Hot Rods T5 behind flathead .72 O/D ,too much?.

I have a thread going about changing the 5th gears on an S10 t5 , " gimpyshotrods" gave me a thought that changing to .72 O/D would mean a 1000rpm drop from 4th to 5th .
Has anyone real world experience of running a flathead with .72 5th gear.

 

I did that with no problem, but I had a 3.90 rear end gear and 7.00-16 rear tires. What are you running?

 

The stock Ford 3 speed has about a 2.5 first gear ratio? With 3.90 gears the 3.75 ish T-5 first gear must wind out very quickly

 

I don't but I do have a few questions that might help you decided.

? is this in the spinner or a rod or another car.
weight of car roughly, as in spinner or A roadster

regardless of what car, do you know rear end ratio? what sized tyres are you running.

and what rpm does the car pull at the moment at 100kph?

I would then plug this info into a rpm calculator to see.

At the end of the day, you have a 1:1 ratio in 4th, so if your concerned , just shift down to 4th and your good for the hills.

Personally I would do it, I have .82 in my roadster with 3.9 rear and 7.50x16 -31" tall. im about 2100rpm at.

http://www.csgnetwork.com/multirpmcalc.html

try this one, I plugged my data in and found that changing from .82 to .72 only dropped the rpm by 300ish.

but 1:1 to .72 dropped it about 800-900rpm

 

Not for the 49 spinner. We want it for our 32 3W highboy. 750 x 16 tyres , 3.54 rear , .86 od at present and spins at around 2400 in 4th and only seems to drop to 2200 in 5th according to the tach. ( maybe the tach is wrong)
Have done the maths and it does seem a big drop .

 

My T5 was a WC from a Camaro. My records are flaky, but I think 1st gear was 2.95 and the OD was 0.63. 1st gear was very useful, and having five gears to choose from was a delight compared with the '39 3-speed that was in it previously.

 

If the flatty has enough low end torque it should go okay.

 

2400x.86=2064=336 drop.....2400x.82=1968=432 drop...2400x.72=1728=672 drop...

 

So with 3.78 gears 4th @60=2766rpm
x.72 =1992 @60mph
With 4.11 gears 4th @60= 3008
X.72= 2166 rpm

First gear with the 4.03 1st ratio will be at 3000 by 15mph with 4.1 diff
Sheesh could climb a wall with that.

 

My company builds T5 transmissions for Cornhusker Rod and Custom, and we build specifically the 3.76 1st gear ratio transmissions with 0.72 or 0.76 OD ratios. The 0.86 ratio is barely noticeable, and the 0.63 ratio is to deep.

 

Tell us more please . We have an S10 with 4.03 1st, what is involved to change to 3.76 1st gear for a W/C t5?

 

The answer depends on your rear differential ratio.
The stock Shoebox BW OD had a 0.70 OD (with a 4.10 rear in the Fords and a 4.27 rear in the Mercs), so why wouldn't a T5 with 0.73 OD be fine in a shoebox?

 

^^^^^^^^^^ is true as far as it goes, but tire diameter, vehicle weight and engine torque at that RPM are also important factors. If the flattie is 'high strung' (cammed with hp & torque at higher RPM), it makes a difference.

 

Have a T-5 from a 93 Mustang in my 50. With a full race flatty and a 3:50 eight inch Maverick rear end. My fifth gear is .68 OD. I run about 2K RPM'S at 70 MPH.

 

The gears, 1-4, are not changeable individually. While the gears on the main shaft slide, as actuated by the shift forks, the ones that they engage on the counter shaft do not, as the counter shaft is a one-piece deal.

Cluster gears:

Shown, out of the case. Note, this is one single piece of steel:

From your other thread, it appears that this is a World Class T5, from an late S10. In that case, it should be of the Ford (yes GM used the Ford pattern, 1993-on) pattern to the bell housing, 26-spline 1-1/8" S10 length input, and an electronic (not mechanical) speedometer drive.

At-least that is what it would be here in the states. If you have a GM pattern on the front of the case, you either have a unknown to the US version, or it is not a World Class unit (or it is a composite that someone built).

That combo, unfortunately, was in the dying days of the T5 in the S10. The V6's got the NV3500. The 2.2 L4 got the T5, with the low gear set, World Class, large/long input shaft.

I am not sure that there was a 3.76 gear set that fits the late S10 T5 WC mainshaft. Previous ones with the 3.76 gear set were all NWC.

This might leave your only interchange as GM V8 gears, which might all be too tall for the flatty.

Then again, we're talking about changing everything but the mainshaft inside the main case.

A decent rundown, from our pal FlatEarne, can be found here:
http://www.flatheadv8.org/ernie/ernie-t5.htm

 

Gimpyshotrods is spot on in describing our trans. So in all practicality if we change 5th to .72 O\D ,the rest are best left alone as it means a full tear down and replacement parts in an already rebuilt trans. So we will have to live with a wall climbing first gear.

From your other thread, it appears that this is a World Class T5, from an late S10. In that case, it should be of the Ford (yes GM used the Ford pattern, 1993-on) pattern to the bell housing, 26-spline 1-1/8" S10 length input, and an electronic (not mechanical) speedometer drive.

 

The only other near-ish gear swap would be the Mustang 1-4 gear set, but that might leave you with a 1st that is too high.

Posted using the Full Custom H.A.M.B. App!

 

The mustang 1-4 set can be either 3.55 first gear ratio or a 2.95 first ratio. A Camaro V8 1-4 set is a 2.95 ratio the same as a ford "cobra" gear set. OD ratios can be changed with out affecting 1-4 gear sets.

 

The 3.76 S10 ratios were only for the non-world class applications. The only S10 world class ratio that I'm aware of is the 4.03 low gear ratio.

 

Yup. This is my conclusion, as well.

For the OP's application, changing 5th, the rear gear, and the tire size, are the only possible variables..

A Mustang or Camaro gearset will leave him with issues getting off the line.

 

Meanwhile, we still don't know the OP's existing differential ratio, so what are we really talking about?.

I just had a hybrid T5 built with 2.95, 1.94, 1.34, 1.00, and 0.76 gears. It's going in a car that currently has a 3.25 rear but will have a 4.11 swap soon. I think this will work out well, but without that rear end change---- not so well getting off the line and kind of lugging on the interstate.

 

What would be the best rear axle ratio / tire combo?
Ive got a 7.00 rear tire and was thinking of running a #2 gear set with my 3.54 gears in my QC which would give me a 3.67 final gear.

 

Apologies if you missed post #5 we are running now 3.54 gears in a converted banjo to late model axles. Plan to change to lower rear gears and taller o/d .
Was the hybrid T5 built for a flathead? Just down here we don't get the long freeways , sure it's flat in places but a lot of our roads seem to follow the old goat tracks corners and hills, plus 60mph is our limit and they are getting more revenue hungry all the time policing the limit. ( spoil sports)

 

So I presume you are running a T5 , do you know the O/d ratio? Is this a flathead powered rod?

 

According to cokar a 16 x 700 is 30.4" tall and a 16 x 750 is 31"

 

Sorry I missed the post about your particular application, I assumed from your OP it was for your avatar shoebox. My hybrid was built for a Ford 302, but my thoughts were towards pure gearing calculations, not necessarily the engine output, and I'd probably make the same choices for my flathead if the time ever comes.

If I was limited to 60mph, I would probably not even consider OD.

 

Why did the next 25+ posters waste their time after this insightful bit of information? Ahh!! I forgot about post count.

Frank

 

Yes I think you are correct I was taking a hillbilly guess, I assumed and you know what

 

Yes mike I think you are right , but if I can save a few $ on the high gas cost here I am too miserable to pay more. I need excuses to drive not reason why I can't.

 

Have found a new matched 5th gear set locally which should give us .72 O/D but will need to get the other tooth counts first to be sure , even .78 would be great. . First will be a crawler granny gear I suspect . Watch this space.