the transmission adapters (?) I don’t know where to get.
Any help would be appreciated, thanks.
 
rumblefish360 said:
Professor, where can I find the proper attaching hardware? I figure, fuel line can be used and bent up to route the fluid. But the attaching ends and the transmission adapters (?) I don’t know where to get.
Any help would be appreciated, thanks.
Click to expand...
It's actually pretty straightforward- they came on 318s and V6s, so it has a standard small block bolt pattern, no adapters needed. It still uses a standard '66 and later 904 slip yoke, and the driveshaft stays the same length as with a 904. Naturally if you're putting it in a '65 or earlier A, you need to ditch the ball & trunnion shaft and get a suitable slip yoke shaft. I used the B&M 10239 flexplate to bolt the stock torque convertor (neutral balance) up to a 360. Not an ideal convertor for optimum performance, but it suits my purposes on my wagon (cruiser). On my '66, I used the shift and kickdown levers off the old '66 904 and bolted it up to the stock column linkage. The 999/32RH lockup is all hydraulically controlled (no electronic or pressure controllers needed like on the later OD transmissions), with just a lockout for the convertor lockup (the tow/haul button on the original truck application) that can be wired to a simple on/off button or toggle.
It uses a typical late model speedo drive, so on the early A you need to run a '66-'67 cable (threaded ferrules on both ends) in order to drive the early speedo, especially if you're replacing the one piece '65 and earlier cable. A standard cable works on later As.
For the cooler lines I cheated and used brass 45* fittings coming out of the trans, I just couldn't make sharp enough bends in that tiny tunnel without kinking them- there's just not much room with the shift/kickdown linkage and speedo cable all crammed into the same real estate... :)
The good news is, I'm looking at doing the same swap into my '75 Dart, and there's LOTS more room in there- doesn't look like I'll have to grind the tailshaft ribs at all, and mucho more room for the linkage/lines and such.
 
Last edited:
rumblefish360 said:
I can only answer that a LU converter drops the rpm’s down approximately 500 rpm. I would not change a gear ratio to work with or without a LU converter. I had my non lock up converter done by Pro Torque. IDK if they work on LU converters. 631-218-8700 to talk to them.

The more information you can give them the better the converter will turn out.
Click to expand...
Good info! Thank you. The search continues for an outfit that does lock up converters - I will give Pro Torque a call.
Thanks again!
Art/ R/T Cheech14
 
Professor Fate said:
It's actually pretty straightforward- they came on 318s and V6s, so it has a standard small block bolt pattern, no adapters needed. It still uses a standard '66 and later 904 slip yoke, and the driveshaft stays the same length as with a 904. Naturally if you're putting it in a '65 or earlier A, you need to ditch the ball & trunnion shaft and get a suitable slip yoke shaft. I used the B&M 10239 flexplate to bolt the stock torque convertor (neutral balance) up to a 360. Not an ideal convertor for optimum performance, but it suits my purposes on my wagon (cruiser). On my '66, I used the shift and kickdown levers off the old '66 904 and bolted it up to the stock column linkage. The 999/32RH lockup is all hydraulically controlled (no electronic or pressure controllers needed like on the later OD transmissions), with just a lockout for the convertor lockup (the tow/haul button on the original truck application) that can be wired to a simple on/off button or toggle.
It uses a typical late model speedo drive, so on the early A you need to run a '66-'67 cable (threaded ferrules on both ends) in order to drive the early speedo, especially if you're replacing the one piece '65 and earlier cable. A standard cable works on later As.
For the cooler lines I cheated and used brass 45* fittings coming out of the trans, I just couldn't make sharp enough bends in that tiny tunnel without kinking them- there's just not much room with the shift/kickdown linkage and speedo cable all crammed into the same real estate... :)
The good news is, I'm looking at doing the same swap into my '75 Dart, and there's LOTS more room in there- doesn't look like I'll have to grind the tailshaft ribs at all, and mucho more room for the linkage/lines and such.
Click to expand...

One of the changes I am making is going to the 8 3/4" rear end. Is there a stock driveline that will bolt in? I would guess a 66 A body with 8 3/4. If there is no such animal, what would be the proper driveline length? it's a 65 Barracuda Formula S - putting a later 904 in place of the cable shift trans. (then putting a B&M cable type shifter on it!) It is also getting an 8 3/4" rear axle.
Thanks, R/T
 
cheech14 said:
One of the changes I am making is going to the 8 3/4" rear end. Is there a stock driveline that will bolt in? I would guess a 66 A body with 8 3/4. If there is no such animal, what would be the proper driveline length? it's a 65 Barracuda Formula S - putting a later 904 in place of the cable shift trans. (then putting a B&M cable type shifter on it!) It is also getting an 8 3/4" rear axle.
Thanks, R/T
Click to expand...
I think A body 8 3/4's came out in 65. My 66 Dart has the original Shure Grip in it.
 
You may want to contact Hughes Convertors as they were making mechanical lock up converters with multiple stalls.
I bought a 3,000 stall lock up from them for my 904.Actually 2 of them. No 999 needed.Unless you have one.It has been a few years ago. Worth a shot.
 
cheech14 said:
Good info! Thank you. The search continues for an outfit that does lock up converters - I will give Pro Torque a call.
Thanks again!
Art/ R/T Cheech14
Click to expand...
I didn’t know about Precision of New Hampton, there is also Dynamic and Ultimate converters to call up, Hughes, PTC, the list is long!
 
Convert the lockup to non-lockup and retain the deeper front drum and wider band. If you're lucky, Duane will chime in here. His posts on mixing and matching lu and non-lu parts are extensive.
 
cheech14 said:
One of the changes I am making is going to the 8 3/4" rear end. Is there a stock driveline that will bolt in? I would guess a 66 A body with 8 3/4. If there is no such animal, what would be the proper driveline length? it's a 65 Barracuda Formula S - putting a later 904 in place of the cable shift trans. (then putting a B&M cable type shifter on it!) It is also getting an 8 3/4" rear axle.
Thanks, R/T
Click to expand...
Starting point would be a '66 Valiant/Barracuda/wagon with a 904 and 8.75. If you can't find one, once you get everything mounted up, measure it up and have one made (which is probably the smart thing to do anyways). LOTS and LOTS of threads on here about measuring for a driveshaft, so I won't get into it here. Biggest issue is to not get too carried away with driveshaft diameter on an early A, the tunnels are tiny.
 
It's not that the tunnels are tiny. The problem is that the pinion is not centered in the tunnel; which is not centered itself.
 
CudaFactHackJob said:
It's not that the tunnels are tiny. The problem is that the pinion is not centered in the tunnel; which is not centered itself.
Click to expand...
Yes, and it all adds up. I have to say, though, that my later As do have a larger tunnel than my '66, both in the trans and driveshaft areas. I wouldn't call either one "spacious", though.
 
toolmanmike said:
I think A body 8 3/4's came out in 65. My 66 Dart has the original Shure Grip in it.
Click to expand...
Had a 65 Barracuda with an 8.75 in it. Strange car - Commando engine, 4 speed, 8 3/4 sure grip, itty bitty brakes, 13inch wheels and regular suspension. It was pretty darn fast for a stock Barracuda, faster than my dads Formula S (the one I am working on now.) Got it down into the high 13's at Half Moon Bay. Fun Days!!
 
Darter6 said:
You may want to contact Hughes Convertors as they were making mechanical lock up converters with multiple stalls.
I bought a 3,000 stall lock up from them for my 904.Actually 2 of them. No 999 needed.Unless you have one.It has been a few years ago. Worth a shot.
Click to expand...
Did you put the lock up in front of a standard 904? I have to get down to my storage trailer and compare the transmissions I have there. I know one is a 65 904 cable shift (the original out of the car) and I have another one that I know is a lockup, but am pretty sure it's not an A999.
If that Hughes converter will work on a regular non lu 904, it may be worth a try. How much rpm drop do you get when the lu engages?
Thanks R/T (Art)
 
Thanks to all you guys (all y'all?) for the info! I knew that the tunnel was snug, but never gave it much thought. I guess this is part of the fun of modifying a car - communicating with everyone!

Thanks bunches,
R/T, Art, Cheech 14
 
cheech14. Yes a 71 904.had one made for a 67 904 as well.
But it doesn't lock like a factory high gear only.
The best way to explain it is like a manual clutch. At slow speeds the converter acts normal. After a set rpm the converter locks in all gears,like a manual.No loss from converter slippage.
 
Darter6 said:
cheech14. Yes a 71 904.had one made for a 67 904 as well.
But it doesn't lock like a factory high gear only.
The best way to explain it is like a manual clutch. At slow speeds the converter acts normal. After a set rpm the converter locks in all gears,like a manual.No loss from converter slippage.
Click to expand...
Hmmm. I think I LIKE that idea! I did shoot off an email to Hughes & filled out their data sheet - I know I have read how much slippage can be expected from a 904, but do not remember. I would assume that the slippage would be somewhat more under load also.
I just want to be at a reasonable RPM while going down the highway, if I have to change ratios (or tire diameter), well, that can be done.
Does anyone have an idea what that number/percentage would most likely be?
Inquiring mind(s) want to know!!!

Thanks much, Darter6

Cheech14
 
rumblefish360 said:
I can only answer that a LU converter drops the rpm’s down approximately 500 rpm. I would not change a gear ratio to work with or without a LU converter. I had my non lock up converter done by Pro Torque. IDK if they work on LU converters. 631-218-8700 to talk to them.

The more information you can give them the better the converter will turn out.
Click to expand...

Thanks Rumblefish360, while I would like the car to be somewhat formidable on the street, i am not really tied to 1/4 or 1/8 mile performance. Performance was my life for 26 years, I do still enjoy it, to a degree (okay - a lot). The car does, however, have to handle and stop fairly well and be driveable when going to out of town events. Right now, I just want to get a transmission in it that does not hemmorage fluid and will be accepting of things like a higher stall converter. Finish sanding the paint/buffing it to a nice shine and getting the interior done are also a priority. I understand they are Never Really done - but I just want to drive and enjoy my "family car!" (been in the family from the time it was new, mostly). Thanks again!

Cheech14, Art, R/T
 
Cheech, call me Rob. ;)

I gotta tell ya, we are on the same page on wants. I read this reply and said, Oh hell yea! I get that, that’s just like me. I’m going to try and make my way to a drag strip and be (a little) serious about laying down some numbers. But in the end, I just love a power plant that is fun on the road. It’s gotta move that car well!

cheech14 said:
Thanks Rumblefish360, while I would like the car to be somewhat formidable on the street, i am not really tied to 1/4 or 1/8 mile performance. Performance was my life for 26 years, I do still enjoy it, to a degree (okay - a lot). The car does, however, have to handle and stop fairly well and be driveable when going to out of town events. Right now, I just want to get a transmission in it that does not hemmorage fluid and will be accepting of things like a higher stall converter. Finish sanding the paint/buffing it to a nice shine and getting the interior done are also a priority. I understand they are Never Really done - but I just want to drive and enjoy my "family car!" (been in the family from the time it was new, mostly). Thanks again!

Cheech14, Art, R/T
Click to expand...
 
rumblefish360 said:
Cheech, call me Rob. ;)

I gotta tell ya, we are on the same page on wants. I read this reply and said, Oh hell yea! I get that, that’s just like me. I’m going to try and make my way to a drag strip and be (a little) serious about laying down some numbers. But in the end, I just love a power plant that is fun on the road. It’s gotta move that car well!
Click to expand...
Professor Fate said:
It's actually pretty straightforward- they came on 318s and V6s, so it has a standard small block bolt pattern, no adapters needed. It still uses a standard '66 and later 904 slip yoke, and the driveshaft stays the same length as with a 904. Naturally if you're putting it in a '65 or earlier A, you need to ditch the ball & trunnion shaft and get a suitable slip yoke shaft. I used the B&M 10239 flexplate to bolt the stock torque convertor (neutral balance) up to a 360. Not an ideal convertor for optimum performance, but it suits my purposes on my wagon (cruiser). On my '66, I used the shift and kickdown levers off the old '66 904 and bolted it up to the stock column linkage. The 999/32RH lockup is all hydraulically controlled (no electronic or pressure controllers needed like on the later OD transmissions), with just a lockout for the convertor lockup (the tow/haul button on the original truck application) that can be wired to a simple on/off button or toggle.
It uses a typical late model speedo drive, so on the early A you need to run a '66-'67 cable (threaded ferrules on both ends) in order to drive the early speedo, especially if you're replacing the one piece '65 and earlier cable. A standard cable works on later As.
For the cooler lines I cheated and used brass 45* fittings coming out of the trans, I just couldn't make sharp enough bends in that tiny tunnel without kinking them- there's just not much room with the shift/kickdown linkage and speedo cable all crammed into the same real estate... :)
The good news is, I'm looking at doing the same swap into my '75 Dart, and there's LOTS more room in there- doesn't look like I'll have to grind the tailshaft ribs at all, and mucho more room for the linkage/lines and such.
Click to expand...

OK - I made a trip to my storage trailer today to look at my core lockup transmission. Turns out (according to Mr. Hand's book) it is a 998 out of a 1980 Chrysler. Just looking at it, it is Very similar in case/tailshaft housing dimension. This is as compared to a 1965 cableshift gearbox. Should fit right in the same space.
That being said, does anyone know if that particular breed of 904 have any particular problems? it's a 4130956. It should have a lot of the upgraded parts and a 4 disc front clutch retainer as well as the wide ratio gearset. (some of the early 998's even had 5 disc clutches - but that would be too much to ask for!)
While I was messing around, I pulled the cooler line fittings off and took a look down the outlet hole. It is quite close to .250" (sits back in there a ways and I didn't have my inside mic handy) So, now I am wondering, just Why would I need to have cooler lines any larger than that??? The inside diameter of the fittings (-4 to 1/8" pipe) is even smaller - around .228 at best. I pulled a stainless AN -4 to 1/4 pipe thread adapter out of my parts bin and even it was less than .250! So - what we have here is not one, but two flow restrictor orifices. Not gonna get much, if any, better flow with larger lines. (same volume, less velocity) That being said, I will still put -6 (3/8") lines to my cooler, just because it makes me feel better. And the guy you run over will say "Wow, look at those fancy cooler lines!"
 
There is no issues between the various models.
Just what there built with inside.

Later years have bigger lines. Why they did this I’m not sure but it might have to do with the 904 variants (A-500) being installed in trucks. Those have the extra gear and have the potential of more weight when the truck is loaded. My 4X4 ‘03 quad cab Dakota wasn’t exactly light.
 
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