T5 and speedo accuracy question

[mark '87 930]

I recently installed a T5 in my truck (love it btw) and my speedo is is running about 25-30% too fast.

What speedo gears (i have the mechanical speedo) are you folks with T5's running? I have a 20 tooth driven gear and i think my drive gear is 6 tooth, although that one is hard to count i find.

I have a 3.90 rear gear ratio and 29" tires. What are you guys with T5's running?

[AZ59apacheguy]

Subscribed, I'm getting ready to do the exact same thing in my '59 with 3.90 rear. You got any pics or installation advice you could throw my way???

[mark '87 930]

AZ59apacheguy... No pictures but tons of advice.. depends on what you are pulling out of there though.

bottom line... 1) get the Astro minivan clutch pack (11" clutch and pressure plate combo) 2) Your driveshaft will need to be shortened or lengthened (again depending on the tranny you pull from it ) 3) make sure you get a short shift kit and an S10 tail housing (unless you have bucket seats).

Everything else is easy peasy.

As for the accuracy of the speedo, I pulled an SM 420 from there which I think had a 7 drive gear and 13 driven.. so maybe i have an adapter at the speedo gauge to speed it up. I'll check in the morning to see what there is.

[Highsider]

I could use a widget to speed up my mechanical speedometer.
Reads slow, as indicated with my Garmin.

[oldgoalie]

Probably not going to be make up the diference by changing the driven gear and the drive gear is kind of a paine to change on a t-5. You have to pull the tail housing off and that means pulling the trans back out because of the shift linkage set up. That said there are adapters you can get in different ratios. Near me ( Washington State. ) there is a company that will make any ratio you need, about $70. Just have to give them a little info and they can figure it out. Getting one from Wa. might be kind of a paine for you but there may be a speedo shop near you that could build one. I also think that I have seen a company that makes them on E-Bay. good luck !!

[_Ogre]

you can change the gear for the speedo cable drive, sometimes you need to change the housing too.
i went thru this with truk when i first got it on the road, my speedo was reading 10% fast
most tranny shops will carry the parts to convert your speedo drive
read this transmissioncenter.net/speedometer_calibration

[mark '87 930]

Thanks Ogre. Turns out i did have something on there to 'speed' it up. I guess with the SM420, it wasn't turning fast enough so it was uped by about 25% with this little gizmo that was screwed directly onto my gauges. I thought it was a stock piece but it wasn't. I pulled it out and immediately my speed was almost bang on. I wasn't looking for dead accurate... but at least within a 10% range... now I'm off by about 3% which is great. The best part is that it cost me 0$!

Thanks for your help.

[judd55]

Here's a site I used to calibrate mine, in case you're interested in getting it dead on ..........

http://www.novaresource.org/speedo.htm

[mark '87 930]

Thanks, that's a great resource. I currently have the 29" tires on there, but ordered slightyl smaller ones (28") so my 7X20 gear setup will be inder 2%. Maybe i'll buy a 19 tooth in the event i ever go back to the 29" setup.

[AZ59apacheguy]

Originally Posted by mark '87 930

AZ59apacheguy... No pictures but tons of advice.. depends on what you are pulling out of there though.

bottom line... 1) get the Astro minivan clutch pack (11" clutch and pressure plate combo) 2) Your driveshaft will need to be shortened or lengthened (again depending on the tranny you pull from it ) 3) make sure you get a short shift kit and an S10 tail housing (unless you have bucket seats).

Everything else is easy peasy.

As for the accuracy of the speedo, I pulled an SM 420 from there which I think had a 7 drive gear and 13 driven.. so maybe i have an adapter at the speedo gauge to speed it up. I'll check in the morning to see what there is.

Thanks for the great info. I bought a spacer plate that goes between the T5 and Bellhousing so I won't have to cut the shaft. I have a bench seat, so is that why you say get a short shift kit? Also, how does having an S10 Tail Housing affect having a bench seat? Thanks

[mark '87 930]

i sent you a PM.

[judd55]

Originally Posted by AZ59apacheguy

Thanks for the great info. I bought a spacer plate that goes between the T5 and Bellhousing so I won't have to cut the shaft. I have a bench seat, so is that why you say get a short shift kit? Also, how does having an S10 Tail Housing affect having a bench seat? Thanks

If you have the Camaro box the shifter will exit under the bench seat ......... the S-10 tailshaft will move the shifter up 10 to 12 inches or so.... !!! I used a Pro-5 shifter from a Camaro on the S-10 tailshaft for a shorter shift, positive stops and the ability to bolt any of the Hurst sticks on.

Here is a bunch of T-5 info all in one spot............

http://www.jalopyjournal.com/forum/s...d.php?t=171291

[mark '87 930]

just to update everyone. The speedometer reads very accurate now, BUT, it pegs out at 58mph! I seems to work fine up until 58mph and then gets stuck.. When i slow down enough and long enough, it 'unsticks' and starts reading normal.. as long as i don't go past 58mph. Not that i drive past 70.. but what's teh deal? Speedo cable?

It was readin all the way to 80mph when it was fast.. the only think i can think of is the cable to the transmission speedo gear. Thoughts?

[_Ogre]

i had the same problem when i first put truck on the road
i'd pull the speedo out and run it with a drill, it was smooth up to 100
then i'd put it in and it would consistently hang at 47 unless i hit a bump and it would free up
my needle was hitting my volt gauge, a little tweaking towards the face and all was good

[mark '87 930]

Ogre, do you mean the physical red/orange speedo needle was touching the voltage gauge and hanging up on it?

[mknittle]

Go to a speedometer shop they have gear drives that fit on the speedometer drive. That way you wont have to take the trans out! we use them on the log truck. they can be used for under or over drive on the cable. like this.

http://www.ebay.com/itm/64-65-66-67-...fdc49e&vxp=mtr

[mr48chev]

Originally Posted by mknittle

Go to a speedometer shop they have gear drives that fit on the speedometer drive. That way you wont have to take the trans out! we use them on the log truck. they can be used for under or over drive on the cable. like this.

http://www.ebay.com/itm/64-65-66-67-...fdc49e&vxp=mtr

That would be quite similar to what Mark 87 930 tool off the back of his speedometer or what is shown as one of the items in the link Ogre Posted earlier.

Those boxes should be available at most semi truck shops like a Kenworth or Peterbuilt dealer's parts counter.

The best way I can offer to figure out what you need is to take a run down a straight smooth road where you can hold a steady speed and take a GPS with you (handheld works great but the trip kind works too. And when you read a speed on the truck's speedometer read the actual speed on the gps and remember both. Then figure out the percentage of difference between the two and which way you need to go to correct the speedometer and get a conversion box that will create that difference. if you poke around wrecking yards a lot of the 4x4 trucks and big trucks may have one of those boxes between the speedometer drive and the cable ready for the picking and then you would have to get the right gears for it.

On your speedometer not wanting to go past 58, most likely it needs a good cleaning. Most cities have guys with speedometer shops in them.

[mark '87 930]

to clarify, the speedometer is now accurate (within 2%) seeing as i found and removing that gizmo that you guys are referring too. Now my issue is that the speedometer stops working at 58mph. It's like it is stuck there and won't go higher. When i slow down, it comes abck down. Maybe a newly lubed speedo cable is in order.