4th gear not 1:1??????Why??

fastsc92

Registered User
Ok i just got back from FFW at epping, NH. I live 30 min away so its a short drive. Anyways...i took the chance to get on the dyno there to make 3 pulls with a wideband 02 sensor. This dyno is a new style which doesn't use any drums. It is basically two boxes that bolt dirrectly to your rear wheels and the car rests right on them. They claim is the most accurate because there is no slipping. Anyways...they ask you what rear end ratio you have and what rpm you want to stop at. I told the guy 5500 to shut it down. The first pull he made, the rpm's were getting up there and it hit the rev limiter and he shut it right down. The dyno was supposed to tell him to shut it down at 5500. The car is run in 4th gear which is a 1:1 ratio. BUt, the machine said it was only at 5235rpms. For some reason the final drive in 4th gear is not 1:1. He asked me 3 times if i told him the correct rear end ratio, which is 3.27. I installed the gears myself and they are indeed 3.27's....the first thing when i opened the box was to count the teeth and divide and it came to 3.272727272727272727. The rear end ratio is correct..so something must be wrong with the tranny. He ended up tricking the computer and had to tell it that it had a 3.89 rear end ratio...which is bogus. I just rebuilt this tranny and there is no way that it could go together wrong. all the other gears are correct and shift smooth and fine. Why isn't 4th gear 1:1???? When i figured it out....the 4th gear is acttually 1.2 : 1. Why is this happening and how can i fix it? I am 100% sure that the rear end ratio is 3.27. Help me please. this also seemed strange because at the track...i am in 4th gear for almost half the track and pass the lights at 5100. Does anyone else have this problem with 3.27's in a speed???
 
4th gear is 1:1. Something else is mixed up. I don't know anything about that dyno, so I can't help much.
 
Sounds like the clutch must be slipping. If you look in an exploded view of just about any 5 speed trans you will noitce that there isn't a fourth gear anywhere in there. This is because the input and output shaft are locked, hence 1:1 gear ratio.

Jeff
 
i know...thats what i cant fiugre out. This has me sooo confused. I know his car inside and out and still...i cant figure it out. The clutch isn't slipping because there was a good size load on the engine and no slippage. Like i said...i dont see how the tranny could be messed up because it would't work right if it was together wrong. When i just rebuilt it i changed all the blocker rimgs and i also changed the 5th gear and 5th/reverse sleeve. Thats the only thing i've changed. All the gears work fine and each follows the one before it nicely. I dont know why......please help me fiugre out this huge headache.
 
There is nothing to figure out...if there is any problem, it's with the dyno. BTW, I've never seen a dyno that used wheel speed to determine RPMS. They always use a plug wire or the negative side of the coil to pick up a tach signal.

David
 
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the kick who dynoed before me had a 90 sc....with a 5 speed and 3.27's also. His was right on the money. BEcause if 4th is 1:1.....then wheel speed should be rpm's. In my case it was way off.
 
4th gear through the traps @ 5100 sounds like 3.73's to me.....

With your tire size and trap speed, I could tell you for sure.
 
The clutch couls still be slipping. It's not like it's all or nothing (slipping), your brakes aren't all or nothing.

Like Dave said it could be the dyno or it HAS to be the clutch, since you say there cannot be slippige between the drive wheels and the dyno.

Jeff
 
its a brand new clutch too...with about 1200 miles on it. I dont smell any clutch either. Usally it will stink, because i've had clutches slip before. my tire measures 26" in the back...and the mph is 101. I did the same thing and it says that i have a 3.89 rear end ratio. The dyno was suposed to be the most accurtate one on the market so i dont think its that. Like i said...there was an sc right before me and it worked flawlessly. It could be the clutch but i highly doubt it.
 
it has stock rims and a 225 60 16 tire. still....i'm baffled. I opened the inspection cover today and there was no clutch dust or any residue in there from slippage.
 
Well, if you are sure about most all the stuff, it makes me think that you might have made a mistake on the gears. I know that stock and FMS gears have the ratio stamped right on them.

It should be really easy to verify gear ratio just by driving down the road and have someone pace you. Then just do the math to figure it out.

Clutch slippage would stink for sure, I don't think you'd miss that.

Also regarding the transmission, since the countershaft is solid, you can't mix anything up. It's not possible because it wouldn't go back together.
 
As far as I know Richmond does not make a 3.27:1 ratio for the 8.8, you might want check again. I wanted Richmond gear for my SC, when I called Summit to order them, they couldn't find them. I think they start at 3.55:1 for the 8.8, Good luck
 
i ended up getting the gears from a local speed-shop. I too didn't see them in jegs, but he was able to get them and the first thing i did when i opend the box was to make sure that i counted the teeth on the ring gear and divided by the pinion teeth and it came to 3.27272727.......
 
There could only be 2 things causing that if theres no tire slipage involved.
1. The clutch is slightly slipping.
2. The guy running the dyno messed something up.

I dont have alot of faith in chassis dyno's and this kind of thing is why.
Its too easy to manipulate things in order to come up with #'s.
I will not use one unless I own it.
 
i mean...it worked fine with the kid before me. also...does anyone else have 3.27's with a 5 speed. cause at the track i am holding 4th gear through the lights at about 5000rpms at 101mph. It seems like i'm in that gear forever, and i'm searching for another. anyone else have input on their gears?
 
fastsc92 said:
i mean...it worked fine with the kid before me. also...does anyone else have 3.27's with a 5 speed. cause at the track i am holding 4th gear through the lights at about 5000rpms at 101mph. It seems like i'm in that gear forever, and i'm searching for another. anyone else have input on their gears?
I understand what youre saying but knowing what you know about your pull can you really say that 100% for sure the fella before you got any legitamite #'s either?
I've messed with dyno's for over 10 years and the only dyno I will use is a freestanding dyno that only has the engine bolted to the dyno pump.
Chasis dyno's could if used properly be usefull. Truth is I havent seen them used properly but a couple of times.
Most of these places offering dyno pulls are doing it for 1 reason to make money.
Alot of younger guy's put way too much faith in what gets printed out on a piece of paper after there pull like its some kind of trophy. Nothing could be further from the truth.
98% of the dyno printouts made today are only good for wiping your butt with.
Your experiance alone proves that.
I'm not trying to be a horses arse to you and I'm sorry and already appologised for our earlier misunderstanding. I really am sorry about that.
If you would like for me to further explain my stand on these dyno's let me know, I'd be happy to.
 
oh i get what you're saying....but it jsut didn't make sense to me how it worked for the kid before me. and whe he said that it all kinda came together with how it was in 4th forever at the track. just making me think a lot.
 
fastsc92 said:
i mean...it worked fine with the kid before me. also...does anyone else have 3.27's with a 5 speed. cause at the track i am holding 4th gear through the lights at about 5000rpms at 101mph. It seems like i'm in that gear forever, and i'm searching for another. anyone else have input on their gears?

When I had 3.27's, I had to shift into fourth at about 1300 feet, just before the traps, and that's was with 275/40-17 DR's, about an inch shorter than the stock tires.

4th Gear 1:1 @ 5000 RPM with a 26" tire and 3.27's = 118MPH

4th Gear 1:1 @ 5000 RPM with a 26" tire and 3.73's = 104MPH

You don't have 3.27's.
 
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