CRX HF; A tale of 2 trannies...
 

There were two different transmissions that the '88-'91 Honda CRX HF came equipped with (High altitude model VS. Low altitude model). Without knowing a lot about transmissions, I can break it down best by saying that one of these models runs at lower RPM's in 5th gear (at a given speed) than the other model. It's almost a 500 RPM difference between the two cars. I'm sure of this...I've owned both models. Here's my question; what's the easiest way for me to decipher which transmission is which? I don't believe I can turn the wheels in 5th gear in a car that doesn't run (to try to compare ratios)...yet I'd like to know if the transmission that's sitting in an old HF in a local junkyard is the one that I want (the taller geared one). Please help.

Yep, one was the california model with a shorter FD, giving higher RPM's.

Best bet is to pull the transmission, put it in gear, and count the revs it takes to make the diff spin one full revolution (you're turning the input shaft).

I really don't think there are any codes or anything on the case to tell you the difference. If anyone would know, it would be "mista bone" on H-T - PM him, maybe he can help.

You probably can turn the wheel/engine! (unless the engine is siezed or the brake caliper is siezed).

I did this to rule out a non running crx at a junkyard that I was hoping would be am HF (it wasn't). It was not hard to do-

I brought my own jack with me and it took 5 minutes.

Just pop the hood and jack up the driver's front tire only. Turn the drivers wheel while looking down at the timing marks on the crankshaft pulley with the trans in 5th gear.

With the 87 dx trans (poor economy), you can turn the front wheel 2 times to get 3 revolutions of the crankshaft. That will equal 2600 rpm at 60 mph.

For the HF trans (2100 rpm at 60 mph), you can turn the front wheel 2.5 times to get 3 revolutions of the crank pulley.

It might be worth a try.

Erik, thanks!! I will give it a shot. I just hope I really can turn it. Will let you all know if it works out.

what state is the junkyard in?

You could get the VIN and run a carfax report and see where the car came from, i imagine they only sold the high altitude ones out west and not in every area.

not sure about the locations/disbursing of high/low altitude models across the country. One would assume there were only certain areas these were sent. These cars are so old, however, that they've all probably migrated outside of the locations where they were originally sold as new.

As for the old 5th-gear crankshaft turn....it makes no sense to me. I put the trans in 5th (remember, this car doesn't run) and turned the driver's wheel/axle and wound up with basically 1:1. For every 360-degree/full turn of the crankshaft, the driver's side wheel makes almost one complete revolution (about 5/6ths). How does that measure up on determining HF or not? Could I have done this incorrectly?

It sounds like that trans may be geared about like mine (2100 rpm at 60 mph). Do you recall what the rpm was at 60 mph on the trans type that you want?

I gave you the info on 3 rotations because you can be more accurate that way.

If we talk about 1 crankshaft rotation, it took 2/3rds of a wheel rotation to give 1 crank rotation on my DX trans (2600 rpm at 60 mph).

On my present 84 crx HF trans (2100 rpm at 60 mph) it takes 83% of a turn of the wheel to give 1 turn of the crankshaft.

If you know what size tires you will be running on, you can calculate the rpm at 60 mph for this trans. Use the circumfurence of the tire (in feet) and remember that a mile is 5280 feet. Oh yes- and you probably already know that since you turned just one wheel (with the other tire stationary) with teh action of the differential gear, it was actually spinning the engine twice as fast as it will be while driving (so in reality one crank rev will yeild about 1/2 of a tire revolution). 1 rpm will yeild about half of a tire circumference for your trans.

Hmm- why not do the rough calculations now - say you are using what I use- 175/70 13. The circumference for that tire is 71.14 inches (https://www.csgnetwork.com/tireinfo4calc.html) That is 5.928 feet per revolution. So, at 2000 rpm X 2.964 feet (assuming exactly 1/2 revolution per engine rpm)= 5928 feet= 1.123 miles/minute= 67.38 miles per hour at 2000 rpm- that's some pretty good gearing!!!

Let's be more realistic and use the 5/6 figure you stated above. Half of that is 2.5/6 = .417 X 5.928 (tire circumf) = 2.46 feet per engine revolution X 2000 rpm= 4940 feet= .936 mile= 56 mph at 2000 rpm. Not bad....

So- just a little difference on one turn vs. 5/6 of a turn can mean some noticiable difference in gearing. To nail it down, you may want to go back and turn the tire 10 times and count the crank revolutions.

Just out of curiousity- how much does the junkyard want? I talked the junkyard owner down to $200 on an 85 crx trans (he started at $250) but that price was only if I pulled the tranny myself!

Check out carpart.com That's where I found my 84 crx hf trans for $75

Erik, I said 5/6 but it's not exact. It's close. I can recheck again. Before I do that, however, I'll be jacking up my own HF today to compare notes. At least I know what I'm looking for now. I have to assume that if my own HF gets less of a tire rotation per one full 360 turn of the crank (in 5th gear), then the one that I cranked in the junkyard, then the 'yard tranny is probably the one that I want. I wish the serial # of the transmission would shed some light on the matter. We'll figure this thing out yet. Thanks so much for your help thus far.