I have an issue with trans to flex plate

[peedee]

Hi guys I have an external balance 360 with the b&m flex plate that lets me run an a904, which has been working well for a number of years, I also have the 148 tooth ring gear on the converter so use the odd starter.
My issue is that recently I started having starter engagement issues in that occasionally it would grind and not engage with the ring gear teeth, after burning out the factory style reduction drive starter I had I bought a mini starter for it which initially worked for a few months, I have checked engagement and it seems fine.
What I have found is that winding the motor over by hand it gets to a point where it goes tight and really needs some pressure to continue to be rotated, even removing the spark plugs doesn’t make any difference, I disconnected the torque converter from the flex plate and the motor turns over easily by hand, and so does the transmission until I put a bolt into it again to re engage the converter completely.
Any ideas where in the transmission I would be looking, I have not pulled it yet, but it was completely rebuilt back in 2012 and would be lucky to have had 5000 miles put on both the motor and trans since being built, by the way both are fairly stock builds the motor is 40 thou over size and stock heads with a small cam that performs mainly in the 2500 to 3000 rpm range and a converter stall of 2000 rpm and had the transgo stage 2 modification done to it.
Thanks for reading the novel

 

[jbc426]

That is interesting. Confirm this is an LA based engine and not a Magnum based engine?

How much clearance in "inches" (sorry about my ignorance of the metric system, I have to use a conversion app) do you have between the torque converter when it's unbolted from the flexplate and pushed all the way into the transmission as far as it can go, and then pulled forward to the flex plate all the way?

Is there any run-out at the flexplate or torque converter ring gear when rotated? Do you see any cracks in the flexplate near any mounting holes etc?

Can you post some pictures of the wear on the ring gear and starter drive gear? How much play is there at the crank when measuring the thrust movement ( use a pry bar to push the harmonic balancer forward and aft)?

 

[Syleng1]

I would double check the bell housing bolts for tightness. From what was typed- I feel like the ring gear is out of alignment with the starter- bell housing alignment or double check the ring gear mount on the torque converter. The other issue I had with a 904 that was commercially rebuilt was the pump bushing was not installed (may not be your case) but the converter started to oblong and the starter would grab and go. Sometimes binding up. Again just a thought. If mine I would be pulling the transmission and checking crank runout to start. Once apart I believe you will find the start of your answer.
Good luck!
Syleng1

 

[hemifiedbird]

Do you have access to a dial Indicator? If you do you can check the torque converter run out bolted up to flex plate and then unbolted. Turn over by hand and you will see where the highs and lows are and compare to bolted up to unbolted. Also Syleng1 has a good idea as well that maybe the bolts are loose on the bell housing.

 

[Oldmanmopar]

1. do you have an early small register hub converter from a pre 69 trans with a large register crank that all later engines have?
2. Your flex plate, Does it have holes for 7/16 converter bolts and your using a 5/16 bolt converter.

That would be the first questions I would have.

Also did you know that some of the mini starters require a bushing to be used on the top bolt. Some of the starters come with the bushing and some don't. Many times this is over looked.

My guess is you have a small register converter with the large crank hole . Also together with the large bolt hole flex plate with the smaller 5/16 converter bolts.

 

[hemifiedbird]

Another thing you could try is bolt your tourque converter back up and then loosen or pull the starter and try turning by hand.

 

[peedee]

Hi guys I appreciate the ideas so far
Yes it is definitely a LA block and not a magnum block
I will need to get under there and do some measurements to be able to answer some of the questions
I have checked the bell housing to block bolt as that was one of my first thoughts
The torque converter bolts are 7/16th as I did have to helicoil one that was stripped
The mini starter came with a shaped steel plate to put in between the starter and the mount to spacer it, I have tried with and without it, as well as with and without the dust shield

I will get back about the other suggestions as soon as possible, Iam working on the car under a carport with it elevated on axle stands as my garage is not big enough to work in or have the luxury of a hoist, the whole car was built either in the garage or under the carport from a paint less shell

 

[transman]

1. do you have an early small register hub converter from a pre 69 trans with a large register crank that all later engines have?
2. Your flex plate, Does it have holes for 7/16 converter bolts and your using a 5/16 bolt converter.

That would be the first questions I would have.

Also did you know that some of the mini starters require a bushing to be used on the top bolt. Some of the starters come with the bushing and some don't. Many times this is over looked.

My guess is you have a small register converter with the large crank hole . Also together with the large bolt hole flex plate with the smaller 5/16 converter bolts.

1.550" converter pilot used from 1960 to 1967. Large converter pilot 1.810", used from 1967- on for the 904's. Front pump bushing (converter hub) Used only one and it was used from 1960-- on. There are two types though of front pump bushings available, one a babbit bushing the other a bronze bushing. Peedee did not say what year the converter was for, but I if he had the wrong size pilot converter, issues would have been present very soon after installation.

 

[peedee]

Ok guys I’m not 100% sure of the converter year as it as an exchange reco one that was identical to the original and was put in as the trans was rebuilt as the converter was an unknown quantity and I did not want to have to pull the trans if it was faulty after the initial rebuild, now the engine and trans were rebuilt back in 2012 and as I stated the car had probably had 5000 miles on it since 2018 when it was finished and registered for road use.
The converter at its rear most position is inside the bell housing approx 1 1/4th inches and up against flex plate without bolts in approx 1 1/8th inches I would estimate maybe a 1/32nd or 1/6th more with the converter bolts tight.
There is no movement of the crankshaft forward or back levering on the balancer against the k frame or stabiliser bar.
The teeth on the converter have some marking from trying to get it to engage, see pics
This has come on suddenly and got worse very quickly, I can rotate the engine with a breaker bar and the starter will engage but after it kicks out it needs to be turned by hand again to get the teeth to mesh again

 

[Oldmanmopar]

And you are sure the bolt holes in the starter are the correct size for the 7/16 bolt and stud. Many of the mini mstarters have a larger hole and require a bushing.,

We had a Race truck engine come back due to a similar problem. It destroyed the rear main after a couple races. We asked the customer to bring the converter to the shop. After chucking it up in the lathe we found the pump drive hub was welded on crooked. At the ring gear it was over 1/2 inch out. The converter came from a reputable trans builder always mentioned on this site. It was overlooked when built and shipped.

I found it is very important to check all parts being used when assembling everything today. Quality is not what it use to be. We can blame it on what ever. But it always comes back to the bumpy ride crossing the ocean. The waves are getting bigger due to climate change.

 

[peedee]

Thank you oldmanmopar I will double check the bolt holes and reassess although it was doing it with the factory starter as well until I burnt it out trying to get it to start with what I thought was an ignition problem but wound up being a stuck needle and seat on the secondary’s of the carb

 

[transman]

And you are sure the bolt holes in the starter are the correct size for the 7/16 bolt and stud. Many of the mini mstarters have a larger hole and require a bushing.,

We had a Race truck engine come back due to a similar problem. It destroyed the rear main after a couple races. We asked the customer to bring the converter to the shop. After chucking it up in the lathe we found the pump drive hub was welded on crooked. At the ring gear it was over 1/2 inch out. The converter came from a reputable trans builder always mentioned on this site. It was overlooked when built and shipped.

I found it is very important to check all parts being used when assembling everything today. Quality is not what it use to be. We can blame it on what ever. But it always comes back to the bumpy ride crossing the ocean. The waves are getting bigger due to climate change.

Good advise. Obviously not all converter builders check the hub runout. Can't blame the transmission builder though, he bought the converter in good faith. It would be interesting to know who the converter builder was.