[Fot] best gearbox for TR6 more...

Thu Jul 19 19:14:15 MDT 2018

Jack...

Mike Belfer shared your feelings that an overdrive offered an early chance for parasitic loss.  He said it would probably be the first thing to let go.  But they were sure sweet when they were working.

Don Brick, in our tent, always ran one...and kept it working too.

Bill Dentinger

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On Thursday, July 19, 2018, Jack Wheeler via Fot <fot at autox.team.net> wrote:

Hi Glen.  I agree with most of your comments.  I raced a TR-4 in SCCA for 24 years, and used both close ratio, and stock ratio gearboxes with, and without overdrive.  I always used the later housings (TR-4A - TR-6) and the "A" Type overdrive, and I did all my own maintenance.  Early in my career, I always thought a straight 4 speed (without overdrive) would be more efficient for racing, due to less parasitic losses.  When close ratio gears became legal (about 1980), I thought this would be a big improvement over the overdrive option.  I had all 6 gear sets set up for my IRS car, so I could gear to use either transmission option at all the tracks I raced at.

However, after years of experimenting at Road Atlanta, during The Runoffs, I concluded that using a close ratio overdrive gearbox with the 4.3 rear end gear was about 1 second per lap faster than using a straight 4 speed with the 3.7 rear end gear.  The 4.3 rear gear gave me a more usable second gear for some tight turns (like turn 7 at Atlanta) than the 3.7 rear gear.  I also tried the 4.1 rear gear with the straight 4 Speed, but the overdrive option was still faster.

I did less research at other tracks, but long tracks with tight turns (like Road America) would certainly favor the overdrive option.  There may not be as much difference on short, tighter tracks.  But, numbers don't lie, and a second a lap was worth it to me, to learn about building and maintaining overdrives, with high pump pressure for quicker shifting.  And, I found them to be very reliable mechanically.  The only problems I ever had were electrical.

Take it for what it's worth, but that's my story, and I'm stickin' to it!

Jack

On Thursday, July 19, 2018, 5:30:21 PM EDT, fubog1 via Fot <fot at autox.team.net> wrote:

In all fairness to the conversion advocates, in spite of the benefit of both intermediate gearing & the extra top gear with the O/D unit, there are some downsides to the O/D.
First, it's getting hard to find good units, a lot of what I run into is junk. These have been in high demand since forever, I've bought many junk TRs just for the overdrives.
As Larry pointed out, there are alternatives, ie Volvo, but then you have to mod it to suit.
Unless you find a guaranteed plug-and-play TR box & O/D assembly, you'll most likely be having to go through the gearbox as well, and certainly if you're converting a standard gearbox to overdrive cuz' the mainshaft is different.
That leads to another problem, parts availability for overdrive parts is a bit limited, especially some of the early A-type stuff, and as is normal these days, quality is always a big concern.
Then if you have a rebuildable unit, and all of the parts, it has to be properly rebuilt, by the book.
It's a fairly labor-intensive job and requires some degree of mechanical finesse.

If you have to pay someone to do the entire job, the cost could easily get up there to the point where a conversion gets more attractive.

There are also a few other negatives, the TR box & O/D unit may weigh more than some alternative units, there is some very slight power loss with the O/D, and some replacements may have better ratios available.

Having said (typed) this, for a street car, a later TR-6 box, with the 17 tooth laygear, better 1st ratio & much-improved 2nd mainshaft gear, with a J-type on the back of it is hard to improve on.
For racing, late 6 box with a set of close ratio gears & a "big piston" A-type works well.

I see both side of the argument but personally I like the TRs as TRs, iff'n in doesn't say Stanpart on it, I'm not interested (grin).

Glen

-----Original Message-----
From: Larry Young via Fot <fot at autox.team.net>
To: fot <fot at autox.team.net>
Sent: Thu, Jul 19, 2018 12:32 pm
Subject: Re: [Fot] best gearbox for TR6

Yeah, Glen is right. I should have shut up. I did a cost comparison a few years ago. Someone was making a Ford 5 speed conversion also. The cost was more or less the same, but of course, it depends on how much you are going to do yourself. I have heard the Toyota boxes are getting scarce also ($550 seems like a lot). Quantum Mechanics does (or did) a turnkey A or J type overdrive. He has everything you need to convert a Volvo J-type to any of the TR series. I've helped a couple of guys do this conversion. Volvo's from the 80's are relatively unloved, so a couple years ago I could find the Volvo J-types on Ebay for $150. Of course, buying the Volvo overdrive or a Toyota 5 speed is just the tip of the iceberg. If you want a turnkey deal that you install, you're probably looking at $2500 - $3000 regardless of the route you go. If you do everything yourself, you can probably get by for half that.

I've had my TR250 from new and didn't have an overdrive until 5 years ago. I did a 7,000 mile road trip in it a couple of years ago and found all 7 speeds to be useful. Even 2nd OD was nice when stuck behind an RV going up a mountain pass.

Like I said, I should have kept quiet, but my point is that I think you will find the cost similar regardless of the direction you go. It really boils down to what you prefer.
 - Larry

On 7/19/2018 7:43 AM, Bill Tobin via Fot wrote:
I dunno larry, I got my conversion from Eaglegate, who was also from New Mexico, and it bolted in. Plug and play. Works great, shifts smoothly, and  (so far!) reliable.
Me being me, at the time, '13 I think, I picked up two spare transmissions. Celica W58. For about $175 each. A friend with a wrecking yard looked them  up yesterday: around $550. No, they are not for sale!
I believe a guy in Kansas City took over Eaglegate. If anyone is interested, I could look it up.
Cheers, Bill

On 7/18/2018 11:56 PM, Larry Young via Fot wrote:
I'd rather have an A-type (or even a J) overdrive - 7 gears, easier to shift, easier to install, probably less expensive - What's not to like? Keep the wife definitely.
 - Larry

On 7/14/2018 4:13 PM, dustin nicholson via Fot wrote:
Is the HVDA conversion kit for the Toyota 5 speed still available since Herman’s passing?

Dusty 

Sent from my iPhone

On Jul 12, 2018, at 8:05 PM, Bobby Whitehead via Fot <fot at autox.team.net> wrote:

My wife is trying to convince me to keep our 1971 TR6 we've owned for 26 years...mhhhh.... I told her if we did I needed an overdrive or 5th gear...what's the best conversion?

Bobby Whitehead
Jester's Racing
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