Just a few questions

[SlantSixSullivan]

I am picking up a parts car for my '80 Diplomat coupe this week. It is an '89 5th Avenue.

Here's the plan:

Take the 7.25 rear out of the Diplomat, put in the 8.25 from the 5th Avenue. I do not know the ratio but I am suspecting it to be the 2.26 or 2.45. I have read that the 2.45 carrier will not accept any other ratio.

Any truth to this? I hope to one day upgrade to a more performance-type ratio.

I will have to use the transmission from the 5th Avenue as well, since I have no other option. I believe it to be the A999 variant of the A904. Again, this is not a performance piece and will likely be upgraded down the road, when time, money and availability permit.

With this transmission and rear end combo coming from a 4 door car, going into a 2 door, will my 2 door driveshaft work?

As for the engine, I have a 360 ready to drop in. I have two options here. I could use the stock torque converter from the 5th Avenue, which has a 318. In this case I would need a 360 flex plate from B&M for balancing purposes. Or, more preferably, I could just go with a better stall converter for a 360.

Am I correct in assuming the above?

Finally, the carburetor is a thermoquad. I have heard that the lockdown linkage may need modified. What modifications, if any, are necessary?

This is the first drivetrain swap I've ever done by myself, hence the questions. Thanks in advance.

Note: When I am done robbing the 5th of what I need, I will sell it whole for parts, or parts individually. Just let me know what you need.

 

[Mikes5thAve]

Make sure the 5th does have an 8.25 axle. If the axle tubes shrink down in size at the housing it's a 7 1/4. Your current driveshaft will be too long for an 8.25 but the one from the 5th should work. Or have yours shortened.

For 360 you can use the b&m flexplate or if you have a good transmission shop near by some can add the 360 weight to your existing converter. The flexplate is reusable tho and handy to have if you ever need to change the transmission again and don't have access to a shop.

Yes, Thermoquad needs a different kickdown rod and throttle bracket that bolts to the intake. You can also modify the current parts or get something aftermarket.

 

[SlantSixSullivan]

I identified the 8.25 by the cover. It is round and not octagonal. I am fairly sure that is a positive way to tell.

I know my cheapest and easiest route will be the b&m plate, so maybe that will do for now. However, I do want a better converter in the future. Perhaps my options will be greater if I just use the b&m plate.

As for the lockdown rod and throttle bracket, I will have to figure that out. Do you know of any aftermarket brands to look for?

Thank you so much.

 

[SlantSixSullivan]

Upon further research, it appears I may have misspoken about the A999 not being a performance piece. Turns out it is actually considered by many to be better than a 904, having five friction discs in the front drum instead of three. The lower gear sets also seem to help the heavier M body cars with low to moderate horsepower.

At this point, I'm feeling quite confident with the pieces I have to complete the swap, all except for the kickdown linkage and throttle bracket for the thermoquad. I'm not quite sure what I need to buy, or modify to get it to work. Speaking purely from memory, I think I'm running an Edelbrock intake. Not sure how it compares to a factory iron one. If more information is needed to get a definite answer, I will work on getting it. Thank you

 

[M_Body_Coupe]

Which Edlebrock intake? Performer, or Performer RPM?

The RPM piece is a bit taller, so depending on what you intend to do with the air cleaner housing, etc., you may run into an overall height issue. Measure and check, I can't help much since I went to a fairly deep drop-base housing b/c I am running the RPM intake with a 1" adapter plate.

As to the kickdown, you can do the cable setup, Lokar is fine, but pricey, and if you don't mind wrenching a bit you can easily pick up a knock-off for 1/3 the price.

Is it going to be worth it? Umm...well, that depends of what starting budge you have to work with. The knock-off stuff is cheaper made, cable is thinner, etc.

eBag listings:

1) Lokar
Lokar KD-2904HT - Chrysler 904 Transmission Transmission Kickdown Cable | eBay

2) knock-off
Chrysler 727 Stainless Braided Kickdown Cable Detent Mopar Transmission Trans | eBay

EDIT
====
BTW: I am NOT saying buy one of the above, just using these listings as an example of what you are getting.

 

[Aspen500]

Someone please correct me if I'm wrong on a performance converter. An '89 5th Ave would have a lock up converter and a lock up higher stall converter may be hard to find. Can't remember right off hand but a non-lockup can be used if the input shaft, pump and valve body are changed. I used to know this stuff but sometimes certain information gets deleted to make more memory space for new data, lol.

JMO, I'd go with a cable throttle valve (a.k.a. "kick down"). It solves a lot of problems of trying to find the correct linkage and parts, plus it takes up less room.

I used the Bouchillon kit on my car, although the price has gone up a tad since I bought mine in the mid '90's. They were under $100 back then. At any rate, it works perfectly. Added bonus, it comes with every part you need including brackets.

BPE TorqueFlite Kickdown Cable Kit - Bouchillon Performance Engineering

 

[SlantSixSullivan]

I have been having trouble finding a higher stall lockup converter. They might be out there but they're difficult to locate.

As for the intake, I can't answer that just yet. The engine is not at my house, and I haven't set eyes on it for some time. It's been waiting for me to gather the parts. Likely what I will do is go with the cable system, for ease of installation/availability purposes.

This project has been postponed for awhile due to finances, but finally I found a decent job that affords more freedom than I've had in years.

I thank you all for the input, and I will gladly keep updating this thread as the project moves forward.

For now I'll be running the stock converter, stock rear gears, and just using the B&M flexplate to get past the balancing issue. From there I'll figure out a throttle/lockdown solution and make upgrades after it's driving. Thanks again.