speedometer question
Thread Starter
Racer
Joined: Apr 2007
Posts: 275
Likes: 1
From: Lafayette/marquez La/tx
speedometer question
I just purchased/installed Th350 trans from summit. I left the speedometer gear that came with the trans in the new trans. Speedo read about 140 at 70mph. Following weekend I installed the gear from my old original trans into the new trans. Still about 10 miles per hour difference. I know.......like a dummy i didn't count the teeth or notice the color. I just thought the one from the old tranny would be correct. I have a 3.55 rear end and 255/60-15 tires. Ant help with the correct gear would be appreciated.
Le Mans Master
Joined: Mar 2001
Posts: 6,638
Likes: 287
From: Ann Arbor Michigan
Le Mans Master
Joined: Sep 2004
Posts: 5,116
Likes: 5
From: Livonia MI
You'll need to change out both the speedometer driven cable gear and the the tranny output shaft drive gear to make it right. You have to pull off the tranny tail housing to access to the shaft gear. Good idea to use the original driven cable gear plug in housing too.
Pro
Joined: Apr 2008
Posts: 596
Likes: 6
From: Irving Texas
The easiest way is to remove BOTH gears from the old trans and install them into your new transmission. The little gear is pulled off from the side. The larger gear is held in the main rear shaft with a clip. You need to pull off the tail cover (4 bolts) first, then unclip it.
By the way, I bought the same TH350 Trans from Summit.....cant beat it for $700!
By the way, I bought the same TH350 Trans from Summit.....cant beat it for $700!
Thread Starter
Racer
Joined: Apr 2007
Posts: 275
Likes: 1
From: Lafayette/marquez La/tx
Yeah, I was going to go with the 700r4. But the money ain't there right now. And my other tranny was on it's last leg. The New one shifts pretty hard when you get on it, and it pulls good. The stall converter I bought is fun to. I think I'll pull the other gear out this weekend and make the swap with both gears
Thread Starter
Racer
Joined: Apr 2007
Posts: 275
Likes: 1
From: Lafayette/marquez La/tx
Ok.... I looked at and count 22 teeth on the gear. The tranny gear is purple i can't count the teeth with the tranny installed. It really is more work than I felt like doing this weekend to remove the tailshaft and install the old trans gear which is orange.....it's easy to remove when trans is out if car. I tested my speedo at 60 mph took 70 seconds...which i believe is around 51 mph......feel free to correct my math. From what i understand i need one tooth for every 5% error. my error is appox. 17.6% again correct my math if needed. So i need to add 3-4 teeth to the gear? 25-26 teeth which i don't think is available. Therefore I need to remove the tailshaft and change the gear from my old tranny? Just verifing that i have to crawl under there and dig it out from the bowels of the trans.exhaust, crossmemer...etc. Which would have been much easier if I'd done all that BEFORE I installed the new trans.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
Your options are these: 1) remove the tailshaft and install the correct drive and driven gears in the tranny for the rear gear and tire size you have on the car; 2) change the speedo driven gear to one with 3-4 LESS teeth than the one you now have {since you are going slower than actual speed, you want the driven gear to rotate faster, not slower, than the one you now have...that means fewer teeth}; 3) purchase a speedo ratio change box that will convert the drive ratio the proper amount (do this only if you cannot get a driven gear that corrects the speed adequately).
I think that #2 is your solution and 5 teeth less is probably your best choice for it {4 teeth less would be your second choice}.
P.S. Why the he!! didn't Summit racing ask what rear end and tire size you had so they could install the correct driven gear????? {Very POOR customer service!}
I think that #2 is your solution and 5 teeth less is probably your best choice for it {4 teeth less would be your second choice}.
P.S. Why the he!! didn't Summit racing ask what rear end and tire size you had so they could install the correct driven gear????? {Very POOR customer service!}
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Thread Starter
Racer
Joined: Apr 2007
Posts: 275
Likes: 1
From: Lafayette/marquez La/tx
I emailed Summit. They suggested 18 teeth which is 4 less. I asked them to send it free of charge, as i did purchase a trans. and torque converter. Seems only fair to me. It's only like 9 bucks. But i agree it should have been matched to my vehicle. So maybe if you buy a trans from them ask them to install the correct speedo gears......cause they don't ask
Thread Starter
Racer
Joined: Apr 2007
Posts: 275
Likes: 1
From: Lafayette/marquez La/tx
hey snoopykissedlucy.........Just an FYI for your new summit transmission.. I had to install helicoils on my transmission mount bolt holes as there were no threads left. Also after i installed the trans. and filled it with fluid and followed summit's start up instructions. I noticed a big puddle of transmission fluid on my shop floor. I'm thinking maybe I messed up the front seal. Flashlight in hand I rolled under the car and discovered the pump housing bolts were leaking fluid behind them. I was able to get a wrench on them to tighten them and the leak stopped. Just something you might wanna check before you install your tranny
