MGB & GT Forum

Welcome! Sign In Register
Please Sign In or Register to Search

Speedometer problem

Posted by CtCarGuy 
Larry Boardman
Simsbury, Connecticut, USA   usa

The speedometer in my 70B was not working when I got it. I checked the angle drive on the transmission and the drive into the transmission was distroyed. I think the previous owner did not put in the washer. I put in a new angle drive (with washer) and now the speedometer jumps all over. The cable is good with no kinks and is lubricated. I took the speedometer out and made a tool the same size as the cable end and used a drill at very low speed to see if it was the speedometer/speedometer angle drive. It ran perfectly.

I am now concerned the pinion gear in the transmission is bad, maybe missing a tooth or 2. Replacing it crates 2 problems. 1) I cannot get the drain plug out of the transmission. I think the steel/aluminum corroded. I am concerned with putting too much force on it. I don't want to crack the housing. 2) The second problem seem to be that Moss and BV don't list the pinion or gear. In order to pass inspection the speedometer must work.

Thanks in advance for the help. The car is coming along great so far. Just these little gremlins that keep appearing.

Larry
. You can hide this ad & support this site by upgrading to a Gold Membership ~ click here for more info
chris Avatar
Chris Roop
Pendleton, OR, USA   usa

You don't need to drain the trans to replace the gear in the trans. I would look to the cable for dirt, broken strands, etc. first. If that is fine, then pull the gear housing and check the gear. They can be bought used on the trader or some such.

Roop's MG   – Pendleton, OR USA Quality new parts at 15% off of list. Can kozees at $2 each, black hoodies $25 both plus postage. Check out the Vendor Market page.
ozieagle Avatar
Herb Adler
Geelong Victoria, Australia   aus
1958 Wolseley 1500 "Wooly"
1966 MG MGB "Bl**dy B"

It could also be gunk in the speedo input bearing. The drill has enough torque to overcome it, by the cable drive, being somewhat springy, winds up till the gunk lets go and then the cable unwinds, giving a high reading, to only stall again, once it has unwound. Then repeats, giving a waving needle.

I hope all that makes sense.

Herb
Larry Boardman
Simsbury, Connecticut, USA   usa

Thanks Herb:

We actually tried turning the right angle drive on the speedometer by hand and had very little resistance. The action was smooth and the needle steady. I pulled the cable out from the speedo end and it was well lubricated with no kinks or strands. Looked perfect. I held one end and my friend the other. He twisted his end and there was no slack felt. The more I get into it, the more I think its the gear in the transmission. The next test will be to drive the car with the speedometer out and feel the action of the cable. I did test the cable when I put in the lower angle drive and it was smooth.

I think its interesting that the reproduction houses don't offer the pinion or gear based on the material used. I would think that there parts would be in demand.

Larry
. You can hide this ad & support this site by upgrading to a Gold Membership ~ click here for more info
Larry Boardman
Simsbury, Connecticut, USA   usa

Hi Chris:

Thanks for the reply. I thought I read somewhere that if you remove the plate where the speedometer cable enters the transmission, the oil will come out. I would love to change it be the drain plug is corroded in place. I imagine filling it from inside the car behind the console is going to be fun.

Thanks

Larry
chris Avatar
Chris Roop
Pendleton, OR, USA   usa

Jack up just the one side to be sure. As for checking the cable, pull it out of the housing and look carefully. Good luck!

Roop's MG   – Pendleton, OR USA Quality new parts at 15% off of list. Can kozees at $2 each, black hoodies $25 both plus postage. Check out the Vendor Market page.
Clay Johnston
Mt. Olive, MS, USA   usa
1972 MG MGB

First, replace the cable; may/may not fix the issue but its the least expensive, most direct.

Someone posted a PDF recently on attempting to repair a waveing needle.

Nisonger can fix the waveing.
. You can hide this ad & support this site by upgrading to a Gold Membership ~ click here for more info
ozieagle Avatar
Herb Adler
Geelong Victoria, Australia   aus
1958 Wolseley 1500 "Wooly"
1966 MG MGB "Bl**dy B"

Hi again, Larry,

A thought I had, about testing, is to use the cable attached to the speedo and run it with the drill. This would clear or condemn the whole cable / speedo bit.

Herb
Larry Boardman
Simsbury, Connecticut, USA   usa

Thanks for all of the help. The speedometer tested fine using a drill to drive it. I pulled out the cable again but this time cleaned all of the lubricant off it and lightly machine wire brushed it ti see if there were any kings or frayed windings. It looked fine and I re-lubricated it and installed it. I was careful not to over tighten the connection into the angle drive on the speedometer. I wanted to be sure the nylon collar on the cable was not binding. Bottom line is it works great with only a very slight waiver.

Larry
. You can hide this ad & support this site by upgrading to a Gold Membership ~ click here for more info
Larry Boardman
Simsbury, Connecticut, USA   usa

Here we go again. The speedometer worked fine for awhile and then quit again. We pulled the lower angle drive and the transmission end was ripped like the one we took out. The car is a 1970. Can the lower (and upper) angle drives be removed? The cable looks perfect. We tried turning the cable from the transmission end by hand and it seems stuck?? Both angle drives were checked and the bottom washer is in place. Both angle drives turn fairly easily by hand and the speedometer internals are free. Next is to check the cable with both ends disconnected to check for a krimp in the sheath. I do remember it was a little hard pushing the cable into the sheath for a bit and then it went in easily.

Thanks in advance for the help.

Larry
Clay Johnston
Mt. Olive, MS, USA   usa
1972 MG MGB

Larry,
Wonder if the cable sheathing has an issue?

One option, is to replace the cable and angle drives with a OD cable and no angle drives.

One other thing. I was having problems with my speedo acting inconsistently. I found that if the night-light fitting is pushed completely into the speedo the end of the bulb will hit the speedo pickup.
. You can hide this ad & support this site by upgrading to a Gold Membership ~ click here for more info

Reply to this topic or post your own questions!

Members Sign In if you've already registered, or

Register a New Account

Registration is free and takes less than a minute

Having trouble posting or changing forum settings?
Check the Forum Help File (FAQ) or contact the webmaster.


Join The Club

Sign in to ask questions, share photos, and access all website features

Adjust Text Size

Larger Smaller
Reset Save