Art,
In an A-Type definitely yes.... There are actually 3 ways to setup an
accumulator system on the A-Type:
1- Preferred for racing is using the early main case designed for the large
accumulator piston set. You can identify this case as it has a Welch plug
on the bottom of the main case where the later cases are just molded
aluminum at this area. With the large piston I can get the competition
accumulator spring which will easily obtain 450 lbs of pressure will really
let you know when you hit overdrive!
2- If you like a softer engagement you can go with the standard mid cycle
Triumph or Healy overdrive which use the smaller accumulator setup. I run
these at around 350 to 400 lbs of pressure and they slide into overdrive
without the aggressiveness of the above setup.
3- This one is interesting where I use the smaller accumulator piston setup
but with a Jag spring setup which is middle of the road and the pressure is
around 475 lbs.
The huge difference here is that the A-Type overdrive uses an accumulator
system which gives immediate pressure to the operating pistons when engaged.
The J-Type uses a bleed off system where there is always about 15 - 20 lbs
of pressure on the system in a bypass mode and this is to provide
pressurized oil for the mainshaft to oil all of the rear bearings, bushings
etc. When you engage the J-Type the solenoid blocks the bypass and send the
pressurized oil to the operating pistons but since there is no accumulator
it takes time for the pump to provide enough oil and pressure to move them
to the point of clutch engagement.
What to use in your car is of total personal preference. Both units have
their advantages. The A-Type is more adjustable in operation as stated
above but it contains nearly twice the number of parts vs. the J-Type
(reliability). A well sorted A-Type is very reliable but is more difficult
to get to that point. The J-Type is much less aggressive in operation and
not as adjustable but they rarely fail! I have built a couple of J-Types
that are hard to discern in engagement speed over an A-Type even without the
accumulator setup and on occasion I have added in a lockout switch on the
top cover to allow J-Type operation in second gear which I love to use
especially on the Tail of the Dragon!!!
Again it boils down to what you have and what you would like to run. They
are both very good units. There is a key fact that everyone with an
overdrive needs to understand and that is oiling pressure. The J-Type as
described above provides constant oiling pressure with the bypass valve
which allows the 15-20 lbs of oil pressure to run through the mainshaft to
keep all the parts well oiled and cool. The A-Type provides total
accumulator pressure to the mainshaft through the center bushings. This
pressure is a must or you will not have lubrication to the remaining parts.
I have seen a number of A-Type drivers that tell me their overdrive is not
working and just let it go at that. If there is a pressure issue it WILL
destroy the overdrive!!!! Always check your pressure at the top operating
port valve plug on the A-Type and at the bottom oil pressure port on the
J-Type.
Steve
-----Original Message-----
From: riverside@southslope.net [mailto:riverside@southslope.net]
Sent: Friday, November 09, 2012 11:07 AM
To: tr4@wi.rr.com; 'Chuck Arnold and/or Kathleen Kelley'; 'Friends'
Subject: Re: [Fot] J-tpe OD enhancements for racing
Is there any value to using a stronger accumulator spring?
art de armond
-----Original Message-----
From: Steve Yott
Sent: Friday, November 09, 2012 9:16 AM
To: 'Chuck Arnold and/or Kathleen Kelley' ; 'Friends'
Subject: Re: [Fot] J-tpe OD enhancements for racing
While I have done a large number of overdrives, mostly A-Types I have to
admit not too many for racing purposes. It is said that the A-Type does a
better job for the race cars because it has an accumulator system which
enables quicker engagement. There is a list of items I do for the A-type
units for racing but there are actually very few for the J-Type.
Replacing the relief valve with an uncushioned type and setting the pressure
for about 500 lbs would be one of the first steps.
Replacing the Uni-directional clutch with the new style Replacing the main
clutch and starting with an unfinished unit so that one can machine the
thickness to ensure the minimum amount of engagement movement required.
Polishing the pump check valve seat to ensure a good seal.
Other than that a high quality rebuild and inspection of all bearings,
shafts etc.
The idea behind race prepping either unit is to have the unit engage as fast
as possible, hold the torque without slipping and then disengage as fast as
possible.
Steve Yott
-----Original Message-----
From: fot-bounces@autox.team.net [mailto:fot-bounces@autox.team.net] On
Behalf Of Chuck Arnold and/or Kathleen Kelley
Sent: Thursday, November 08, 2012 11:20 AM
To: Friends
Subject: [Fot] J-tpe OD enhancements for racing
Anybody have any good suggestions, documents or references?
--
Chuck Arnold and Kathleen Kelley
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