Bouncing speedo after gear swap

[needlenose]

I just swapped in 3.73s from 4.10s and now my speedo is randomly jumping back and forth about 10mph. I chickened out and paid a shop to do the work and this was the result. This and really good cruising engine speeds.

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[cpdenton]

Take it back to them!

The speed sensor on a 94 is in the rear end. Obviously, something is misaligned in the tone ring or the sensor itself.

 

[crash-harris]

X2 on that. I would stay and watch them work on it again too. If your electric speedo is bouncing after they did a gear swap, they may have not done it right. Personally, I would be enraged because something misaligned back there could mean catastrophic failure, or just a bent tone ring, which I would still be red in the face about. I've done a few regears and there is no reason why something should be that off. Check to make sure that they reinstalled the speed sensor on top of the differential case. Could be as simple as that.

 

[riotwarrior]

Sounds funky in gear swap...shouldnt have removed speed semsor to do rear gearing...but yuppers back it goes.

How much difference jn rpm shoud be 150 rpm or so

 

[crash-harris]

Shops/dealerships seem to be doing more of that. Grandparents took their 98-99 F150 to local Ford dealership to get the speedo fixed. These use gears in the t-case likethe pre-93 trucks, but send an electrical signal instead of a cable drive. The factory driven gears on the sensors are notoriously thin. They qouted them $200-$300 to fix. I got the proper, better made gear for $30 and installed it only to find that the dealership had removed the drive gear inside the t-case. Niether Ford nor B&W sell the speedo drive gears individually. They'll have to get a new t-case now to fix it (since they couldn't understand the problem and I wasn't able to get to the dealership and rail them on grandparents behalf).

Bottom line, they keep touching s**t that they have no business touching.

 

[needlenose]

This is the first time I've given my vehicle to someone else to work on besides tire mounting or alignments in about 25 years. And this is what I get...

I will say though, the gears are silent and smooth. So at least that part is right. I would rather have to fix the speedo my self than mess with the gears. The owner seems like a good guy but I doubt he actually did the work; probably a shop hand.

...How much difference jn rpm shoud be 150 rpm or so

Unfortunately, I don't have my tach ring installed yet. This is a 12v swap, so the 4.10s were killing me. Even running it so high it was still getting 19.8 mpg highway/city mixed. So far I've put a little over 200 miles on right at 1/2 a tank of fuel. Again, highway/city mixed. Won't know any exact numbers on this run until I refill. I have 300 miles to go before I'm supposed to tow heavy. I'm hoping I haven't affected my towing too much with the taller gears. If so... time for a fuel pin.

 

[needlenose]

I replaced the VSS and pigtail with the same results. So I lifted the rear axle and tapped into the VSS output and measured it with a meter. The meter reads stable, but the speedo is still twitching. Would this indicate that the problem is in the PSOM? Or just that the meter isn't sampling fast enough to catch the fluctuation?

I did pull the VSS and check the ring. I found 2 teeth that looked like they had been chipped. But they weren't next to each other. I couldn't get my little Starret indicator into the hole far enough to check ring runout.

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[79jasper]

That meter probably can't react fast enough.

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[needlenose]

That meter probably can't react fast enough.

Thanks!

I'm just trying to eliminate any other possibilities before I give it back to them again. I would like to avoid the awkward we-found-another-problem-and-you-have-to-pay-for-it thing. I can already tell they are going down the "Must have not worked before we touched it" path.

I've read that the PSOM can have broken solder joints, so I pulled it to check that as well.

 

[needlenose]

So just an update. I gave the truck back to them and they determined that it was indeed the tone ring. Apparently it was the two teeth I had found earlier that were causing the problem. Looked like they may have gotten banged during the install. They replaced the ring and now it's all good.

So if your tone ring has a few mis-shapen teeth, your speedo will bounce. It really doesn't take much.

 

[tbrumm]

So just an update. I gave the truck back to them and they determined that it was indeed the tone ring. Apparently it was the two teeth I had found earlier that were causing the problem. Looked like they may have gotten banged during the install. They replaced the ring and now it's all good.

So if your tone ring has a few mis-shapen teeth, your speedo will bounce. It really doesn't take much.

Good to hear you got it fixed - Did the shop stand behind their work and fix it on their dime?

 

[dunk]

Glad you got it fixed. Today mine said no thanks, maybe another day. I guess it's winter for real now.

https://youtu.be/jppnsbAlrgM

 

[riotwarrior]

So just an update. I gave the truck back to them and they determined that it was indeed the tone ring. Apparently it was the two teeth I had found earlier that were causing the problem. Looked like they may have gotten banged during the install. They replaced the ring and now it's all good.

So if your tone ring has a few mis-shapen teeth, your speedo will bounce. It really doesn't take much.

Thanks...thiz almost well *** it does rate sticky inmy books

 

[needlenose]

...Did the shop stand behind their work and fix it on their dime?

Yeah, they took care of it. The owner is a good guy. I'm going to put them in the Hall of Fame. I don't seem to hear of many shops who will just do the right thing.

My dad took his PSD into a tranny shop here in Ft. Worth to have it rebuilt a couple of years ago. He got it back and drove it for about 4 days before the t-case locked up. It had no oil in it. He had it towed back and the shop owner had the sand to tell him it was full when it left the shop 4 days earlier. Funny thing was all the seals were good. They had taken the t-case off and laid it over and all the oil drained out. They just forgot to check it before sending it out. There are a million stories just like that.

It's good to know a shop isn't too proud to double check their work. If I chicken out of the ZF5 rebuild too I will definitely be taking it to them.

 

[needlenose]

Glad you got it fixed. Today mine said no thanks...

Holy smokes Batman! Look at that wheel-spin!

Good luck with it!