From 727 3-speed to a Tremec 5-speed on 318LA motor

[vivalibre]

Hi mopar friends!

I have a 1973 Plymouth Satellite Sebring Plus. I'm having a nearby shop remove the leaking 727 slushbox and replace it with a TREMEC 5-speed manual trans (and new driveshaft).

I know I will want to change the gearing ... probably to 3.22. Is it possible to upgrade the diff to posi at the same time? Who makes such a kit?

I also plan to keep the original 318LA block, and get up to 400HP at the crank with top-end upgrades only (carb, intake, heads). Will the 8.75" diff I have in the car take that kind of power? If not, what kits are available to prevent axle twist under load? I see some $100 weld-on kits as well as some diff covers and axle braces from LMR racing. Anyone tried either?

You can follow the build at https://www.73satellite.com

 

[70chall440]

The 8.75 will take that power without a lot of problem unless you are going to run some deep gears and slicks; for a street car you are find. I seriously doubt you are going to twist any axles, you would snap U joints before that in most cases. 400HP is not all that much in the grander scheme of things and again, on a street car its highly unlikely but if you are really worried about it, get a better center section and better axles. Remember its all about the weakest link in the system.

Be very careful about having a shop put this trans in, I have a 70 Satellite here for a client that a "shop" put a Richmond 5 speed in and the engineering on the torsion bar cross member is nonexistent meaning that they just hacked the cross member and then put the trans in not understanding that the cross member is responsible for supporting the entire front suspension via the torsion bars. On top of that they didn't support the trans in any meaningful way holding it up with 2 5/16" bolts; complete trash.

 

[vivalibre]

The 8.75 will take that power without a lot of problem unless you are going to run some deep gears and slicks; for a street car you are find. I seriously doubt you are going to twist any axles, you would snap U joints before that in most cases. 400HP is not all that much in the grander scheme of things and again, on a street car its highly unlikely but if you are really worried about it, get a better center section and better axles. Remember its all about the weakest link in the system.

Be very careful about having a shop put this trans in, I have a 70 Satellite here for a client that a "shop" put a Richmond 5 speed in and the engineering on the torsion bar cross member is nonexistent meaning that they just hacked the cross member and then put the trans in not understanding that the cross member is responsible for supporting the entire front suspension via the torsion bars. On top of that they didn't support the trans in any meaningful way holding it up with 2 5/16" bolts; complete trash.

Thanks! I think I'll just stick with changing the ratio and adding posi then.

I chose this shop very carefully and have been working with the owner for months on planning this upgrade. They are licensed to install TREMECs in B body mopars from a company that makes a kit especially for doing so ... no need to hack up the K frame nor remove the torsion bars. More importantly they've been around for 10+ years and I can only find positive reviews. The owner has been friendly, knowledgeable, and responsible.

The other upgrades going in are bigger torsion bars (1.08"), replacing all the suspension bushings with polyurethane, upgraded tubular upper control arms, stage 2 power steering upgrade (less assist, fewer turns to full lock), and 1 1/8" front anti-sway bar -- plus upgrading to adjustable, firmer shock. I'll set the preload on the torsion bars to lower the front end about 2 inches for that mean, stanced look.

I think I'm going to keep the slotted police wheels I have on them now and shine up my dog dishes for that old-school-cool look.

 

[70chall440]

Thats cool and I hope it works out well for you. Based on what you are saying it sounds like you have a decent plan overall, of course there are a lot of options and products out there. I run stage 3 (Firm Feel) boxes with quick ratio pitman/idler arms in all of my cars and really like them. My Cuda has 1.14" T bars and it is VERY stiff. Good shocks, good tires and good brakes will help to make it a fun car to drive.

 

[vivalibre]

Nice! Yes I've been working with Matt at Firm Feel for my suspension and steering upgrades.

While I'm waiting for all this work to get done, switching to interior re-do of my 1985 Mark 1 Toyota MR2 five-speed! I love these first-gen MR2s.

 

[Kern Dog]

Ha ha

 

[vivalibre]