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GilsTR
05-13-2011, 11:44 AM
Trying to help a friend on his project...and he thinks for his TR3A he is wanting to marry up a TR4 tranny with a TR6 rear end that has 4:11 gears. Are 4:11 TR6 rear ends around?
What if any will be the challenges marrying these up? What he tells me is he has a TR3 engine that has been bored out and this is what he wants the power train to be. Any feed back appreciated. Gil NoCal

TR3driver
05-13-2011, 12:09 PM
He is going to put IRS under his TR3A ?? Lotta work there, starting with some major frame fabrication. Be easier IMO to put a TR3A body onto a TR4A frame (ala TR3 beta).

I don't know how many TR6 came from the factory that way, but 4.10 gears are not hard to find. Try BFE or TSi. Carsten Conrad (in Germany) used to sell them as well, not sure if he is still in the business. Same (early) gear set will fit either solid axle or IRS diff.

However, my TR3 came to me with 4.10 gears, and I have to say they are way too short, especially without overdrive. I have to be careful not to spin the rear wheels, and even at 6000 rpm, the rpm is limiting top speed.

Steve Hedke did a careful study with 'Scrappy' (the TR3 he ran in The Great Race https://www.fot-racing.com/tr3/caption/TR3Hedke.htm) and found that he actually got better acceleration with 3.45 gears!

TR4 tranny is no problem. Just elongate the holes in the rear crossmember, to move the rear mount back by about 3/8". If the body is pre-TS50k, he'll need to rework the trans tunnel a bit to fit over the starter bulge. Personally I prefer the TR3 shift lever but the TR4 lever will work.

PS, TRF has 4.10 gear sets on sale for $500 at the moment, PN 505014

Andrew Mace
05-13-2011, 01:29 PM
For whatever it's worth, I think the "guts" of the TR6 differentials, regardless of gear ratio, are pretty much the same as those of the earlier axles, at least as far back as TR4/4A solid axles and possibly to the later 3/3A "Girling" axle. I know a friend of mine bought a TR4 axle from me years ago for use of the diff. in a TR6 housing.

Randall, does that sound about right to you?

TR3driver
05-13-2011, 02:36 PM
Randall, does that sound about right to you?
Yes, except that I'm not certain what is involved in installing a late TR6 gear set (designed for the collapsible spacer) into an earlier differential (designed for a fixed spacer). The part number changed, so there must be some difference in the gear set. But possibly all you have to do is use the collapsible spacer.

PS, never mind. The late TR6 housing stayed the same part number, so all you have to do is use the collapsible spacer to fit a late gear set.

The gear set will even fit into the TR2-early TR3 "Mayflower" axle. For very early TR2s, it may be necessary to ream out the holes in the carrier (a factory-approved modification).