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#1
06-01-2021, 07:33 AM
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BW Super T10 4-Speed Differences - 79 T/A
Good morning, Guys.
Question: for 1979, anybody know what are the differences in the Borg Warner Super T-10 transmission that was mated to the 400 engine vs. the one mated to the 301 engine, and that were coded UH vs. UF, respectively? Kindly advise. Thanks so much. |
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#2
06-01-2021, 02:14 PM
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Most late seventies Super T-10s.....had a 2:64 or 2:88 low gear........
Low gear in the 79 301 ST-10 was 3:44...Which made it launch real hard with the 3:08 rear gear they came with, 1st and second were correctly spaced....but 3rd was about 3 notches up the ladder....so you fell right out of the power band... I always called them a poor mans 5-speed....with NO 3rd gear... |
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#3
06-01-2021, 02:21 PM
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Quote:
Interesting, as the following site lists the gear ratios available: http://www.pontiacpower.org/BW.htm Appears outer case is also the same as for the 400. So question is how does one tell the difference? Code UH should be with the 400 and code UF for the 301. I have never seen these codes, so I do not know what to look for or even if these codes were just stamped in paint, so likely did not survive the years. Any insights? |
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#4
06-01-2021, 03:02 PM
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You can usually identify gear ratios in side by the the # of rings/grooves cut into the clutch disc splines on input shaft.
A W72 4-speed should have 2 or 3....and the 3:44 trans will have 5...or none... None could also indicate that Input shaft mat have been replaced (service part) The 301 4-speed is fine for spirited street driving behind a moderate HP Pontiac V8.....but will break the smaller gear tear teeth off easier...if subjected to abuse...of a big HP motor...And NOT really suitable for drag racing... |
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#5
06-01-2021, 03:11 PM
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Quote:
Transmission I am looking at was built and installed at the Van Nuys plant, which was the only plant I believe that built the W72 4speed Y84 cars. Seems likely that this is the correct UH transmission for my car. Would like to be more certain, though. Any other recommendations? |
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#6
06-01-2021, 03:23 PM
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So you are saying that the trans is still in car?
If so....check for partial vin stamp on small pad (upper main housing) and if it matches your car...you will know for sure. 79 Y84's were built at BOTH Norwood and Van Nuys...IIRC. Were you able to find a build sheet? |
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#7
06-01-2021, 03:34 PM
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I have the build sheet and all the paperwork. All the casting numbers and dates on the new SR block match for a W72, along with the heads, etc. So, just looking to put in a more date appropriate 79 BW Super T-10 and found one for sale in PA that was built and installed at Van Nuys. Just cannot be sure yet if it is the correct UH code for the W72. Any ideas as to how to tell without getting the current owner to take it apart? |
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#8
06-01-2021, 04:28 PM
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Get a picture of the input shaft....That has the rings cut in the splines..
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#9
06-01-2021, 04:43 PM
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FYI.......If your original motor blew up....it was likely due to operator error....
There were some issues with the non-W72 500 series blocks....but not W72 XX blocks from the factory... |
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#10
06-01-2021, 05:02 PM
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To reiterate (and somewhat clarify) above, the 301's Super T-10 four-speed had a first-gear ratio of 3.42:1 and its input shaft had 6 grooves. The W72 400 (and all midyear-74 onward 400 and 455 units) had a ST-10 with a 2.43: 1 first-gear ratio. Its input shaft had 2 grooves.
Chevrolet used the 2.64:1 (with 3 grooves) behind its 350, while the same 3.42:1 unit Pontiac used behind its 301 was also used behind the Chevrolet 305. Original identification was an application code applied with stenciled paint. Today, you're best to use the input shaft grooves and/or stamped VIN to determine what it was originally installed in. The VIN stamp will not, however, contain the engine identification character. |
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#11
06-01-2021, 05:03 PM
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#12
06-01-2021, 05:44 PM
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Quote:
https://www.ebay.com/itm/1978-79-PON....m46890.l49286 Can see the splines. Does it look correct? Kindly advise. Also, SR stamp pic and block cast date code attached - as requested, but I am not questioning these, though if you have any helpful comments, they would be appreciated. Thanks so much. |
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#13
06-01-2021, 07:11 PM
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The partial vin stamp has an L...which indicates Van Nuys build. I think you may be looking for a WC stamp beside side cover not WF....but need to check some build sheets..as I can't recall what mine is.. |
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#14
06-01-2021, 07:15 PM
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On your block...there is a 6 digit # cast behind/below pass. side head...that you should check........Also look for XX cast into block skirt behind fuel pump....where you should also see 400 #'s cast
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#15
06-01-2021, 10:22 PM
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Quote:
Last edited by Brock1030; 06-01-2021 at 10:35 PM. |
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#16
06-01-2021, 11:08 PM
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Quote:
I might suggest that until you find a correctly-dated 2.43:1 unit for your '79 Trans Am, you can always run the 1975 transmission. Assuming yours is a 2.43:1 gear box, it's functionally identical to the 1979 400 gearbox and it'll be an easy swap when the time comes. Thanks for sharing the info on your block! I collect information on service replacement blocks and there's no question that yours is an original (and correct) service replacement 400 block for the application. It's interesting to see the cast date on it. Does your paperwork happen to show what prompted the installation of the SR block? Pontiac was having some main cap/crankshaft issues with the W72 during that time. |
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#17
06-02-2021, 08:15 AM
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Quote:
A similar closer inspection of the one installed in my car with the SR engine, shows that while it was produced in 1975, it was for the 1976 model year, having been built in September and at the Norwood, OH plant - pics attached. What specifically prompted the SR engine and transmission was not detailed, simply that it was replaced under warrantee and by Pontiac. Given it happened in the warrantee period in 1979, one can surmise that it was that main bearing cap/crankshaft issue that John Witzke has documented and discussed in his work on W72s. As for why this particular transmission was placed in car and mated to the SR, its hard to say. This car clearly is one of the 1107 SE Y84 W72 WS6 cars and thus a 4-speed. It was a one adult owner car and had 58K on it when I obtained it from a collector. In doing restoration on it, there are no signs that it was in any way abused. Thus, when the original engine failed, perhaps its safe to surmise that the engine failure also tore up the original transmission. Not sure if GM had SR transmissions available to mate with the SR blocks. In your study of SR engines, any research on that point? Kindly advise. Could the warrantee have provided a rebuilt, but older 4-speed unit? Seems odd, if so, agree? This transmission now in the car is working just fine in the interim, as I keep on the look out for a 79 BW Super T-10, UH code, which would be correct. If this SR engine and this trans were indeed installed together as the warrantee replacement, may be best to leave it alone, as a bit of history of the remedy provided for what is documented to have occurred in the manufacturing process in the 1979 model year. |
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#18
06-02-2021, 09:42 AM
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I can say that John Witzke's research is accurate. He and I collaborated often and I believe we have the same internal documents that relate to 1977's 500557 block issues as well as those relating to the last W72s. I would imagine that SR block.
You're correct in your transmission's assessment. It was built in 1975 and used in an early 1976 Firebird. The WJ252 breaks down as follows: W=Warner, J= October, 2= 2nd day of month, 5= 1975 calendar year, 2= second production shift. Like you, I sincerely doubt that Pontiac would have used that particular transmission as an SR unit, but stranger things have happened (like this https://www.pontiacv8.com/blog/2019/...2-455-ho-block). While it's possible whatever lead to the SR block installation damaged the original transmission, I would guess that something happen to the original transmission well after that and the owner sourced a replacement, whether good-used or rebuilt by someone locally. Where SR blocks are concerned, I have been gathering block casting information, cast dates, and SR8 numbers in my files. I am hoping to determine some correlation between sequential SR8 number, but have yet to. Can you confirm that yours is indeed an XX481988 block? It's also worth nothing that when Pontiac provided an SR block for warranty work (or a customer purchased on through the parts department, it wasn't a complete engine assembly. Instead, what was delivered was a fitted block assembly which included a machined block, main caps, and pistons with wrist pins. Pontiac intended that the everything else be reused during the repair. Obviously, if a crankshaft or connecting rod(s) were the cause of failure, those components were available separately (and covered by warranty where applicable). It sounds as if you're car will be great looking when finished! |
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#19
06-02-2021, 09:45 AM
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It's unlikely that you'll find much left of the painted application code after so many years, but I took this photo of an all-original '79 Trans Am with a couple thousand miles on it while writing my second-gen Firebird book. The UH is clearly visible.
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#20
06-02-2021, 10:37 AM
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As for the SR block, from what I have found with this one in my car, you are correct regarding the transfer of the correct W72 heads, intake, distributor, etc. onto the SR block provided, as all the casting numbers and date codes are accurate for what should be there. Interesting though on this SR block, as it is not the later XX481988 block, but rather the earlier 500557 - pic attached. This car was sold Thanksgiving week in 1978 in Houston. When the failure happened, I surmised that perhaps the SR blocks available at that point in 1979 may have only been these earlier blocks or that they were using up the older SR stock W72 blocks first - any thoughts on that point? As I mentioned, this car was a one owner and adult owned from new, with no evidence of abuse and only 58K on it when I obtained it from a collector. In taking it apart, mileage is correct, as everything is in great shape, including zero rust issues. The previous owner did the paint and used Phoenix Graphix for the decals, doing a decent job, though not show quality. I am working on the remainder in sections, with restoration complete on the interior, all the glass (date code correct and replaced), trunk and the upper front end (all metal parts removed, chemical stripped and powder coated correct, new wiring harness and fully restored a/c components). Engine still need detailing, but I did not want to get into the bigger job of taking that and lower front end apart just yet, save the core support bushings, which were replaced, as I had the core support cleaned and powder coated. Next up is new exhaust, with a 2.5” Pypes x-pipe system, with their new Turbo Pro mufflers for installation. Not stock, I know, but thought the Y84 W72 gods would not be too disturbed to wrath! Recent pic of the exterior from above, is attached, but prior to all the panel alignment work. Thanks so much, Rocky. Last edited by Brock1030; 06-02-2021 at 11:05 AM. |
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