Preload Springs Effect on an Eaton Posi: Gary Ramedei

[Joe C.]

Is there an advantage to building a new Eaton 65-79 posi differential without preload springs?
What would be the pitfalls, if any?
Thanks in advance.

[Gary R.]

Re: Preload Springs Effect on an Eaton Posi: Gary Ramedei

Is there an advantage to building a new Eaton 65-79 posi differential without preload springs?
What would be the pitfalls, if any?
Thanks in advance.

Every Eaton posi I build is without the preload springs. There are members here with them in their vettes in fact.
The springs apply force to the side gears and posi clutches, to give posi action. The spider backlash spec is 001-008", depending on how tight they are setup will determine how well they will "slip" in a corner. Most of the typical chatter in a posi is because of tight lash and heacy spring preload. This setup works, I can't say it doesn't, but with the tuned posi there isn't a spring preload. The axles will easily spin against each other by hand- a contradiction to the factory manual test on a spring loaded posi which states to test the axles for slippage past 40 ft/lb. There will be better action and less wear on the clutches with a tuned posi.

Now I have been "debating" this setup for years and really don't want to get into again with those who say it won't work, isn't correct, etc. Bottom line it works but I'm not debating it further.

Pitfalls,
Yes, you have to tune it correctly. That means to balance it correctly, set the spiders correctly and seat them with 100's of rev's. Properly done they work great - I have them in street, road racers, and drag cars. Tom's has been doing them for 40 years and Pepe Estrada before him most likely close to 50 years ago.

However, if you don't set them up correctly they will not work as intended. Look over the videos on you tube by Tom's on tuning a posi. Most times I have to grind shims to size to dial them in. It takes me 5-6 hours to polish and tune a vette 10 or 12 bolt conversion. Most failures I have seen are from guys not following the procedures shown in the video's and not seating them with the correct rev's. There are very few in fact who offer to do this and the ones I have seen as tuned are not - as on CF. Tuned posi's do not have springs in them anything else is not a tuned posi.

[Joe C.]

Re: Preload Springs Effect on an Eaton Posi: Gary Ramedei

And as the clutches continue to wear, the posi "tune" changes? The springs will compensate for wear, but how is wear compensated for, without the springs.

[Gary R.]

Re: Preload Springs Effect on an Eaton Posi: Gary Ramedei

Age old question, properly tuned there is less load on the clutches then with the springs. Part of the procedure is correctly seating the new clutches and once set there is no lash & there is little clutch wear, unless the new fiber coated clutches are used, which I do not use. Those will wear by rubbing your finger over them. If you are planning on using them, stay with the springs.

However, not correctly tuning will not fully seat the clutches and once in the car they will seat and open up. That is another area I have seen guys fail to complete correctly. Heavy Drag use cars I recommend going through the diff during the off season to check all internal parts including the clutches.