will speedo gear from an 80 work in a 100?

[dclee]

Hi all -

Just sitting at work and thought of this, so don't have my truck to look at, but had a question about the 5-speed tranny on the later trucks and speedometer correction. For those with 80s, this is not new, but on the A442F and A343F (at least) you could replace the speedo gear in the tranny with one that had a different number of teeth (can't remember how many off the top of my head) and it would correct the speedo for about a 33" tire (stock was also 31" like our 100s, with the 4.11 gear ratio). My question is, does such a gear exist for the later 100 tranny, or can one from an 80 be used?

Also, given that 100s up until 2003 had the A343F, couldn't this gear we all used for our 80s when the 33" size was all the rage, also be used in the 100 to help correct for a 31-33" tire size increase?

Thanks,

 

[hoser]

I've always wondered the same thing about the 100 using the correction gear. But I figured why only get partial correction (3.2%) when you can get full correction for $100. Range of +/- 28%

http://www.blackrobotics.com/

 

[dclee]

Heh, what can I say, I like "bolting on" more than "splicing into!"

...plus, I already have one of those correction gears laying around after I properly re-geared the 80...

 

[Sno bored]

I got the speedo correction gear for my 80 from Slee. If you call and ask them, they might be able to tell you.

 

[spressomon]

Now that I have the 4.88 project completed...I will need to figure out what speedo calibration product I will use too!

Knowing nothing about the stock set-up is it possible/simple as swapping a speedo gear out? Certainly it couldn't be that easy

 

[CPJONES1231]

I used the gear from the 100 in my 80.....

 

[dclee]

Now that I have the 4.88 project completed...I will need to figure out what speedo calibration product I will use too!

Knowing nothing about the stock set-up is it possible/simple as swapping a speedo gear out? Certainly it couldn't be that easy

It is on the 80. However, by going to 4.88s (didn't the `99s originally come with 4.3 gears?) for a two inch increase in tire diameter, you should already be back to stock ratios and your speedo shouldn't be off anyway.

 

[hoser]

4.88's and 35's will bring a 100 exactly back to stock ratio, no correction needed. However, Spresso is still running 33's.

 

[dclee]

4.88's and 35's will bring a 100 exactly back to stock ratio, no correction needed. However, Spresso is still running 33's.

Interesting. On the 80, 4.88s w/ 35" tires also brings the ratios back close to stock, but an 80 starts out at 4.1 with 31" tires. The 100 starts out at 4.3 with the same 31" tires (except the later trucks which have 4.10s...). On the 80, 4.56s with 33s brings you back close to stock, so it follows that 4.88s on the 100 and 33s would do the same? What am I forgetting? Christo? Hello?

Thanks,

 

[hoser]

IIRC, 35's and 4.56 almost bring an 80 back to stock. But 80 guys like to go with 4.88's to compensate for the extra drag, weight, etc.

Calc:
Tire
35/31=12.9% increase

R&P
4.1x1.129=4.63

So, 4.63 gears (if they made them) with 35's would bring the 80 back to stock.

 

[dclee]

IIRC, 35's and 4.56 almost bring an 80 back to stock. But 80 guys like to go with 4.88's to compensate for the extra drag, weight, etc.

Calc:
Tire
35/31=12.9% increase

R&P
4.1x1.129=4.63

So, 4.63 gears (if they made them) with 35's would bring the 80 back to stock.

Yes, you are correct. So going from a 31" to 33" tire is a 6.5% increase.

4.3 x 1.065 = 4.58, perfect for 4.56 gears!

So in fact, Spresso, with 4.88s, is actually a little "over-geared" for those tires. If anything, he'd need speedo correction in the opposite direction...

 

[spressomon]

4.88's and 35's will bring a 100 exactly back to stock ratio, no correction needed. However, Spresso is still running 33's.

Good point...D'oh! The 35"s go on tomorrow

 

[hoser]

Ah, cool! How's the new gears working out so far? Any more noise than stock? How has the 33/4.88 combination been working out? Would you say its overgeared for a daily driver?

 

[spressomon]

Ah, cool! How's the new gears working out so far? Any more noise than stock? How has the 33/4.88 combination been working out? Would you say its overgeared for a daily driver?

Believe it or not the 4.88's are fine with the 33's: Absolutely fine. In fact I am moving to 35" for that little extra ground clearance...but wish the gearing would be the same with the 35" as with the 4.88/33" combo! With my heavy rig the 4.88's are great. Got me wondering if the 5.29 with 35" might be the bomb (I'll never know as I am tired of working on this rig...time to drive it now)!

It is hard to tell if there is any more noise with the PG 4.88s over the buzz from the M/TR's Maybe with the new tires that get slapped on tomorrow I will be able to detect any gear noise...stay tuned

 

[hoser]

That's good to hear as I still plan on going 5.29 with the 35's. That would put me almost the same as 33's with 4.88's (2914 RPM @ 75 mph). I won't be driving any faster than that anyway. Peak torque occurs at 3200 RPM so it should be really nice on the freeway without having to downshift. I don't think the extra 266 RPM (over stock gearing) will make that big of a difference in fuel economy.

 

[spressomon]

That's good to hear as I still plan on going 5.29 with the 35's. That would put me almost the same as 33's with 4.88's (2914 RPM @ 75 mph). I won't be driving any faster than that anyway. Peak torque occurs at 3200 RPM so it should be really nice on the freeway without having to downshift. I don't think the extra 266 RPM (over stock gearing) will make that big of a difference in fuel economy.

In retrospect I think the 5.29/35" combo will be perfect. When are you going to tear down?

 

[Cruiserdrew]

Spresso-Bring that rebuilt truck out to Deer Valley with us next week! I want to see it in action. Details on the Norcal list.

 

[spressomon]

Spresso-Bring that rebuilt truck out to Deer Valley with us next week! I want to see it in action. Details on the Norcal list.

I'd love to but we have private chartered the Eldorado for Gate area fishing...and the beach bass have been 'on'!

I'm hopefully going to get out with you guys soon!

 

[spressomon]

Spresso-Bring that rebuilt truck out to Deer Valley with us next week! I want to see it in action. Details on the Norcal list.

Wait a minute...I thought your were doing Rubithon next weekend...and Deer Valley at the end of August. Now I'm really confused about the run calendar!