I have a 1985 d100 slant six 4 speed with 8 1/4 rear 3.91 gears. I bought a new posi unit a few months ago. Do they make a ring gear spacer for these units, or do they make more than one posi unit for the 8 1/4? With this posi unit installed there is not enough adjustment for the ring an pinion to mesh. If so do you know who makes them? Any thoughts or ideas would be great. I'm trying to get this truck back together for the /6 race this weekend. Thanks.

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Ryan Covalt
62 Plymouth Valiant Race Car 2170# 11.008 @ 117.65 MPH 1/4 Mile Best
72' Dart Swinger Street Car, 4 spd, 3330# 14.061 @96.58 1/4 mile Best

There are 2 different carriers for the 8 1/4, one for ratios higher then the 2.40 and the other for lower ratios.
It sounds like you have the wrong carrier unit for the ratio you want to install.
I do not know of a ring gear spacer for these.
DD

Thanks for the info Doug. You are exactly right. I bought the wrong unit. I guess there was a reason it was cheap. I might see if I can get a 1/4" spacer made to see if it will work. If not I will have to buy the right carrier. I hope I can make this work. Thanks again.

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Ryan Covalt
62 Plymouth Valiant Race Car 2170# 11.008 @ 117.65 MPH 1/4 Mile Best
72' Dart Swinger Street Car, 4 spd, 3330# 14.061 @96.58 1/4 mile Best

The split is at the 2.71 mark...The 70's, but mostly 80's cars could be had with the 2.45:1 (318) or 2.26/2.24 rear gears(check that dippy or Mirada)... which will have a different carrier than the 2.71-4.56 gearing...

Most people give up a good 8 1/4" deal because they can't locate a good open carrier to replace the 2.45 version...

Good luck on the spacer.

-D.Idiot

Thanks DI...
I know there were 2 different units but I did not remember the exact split point. One source I looked at said the change over was between the 2.40 & 2.45 ratios.

Anyway... your point is a good one, the "highway" ratio carriers are all over the place and the "lower" ratio carriers are much harder to come by.

To be honest, I wish Mopar would have done this with the 8 3/4 gears and carriers. I hate having a 3 inch thick, 20 pound ring gear, like the one in my 5.38 "pig".
DD

The local machine shop I usually deal with is in the process making a ring gear spacer on a cnc machine. If it works out ok I will let you know. Thanks for the info guys. I realize now before I buy anything I should ask here first!

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Ryan Covalt
62 Plymouth Valiant Race Car 2170# 11.008 @ 117.65 MPH 1/4 Mile Best
72' Dart Swinger Street Car, 4 spd, 3330# 14.061 @96.58 1/4 mile Best

I sat down one day and had some theories about running a 5.13 rear ratio for race only...I've got to ask, the 5.38 is for that 170 that winds up to about 9500 on the clock, right?

Of course running a 5.38 with one of the "double OD" 6 speed manuals might make that almost streetable...

-D.Idiot