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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