When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Got the car out today to clean it for a show tomorrow and thought I would take some pics while it was on the lift. I have had on the road for about 1200 miles at this point. 1000 before paint and a little over 200 since I finished it.
Had a little setback this weekend. I dropped the car off to get tuned last Thursday and on the third pull this happened: The good news, the car was making about 340 hp at the wheels at little over 4K RPM when this happened. So it should be in the mid 400's at the flywheel if not higher once the final tune is done. The bad news is that obviously I need a new driveshaft as well as the tail housing on the trans and some repairs to the exhaust.
My Muncie tailshaft broke during a chassis dyno run, the shop didn’t have my car tied down correctly, allowing the driveshaft to hit the tunnel, bad day...
on my trucks ive broken 2 driveshafts, both times the shaft had been comprimised by rust at a lubrication sleeve that trapped road salt and debris.
both times it happened when i was just getting moving from a stop, so at slow speed, one time no other damage, the other time the broken part at rear axle poked a hole in my gas tank
No dents or anything beyond surface rust. It did have a little bit of vibration over 70mph that I did not think would cause any issues until I had it balanced, but I think that is what did it. It happened on deceleration coming off of about 4600 RPM and 94 miles per hour. It did some damage to the floor, but nothing too bad. As I said, I am just very glad it happened on the Dyno and not while I was driving. I will be calling PST this week to get a new shaft made.
My Muncie tailshaft broke during a chassis dyno run, the shop didn’t have my car tied down correctly, allowing the driveshaft to hit the tunnel, bad day...
Did they strap the car down by the frame (keeping the body from moving up during the pull)? If not, I am not sure how tying the axle down could cause the driveshaft to hit anything it wouldn't be hitting while driving. Just to be clear, I do not in any way fault the shop for my driveshaft letting loose..
So apparently driveshafts have an RPM limit based on length, diameter and material. Some of you may have known this but I didn't. I usually have a few driveshafts sitting around and just put one in a project if it fits. I always thought the only real consideration to worry about was horsepower but RPM is much more important apparently especially with overdrive. This driveshaft was a 3" steel shaft that was about 63" long. After looking at the PST driveshaft site, this shaft would have had a critical speed between 4000 and 4500 RPM. This is the range it broke at. According to the the PST site, exceeding critical speed will cause the drive shaft to bend in the center and whip around which is exactly what happened. Knowing this information I am very thankful that it did not break on the road because I have had it in this speed range before. I now have a 4" aluminum driveshaft on order from PST. It is rated to be good to 2000 horse power and about 7400 RPM. From my measurements, it looks like it will fit even with the car aired out (the whole way down). Should be about 4 weeks before the new shaft is ready so the car will be out of commission for a little while.
i wonder what the OE driveshaft was dimensions were? It must have been made to withstand ~5000 rpms i would guess that to be within the realm of somewhat normal operation? I realize back when the vista was new most buyers werent taking it to 5k rpms, but i think its not unrealistic to thinkthat 5 k rpms would be possible?
it this why some DS have a center carrier bearing or some have a double carden joint ?
it this why some DS have a center carrier bearing or some have a double carden joint ?
carrier bearing: I would think so. Driveshafts with a double u joint usually have it to allow a steep pinion to drive shaft angle (like a 4x4)
The original driveshaft was 3.25 or 3.5 diameter (I don't remember which). The problem is that these cars used a long tail housing trans from the factory, so the 4l60 is quite a bit shorter leading to a longer drive shaft. Then there is the issue of overdrive. With a .7:1 final gear, the driveshaft is spinning faster than the motor. The new shaft should give me a max engine RPM of just over 5K in overdrive. I doubt I will get near that as the car was running at 94 mph in drive at around 4600 RPM when the first shaft let go. I do believe this is why most newer cars with overdrive run aluminum driveshafts.
Last edited by Loaded68W34; November 15th, 2020 at 03:00 PM.
Wow!! That is a nice car!! Congrats on a great restore!! You did a fantastic job of bringing that back from the brink.. Well it as a solid car to start with, but it looks better than new, now!
I am in the process of upgrading to a Tremc 5 speed and bought a new drive shaft from the company that sold me the transmission. I would never buy anything from them again the way I was treated during the process. They had a different company build the shaft. So I have no idea what I have. I am going to contact the company that built the driveshaft and see what the limits are on their drive shaft. Thanks for the knowledge, always good to learn about the things we take for granted!!
Another question, I see your frame is boxed. Is that a Station Wagon thing or did you box it with the kit that is available these days?
Thanks. The wagon frames are boxed from the factory like convertibles. Hard top wagons are longer than convertibles and vista cruisers are longer than hardtop wagons so it is a pretty long car with a pretty long wheel base. I just started working on a holiday coupe that I got for free when I bought this car. The difference in space that the each take up in the garage is unbelievable. The vista has a little bit of room in the front and the back to walk around. The coupe has a few feet at both ends. As for a driveshaft company, PST was awesome to deal with. I got the new driveshaft the week before Christmas (still not in the car yet). They were extremely helpful on the phone when I ordered and knew what they were talking about. The only thing I would say is that they gave me a time estimate for delivery but I forgot to ask for a confirmation number, so If there had been a problem, I am not sure how looking me up in their system would have gone.
Thanks guys. The new drive shaft showed up just before Christmas. I keep the car in a 12' x 20' garage in the backyard so with the snow we had up here, the car has been "trapped". I have been working on the white holiday coupe that I started another thread on. Now that the snow is gone, I am working on getting the cars ready to switch (holiday coupe in the back yard and vista in the main garage) to get the new driveshaft in and build a new exhaust.
You have done great research on the components. You found an extremely knowledgeable drive shaft manufacturer. Their solution will work well.
My trans is longer than yours, so a 3.5" Metal Matrix Composite shaft was sufficient for 7500 rpm. With rear springs out, a 4" just touched the tunnel, so I didn't risk using that size.
So I finally got the vista back in the garage on Friday. The PST drive shaft fits great. I also upgraded to 1350 u-joints and rear yoke. All in, yoke to yoke the driveshaft from PST was $750 plus shipping. With the rear bags fully aired out and the rear end sitting on the frame blocks there is still 1/16" - 1/8" between the top of the driveshaft and the closest floor brace. My new mufflers should be here tomorrow, then I will make a new exhaust and the car should be good to go.
Here is what happened to the tail shaft:
New driveshaft installed:
That's a nice driveshaft!! I have a new on in mine and it isn't going to cut it with the OD.. Didn't know about the critical speed rating prior to ordering it with the transmission. The place I bought the Tremec and driveshaft from said they were experts and never mentioned and issue with it.. Live and learn and spend money!!
The problem I have is that the car is so long. Added to that, the 4l60 is shorter than the long tail trans that the car had originally and then overdrive to boot.
That chart is very helpful. Thank you Loaded68. From what I see, that chart says I am good to 6300 shaft rpm. I contacted the manufacture and the lady couldn't give me a concrete number. But it is a 3.5" dia x 56" L with 1330 joints. She told me they sell a ton of them and lot of them have been at 150mph or better. My math tells me 150mph is 6823 rpm.. So I guess I will have to limit my top end to 140 till I upgrade to a 4" shaft. I will say, it was much easier to go that speed when I was in my twenties rather than now in my seventies!!
Thanks for the info.. always good to learn something new!!
The problem is 150 mph is a totally subjective (benchmark) description and would not be directly related to driveshaft RPM which your builder should know. The rear tire size (dia) and rear end ratio would be needed to work backwards for shaft speed. I assume you know these things and that is what you meant when you said you calculated 6823, so I am only pointing this out to agree with you that the company you used is less than knowledgeable to say the least. The image below is also from PST. I am not sure which measurement is 56" for you, but to give you an idea of the difference in wheel base between our cars my "W" length is 65.625". If you know your OD gear ratio (.7:1 for me) you can figure out your OD engine redline rather than top speed. 7400 (shaft critical speed) x .7 = 5180. I don't see myself taking the car to 5000 RPM in overdrive. On the dyno, the car stays in drive so hopefully I will not have a repeat of the previous shaft on the street or rollers.
You are correct, I did work it backwards from data on the tires, revs per mile. Then I guess at speed numbers to give me an idea of what ball park I was in.. I have .64 OD in my Tremec. So if my critical is 6300 per the PST chart ( my shaft is .083" wall 3.5" dia tubing.. I roughed the length of the shaft at 56". No one to help my hold the tape measure.. So that puts my max rpm in OD at 4032rpm engine. That puts me in the neighbor hood of 140mph.. Faster than I need to go at any rate...
Thanks for the added info.. I will take a better measurement!!
Here is the damage done to the old exhaust:
I was not all that happy with the exhaust when I did it originally. So, rather than try to cut out the dented sections, I started over from scratch.
I might have been, but I modified a set of regulators I had laying around to fit my doors when I redid the car. There are some other members with vistas and wagons who might be interested if you post them in the parts for sale section.
Thanks
-Tom
So after a month and a half of test drives (700 miles), the new drive shaft seems to have pretty good clearance. I had to grind away/ dent the rear most floor brace to clear, but only so the car can air out the whole way and still roll. I did encounter another problem. The trans was running very hot despite the radiator trans cooler / additional front cooler. The problem is that the high stall converter runs a lot hotter than a stock one. It was running between 200 and 230 even with the converter locked up. I think I caught it just in time to save the trans. To solve the problem, I added a new 40K GVW rated pass through trans cooler after the radiator cooler. Running 140 - 160 now and as soon as the converter locks up or the radiator fans kick on the trans starts cooling down which did not happen before. At the same time, I added a large pass through cooler to the hydroboost/ power steering system. With a small cooler, the fluid in the reservoir would get that hot that you could not touch the reservoir. Now the reservoir stays luke-warm. I also added a temp sensor and module to monitor the trans temp through the dakota digital dash so I don't have to look at it through the GM tech II. The dakota digital VHX system is not cheap, but you can add just about any gauge into it that you might need by simply plugging in a module and wiring a sensor to the new module. At this point I am reading my gear position, fuel pressure, air ride tank pressure, trans temp, and I have a module on the way to read my power steering fluid temp. Each of these has a programmable high and/or low warning that will flash on the speedo display if it is reached. I will post some pics of the coolers the next time I have the car on the lift.
Great build! I am very interested in your power steering cooler and reservoir systems. My '68 Chevelle has a hydratech hydroboost system and it whines after running for just a few minutes. It drives me nuts. Sometimes nuggets of information on how to solve problems like I am dealing with, like you've posted in this thread, are scattered about the forums and which can be very helpful. Thank you sir! Wonderfully cool car. Vista Cruisers ooze style.
I only just got the steering/ brakes fully sorted out (I think) a few weeks ago. I would suspect you still have air in your system if it is whining. The improved reservoir made a huge difference for me, but in addition to what I did above, I just added a huge pass through cooler in front of the radiator as well (18" x 8.5" and 1.5" thick). Before, the reservoir would get that hot that you could not touch it after driving the car. With the new cooler setup, it gets just a little warm after sitting in traffic standing on the brake peddle (which is when it would heat up the most before). Also, before adding the cooler, I bled the steering and brakes through at least a few dozen cycles. With the engine off, front wheels off the ground, and the car cold turn the wheel lock to lock 5 full cycles. Then press the brakes three times. Repeat the whole sequence over and over. I probably did it 20 - 30 times and then again another few dozen cycles the following day. My car had the opposite problem of what you are describing even after the new reservoir before I fully bled the system. It would whine at start up and then after a while the whining would go away. After bleeding the system over and over, the whining seems to be gone completely at this point.
Great input, thanks! I've bled it and burped it quite a few times. I think my next step will be the cooler. What fluid do you use? I started with Dexron VI and had my current problem, so I drained the Dexron VI and used GM PS fluid called for by Hydratech in their directions and it foamed terribly almost in seconds. I couldn't even get out of the driveway it was so bad. So I flushed that back out and put the Dexron VI back in and I'm back to where I started. Each time I bled the system, I did the lock to lock procedure probably 25 times. Sorry for the OT, I don't mean to take the focus of the thread away from your beautiful car.
No apology necessary. I am running swepco 715 as it is what PSC recommends. I got it on Amazon as PSC was out of stock.
Here is the power steering cooler I am running (plumed in line with the return from the power steering box before the reservoir): https://www.ebay.com/itm/22418254363...53.m2749.l2649
This is the trans cooler I am running (plumed in line after the radiator trans cooler): https://www.ebay.com/itm/22418254363...53.m2749.l2649
I had the car out on a long run yesterday and the power steering fluid temp stayed in the 90 - 100 degree range even sitting in traffic with my foot on the brake.
Using the VHX dash, I was able to add temp sensors to the trans fluid and power steering fluid.
Last edited by Loaded68W34; May 18th, 2021 at 09:16 AM.
October 9th, 2020, 02:09 PM
