[Fot] Big TR OD and Gearbox rebuilding - reversing

Larry Young cartravel at pobox.com
Wed Mar 12 09:44:30 MDT 2014


If you look through the archives, you will find several times we've 
debated the J-type vs A-type overdrive for road racing.  If you use it 
only on long straights, it really doesn't make much difference. There 
are other times when an overdrive is just more convenient and quicker 
than shifting the transmission.  In those cases I believe an A type 
overdrive is preferred.  An early one with the large accumulator which 
is shimmed for extra pressure will make the shifts virtually 
instantaneous.  You might also want to consider changing your rear axle 
to something like a 4.55 which will give 3.73 in 4th overdrive.

Whenever I hear the comments about how overdrives easily fail, I mention 
that mine saved me once.  When a bad throw out bearing made the 
transmission impossible to shift, I put in 3rd and ran a couple of races 
using just 3rd and 3rd overdrive.  I think my lap times only dropped 
about one second.

On 3/10/2014 6:47 PM, Marcel Van Mulders wrote:
>   You must be Tony Sheach from the article in Kas Kastner's book "Triumphs,
> race cars, street cars and special cars". Flat out rallying is something to
> have respect for!
> In 1997 I bought a rough TR3 and restored it as a road car, with a Triumph
> Saloon J-type O/D and fitted the logic device of Revington. Indeed it worked
> great, doing exactly what you expect in every situation with just one push
> switch to command. In fact the small box is still in my car, but when I
> started road racing the TR3, the O/D was removed because I saw much failures
> and at that time I was not convinced it would make the car faster and top
> speed in 4th gear with a 3.9:1 rear axle was 120mph.It also makes the car
> 10kgs heavier. Contrary to the USA (and UK?), the use of an O/D in road
> racing TR's is rare in Europe.
> But I've changed my mind (thanks to Chris Marx!) and will fit a J-type O/D
> together with a higher rear axle ratio. The logic switch box of Revington is
> unused since 10 years and it has 6 pins/wires, so I don't thrust it enough.
> A hold relais and push switch will do, because I will only use the o/d on
> 4th gear. The overdrive is sapping some power and I would only engage it on
> long straights.
> Marcel, Belgium.
>
> -----Oorspronkelijk bericht-----
> Van: TR4 Tony [mailto:tr4.tony at virgin.net]
> Verzonden: maandag 10 maart 2014 8:36
> Aan: Marcel Van Mulders
> CC: Larry Young; fot at autox.team.net
> Onderwerp: Re: [Fot] Big TR OD and Gearbox rebuilding - reversing
>
> Marcel
>
> Revington TR and TR Enterprises in the UK supply such a part already, both
> slightly different but very effective - I use the Revington one and have
> done so for 10 years as they were the original maker. Both are equally good.
>
> It works very well on my TR4 with an A type overdrive, very reliable and
> because I use a 4.875 cw&p plus a 28% overdrive I get a direct switch up and
> down a full gear due to the gear / rear end and overdriven ratios - for
> example I don't have to shift across the gate from 2nd to 3rd as overdrive
> 2nd = direct 3rd.
>
> similarly I can drop from OD top straight to 2nd by heel and towing across
> the gearbox and shifting out of overdrive automatically without activating
> the switch ie hands on wheel and lever. This makes my entry to low speed
> corners when trail braking very quick, and handbrake turns very tight (I've
> got to be quick between the gear lever and handle!) as I don't reach for 1st
> to come out of a tight one for the two or three seconds that I need to pull
> the car round 180 degrees.
>
> I know you guys don't do handbrake turns, but they save you from big
> accidents more often than I like to admit ...
>
> Regards
>
> Tony
>
>
>
> Sent from my iPhone
>
>> On 9 Mar 2014, at 19:34, "Marcel Van Mulders"
> <van.mulders.marcel at telenet.be> wrote:
>> Thanks. I'm thinking of using a J-type with a push switch actuating a hold
>> relais, and keeping the gearbox case switch. Changing gear will
>> automatically disengage the overdrive. I would also mount an override
> switch
>> directly between battery12V+ and the solenoid, just in case the push
> switch
>> would be dead. But my engine is still on a dyno, 5 weeks before the 1st
> 2014
>> saison race...
>> Marcel, Belgium
>> -----Oorspronkelijk bericht-----
>> Van: Larry Young [mailto:cartravel at pobox.com]
>> Verzonden: zondag 9 maart 2014 19:54
>> Aan: Marcel Van Mulders
>> Onderwerp: Re: [Fot] Big TR OD and Gearbox rebuilding - reversing
>>
>> The J type has the same unidirectional clutch, so it has the same problem
> as
>> the A type.  However, all of these units leak down after a while when the
>> pump stops.  The A type leaks down more slowly because of all the fluid
>> stored in the accumulator.  The J type without an accumulator, will leak
>> down much more quickly (maybe 10 seconds vs. at least several several
>> minutes).  For example, if you stop, shift to reverse and start backing
> up,
>> it will likely be disengaged.  The leak down rate also depends on the
>> condition of all the various seals within the overdrive. One A type that I
>> rebuilt would hold pressure for several days, but that was exceptional.
>> Larry
>>
>>> On 3/9/2014 10:14 AM, Marcel Van Mulders wrote:
>>> Not quite the same subject : it's very unhealthy to an A-type to
>>> reverse the car with the overdrive engaged for some unorthodox reason.
>>> Can you wreck a J-type overdrive in the same circumstances?
>>> Marcel, Belgium.
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