>Has anyone replaced the Crown Ring and Pinion on a TR6
differential?
Yes - twice
>I have a TR6 with catastrophic differential damage.
>The crown ring and pinion are both missing teeth.
>I have opened the diff case and have confirmed the broken
>teeth. Everything else seemed normal to the eye, plenty of
>oil, etc. Pinion isn't loose, and spins normally till it
>encounters the damaged areas.
>Any speculation on the cause of the damage? What else might
>need replacing?
Read an article several years ago by a fellow named Len (cannot remember his
last name). He claimed to have seen several differentials where teeth had
broken off at their roots. Speculated that the factory cast the ring and
pinion "cold" which resulted in their breaking at about 75,000 miles. Said
that the new ring and pinions have corrected this.
>The diff mounts (always a weak point) are fine, and I have
>replaced the 6 Universal Joints while the diff is out just
>because it seemed like time to do it. None showed exessive
>wear.
>The gears are in the catalog at 3.7:1 or 3.45:1. What's the
>difference? Why 2 ratio's?
One is for the PI (petrol injected models) and the other is for carburetor
models.
>I'd be interested to hear from anyone who has rebuilt, or
>tried to, a tr6 rear-end. Any advice would be apprecieated.
You will need some mechanical skill and LOTS of patience. The Bentley shop
manual assumes you have the required "Specialty" tools which would normally
be found at the factory or dealer's repair center. This manual is good for
reference but does not help those who are specialty tool disadvantaged. Try
to get a copy of the Haynes manual if you don't already have one. They show
you step-by-step how to repair, set-up, and adjust the differential using
normal tools (you will need a dial caliper - but they are moderately
inexpensive). Follow the steps in the Haynes manual - The manual recommends
the use of a blue machinist dye that visibly shows the contact pattern
between the ring and pinion - this is where patience is required because you
may have to shim, assemble, inspect, disassemble, re-shim, assemble,
inspect, disassemble, reshim, - you get the picture - until the tooth
contact patterns are correct. You will also need to borrow (or build) a
case spreader. They are not difficult build - I made one out of angle iron
and 1/2 inch threaded rod. It wouldn't win any beauty awards but it did the
job.
There are some who will say that you should buy a rebuilt unit and save
yourself the time and aggravation. Buyer beware. I had a differential with
a broken pinion tooth. I examined the differential, read the manual,
thought about it, and bought a rebuilt unit from one of the big three with a
twelve month or twelve thousand mile warranty. They will only give you back
your core charge if your ring and pinion in your existing unit are good and
in a rebuildable condition. Alarm bells ringing yet? They should be! They
reuse the ring and pinions in their rebuilt units. I kept my old unit and
fourteen months after I installed the rebuilt differential, guess what
happened? Yep. Came off the interstate, stopped at a stop sign, and upon
commencing to cross the intersection the teeth in the differential broke
thereby causing the rear end to begin hopping around like a frog (pieces of
broken teeth were getting caught in the good teeth and causing further
damage). No - I didn't abuse the differential by popping the clutch or
aggressively accelerating. I didn't even bother calling the rebuilder.
Got out a catalog and ordered two sets of ring and pinion gears from
Vicky-Brit (they had the best prices at the time). Rebuilt both units and
have been satisfied since. I want to say the rebuilt unit cost me about
$800. The new ring and pinion set cost about $300-350. Add additional
money for bearings, seals, shims, spider gears and other miscellaneous
items. If your differential does not have it, I would drill and tap an oil
drain hole in the bottom of the differential. The rebuilt units will have
this nifty little feature. It allows you to drain and replace the
differential oil without having to remove the rear cover.
Robert
72 TR-6
http://members.visi.net/~kohout/index.html
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