EFI Distributosr T2T52371 vs T2T52371B

[1990new]

I needed to replace the o-ring on my 1990 5 Speed and decided to get o-rings for
a couple I had on the shelf, clean them up and put new o-rings on them.
I then pulled my distributor out to exchange and found that it was
a T2T52371 and the ones on the shelf were T2T52371B's.
So I just put a new o-ring on my original and put it back in.

Asking the experts here... what's the difference in these distributors?
Are they interchangeable?


Darn... transposed letter in the topic line (why can't we edit this?

[Pu241]

Is that what you meant?

[1990new]

Is that what you meant?

Just ignore the ramble.... whats the difference between these two distributors in relation to the cam?

[1990new]

Researched this and here is what I found. (Note: Mismatched rotor sizes can cause timing problems.)

The T2T52371B is a Hall effect distributor and the T2T52371 is an optical distributor.
The rotor cams are of two different sizes .526 and .475 inches. And to make it
even more confusing it looks like both sizes are on both distributors.
Hall effect sensors used as encoders for the distributor in a car engine: the sensor is placed on one side of the path of a distributor's vane, and a magnet on the other. When the vane is not in place, a normal magnetic field passes through the sensor. When the vane passes between the two elements, the magnetic field is short circuited, and the sensor sends a signal.
While they don't have the same resolution, hall effect sensors have a practical advantage over optical encoders in that they can get greasy without inhibiting performance.

Because there can be two rotor cam sizes, you must take care to match the size of the rotor button to the size of the rotor cam.

Certain Chrysler, Dodge, Ford, Kia and Mazda distributors. Example
application: Chrysler Cirrus with 2.5L engine with large rotor cam or small
rotor cam (Please see the CARDONE catalog for other applications).
No start, poor drivability, cam code set. Rotor fits loosely or not at all.
There are two different rotor cams, large and small, for the same OE
number. How can the correct replacement unit be determined?
The size of the rotor cams can be used to determine the correct part
number. There are three flats on both cams, one long and two short.
To determine the cam size, measure from the long flat to the opposite
side (see below). The large cam measures approximately
.526 inches, the small cam measures approximately .475 inches.
The long flat on the cam keys the rotor to the correct position. If the
large rotor is used with the small rotor cam, the distributor will be mistimed.
This will cause poor engine performance and possible engine
damage.

And I notice that I just became a Senior Member (1000 posts).

[zoom zoom]

Good stuff I haven't seen before, and you included part numbers! Sticky worthy IMO.

They always ask me what the rotor size is when I buy a rotor button, most of the time I get the only one they have In Stock and I haven't had any issues yet. I'm sure everyone else is asked too so why hasn't this info already been brought up before? Anyway, good stuff, thanks!

If you have these side by side can you see a difference in the physical size of the distributor unit? There was a guy on here asking about it just a day or two ago. Here's the thread...

[1990new]

Thanks zoom zoom.... I learned that I need to do a lot more studying about ignition systems. The proper operation of the modern ignition system
is critical for an engine to perform at peak efficiency. The old mechanical system using points and a condenser were pretty easy to understand
but they required frequent adjustment because of the constantly changing conditions and wear.
Anyone who is having problem with their ignition system should read up on them before trying the guessing game to attempt to fix their problem.

[i218127]

71 vs 71B Distributor

1990new: Thanks for the information. I've wanted to replace my distributor for some time. Got confused when I went to Rock Auto looking for a good replacement. I have a very low mileage 1990 5-speed engine with 1992 parts installed (Distributor). Questions: 1. Do you have to use an inside caliber to measure the cam? 2. I can't seem to see the number on my old distributor, where is it located? 3. Do you have to pull out the old distributor to find the number, or can you see it as installed on the car?
I looked at a picture of a Optical Ignition Units operation and can easily see that oil on either one of its components will cause misfires. Oil covers the optics like the disruptor. This may be the reason I seem to feel the my car is not pulling as hard as I think it should. Dirty, oily, gritty inside my unit. (246,000 miles on the old distributor)

You contribution is really appreciated.

[i218127]

71 vs 71B

Think that may be an outside caliber. I always get confused. Inside calibers are inserted inside the unit to be measured and Outside calibers measures the outside of an object from one side to the other. Sorry about that.

[1990new]

This may help you:
Click on the ProTec Bulletin link after you go to this site to see a diagram of how to measure the rotor cam shaft.


http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=NRD4835404_0407413615

If you get a Hall Effect distirbutor (B suffix) you wont nave to worry about the dirt and oil so much.

The number is on the side of the distributor between the two flanges here you bolt the distributor to the head.
It's almost impossible to see the number without removing the distributor and cleaning it.

[i218127]

I expected as much.

[i218127]

I've never been asked what size my rotor was. They just give me the one in stock for that year. I suspect that older EFI years have the 71 with optical sensors, later years have the 71Bs with hall effect. I also see that there may be a difference in distributors between automatic and manual. (Had AUTOZONE check a 94 Aspire, they list auto and manual)

That may be reason they don't sell to many replacements!!!!!

[zoom zoom]

Aspires are different for obd1/2, the ckp sensor is mounted externally on later models, I don't think auto or manual has anything to do with it.

[i218127]

Thanks for the info. Just noting that the AUTOZONE splash screen lists auto and manual. I was surprised. I didn't ask why. There should be some reason. Just alerting others to this possibility.

[1990new]

I checked autozone and I don't see what you mean by automatic vs manual for distributors.
Also regarding the difference in size of the rotor shaft... I could find none of the autoparts online sites that list sized for the rotor buttons, so
it appears that you cannot get different size buttons to fit different size shafts after all. Nothing in the rotor button info mentions the size. (all appear to be spring loaded)

The only real required differences in distirbutors that I see in the auto parts listings is for the 88-89 vs 90-93.
88-89's have the vaccum advance connection and the 90-93 do not. No difference is shown for the 89 efi vs 89 carb.

So it looks to me like there may be no need to worry about the size of the rotor shaft if the buttons are all the same.

Assuming you can trust the auto part store listings.

[i218127]

71 vs 71B

I don't want to get people confused. The distributor I was talking about was for a 1994 Aspire 1.3L. The splash screen I'm talking about was the one in the AUTOZONE store, not on line. This was just a check to see if the 92 Festiva distributor was similar to the Aspire unit. I'm going to pull my old unit tomorrow. In my old tool box, I found a rusty set of calibers that measures in fractions of inches. Will measure and post the results.