TR5/TR250 A-type overdrive questions

[arbs_53]

Last year I bought a newly rebuilt transmission with an A-type overdrive with all of the electricals, switches, plinth, etc. on E-Bay for my TR250. This has been a goal of mine since I bought the car in '94; I even bought the "overdrive" badge for the rear of the car some 10 years ago in anticipation of this day. The original non-overdrive transmission was replaced by the previous owner the year before I bought the car and was replaced with one from a late model TR6, also non-overdrive. So, now I'm getting ready to install this new unit next week and I have a few questions. 1). Is there a way to test the overdrive to make sure it operates properly before installing it in the car? 2). Will I need to replace the existing transmission mount to one for an A-type, keeping in mind I'm going from a J-type, non overdrive transmission to an A-type with overdrive? and 3). how hard is it to remove and refit the shifter?
Any information you can share will be greatly appreciated.

 

[Tybalt]

The gearbox extension/third motion shaft/tail shaft housing is the same as far as I know for all late TR-4/TR-5/TR-250/TR-6 non-OD transmissions. The change in the mount at the rear of the transmission for the later TR-6 cars was to accommodate the J Type overdrive. To use with an non-overdrive transmission, an adapter plate was bolted to the new style mount on the later cars. Bottom line is that as long as your transmission is properly mounted at the rear, it should work with an A Type overdrive. Please see the attached screenshot from TRF catalog with notes:

 

[HerronScott]

Check out this thread on testing the overdrive outside of the car.

https://www.britishcarforum.com/bcf...-an-A-type-overdrive&highlight=test+overdrive

Removing and replacing the shifter is not difficult but curious why you are asking.

Scott

 

[Geo Hahn]

...Removing and replacing the shifter is not difficult but curious why you are asking...

My guess is that the OD box he got came w/o a shifter.

You'll love the OD but the installation is a bit of a test of upper body strength & patience -- at least it was for me working alone.

 

[arbs_53]

Scott, thanks for pointing out the thread. Very helpful. And Geo is right, it came without the shifter.
This unit is definitely heavier than one without overdrive. I have removed and installed the non-od transmission by myself a couple of times over the years and thought it fairly easy-but I'm going to enlist some help with this unit.
Curious about the pressure gauge shown in a photo in that thread: what range should it cover and how does it hook up?

 

[HerronScott]

Ah sorry, when you said shifter I was thinking the whole cover which didn't make sense as you would need an overdrive cover with the lockout switches.

I'll let someone else respond on the pressure as I haven't done that part myself and I believe there are differences between early and late A-type overdrives due to different accumulators.

Scott

 

[philstr6]

Dave
what are the numbers on your overdrive,I will look up the pressure,also the gauge goes were the operating valve is
just take the plug out,and screw the gauge in
Phil

 

[titanic]

360 psi for the large accumulator. 450 psi for small accumulator units used on IRS cars (the brass tag should have the #22/1753 or 22/1985. Identification can also be made by removing the sol. bracket and examining the springs-large accumulator will have 2 springs, small accumulator 1 spring.
Berry

 

[arbs_53]

I finally uncrated the tranny-it's only been a year! The serial number: 28/1292/2728-so this is not an A-type overdrive. I know A-type's had a 22% gear reduction, hence the #22 at the beginning of the numbers listed above in Berry's response. This one is a 28% reduction, which probably came out of a Volvo or some other vehicle of the era. I'm not overly disappointed, although I wish the seller had disclosed this in his description of the unit; I thought I was getting an original rebuilt A-type overdrive. I now wonder what else was misrepresented. A number of years ago, I bought, from some guy in New Zealand, and still have, an overdrive unit that is also a 28% reduction with the idea of having my current transmission rebuilt with this unit. The 250 has the 3.70 rear end. How will this affect the car's overall performance? Is this a desirable combination? Should I sell this unit and hopefully make back what I paid for it and try to find a 'real' A-type? How else is this unit different from what I was expecting. I once owned a 67 TR4A IRS that had an A-type overdrive with 4.11 gears so I know what I expected from having that. Now, I don't know what to expect.

 

[titanic]

Dave-The A types used on Jags,AH, and probably other applications, had a 28% gear reduction. The ratio was determined by the number of teeth on the planets and annulus. You might contact John Esposito at Quantum Mechanics https://www.quantumechanics.com/qm-htm/home1.htm to help identify the OD.
I think all TR250s and carb TR6s came with 3.7 diffs, even with OD. The A types were 22% reduction, but 27 or 28% was used in the J type OD found in the later TR6s.
Berry

 

[KVH]

I went into Harbor Freight and bought a 2.5 HP electric motor, mounted it to a stand I made, then fabricated a four bolt pulley wheel that attaches to the rear transmission/overdrive flange. That finally gave me enough torque to test my transmission and OD. Others here said they were able to test and spin the transmission with just a 1/2 HP drill--but no way for me. I was going to burn up anything small like that. When I finally got it spinning, it worked great. I followed all of the articles on the Net. You'll see the motor and stand set up here: https://vintagetriumphregister.org/maintain/TransRebuild/OverDriveA02.pdf

Good luck.

 

[Toast]

Just because the tag on the overdrive unit is stamped 28/1292/2728 does not mean that the overdrive is incorrect. Over time as overdrives get damaged and need to be rebuilt, the original overdrive main case (the one with the tag on it) is found to be damaged beyond repair and it becomes necessary to replace it. All the tag signifies is what that case originally came from (overdrive ratio/model-car it was used on/serial number), which in your case means it came from an Austin Healey BN1. Since most all of the main cases were identical (except for the very early TR2/TR3), replacement cases can be sourced from another A-type overdrive such as an Austin Healey or Jaguar. It very well could be as simple as that being a replacement case, and the rest of the parts are the correct parts as used in a Triumph overdrive. I would not automatically assume the seller purposely misrepresented the transmission.

 

[HerronScott]

With it possibly being a different overdrive unit (non-Triumph), it's possible that the speedometer gearing might be wrong as that's the typical issue with using a Volvo A-type in a TR.

Scott

 

[philstr6]

Dave
can you take a picture of the overdrive unit,The tail housing is another part that could be different and needs to be correct for installation,I prefer the 28 if you can find them,I just did a 28-63034 jag150,double spring,520 Lb of pressure when tested
Phil

 

[arbs_53]

View attachment 33531View attachment 33532 Toast, thanks for that information and one I hadn't considered. Still, if that is what happened, I feel the seller should have mentioned the serial number is from a non-Triumph case but the internals are as advertised. Now that this might be an A-Type in BN1 clothing, is there any way for me to tell what I actually have here?

Phil, do these pictures help? I have others I could post, if needed.

I have a 1/2 HP 1750 rpm motor with a 4-step pulley that I use on my wood lathe. I plan to use that when I test this thing. I just need to get a pulley for the flange. I haven't had a chance yet to read through some of the other links yet on Buckeye Triumphs and the like, but I will this weekend when I have some spare time.

 

[Toast]

The pictures aren't showing up.

I would suggest contacting the seller or rebuilder as they could probably answer the questions you have about the overdrive.

 

[philstr6]

Dave
send me the pictures on my reg email
Sjaegeling@aol.com
Phil

 

[arbs_53]

Funny... the pictures were there before I uploaded the thread. Phil, Check your in-box.

I contacted the seller. He bought the unit on E-Bay from a company in northern New Jersey called "Cookeworks" that dealt with British car and parts restoration. He said the unit was advertised as an A-type and re-built to fit Triumphs TR3's thru early TR6's. He bought it last year to put into his '71 TR6 that was unfortunately totaled before he had a chance to install it. I'm sure he felt like he bought, and sold, an A-Type. A google search on Cookeworks didn't turn up anything, I haven't checked E-Bay yet.

I think that Toast may be right in that this is a case from an Austin-Healey, but has the internals for an A-Type. But I'd like to know for sure. Is there a way to tell-maybe by counting the rotations when I bench test it? I think I could rig up a couple of mechanical counter to count the revs on the flange end and at the transmission shaft. The difference should be either 22%, or 28%, once the overdrive is engaged, right? Or something simpler?

Another question I have and it won't matter if this is an A-type, but if this a 28%'er, how would that affect the way the car rides given that I have 3.70 gears? I guess I wondering more about the ratios between 2nd and 3rd and between 3rd and 4th. I'm sure it would be fine above 4th, less wear and tear and better mileage. But would the reduced ratios between the other gears be off? What I'm wondering, would the gearing between 3rd and 3rd overdrive be longer than between 3rd overdrive and 4th. Would 3rd overdrive and 4th be so close that it would be nearly redundant to use it?

 

[philstr6]

Dave
I looked at the trannie and everything looks good from the pictures,the top is correct with three switches,3rd and 4th overdrive,2nd overdrive,and reverse lights,the tail shaft has the right housing as well,for your trans mount,as far as the overdrive you will see the most out of it when you are driving at 70 miles per hour,normal trans will be about 3500rs@70 when you shift it into overdrive 22 your rs will drop about 600 rpms,28 will drop you to 900-1000 rpms,the 28 is more desirerable for crushing and also running thru the gears,the 22 is just as good,some one may have the exact rpms out there,I would test that puppie and you get the correct pressure,install the trans.just one other thing to ask,does the noise of the input shaft flush with the housing,or stick out a little past the housing
Phil
Phil

 

[philstr6]

Dave
the number on the transmisson is from a 70 tr6
Phil