• Hi Guest! Being a Paying Supporter is NOT a requirement to participate at BCF. However, subscribing will help ensure we can continue to serve the LBC community for years to come. If you enjoy BCF and find our forum a useful resource...Please consider supporting us by **Upgrading**
    (PS: Subscribers don't see this banner)
Tips
Tips

TR6 J-Type or A-Type Overdrive for 1972 TR6

R_Lyle

Member
Offline
I've got a late 1972 TR6 (Aug '72) and I have the opportunity to buy an overdrive transmission (the transmission and the overdrive unit) for it from another British car enthusiast. What I'm wondering is which transmission should I buy: the one with the A-Type or J-Type (he has one of each). The seller tells me that he thinks I need to use the one with the A-Type since there is some difference with the spline (the 1969-1972 had the A-type while the 1973-1976 used the J-type). What will work with my car? Is the J-type any better or mor reliable then the A-type?

1972 TR6 cc84566
 

TR3driver

Great Pumpkin - R.I.P
Offline
The splines aren't so bad to deal with (you just have to find a flange from a later TR6 w/J-type) but the rear mount looks like a pain to deal with. The J-type goes right through where the early rear crossmember went, and it's mounting point is maybe 5" farther back than with the A-type. There's a good article at https://www.buckeyetriumphs.org/technical/jod/AdaptingJOD/AdaptingJOD.htm that outlines one good method of dealing with it.

IMO the J-type is an improved design and will likely last longer. There are also more ways it can be serviced in the car, and parts are more readily available (I picked up an entire unit for spares, for about $130 on eBay). But it shifts slower than an A-type, which IMO is less 'sporty'; and because the shifts are even slower at low speed, it's normally not setup to work in 2nd gear. Given the choice, I'd go with the A.
 
OP
R_Lyle

R_Lyle

Member
Offline
It was my understanding that the J-Type had a different mounting point on the rear of the transmission so you had to build (or buy) a bracket. I found some directions on the internet on how to build the metal bracket so that is not a problem. What I worry about with the A-type is the solonoid switch which is so expensive to replace. I was not aware of the different flange situation.
 

DNK

Great Pumpkin
Country flag
Offline
<span style="font-size: 26pt"> <span style="color: #FF0000">A</span></span>
 

TR3driver

Great Pumpkin - R.I.P
Offline
R_Lyle said:
What I worry about with the A-type is the solonoid switch which is so expensive to replace.
Huh? You lost me there; the J-type solenoid is more than twice the price of the A-type! See for example https://www.zeni.net/trf/TR6-250GC/158.php

That's reasonable of course, as the J-type soleoid is more complicated (it includes a hydraulic valve while the A-type is just a solenoid).

BTW, I feel it's a worthwhile modification to add a fuse to the circuit for the A-type, to protect the solenoid in case it hangs up for some reason and the contacts don't open.

A-type solenoids have two coils internally, the holding coil only draws about an amp and can run forever; but the pull-in coil draws about 20 amps and normally is only energized for an instant. When the plunger reaches it's final position, it pushes against some internal contacts that open the circuit to the pull-in coil. If the plunger hangs up for some reason, or the little plastic pushrod for the contacts breaks or falls out; the pull-in coil will quickly overheat. By using a fuse smaller than 20 amps, the fuse will blow first and offer at least the potential for fixing the problem with the solenoid.

Stags actually came with such a fuse, but TRs did not. On my 3A, I used an 8 amp "slo-blo" just because that's what I had on hand, but I believe an ordinary 5 or 10 amp fuse would do fine.
 
OP
R_Lyle

R_Lyle

Member
Offline
Yes I see that you are correct on the solenoid cost (A-type is much cheaper). I also checked on Quantumechanics web site to see what the cost of the wiring kit and other parts needed to add the A-type overdrive (The Roadster Factory also lists a bunch of parts). Not sure if I have the complete list here but it appears you need the longer speedometer cable, right angle drive, plastic trim on the steering column, two wiring harnesses, and a relay. Any instructions out there on how to do the wiring? In the final analysis I think the A's have it.
 

Geo Hahn

Yoda
Country flag
Offline
R_Lyle said:
...it appears you need the longer speedometer cable, right angle drive, plastic trim on the steering column, two wiring harnesses, and a relay...

On a TR4 you need either the longer cable or an angle drive (not both) perhaps the 6 is similar? You will also need a switch. Again I only know a TR4 which may differ but I modified the existing non-OD nacelle to take the OD switch (had to make a D-shaped hole).

I also added a few holes in the tunnel to simplify service and maintenance. The oil change hole takes a standard rubber plug, the access for the solenoid and on the opposite side for the angle drive and adjustment (not shown) are covered with sheet metal plates.

Tunnel%20Holes.JPG
 
OP
R_Lyle

R_Lyle

Member
Offline
I asked the guys at Quantum Mechanics to see what they thought and their opinion was the J-type uses 1970 technology while the A-type was 1948 technology. Their feeling is the J-type is a better design and that I just needed to build the rear mouning bracket to make it work in my 1972 car.
 

TR3driver

Great Pumpkin - R.I.P
Offline
Basically what I said. But you'll never know what it feels like to flip the switch at about 4500 rpm in 2nd and have the front suspension pop up again while an unseen giant boot kicks you an extra car length down the road.

And the technology ain't all that different, it's still a 2-speed planetary transmission behind a hydraulically operated cone clutch. Biggest difference is that the A-type carries pressure all the time for those instant shifts; while a J-type has to 'think' about it while the 1-lung pump (running at driveshaft rpm) builds up enough pressure/volume to move the clutches.
 

bigbadbluetr6

Jedi Trainee
Offline
You should be able to put either one in your car. I have a 73 TR6 and was able to get an A type and put it in my car. Do I use it in 2nd gear? Hardly ever. I mostly use it on the highway and it sure is nice.
 

TR6BILL

Luke Skywalker
Offline
<span style="font-weight: bold"><span style="font-size: 26pt"><span style="color: #FF0000">J</span></span></span>
 

TR3driver

Great Pumpkin - R.I.P
Offline
TR6BILL said:
Why does one have to edit a "<span style="color: #FF0000">J</span>?"
To make it big and red?
 

DNK

Great Pumpkin
Country flag
Offline
<span style="font-size: 26pt"><span style="color: #FF0000">HVDA</span></span>
 

kodanja

Obi Wan
Offline
<span style="font-family: 'Arial Black'"><span style="font-style: italic"><span style="text-decoration: underline"><span style="font-weight: bold">lol'</span></span></span></span> <span style="font-size: 26pt"> </span> <span style="color: #6600CC"> </span>
 

MDCanaday

Jedi Knight
Offline
What you need to check since your 72 was built near the break from A to J is weather you have the tabs welded to the lower frame flange to bolt on the J style
crossmember.They may be there or not.If there, get the J type.IMHO the sweeter of the two.
MD(mad dog)
 
OP
R_Lyle

R_Lyle

Member
Offline
Bought the J-Type transmission. Now I need to install it. Does anyone happen to know if there is a wiring diagram out there? I can get the parts from TRF or Quantum Mechanics but I don't think I know how to do the wiring.
 

TR3driver

Great Pumpkin - R.I.P
Offline
R_Lyle said:
Does anyone happen to know if there is a wiring diagram out there?
It's pretty basic, as the J-type doesn't require a relay and has only one lockout switch. One source is
https://www.advanceautowire.com/tr2506.pdf
Scroll down to the page for a 72 TR6 (page 4), and look for the box with the OD wiring at the upper RH corner.
 
Similar threads
Thread starter Title Forum Replies Date
H TR4/4A A-type overdrive pump Triumph 4
Got_All_4 TR6 Refurbishing gearbox with A type overdrive Triumph 7
D TR2/3/3A Type A overdrive not engaging Triumph 0
D TR2/3/3A Type A overdrive not engaging Triumph 16
M TR4/4A A type Overdrive Oil Leak Fix Triumph 3
Graham H TR2/3/3A A type overdrive Triumph 6
KVH General TR Type A Laycock Overdrive Questions Triumph 8
C TR2/3/3A A-type overdrive drain plug oring Triumph 1
J TR4/4A TR4 A Type Overdrive Part mixup Triumph 4
CJD TR2/3/3A A type Overdrive Seal Triumph 9
T Spitfire J Type overdrive Triumph 2
T TR2/3/3A Question on A-type overdrive solenoid Triumph 21
BillyB62 TR2/3/3A Type A TR3 Overdrive Wiring Triumph 13
T TR2/3/3A Question on A type overdrive spec for "clutch movement from direct to overdrive" Triumph 7
M_Pied_Lourd TR6 J Type Overdrive High Pressure Filter Cap-Major Problem Triumph 6
R A Type Overdrive reassembly question Austin Healey 3
R TR2/3/3A A-Type overdrive question Triumph 8
T TR2/3/3A My A-Type overdrive rebuild project, some questions Triumph 36
T TR2/3/3A Will Spitfire D-type overdrive work in TR3 with TR4 transmission? Triumph 3
R Overdrive [Type A] brake ring gaskets Austin Healey 1
R TR2/3/3A Overdrive [Type A] Brake Ring Gaskets Triumph 14
J General TR D Type overdrive not working need suggestions Triumph 5
Gordon_Dedrick TR2/3/3A A type overdrive installation Triumph 7
T TR2/3/3A Type A Overdrive, Physical Differences between Roadster Brands? Triumph 2
T TR2/3/3A Type-A Overdrive Handling Differences Triumph 9
A TR5/TR250 A-type overdrive questions Triumph 25
71tr TR6 Overdrive Mount / J-type on A-type frame Triumph 1
D TR6 76 TR6 J Type Overdrive Triumph 7
Gordon_Dedrick Testing an A type overdrive Triumph 20
Simmo I need help with J Type Overdrive Triumph 15
Q "A" Type Overdrive Annulus End Float!! Triumph 4
D A type overdrive question. Triumph 3
John_Mc J-Type overdrive for sale on CL Triumph 4
KVH More on A Type The Overdrive Triumph 2
Coyote1 J Type Overdrive engage problem Triumph 3
J A Type Overdrive Triumph 17
K TR6 TR6 J Type Overdrive...Link to Schematic? Triumph 3
O J Type Overdrive Conversion Triumph 19
Marvin Gruber J type overdrive unit on BCF classifieds Triumph 2
HerronScott TR4/4A TR4A A-type overdrive and Moss Europe TR2-4A cat. Triumph 2
T A-type Overdrive & Gearbox Triumph 9
TR3TR6 J-type overdrive question Triumph 5
CinneaghTR A-type Overdrive Model Number Triumph 14
71tr J-type Overdrive Pressure Port Question Triumph 2
T A-type overdrive / gearbox trouble shooting Triumph 69
TR4A_IRS Looking for a J Type Overdrive? Triumph 0
7 question after testing a J type overdrive Triumph 5
mgedit Fluid for J-Type Overdrive Triumph 22
Got_All_4 A type overdrive that has been sitting for years Triumph 6
Tinkerman Type A overdrive Triumph 7

Similar threads

Top